A Practical Guide to Piping and Valves for the Oil and Gas Industry 0128237961, 9780128237960

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A PRACTICAL GUIDE TO PIPING AND VALVES FOR THE OIL AND GAS INDUSTRY

A PRACTICAL GUIDE TO PIPING AND VALVES FOR THE OIL AND GAS INDUSTRY KARAN SOTOODEH

Baker Hughes, Oslo, Norway

Gulf Professional Publishing is an imprint of Elsevier 50 Hampshire Street, 5th Floor, Cambridge, MA 02139, United States The Boulevard, Langford Lane, Kidlington, Oxford, OX5 1GB, United Kingdom © 2021 Elsevier Inc. All rights reserved. No part of this publication may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher. Details on how to seek permission, further information about the Publisher’s permissions policies and our arrangements with organizations such as the Copyright Clearance Center and the Copyright Licensing Agency, can be found at our website: www.elsevier.com/permissions. This book and the individual contributions contained in it are protected under copyright by the Publisher (other than as may be noted herein). Notices Knowledge and best practice in this field are constantly changing. As new research and experience broaden our understanding, changes in research methods, professional practices, or medical treatment may become necessary. Practitioners and researchers must always rely on their own experience and knowledge in evaluating and using any information, methods, compounds, or experiments described herein. In using such information or methods they should be mindful of their own safety and the safety of others, including parties for whom they have a professional responsibility. To the fullest extent of the law, neither the Publisher nor the authors, contributors, or editors, assume any liability for any injury and/or damage to persons or property as a matter of products liability, negligence or otherwise, or from any use or operation of any methods, products, instructions, or ideas contained in the material herein. Library of Congress Cataloging-in-Publication Data A catalog record for this book is available from the Library of Congress British Library Cataloguing-in-Publication Data A catalogue record for this book is available from the British Library ISBN: 978-0-12-823796-0 For information on all Gulf Professional publications visit our website at https://www.elsevier.com/books-and-journals

Publisher: Joe Hayton Senior Acquisitions Editor: Katie Hammon Editorial Project Manager: Tracy I. Tufaga Production Project Manager: Sojan P. Pazhayattil Cover Designer: Christian Bilbow Typeset by SPi Global, India

Acknowledgment I would like to express my gratitude to my partner, Ms. Tamara Zhunussova for her constant support.

ix

C H A P T E R

1

Ball-valve applications and design Ball-valve application examples Ball valves are usually selected for process and aggressive services containing hydrocarbon oil and gas. A ball valve (see Fig. 1.1) is used for on/off purposes and not throttling (flow control). Injection lines that inject seawater into the reservoirs for enhanced oil recovery in highpressure classes are mixed with hydrocarbon services. Ball valves are the best valves for on/off purposes in this type of application. Alternative choices such as butterfly and wedge gate valves are not as robust as ball valves in process services. Ball valves for water injection lines in the offshore industry are manufactured in exotic materials such as 25 chromium super duplex, in medium to large sizes such as 1200 , 1400 , and 1600 , and in high-pressure classes such as class 1500. Although a butterfly valve is cheaper than a ball valve, it is not recommended for a seawater injection line since the fluid is aggressive, contains hydrocarbon, and flows at high pressure. Butterfly valves may not be robust enough for high-pressure and aggressive process services containing hydrocarbons. Wedge-type gate valves (see Fig. 1.2) are also not recommended for this application, for several reasons. • Wedge gate valves that are 1200 tall or taller may interfere with operator access to the handwheel. • Actuation of wedge gate valves must be done accurately to avoid seat and wedge overtorqueing and resulting damages. Overtorqueing a wedge gate valve increases the risk of stem bending. • Small-size ball valves that are 200 , 100 , or smaller, can be less expensive than wedge gate valves in the same size and pressure class due to less material usage and weight. • Wedge gate valves can be heavier and more costly due to their taller height and yoke arrangement. • 100 or ¾00 ball valves can be used instead of wedge gate valves for vent-and-drain purposes. • Quarter-turn ball valves can be operated faster and more easily than gate valves. These valves allow a 90-degree turn of the stem and ball, providing for full opening to full closing position, and vice versa. A Practical Guide to Piping and Valves for the Oil and Gas Industry https://doi.org/10.1016/B978-0-12-823796-0.00003-9

1

# 2021 Elsevier Inc. All rights reserved.

2

FIG. 1.1 Ball valve.

FIG. 1.2 Wedge gate valve.

1. Ball-valve applications and design

Ball-valve application examples

3

Actuated ball valves with emergency shutdown (ESD) functions are used for blowdown purposes to release overpressure piping or equipment to the flare (see Fig. 1.3). Relieving through a pressure safety valve (PSV) is another way to discharge accumulated overpressure. Blowdown ball valves are usually closed with a fail open (FO) function. The manual valve located downstream is usually open, but can be closed manually for the maintenance of an actuated valve located upstream (see Fig. 1.3). When compared to through conduit gate (TCG) valves, ball valves have the advantage of being more compact vertically. TCG valves occupy more space vertically, especially if they are actuated due to vertically mounted actuation. Although ball valves may be more expensive than TCG valves in smaller sizes, TCG valves in larger sizes such as 3000 and 3800 are usually more expensive than ball valves. Chapter 2 discusses the selection of a ball valve instead of a TCG valve for the inlet of a 2400 -class 1500 separator. Ball valves are not recommended for fast-opening applications. Generally, it is possible to reduce the opening time of a fail-open actuated valve through installation of a quick exhaust valve on the control panel to release the instrument air from the pneumatic actuator in the fail mode quickly. However, ball-valve seats and disks are in contact during the opening and closing, which can jeopardize the fast opening characteristic. In addition, moving the relatively large and heavy ball requires higher stem torque, a larger actuator, and perhaps a longer opening time. A ball-valve manufacturer was asked about using a soft-seat ball valve for this application, but the manufacturer believed that the fast opening of a soft-seat ball valve in 2 s could result in damage to the soft seat because of rapid contact with the ball.

FIG. 1.3 Blowdown valve.

4

1. Ball-valve applications and design

NPT plug

Ball valve damped x NPT Female

FIG. 1.4 Hydraulic oil header connection in high-pressure class with a ball valve (one end with a hub connection and the other end threaded).

Hydraulic actuators work with high-pressure supplied hydraulic oil in small-size piping and tubing. Small-size ball valves are selected for isolation of the header from branches, as shown in Fig. 1.4. The ball valves have a hub connection at one end and the other end is threaded. Hub and clamp connections are typical in high-pressure piping classes instead of ASME flanges, to save weight and space. However, a hub connection is selected to avoid the ingress of dirt from the external environment to the hydraulic oil in the pipe. Dirt can also enter a ball valve with an RTJ flange face connection. The ball valves on the chemical injection lines can be female threaded (THD) on the tube side and flanged on the pipe side. Threaded fittings are produced in pressure classes of 2000, 3000, and 6000 psi as per the ASME B16.11 standard for forged fittings, socket welding, and threaded fittings. It is not recommended to use class 2000 psi thread due to the potential for a weak connection. Ball valves connected to the tubes can be female threaded on the tube side and flange connected on the other side (piping side). As mentioned earlier, threaded fitting ratings are usually 2000, 3000, or 6000 psi. A ball valve can be selected with two flange ends, as shown in Fig. 1.5. A threaded female flange should be selected to connect the ball valve and tubing, but this solution can be expensive. Another disadvantage to flange connection is the difficulty in dismantling the valve. It is easier to dismantle the threaded tube connection than it is to dismantle the flange by unscrewing the bolts. If the valve is connected to tube sides from both

WN Flange

1" RF/RTJ

valve Male Connector–NPT-M-size according to P&ID Tube

Pipe

Compression fitting Size according to P&ID Piping

Tubing

FIG. 1.5 Ball valve with one end female threaded for tube connection.

Ball-valve application examples

5

ends, then the valve should be female threaded from both sides as per ASME B16.11 standard for threaded end fittings and valves either in class 3000 or 6000 psi. Although class 2000 is defined in the standard, it is not recommended for thread connection in engineering practice due to lack of strength. Fig. 1.6 shows the male end of a tubing connection in the Swagelok brand. The Swagelok connection contains a body, nut, front ferrule, and back ferrule. The body determines the shape and end connector of the meeting that is the male connection in this example. However, it is possible to order the body with a female end connector. The nut creates the force between the tubing and the ferrules. The front ferrules create the sealing on the outside diameter of the tubing (see Fig. 1.7). The back ferrule (smaller one) is used to grab the tube.

Tubing

Swagelok Nut

Swagelok Back Ferrule Swagelok Front Ferrule

Swagelok Body

FIG. 1.6 Tubing connector (male end) (Swagelok brand).

FIG. 1.7 Tubing connector (female end).

6

1. Ball-valve applications and design

Special ball-valve design V-notch ball valves (shown in Figs. 1.8 and 1.9) are proposed for throttling (fluid control). V-notch ball valves are designed with a V-shaped ball, for effective flow control with very low risk of cavitation, noise, corrosion, and vibration, the most common operation problems when using a standard ball valve for controlling the flow.

FIG. 1.8 V-notch ball valve.

FIG. 1.9 V-notch ball valve (internal view).

Special ball-valve design

7

FIG. 1.10 Three-way ball valves.

FIG. 1.11 Three-way ball valves application in well clean up.

Three-way ball valves (Fig. 1.10) can be configured in an L pattern or a T pattern for mixing or diverting the flow and they are usually manufactured in small sizes. The alternative is two ball valves with interlocks on each. Three-way ball valves remove the requirement for having tee and three welds as well as two ball valves with interlocks. One application of a three-way ball valve is in a well cleanup line in the offshore industry. As shown in Fig. 1.11, oil is usually transported to a stabilizer and second-stage separator after production. During the well cleanup, the flow—which contains mud and particles—should not be directed to the main process line, so a three-way ball valve is used to divert the flow toward the well cleanup filters. Well cleanup is performed at least 10 times each year and can take 4–5 h to complete. There is a filter upstream of the pump and the fluid is multiphase hydrocarbon. There is a pump after the filter and a dual plate wafer check valve downstream of the pump. An alternate solution to the three-way ball valve is two ball valves, one on the main process line and the other on the well cleanup, connected through interlocks.

8

1. Ball-valve applications and design

Ball-valve design consideration Bore design Ball valves can be full-bore (FB) or RBbore (RB) design. With an FB (sometimes called full port) valve, the internal flow passage is equal to the full area of the inlet port. With an RB valve, the flow area of the port (closure member) is less than the area of the inside diameter of the pipe and inlet of the valve. Closure member refers to the ball in a ball valve, also referred to in some international valve standards as the obturator. An FB valve allows for the use of a pipeline injected gadget (PIG) in the pipeline. A PIG is designed and run into the pipeline for inspection or cleaning purposes such as wax or scale buildup. Both ball valves in Fig. 1.12 should be FB to facilitate quick and full flow release of fluid to the flare line. FB is also a requirement for ball valves upstream and downstream of pressure safety valves (PSV), as shown in Fig. 1.12. API 6D, the standard for pipeline valves, gives a minimum bore diameter for rating 150–600 equally up to 6000 and separate minimum bore columns for CL900, CL1500, and CL2500 as shown in Table 1.1. But the standard does not provide the minimum bore diameter for large size and high-pressure classes (maximum 2000 bore in CL2500 and 3600 bore in CL1500). API 6D bores are counted as full bore but they are not really full bore—which means that the bore of ball valves as per the API 6D standard is less than the pipeline (piping) bore. Therefore, the valve bore should be equal to the pipe diameter when conducting PIG running for API 6D pipeline valves. The minimum bore in API 6D is usually larger than the ASME B16.34 standard for valves. An API 6D FB ball valve in larger sizes such as 2400 and pressure classes 150–600 has a bore much closer to the pipe. For example, a 2400 ball valve in duplex material and class 300 has about 2 mm less bore than the pipe. However, a 2000 class 150 ball valve as per API 6D standard could have a bore that is approximately 8 mm smaller than the pipe.

FIG. 1.12

Full-bore ball-valve upstream and downstream of the PSV.

9

Ball-valve design consideration

TABLE 1.1

Minimum bore diameter based on API 6D. Pressure class

DN (mm)

NPS (in.)

PN 20–100 (class 150– 600)

PN 150 (class 900)

PN 250 (class 1500)

PN 420 (class 2500)

15

½

13

13

13

13

20

¾

19

19

19

19

25

1

25

25

25

25

32

1¼

32

32

32

32

40

1½

38

38

38

38

50

2

49

49

49

42

65

2½

62

62

62

52

80

3

74

74

74

62

100

4

100

100

100

87

150

6

150

150

144

131

200

8

201

201

192

179

250

10

252

252

239

223

300

12

303

303

287

265

350

14

334

322

315

–

400

16

385

373

360

–

450

18

436

423

–

–

500

20

487

471

–

–

550

22

538

522

–

–

600

24

589

570

–

–

650

26

633

617

–

–

700

28

684

665

–

–

750

30

735

712

–

–

800

32

779

760

–

–

850

34

830

808

–

–

900

36

874

855

–

–

950

38

925

–

–

–

1000

40

976

–

–

–

1050

42

1020

–

–

–

1200

48

1166

–

–

–

1350

54

1312

–

–

–

1400

56

1360

–

–

–

1500

60

1458

–

–

–

10

1. Ball-valve applications and design

According to the API 6D standard, an RB ball valve has one size reduction up to and including 1200 (e.g., 1200  1000 ) and two size reductions for sizes above 1200 –2400 (e.g., 2400  2000 ), and customer and manufacturer agreement for sizes above 2400 . This could result in three size reductions for above 2400 (e.g., 3600  3000 ). Body-piece bolts for FB valves usually have more flange bolts compared to RB valves. An RB ball valve has a full bore at the end flange (Parameter B on Fig. 1.13, right valve), which is reduced gradually (Parameter B1 on Fig. 1.14, right valve). Therefore, both bore sizes are shown on the general arrangement drawing of RB ball valves. However, the bore of a full-bore valve is constant (Parameter B on Fig. 1.14, left valve). Some instruments such as venture flow meters may need some length of straight pipe upstream or downstream to avoid flow turbulence and accurate measurement. Fig. 1.14 shows an 1800 ball valve in class 150 upstream of a flow element (FE) that should have the same bore as the pipe to avoid flow turbulence in the flow element. An API 6D full-bore ball valve usually has a smaller bore diameter than the pipe. As an example, full-bore 1800 API 6D Class 150 ball valves in 22Cr duplex material could have a bore diameter up to 10–12 mm smaller than the pipe. The pipe in 22Cr duplex has no corrosion allowance and less thickness, which makes it have a larger bore compared to the valve and also compared to the carbon steel pipe. The minimum bore diameter (flow passage) is 90% of the inside diameter of the valve end as per ASME B16.34, which is the standard for valve design. The inside diameter of the pipe and valve are different; so, there is a step between the valve body flange and the connected flange. However, there is no need to taper any of the valve connector flanges, unlike the flange connected to the equipment. Therefore, the ball valve should be designed as a special bore to provide a flow open area equal to the pipe bore. The internal surface of the ball, seat ring, and body and seat contact may create very low turbulence. However, a special gasket may be required with the same internal diameter as the pipe bore in the valve and flange connection to avoid fluid turbulence. Another example describes an FB ball valve that is coupled flange-to-flange to a dual plate check valve without any distance. Dual plate check valves usually require a minimum of 2D (2 times the pipe diameter) upstream and 5D (5 times the pipe diameter) downstream straight line to avoid flow turbulence and erosion inside the dual plate check valve. Therefore, it is not a good idea to couple an RB ball valve to a dual plate check valve. Dual plate check valve disk clearance should be taken into account when the check valve is installed upstream of the ball valve, as shown in Fig. 1.15. However, installation of a check valve coupled to the FB ball from the downstream side is not a risk for dual-plate disk clash since the disk opens on the opposite side of the ball valve. Ball valves may need to be FB upstream of the pumps to increase the net positive suction head of the pumps. It is recommended to have isolation ball valves also upstream of the control valves. Although a reducer is designed upstream of the control valve, which makes pressure drop, an FB ball valve instead of an RB valve could be a better selection upstream of the control valve as shown in Fig. 1.16. As shown in the figure, the isolation ball valve downstream of the control valve should be FB as well. Selection of an FB ball valve avoids flashing and having two-phase flow that can increase wearing, erosion, and cavitation in the control globe valve. However, an RB ball valve may be selected instead of FB to save cost.

FIG. 1.13

Full-bore/reduced bore ball-valve drawings.

12

1. Ball-valve applications and design

FIG. 1.14

Full-bore ball valves.

FIG. 1.15

Full-bore ball valve coupled with a dual-plate check valve.

FIG. 1.16

Full-bore isolation ball valves before and after a control valve.

In one project, an RB ball valve was selected instead of an FB ball valve in a subflare line. The process department asked for two parameters of Θ and B ¼ d1/d2 to determine whether the flow capacity (CV value) of the RB was sufficient. These two parameters are shown in Fig. 1.17.

Ball-valve design consideration

13

BALL VALVES

d2

q d1

q

d2

FIG. 1.17 Ball-valve parameters of Θ and B.

Two FB ball valves in series that are closed can be selected for manual depressurization to the flare system. As an example, 200 class 1500 ball valves for manual depressurizing should have at least a 49 mm bore, as per Table 1.1 from the API 6D standard. If one wonders whether a wedge-type gate valve can be selected alternatively, the answer is no. A 200 class 1500 wedge gate valve cannot provide full bore as per the API 602 standard that covers gate, globe, and check valves for sizes 400 and smaller in the petroleum and natural gas industries. The minimum bore of a wedge gate valve in the size and pressure class mentioned above is 38 mm, which is smaller than the ball-valve bore as per API 6D. Except for the example of the ball valve close to the flow element (meter) mentioned earlier, pipeline valves should have a special bore equal or close to the pipe internal diameter, due to PIG running. Although pipeline valves are designed based on API 6D, minimum bore diameters given in API 6D are not necessarily piggable. The bore of a valve is usually less than the thickness of the pipe, especially when the pipe is manufactured from 22Cr duplex material. 22Cr duplex pipe has no corrosion allowance with relatively high strength, which makes the pipe thickness less compared to a carbon steel pipe and the connected valve in 22Cr duplex material. Fig. 1.18 shows a drift test after the manufacturing and assembly of a pipeline ball valve by passing a tool made of a 1 m long bar with three circular-shaped plastic plates on both ends and the middle to make sure that the internal diameter of the valve is suitable for running the PIG.

Face-to-face dimensions The American Society of Mechanical Engineers (ASME) B16.10 standard for face-to-face dimensions of flanged valves, as well as API 6D standards for pipeline valves, include face-to-face dimensions of the valves. Face-to-face dimensions given in API 6D are equal to the face-to-face dimensions given in ASME B16.10. If API 6D does not cover the face-toface dimensions for a specific size and pressure class, ASME B16.10 is the correct reference. However, API 6D covers face-to-face dimensions of high-pressure classes and large size valves (e.g., 2000 Class 1500 face-to-face is 1686 mm) that are not covered by ASME B16.10. API 6D gives end-to-end measurements of the valves based on raised face (RF) flange or ring-type joint (RTJ) flange or weld end. However, ASME B16.10 defines a parameter X that should be added to the face-to-face dimension of a raised face flange to obtain the face-to-face dimensions of a valve with an RTJ flange. Fig. 1.19 from ASME B16.9 shows raised face and RTJ flange faces.

14

FIG. 1.18

1. Ball-valve applications and design

Drift test on a riser ball valve.

Table 1.2 shows the dimensions of two pattern types of a ball valve. Short pattern body design is defined for only CL150 and CL300 in the ASME B16.10 standard. The short pattern has the same face-to-face dimensions as long pattern up to and including 400 in class 150 and 600 in class 300. Therefore, short pattern and long pattern ball plus gate valves have the same faceto-face dimensions up to and including 400 in class 150 and 600 in class 300. Short-pattern ball valves have the same face-to-face dimensions as gate valves according to ASME B16.10 in sizes 600 , 800 , 1000 , and 1200 and class 150. Long pattern ball valves have longer face-to-face dimensions than short-pattern ball and gate valves in sizes 600 , 800 , 1000 , and 1200 and class 150. Table 1.3 shows Table A10 of the ASME B16.10 standard, including parameter X in inches for different sizes and pressure classes that should be added to the face-to-face dimensions of an RF flange valve to get the face-to-face dimension of an RTJ face valve with the same size and pressure class. A tolerance of 2 mm shall be allowed on face-to-face and end-to-end dimensions of valves with sizes of 1000 and smaller, and a tolerance of 3 mm shall be allowed for valve sizes of 1200 and larger, as per ASME B16.10. End-to-end expression is used for those flanged valves where the gasket contact surface is not located at the extreme ends of the flange, such as the RTJ flange face shown in Fig. 1.20. Hub-ended valves are popular in the offshore industry in high-pressure classes to save weight and space compared to normal ASME flanges. Fig. 1.21 shows actuated hub-ended valves, which are more compact at the end connections. Hub-ended valves have the same end-to-end configuration as RTJ flanges.

Other ball-valve dimensions The distance from the back of the flange to the body pieces could be important for layout, due to maintenance requirements. These areas are highlighted with red arrows (gray in print version) in Fig. 1.22.

Ball-valve design consideration

15

FIG. 1.19 Regular standards facing of flanges.

A ball valve is opened from the body-piece connections with a special tool used for doing maintenance on the ball. The valve has an access for dismantling the tool, seat, etc., as shown in Fig. 1.23. However, Fig. 1.24 shows a torque tool for bolt tightening or opening that will not interfere with the body flange. Ball valves with one or both double piston effect (DPE) seats, so called “Double Isolation and Bleed” (DIB) according to API 6D definition, could have a longer face-to-face dimension compared to the values given in the ASME B16.10 standard. DPE seat design is explained in detail in “Seat Design” section. RB DIB valves usually do not need face-to-face enlargement since the body of the RB valve as well as the compact flange and hub has enough clearance for ball enlargement without any need to increase the valve end face-to-face. The DPE seat is pushed more tightly against the ball compared to a self-relieving (SR) seat (unidirectional) through higher torque containing spring. Therefore, the ball in DPE seat design may need to be stronger through adding thickness which leads to longer face-to-face design.

TABLE 1.2 Face-to-face dimensions for class 300 raised face flanged valves based on ASME B16.10.

Nominal valve size

1

2

3

4 Class 250 cast iron

5

6

7

Flanged end (2-mm raised face)

8 9 Class 300 steel Flanged and welding end

Plug

Ball

Short pattern, A

Regular pattern, A

Venturi pattern, A

Globe, lift check, and swing check, A

Angle and lift check, D

Long pattern, A

Short pattern, A and B

Long pattern, B

NPS

DN

Gate, solid wedge, and double disk, A

½

15

…

…

…

…

…

…

140

140

…

¾

20

…

…

…

…

…

…

152

152

…

1

25

…

…

159

…

…

…

165

165

…

1¼

32

…

…

…

…

…

…

178

178

…

1½

40

…

…

190

…

…

…

190

190

190

2

50

216

184

216

…

267

133

216

216

216

2½

65

241

203

241

…

292

146

241

241

241

3

80

282

235

282

…

318

159

282

282

282

4

100

305

267

305

…

356

178

305

305

305

5

125

381

…

387

…

400

200

…

…

…

6

150

403

378

425

403

444

222

403

403

457

8

200

419

…

502

419

533

267

502

419

521

10

250

457

568

597

457

622

311

568

457

559

12

300

502

648

711

502

711

356

648

502

635

14

350

572

…

…

762

…

…

762

572

762

16

400

610

…

…

838

…

…

838

610

838

18

450

660

…

…

914

…

…

914

660

914

20

500

711

…

…

991

…

…

991

711

991

22

550

…

…

…

1118

…

…

1092

…

1092

24

600

787

…

…

1143

…

…

1143

813

1143

26

650

…

…

…

…

…

…

1245

…

1245

28

700

…

…

…

…

…

…

1346

…

1346

30

750

…

…

…

…

…

…

1397

…

1397

32

800

…

…

…

…

…

…

1524

…

1524

34

850

…

…

…

…

…

…

1626

…

1626

36

900

…

…

…

…

…

…

1727

…

1727

TABLE 1.3 Dimensions for ring-type joint flanged valves based on ASME B16.10.

1 Nominal valve size

2 Class 150

3

4 Class 300

5

6

7

8 Class 900

9

Class 600

10 Class 1500

11 12 Class 2500

NPS

DN

X

S

X

S

X

S

X

S

X

S

X

S

½

15

…

…

0.44

0.12

0.06 (3)

0.12

0

0.16

0

0.16

0

0.16

¾

20

…

…

0.50

0.16

0

0.16

0

0.16

0

0.16

0

0.16

1

25

0.50

0.16

0.50

0.16

0

0.16

0

0.16

0

0.16

0

0.16

1¼

32

0.50

0.16

0.50

0.16

0

0.16

0

0.16

0

0.16

0.12

0.12

1½

40

0.50

0.16

0.50

0.16

0

0.16

0

0.16

0

0.16

0.12

0.12

2

50

0.50

0.16

0.62

0.22

0.12

0.18

0.12

0.12

0.12

0.12

0.12

0.12

2½

65

0.50

0.16

0.62

0.22

0.12

0.19

0.12

0.12

0.12

0.12

0.25

0.12

3

30

0.50

0.16

0.62

0.22

0.12

0.19

0.12

0.16

0.12

0.12

0.25

0.12

4

100

0.50

0.16

0.62

0.22

0.12

0.19

0.12

0.16

0.12

0.12

0.38

0.16

5

125

0.50

0.16

0.62

0.22

0.12

0.19

0.12

0.16

0.12

0.12

0.50

0.16

6

150

0.50

0.16

0.62

0.22

0.12

0.19

0.12

0.16

0.25

0.12

0.50

0.16

8

200

0.50

0.16

0.62

0.22

0.12

0.19

0.12

0.16

0.38

0.15

0.62

0.19

10

250

0.50

0.16

0.62

0.22

0.12

0.19

0.12

0.16

0.38

0.16

0.88

0.25

12

300

0.50

0.16

0.62

0.22

0.12

0.19

0.12

0.16

0.62

0.19

0.88

0.31

14

350

0.50

0.12

0.62

0.22

0.12

0.19

0.38

0.16

0.75

0.22

…

…

16

400

0.50

0.12

0.62

0.22

0.12

0.19

0.38

0.16

0.88

0.31

…

…

18

450

0.50

0.12

0.62

0.22

0.12

0.19

0.50

0.19

0.88

0.31

…

…

20

500

0.50

0.12

0.75

0.22

0.25

0.19

0.50

0.19

0.88

0.38

…

…

22

550

0.50 (1)

(2)

0.88 (1)

0.25

0.38 (1)

0.22

…

…

…

…

…

…

24

600

0.50

0.12

0.88

0.25

0.38

0.22

0.75

0.22

1.12

0.44

…

…

Ball-valve design consideration

19

FIG. 1.20 Ring-type joint flange face with the RTJ gasket.

FIG. 1.21 Hub-ended ball valves.

FIG. 1.22 Red arrows (gray in print version) indicating the distance between back of the flange to body pieces.

20

1. Ball-valve applications and design

FIG. 1.23

Special tool on the ball valve for maintenance.

FIG. 1.24

Torque tool for ball-valve bolt tensioning. Courtesy: FCT.

As an example, FB ASME flange ball valves can have face-to-face dimensions that are 10% more than ASME B16.10 in one valve manufacturer design, and have face-to-face dimensions one size larger and the same rating as per ASME B16.10 for some sizes and pressure classes in another valve manufacturer design (As an example, an 800 class 900 DIB valve has a face-toface dimension of 1000 class 900 in the same pressure class).

Ball-valve design consideration

21

FIG. 1.25 Top-entry- and side-entry design.

Body and bonnet design There are two types of body and bonnet design, top entry or side entry (split body), shown in Fig. 1.25. The other point about body flange design is that the flange bodies of classes 900 and 1500 up to and including 200 , as well as flange bodies of classes 300 and 600 up to and including 200 , are identical and compatible with each other. Side-entry ball valves can have two or three pieces. Three-piece ball valves usually start from 600 , 800 , or 1000 sizes. The number of body and bonnet bolts for two-piece body valves is usually twice the number of bolts for two-piece body and bonnet bolts. Some suppliers do not propose three-piece ball valves for high-pressure classes such as 1500 and 2500 since the ball is very large, which makes it very difficult to comply with ASME B16.10 valve face-toface dimensions. In addition, three-piece bodies have more leak points than two-piece bodies, which is a weak point in high-pressure classes. Therefore, three-piece body valves are just designed for pressure classes from 150 to 900. Top-entry design advantages Top-entry design has the following advantages: 1. Easy online maintenance (e.g., seat repair) from the top of the valve by removing the valve bonnet without shutting down the plant. 2. Its one-piece design offers more mechanical resistance against pipeline loads than a splitbody design, according to finite element analysis (FEA) results. 3. There is less risk of leaks. Welded to the line instead of the flange connection, the top-entry design has one bonnet connected to the one-piece body instead of having two or three body pieces and two pieces of adapter bonnets, as in a side-entry design. A top-entry design ball valve can be used in a high-pressure gas service to reduce the possibility of leakage from the valve. In addition, cryogenic valves are recommended to be top entry and welded to the pipe to reduce the risk of leakage.

22

FIG. 1.26

1. Ball-valve applications and design

Top-entry actuated ball valve during the test. Courtesy: ATV.

4. Greater flexibility in stem design and size allows for a larger diameter (thicker) stem for high torque valves with large actuators. Side-entry ball valve stem enlargement requires a design change and a special product, from the manufacturer’s point of view. Top-entry ball valves must be welded in a construction yard, which is a more timeconsuming task than simply connecting a flanged ball valve to the mating flange. Therefore, top-entry ball valves must be ordered early to allow sufficient time for welding activities in the construction yard. Another reason for ordering top-entry ball valves earlier is that they require a longer delivery time due to their large size and high-pressure class. Fig. 1.26 shows an actuated top-entry ball valve with blinded hubs and clamps at the ends for pressure and function testing. The valve has two pup pieces at both ends, which are welded to the line in the construction yard. A top-entry ball valve has a body and bonnet, whereas a split (side-entry) design has two or three body pieces (shown in blue (dark gray in print version) in Fig. 1.25) plus adapter flanges around the stem (shown in purple (gray in print version) in Fig. 1.25). Manufacturing process (forging, casting, etc.) Forged steel material is stronger and has less chance of defects compared to casting. The grains and defects are refined through the forging process, which makes forged valves more reliable than cast valves. The delivery time is also shorter for forged materials compared to casting. Although the forging process is usually more expensive than casting, forging is a more cost-effective product in comparison. Weld repair is allowed only for cast and not forged materials. Casting of a valve body is closer to the final shape; so, it results in less thickness. Forging creates a greater thickness than casting, so it must be machined. Therefore, a cast valve is lighter than a forged valve in the same size and pressure class. As an example, a 1200 forged steel body in Class 300 can be 820 kg including the weight of gearbox. The cast duplex valve in the same size and pressure class is lighter and can be 550 kg.

Ball-valve design consideration

23

Forged body valves are more common in small sizes. However, some manufacturers may avoid casting even for large sizes. For example, one valve manufacturer is producing 22Cr duplex and 25Cr super-duplex body forged valves in sizes such as 2000 instead of casting them. Case studies Lack of body flange thickness

In one case, a 1200  1000 class 300 ball valve, the thickness of the body flange was extra machined to 0.6 mm below the minimum thickness given in ASME B16.5. Lack of body flange thickness was on one side but not both sides. The face-to-face dimension of the valve was based on ASME B16.10, and the API 6D. 0.6 mm reduction in flange thickness on one side was not a problem since 3 mm face-to-face deviation is allowed for a 1200 valve based on the ASME B16.10 standard. However, a lack of body flange thickness can cause insufficient strength against the loads. Because the body flange was not thick enough, the solution was to cast a new body. The valve manufacturer performed an FEA on the flange to make sure that the flange could withstand the piping and bolt loads. Axial and bending loads were provided by the stress department to the supplier for FEA implementation. Lack of space for ball inside the body

In another case, there was not enough space in the body of the valve for the ball to move freely. If there is not enough space, the body needs to be machined and the thickness should be reduced. It is important that the thickness of the body not be reduced to less than the thickness values given in the ASME B16.34 standard for valves. Fig. 1.27 shows grinding the body thinner to facilitate placing the ball in the body. Connected flange bolts clashing

There is a major problem that can occur during the installation of small-size ball valves in construction yards. The problem was observed during the flange installation on the small size ball valves, regarding the bolts and nuts space requirement. As shown in Figs. 1.28 and 1.29, there is a clash between the flange bolts with the valve-body-piece bolts due to the short distance between the two flanges on the body of the valve.

FIG. 1.27 Grinding the body to facilitate placing the ball in the body of the valve.

24

1. Ball-valve applications and design

FIG. 1.28 Clash during the installation of body-piece bolts of a 300 CL300 trunnion-mounted ball valve with the mating flange.

FIG. 1.29

No space for the nuts and bolts of the connecting flange.

The problem could be even worse, as Fig. 1.31 shows, if there is no space available for the mating flange bolt and nuts. The problem usually occurs for 400 and smaller FB ball valves where there is not much space between the mating flange body and body-piece flange. The reason why the bolting clash happens for FB and not RB ball valves is that the mating flange bolt circle is larger than the bodypiece-bolt circle in RB ball valves, as shown in Fig. 1.30. Thus, there is no possibility of clash between the body flange bolts and body-piece bolts. Although the problem is very common for small-size FB ball valves, it was observed for a TCG valve during the factory acceptance test (FAT), as shown in Fig. 1.31. Two bolts and nuts at the bottom and right-hand side of flange connection are very close to the body of the valve. Fig. 1.32 has highlighted lack of bolt-and-nut space for the flange connection on the TCG valve.

Ball-valve design consideration

FIG. 1.30 200 Class 1500 RB ball valve in forged carbon steel (LF2) material. Courtesy: BFE.

FIG. 1.31 300 Class 300 TCG valve during the FAT test.

FIG. 1.32 Lack of space for connected flange bolts and nuts on the TCG valve (Highlighted).

25

26

1. Ball-valve applications and design

Solutions to connected flange bolts clashing

There are different solutions to this problem. One is increasing the face-to-face dimension of the valve. The important point is that ball valves in sizes 400 and smaller have the same faceto-face dimension in both long and short patterns as per the ASME B16.10 standard, face-toface standard of the flanged valves. This means that it is not possible to have a longer valve covered by the relevant ASME standard to mitigate the risk of bolt clashes during an installation. Therefore, some manufacturers may increase the face-to-face dimension of the valves to longer than the values given in ASME B16.10/API 6D, especially for trunnion-mounted ball valves. As an example, a ball-valve manufacturer asked to deviate from ASME B16.10 for the faceto-face dimension for a 3/400 Class 600 trunnion ball valve that was standardized to 190 mm. As seen in Fig. 1.33, the body-closure studs and nuts on the right side of the valve would not allow any space for flange connection bolts. Thus, the valve manufacturer proposed to increase the face-to-face dimension of the valve, as shown in the left side of the valve in the figure. Manufacturing of a standard valve in terms of face-to-face should be communicated with the piping layout (design) section to be reflected in the model as well as the isometric drawings later used for fabrication. The other way is to avoid a clash is by reducing the number of bolt threads out of the nut. Paragraph 335.2.3 of ASME B31.3, Process Piping Code, states: “Bolts should extend completely through their nuts. Any which fail to do so are considered acceptably engaged if the lack of complete engagement is not more than one thread.” On the other hand, the Norsok L-004, Piping Fabrication, Installation, Flushing, and Testing standard has more restrictive requirements than ASME B31.3. According to the Norsok standard: “Manually torque flange bolts and stud bolts shall extended fully through their nuts with minimum

FIG. 1.33 Trunnion-mounted ball-valve face-to-face incensement as per the left-side flange to avoid flange bolt clashes with body-closure bolts.

Ball-valve design consideration

27

FIG. 1.34 Lack of engagement between body-closure bolt and nut to provide enough space for body flanges bolt and nut. Courtesy: LVF.

one and maximum five threads.” The bevel end of the bolts should not be taken into account in the number of threads out of the nut and an air gap is recommended to be between two body closure and connected flange bolts. Therefore, it is recommended to reduce the number of bolt threads out of the nuts as much as possible. The minimum could be set to one thread or, in special cases, lack of complete engagement for one thread as per ASME B31.3 could be acceptable. Fig. 1.34 shows a 200 FB ball valve class 300 with lack of thread engagement between bolt and nut on body closure. The lack of thread engagement between body-closure pieces provides enough space for the bolt and nut of the connected flange. However, it is important that the lack of engagement is not more than one thread to be sure that it complies with ASME B31.3. Fig. 1.35 shows a ball valve with enough space for bolts and nuts between body flanges. Minimum one bolt thread is out of the nut for all the bolts without any bolt-and-nut clash. It is also possible to screw the body-closure stud bolt farther into the body-closure flange to provide more space. The third approach is to reduce the valve body flange thickness by machining. One solution could be reducing the end body flange thickness and/or body-closure flange thickness to provide more space for bolts and nuts. The question to consider is whether it is possible to reduce the thickness of the highlighted areas in Fig. 1.36. The minimum thickness for a 300 class 300 flange as per ASME B16.5 is minimum 22. 3 mm, so when it comes to the body flange, any thickness above 22.3mm can be machined to provide the

28

1. Ball-valve applications and design

FIG. 1.35

No clash between the bolts due to reducing the bolt threads out of nut to minimum of one thread, as per Norsok L-004 standard.

FIG. 1.36

No space for the nuts and bolts of the connecting flange 300 ball-valve CL150 (Evaluation of flange thickness reduction).

required space. It should be considered that the body thickness is subject to a nondestructive test (NDT) and pressure test. The body-closure thickness could also be machined and reduced to solve the problem. The fourth approach is to change the bolt-and-nut types. Usually, heavy hexagonal nuts are selected for stud bolts. Heavy hexagonal nuts are taller than normal standard nuts. Fig. 1.37 shows the length of engagement (LE) between valve-body-closure bolt and nut. The valve manufacturer can calculate the minimum length of the bolt-and-nut engagement

Ball-valve design consideration

29

FIG. 1.37 Bolt-and-nut engagement on a valve body closure.

based on ASME B16.34. If heavy hexagonal nuts have been selected and the minimum required engagement would be more than the actual LE, then it is possible to change the heavy hexagonal nuts to standard nuts. The alternative solution is to change the stud bolts on the body closure to the machine bolts. Machine bolts as per ASME B16.5 are not as long as stud bolts. This solution may not be good enough, since dismantling the valve through body closure requires complete pulling out of the machine bolts. However, loosening and removing the nut on the stud bolt would facilitate disassembling the body closure. In conclusion, this section reviewed bolting and nut clash or the lack of space on ball-valve body closures and connected flanges. This issue is associated with small-size FB ball valves and some TCG valves. Different solutions have been discussed, such as increasing the valve face-to-face dimension, reducing the number of bolt threads out of nuts as per either ASME B31.3 or NORSOK L-004, screwing the bolts more tightly to the body closure, reducing (machining) the flange thickness on both ends body flange and closure member, changing the heavy hexagonal nuts to standard nuts, as well as changing the stud bolts to machine bolts. Long-length bolting for the valve Fig. 1.38 shows a ball valve in three pieces connected to each other with a long-length bolt instead of two sets of bolts. There is no restriction in the piping standards to connecting three pieces of ball valves with a long-length bolt through the body. However, the long-length bolt expands more than the normal bolt in case of fire and may cause more leak from the valve. In this case, the bolt is passed through the body and protected so the expansion and risk of leakage should be less than in a situation where the bolt is completely exposed. Usage of washer for super-duplex bolting The other point related to body bolting is using a washer under the nuts in a 25Cr bolt-and-nut design. This is done to provide more accurate bolt torques and to make sure that the nut pressure distributes evenly. A washer is also used

30

FIG. 1.38

1. Ball-valve applications and design

Three-piece body valve with the long-length bolt.

for 25Cr super duplex bolting. A tensioning tool is more accurate than a torque tool, so there is no need to apply a washer under a 25Cr super-duplex nut if the tensioning tool is used for fastening the 25 Cr super-duplex bolts. In addition, a tensioning tool creates less galling and friction compared to a torque tool. It is important to bear in mind that hot dip galvanized (HDG) bolts are acting as lubricants; so, there is no need to apply a washer for HDG bolts. In addition, a super-duplex bolt is stronger and requires higher torque than HDG low-alloy bolts; so, lubrication is required for super-duplex bolting. Using a washer under the nuts can increase the length of the nut and increase the risk of a clash between body flange bolts and the body-pieces nut in the areas highlighted by a red circle (gray in print version) in Fig. 1.39. The washer standard for the bolt is ASME PCC-1 as per Fig. 1.40, and the thickness is 6.4 mm for 100 size and above. Bolt design for weight saving Fig. 1.41 shows a special nut design to save space on the body pieces. The nut is neither hexagonal nor rounded, but it is mixed. It is rounded to save space and provide space for the torque tool. However, a hexagonal part is required to facilitate using the torque tool for opening and closing the bolts. A torque tool is used for opening and closing smaller size ball valves, and a tensioning tool is required for larger size ball valves with larger bolts. Minimum acceptable length of bolting When it comes to body and bonnet bolting, a machine bolt (hexagonal head bolt) is not suitable for body and bonnet connection for several reasons.

Ball-valve design consideration

31

FIG. 1.39 Possibility of clash between the flange bolts and body/bonnet bolts due to using the washer.

It is not possible to dismantle two body pieces of valves without removing the whole length of the machine bolt out of the body pieces. On the other hand, stud bolts can be removed easily from body pieces by loosening the nuts. Also, the length of the machine bolt must be accurate. If the machine bolt is too long, the hexagonal head does not fit on the flange. If the length is too short, it cannot achieve depth of thread (L) that should be a minimum of 7/8  bolt diameter as per ASME B31.3 Process Piping Code. Another disadvantage of machine bolts (heavy hexagonal bolts) is that uniform torque cannot be achieved easily for these bolts. Fig. 1.42 shows body-piece connection bolts that are not completely through the hole, but they are acceptable since the length of the bolt is more than 7/8 of the bolt diameter and silicon can be used inside unengaged threads to avoid corrosion. Usually, machine bolts do not need a nut to save space, and the hole in which the bolt is entered has internal threads. It is possible to use a stud bolt in a threaded hole that is prepared for a machine bolt, as shown in Fig. 1.44. But it damages the HDG and does not achieve a uniform torque. The machined hexagonal head bolts in Fig. 1.42 have been painted. When it comes to wall-thickness calculation, usually the ASME B16.34 standard should be used for valve-wall-thickness calculation. ASME B16.34 gives the minimum thickness measurement (TM) based on the internal diameter (ID) for all pressure classes, which are standardized for all the materials. The formula for the thickness given in the following

32

FIG. 1.40

1. Ball-valve applications and design

Washer dimensions as per ASME PCC-1.

example is less than TM. Table A1 in the Nonmandatory appendix A of ASME B31.3 provides an inside diameter of “d” based on pipe size. Additional thickness is added to the valve body where the lifting lug, grease injector, and cavity relief are installed. Body-wall-thickness calculation The below details are taken from the ASME B16.34 standard.

Ball-valve design consideration

33

FIG. 1.41 Special body and bonnet bolting design. Courtesy: FCT.

FIG. 1.42 Not completely through the hole bolts on the body of a ball valve.

Body defect (case study) Fig. 1.43 shows the body of a top-entry valve 1400  1000 class 1500 butt welded to the line with a crack in the body. The cracks found during the factory acceptance test in the body and bonnet bolt holes can be seen in the series of photos A–D shown in Fig. 1.44. A radiography test (RT) was done in order to figure out the depth and criticality of the cracks. An RT sketch as per ASME SEC.VIII, Div.01 APP.7 was created. The body area was divided into different sections for the test implementation (e.g., 17, 18, 23, etc.). A crack under the body bolts was discovered during the body test where the valve was leaked

34

FIG. 1.43

1. Ball-valve applications and design

1400  1000 Class 1500 butt weld valve.

Ball-valve design consideration

35

FIG. 1.44 Cracks inside the body and bonnet bolt holes of a 1400  1000 class 1500 butt weld valve.

from the body. The valve body was useless, so a new casting was ordered. Fig. 1.45 shows the valve body with the cracks marked on it, and the sketch of the RT that was performed. Fig. 1.46 shows the image of the RT. The valve-body subsupplier probably forgot to do an RT on the casting. Since there was the risk of a crack on other similar valve bodies, two of the castings were sent for X-ray examination. The fourth body was also useless and a new casting was molded (re-poured) and X-rayed after that. Body internal overlay Inside the body and flange faces of carbon steel, valves may be overlaid with Inconel 625 in 5–6 mm thickness, as an example. The thickness of weld overlay will be reduced to 3 mm after machining. The welding method is tungsten inert gas (TIG) welding. In fact, the filler is Inconel 625, and it is melted by tungsten. It is important to have slow welding and a slow speed of welding dilution. Fig. 1.47 shows an Inconel 625 weld overlay on a carbon-steel body valve.

Body marking When it comes to DIB valve marking, the SR/DPE seats should be written on P&IDs and isometrics, and be highlighted in the Plant Design Management System (PDMN) model. The people in the construction yard need to know the correct directions of DP and SR seats. The SR

36

FIG. 1.45

1. Ball-valve applications and design

Sketches for radiography test on the body casting.

Ball-valve design consideration

FIG. 1.46 Radiography test on the body casting.

FIG. 1.47 Weld overlay of Inconel 625 on carbon-steel body valves. Courtesy: FCT.

37

38

1. Ball-valve applications and design

FIG. 1.48 Typical identification plate for a valve with one seat unidirectional and one seat bidirectional based on API 6D standard.

and DP could be hammered on the body of the valve toward each seat. However, it may not be clear (readable) after painting, so hammering is not recommended. API 6D suggests marking of DPEXSR with a plate that is connected to the body through the rivet as shown in Fig. 1.48. The material of the plate and rivet are in Inox (SS316). Sometimes, the marking could be done on the flange edge. The minimum size of DIB valves is 200 . Generally, when it comes to valve marking, the serial and heat numbers are marked on the body. The heat number is marked for tracing the valve, and it is also written in the material certificates. Fig. 1.49 shows the marking of a heat number on the body of the valve.

FIG. 1.49

Body of a ball valve including marking and heat number. Courtesy: Flow Control Technology.

Ball-valve design consideration

39

FIG. 1.50 Wrong marking on the body (RB instead of FB). Courtesy: FG Valvole.

In this case, marking on the valve was wrong, and it was marked as “RB” instead of “FB” (see Fig. 1.50). Therefore, the marking was ground and corrected as shown in Fig. 1.51. Fig. 1.52 shows the marking on the blind flange installed on the body-cavity-flange connection of a ball valve.

Ball design The ball is basically a sphere port in the housing (body of the valve), as shown in Fig. 1.53. There are two types of ball design: “floating” and “trunnion.” A floating ball is a type of arrangement in which the ball is not fixed from the bottom stem or bottom flange. In fact, the ball is held between fixed upstream and downstream seats. Therefore, the ball has freedom to move and the upstream fluid pressure assists in sealing by pushing the ball back against the downstream seat. Fig. 1.54 shows a floating-ball-valve schematic. As an example, usage of the floating-ball valves in each class could be limited to these sizes: Class Class Class Class Class

150, 800 maximum size for floating ball 300, 600 maximum size for floating ball 600, 400 maximum size for floating ball 900 and 1500, 200 maximum size for floating ball 2500, 1 ½00 maximum size for floating ball

The seat material (soft seat or metal seat) also affects the floating ball. The listed floating ranges are proposed for a floating ball with a soft seat. Selecting a metal seat ball valve would limit the range of floating sizes. All metal-seated valves in all pressure classes can be trunnion mounted in sizes 200 and above.

40

1. Ball-valve applications and design

FIG. 1.51

Correction of marking on the valve body. Courtesy: FG Valvole.

FIG. 1.52

Marking on the ball-valve cavity blind flange. Courtesy: Flow Control Technology.

41

Ball-valve design consideration

FIG. 1.53 Ball inside the housing. Courtesy: FCT.

W

13 12 11 10

H

9

d

8 7 6 4 3 5 1 2 L

FIG. 1.54 Floating-ball-valve schematic.

L1

42

1. Ball-valve applications and design

FIG. 1.55

Trunnion balls.

FIG. 1.56

Trunnion-mounted ball valve.

In trunnion-mounted balls, the ball is fixed through plate or flange or integrated part with the ball. Fig. 1.55 shows two trunnion balls on the floor of a valve factory shop. Trunnion designs are usually found in higher pressure classes and larger valves, and the seats are spring-loaded against the ball. Fig. 1.56 shows a trunnion-mounted ball valve. Some manufacturers may use a plate as a sort of support under the ball in sizes 600 and above, which has the advantage of not having an extra hole and leak path in the body of the valve. Having the trunnion ball with a flange connection requires an extra hole on the body. It is proposed to have the same material as the trunnion ball.

Ball-valve design consideration

43

Trunnion design effect on valve face to face (case study) In some cases, a trunnion design can increase the face-to-face dimension and height of the valves in small sizes. In some cases, valve manufacturers may propose larger face-to-face dimensions than those given in ASME B16.10 for valves in a trunnion-mounted design. As an example, the ball valve in Fig. 1.64 is 100 , pressure class 150, and a trunnion-mounted ball. The red line (gray in print version) indicates the ASME B16.10 face-to-face dimension for 100 and class 150 that is 127 mm. This short dimension of 127 mm could have been easily covered by a floating-ball valve design. But the valve manufacturer instead increased the face-to-face design of the valve to 241 mm. The example in Fig. 1.65 shows a ¾00 class 600 trunnion-mounted ball valve that is designed based on ASME B16.10 face-to-face values. Figs. 1.57 and 1.58 show the problem with the stud clash in mounting to the flange body on the right side of the valve, highlighted with a red arrow (dark gray in print version). Therefore, the valve manufacturer proposed to increase the length of the valve, as shown on the left side of the figure.

FIG. 1.57 Trunnion-mounted ball valve face-to-face increase.

44

FIG. 1.58

1. Ball-valve applications and design

Trunnion-mounted ball valve face-to-face dimension increase due to clash of the bolt.

Ball-valve design consideration

45

Ball valves upstream and downstream of pressure safety valves (PSVs) could be designed trunnion mounted, which is a more robust design due to the loads applied to the line from PSVs during the opening. Trunnion design for actuated valves Actuator valves are always trunnion mounted, since adding a support plate or flange under the ball can make the actuator more compact. Adding a trunnion reduces the required force for operating (opening and closing) the valve. However, very small-size actuated ball valves (e.g., 100 size and less) could be floating, especially in low-pressure classes, due to challenges related to accommodating the trunnion inside the body of the valve. Fig. 1.59 shows a trunnion-mounted ball valve with the trunnion bottom flange connection and a pneumatic actuator and control panel on top of the valve. Block-and-bleed effect in trunnion/floating valves The floating-ball valve is probably not counted as a single block and bleed. However, it may be possible to count a trunnion-mounted ball valve with two SR seats as a single block-and-bleed valve. The reason is that the fluid pressure and the spring load on the downstream seat can provide a single isolation in a standard trunnion ball valve with two SR seats. However, a ball valve with two DPE seats is counted as both DIB type 1 or double block and bleed, depending on the test procedure and leakage monitoring points. DIB valves will be explained more in the chapter about seat design. Ball low roughness and lapping process A ball should have slight roughness in seating areas, as shown in Fig. 1.60. Very slight roughness of 3 μm or even less, such as 0.1 μm, can be achieved by lapping the ball and seat together with diamond paste. The lapping process, shown in Fig. 1.61, is very time consuming. Alternatively, it is possible to use a machine for lapping the ball to provide

FIG. 1.59 Trunnion-mounted actuated ball valve. Courtesy: ATV.

46

1. Ball-valve applications and design

FIG. 1.60

Lapped ball with low roughness. Courtesy: ATV.

FIG. 1.61

Lapping process. Courtesy: ATV.

tight sealing with seats that could be 20 times faster than a normal lapping. Lack of lapping increases the ball roughness and causes leakage for metal seat ball valves. Lack of lapping and significant roughness of a ball could damage the soft seat of a valve. Ball alignment testing Accurate alignment of the ball to the seats and the bore is very important, and is tested for the actuator valves such as the one shown in Figs. 1.62–1.64.

Ball-valve design consideration

FIG. 1.62 Ball alignment test for the actuator valve. Courtesy: ATV.

FIG. 1.63 Ball alignment test for the actuator valve, opening from closing position.

47

48

1. Ball-valve applications and design

FIG. 1.64

Ball alignment test for the actuator valve, open (ball is aligned to the bore).

FIG. 1.65

Internal lapping and grinding of a valve.

Ball machining and nondestructive testing It should be noted that to avoid valve replacement, internal lapping and grinding could be done during maintenance by sending a device inside the valve, as shown in Fig. 1.65.

Ball-valve design consideration

49

FIG. 1.66 Machining a ball.

FIG. 1.67 NDT test on the balls after machining. Courtesy: ATV.

When a ball is machined, nondestructive testing (NDT) should be done on the ball after machining (see Figs. 1.66 and 1.67) to make sure that there is no defect on the ball such as a crack or dent. The method of NDT is liquid penetration that includes three types of liquid. The first one that is red in color is called penetrant. The second one in white color is the developer that can show the defects on the material. The third liquid is called cleaner. Ball design for DIB valves A ball for DIB valves with one or two DPE seats can be larger and heavier than a ball for a standard ball valve. The reason is that more loads during the FEA are observed on the ball of the DIB valves from special DPE seats and the springs behind the seats (see Figs. 1.68 and 1.69).

50

1. Ball-valve applications and design

FIG. 1.68

FEA on ball.

FIG. 1.69

Ball/DPE seat FEA for a top-entry 2000 CL 1500.

Ball-valve design consideration

51

FIG. 1.70 Holes inside the ball for lifting. Courtesy: FCT.

The red lines (dark gray in print version) on the right-hand side of Fig. 1.69 indicate that the stress level between the ball and the DPE seat exceeds the limit. Therefore, the ball should be strengthened by adding thickness that affects the weight of the valve and possibly the face-toface dimension. Lifting of the ball There are small holes inside the ball in Fig. 1.70 that are made for lifting the ball.

Seat design Seat design for DIB valves DIB is defined by API 6D, Specification for Pipeline Valves, as a “single valve with two sealing surfaces, each of which, in the closed position, provides a seal against pressure from a single source with a means of venting/bleeding the cavity between the seating surfaces.” DIB ball valves could be used instead of two standard ball valves and a bleed valve between, to save the cost and space. Ball valves or TCG valves (slab and double expanding) could be designed as DIB valves. It is important to notice that floating-ball valves (Fig. 1.71) are not DIB since they do not have the seat retainers and the springs at the back of the seat retainers. Therefore, the sealing in the floating-ball valves is achieved just through the fluid pressure and not the spring mechanical forces (Fig. 1.71). Actually, the seats of floating-ball valves are neither DPE nor SR.

52

1. Ball-valve applications and design

UPSTREAM

DOWNSTREAM

Ball pushed against the seats downstream

FIG. 1.71

Floating-ball valve seat-and-ball arrangement.

DOWNSTREAM

UPSTREAM

Trunnion

FIG. 1.72

Trunnion-mounted ball and seat arrangements.

Trunnion-mounted ball valve sealing is created by the seats pressing against the ball through the spring’s mechanical forces, as shown in Fig. 1.72. In that case, each seat of the ball valve could be a mean of isolation and the drain plug or the flange between is the bleeder. Although trunnion-mounted ball valves are not DIB by default, they can be changed to DIB through changing the seat arrangements, as explained below.

53

Ball-valve design consideration

Seat types (self-relieving or double piston effect) The seat in a trunnion-mounted ball valve could be SR (unidirectional) or DPE (bidirectional). Ball valves are supplied with two SR seats by default as per Fig. 1.72 from the valve manufacturer, unless DPE single or double seats are requested in the purchase order. Two types of seats are available for a ball valve. The first, unidirectional, also named selfrelieving (SR) or single piston effect (SPE), is a type of seat in a trunnion-mounted design in which the seats are pressed through spring loads. As the body-cavity pressure increases greater than the spring load, the seats are pushed back and the pressure is released in the line. Cavity releases the fluid to the downstream side if both seats in the ball valve are SPE. Therefore, each SPE or SR seat in a ball valve with two SPE seats relieves the body-cavity overpressure to the line separately. Fig. 1.73 shows the single piston effect design for a ball valve. An SR seat has a unidirectional sealing effect, which means that it only seals the cavity from the line when the valve is fully closed or opened. The cavity will be filled in if the ball is moved from open to closed or closed to open positions. In cases where the valve is fully open or closed, an SR seat cannot provide sealing from the pressurized fluid in the cavity. The pressurized fluid in the cavity will be released to the line through SR seats, usually when the cavity pressure is between 10% and 33% over the design pressure as shown in Fig. 1.74.

Body Cavity

Adapter

Seat Ring

Resultant Thrust

Resultant Thrust

ØA

Ball

ØC

Seat Insert Pressure Release

DOWNSTREAM

SIDE

SIDE

BODY CAVITY

FIG. 1.74 Ball valve with two SR seats.

ØB

UPSTREAM

ØA

ØA

ØB

FIG. 1.73 SR or SPE seat design.

54

1. Ball-valve applications and design

The other type of seat design is a bidirectional or double piston effect (DPE) seat, in which the fluid pressure from the line and the cavity, as well as the spring, creates forces that push the seat rings against the ball. Unlike SR seat design, the fluid pressure in the cavity cannot be released to the line from the DPE seat that is shown in Fig. 1.86. Therefore, a cavity relief valve (pressure safety valve) should be designed and placed on the cavity to release the excess pressure in the cavity, especially when the fluid is liquid and noncompressible. Overpressurized trapped fluid in the cavity should not exceed 1.33 times the valve design pressure rating. Therefore, an SR seat releases the cavity pressure at maximum 1.33 times of the valve design pressure as per the API 6D standard for pipeline valves requirement (Fig. 1.75). Overpressurized fluid as a result of thermal expansion, as an example, can apply force and damage the body and stem as well as increasing the required torque for opening and closing the valve. Cavity relief should release the cavity fluid at the minimum 1.1 times of the design pressure for an SR seat. An automatic relief valve could be threaded to the body or flanged connection, which is the preferred choice, as shown in Fig. 1.76. Body Cavity

Seat Ring

Adapter Resultant Thrust

Seat Firesafe Packing

Resultant Thrust

FIG. 1.75

ØA

Ball

ØC

Seat Insert

SR or SPE seat design.

Min. 1/2" relief valve Bracing to main valve

Min. 1/2" piping

Valve cavity vent connection

Valve body Min. 1/2" flanged wedge gate valve

FIG. 1.76

PSV installation on the valve body for low-pressure class.

55

Ball-valve design consideration

Min. 1/2" relief valve Bracing to main valve

Min. 1/2" piping

Valve cavity vent connection

Valve body 2 pcs. flanged wafer erdge gate valve

FIG. 1.77 PSV installation on the valve body for high-pressure class.

The arrangement of PSV installation on the DIB1 valves requires an isolation valve, which is a wedge gate valve for low-pressure class (Fig. 1.76) or a double block-and-bleed valve for high-pressure classes (Fig. 1.77). The isolation gate valve should be locked open, to be closed only in case of PSV maintenance and calibration. A tee is required to have two connections, one for pressure release through PSV and the other one for manual vent. The PSV is usually ¾00 for sizes up to and including 1200 and 100 for sizes above 1200 . A cavity relief line (e.g., ½00 , ¾00 , or 100 size) may be installed to release the body cavity to the valve suction during the maintenance for a through conduit gate valve, as shown in Fig. 1.78. The challenge sometimes is to have a compact modular valve between the body cavity and the suction. As per the API 6D definition, double isolation and bleed type 1 (DIB1) has two bidirectional seats, as shown in Fig. 1.79. DIB valves for double isolation purpose A ball valve can have combination seats in which one seat is SR (unidirectional) and the other one is DPE (bidirectional) and is called DIB2. A DIB2 valve is cheaper than DIB1, and there is no need to make an extra hole on the body of DIB2 valves for PSV installation. Making an extra hole in the body of the valve has the disadvantage of creating an extra leak point. In addition, PSV on DIB2 valves requires regular maintenance and calibration. DIB1 may need higher torque and probably a bigger actuator and higher force on the ball from both seats (less flexibility of the ball). Therefore, DIB2 valves are the preferred choice of some endusers rather than DIB1 valves with two DPE seats. In some cases, an SR seat is located upstream with a DPE seat downstream shown in Fig. 1.80. The other idea is to use DIB valves for maintenance. DIB valves are usually used in highpressure classes that are CL600 (PN 100 barg) and above, as well as in hazardous services like

56

DOWNSTREAM

SIDE

SIDE

BODY CAVITY

FIG. 1.79

Ball valve with two DPE seats (DIB1).

ØB

UPSTREAM

ØC

ØC

Cavity relief line from the body cavity to the suction.

ØB

FIG. 1.78

1. Ball-valve applications and design

Ball-valve design consideration

57

FIG. 1.80 One-seat single-piston effect and one-seat DPE (DIB2).

FIG. 1.81 DIB ball valves for pump isolation.

flammable hydrocarbon or toxic fluids. Toxic fluids can cause permanent injury or death of the operator through leaking like H2S. DIB valves are used for providing a double isolation barrier between the pressurized system and the part that requires being open for maintenance or modification. The pressurized system is upstream of the DIB1 ball valve and downstream of the DIB2 ball valve in Figs. 1.81 and 1.82. The maintenance part could be an equipment like a pump (Fig. 1.81), a filter, or a PSV (Fig. 1.82). PSVs are usually disassembled from the line for maintenance and calibration on the yearly basis. In fact, DIB valves are used as double barriers between the pump or PSV and the upstream or downstream pressurized fluid to protect operators during maintenance or modification. The old-fashioned solution to isolate the PSV or pump is by using two standard ball valves with SR seats and a bleeder gate valve between them (see Fig. 1.83) that increases cost and space. Effect of double piston seat on valve face to face Enlarging the ball of a DIB valve can increase the face-to-face dimension of the valve compared to the ASME B16.10 standard Face-to Face-Dimension of Flanged Valves. Some

58

1. Ball-valve applications and design

FIG. 1.82

DIB ball valves for PSV isolation.

FIG. 1.83

PSV isolation through two standard SR seat ball valves and a bleeder gate valve between.

manufacturers could increase the face-to-face dimension of the DIB valves to the face-to-face dimension of one size larger with the same pressure class as per the ASME B16.10 standard. As an example, a 600 long pattern and FB standard ball valve CL600 RTJ (RTJ) flange end has a face-to-face of 562 mm. If the 600 ball valve is changed to DIB with single or DPE seats, then it is possible to increase the face-to-face dimension to a long pattern 800 (one size larger) CL600 ball valve RTJ flange as per ASME B16.10, which is 663 mm. Some manufacturers may increase the face-to-face dimension of DIB valves due to the DPE seat by 10% compared to a standard ball valve with the same size and pressure rating. Usually, manufacturers try to standardize DIB1 and DIB2 face-to-face dimensions to be the same as each other. However, DIB valves could

Ball-valve design consideration

59

have standard face-to-face dimensions. If the DIB ball valve is RB, enlarging the ball may not affect the face-to-face dimension and the manufacturer can comply with ASME B16.10 standard. The reason is that the RB ball is smaller than the FB ball and the bore has enough clearance for ball enlargement. The default seat design of ball valves is SR  SR in which the seats release the cavity pressure when the pressure is as high as between 110% and 133% of the design pressure. During a cavity test, the cavity is pressurized with 110% of the design pressure and the pressure is increased until one SR seat releases the fluid, and the pressure is increased until the second seat releases the cavity pressure. Why is the maximum pressure in the cavity 33% over the design pressure? That is because the cavity design is based on 66% of the material yield, and 33% extra above the design gives the yield strength load, which is the material limit. A DPE seat provides isolation and minimizes the risk of leakage from the body cavity as well as the line to the body cavity. A DPE seat is pushed stronger to the ball compared to an SR seat (unidirectional) through higher torque containing a spring and/or special seat design. It may be better to consider a DPE seat for a ball valve with a tight shutoff requirement, which increases safety and offers better operator protection during the maintenance on the DPE side. In a DPE seat, both line pressure and cavity pressure help in pushing the spring to the ball. In an SR design, the line pressure pushes the ball to the seat and cavity pressure pushes the seat away from the ball. The floating-ball valve is probably not counted as a single block and bleed. However, it may be possible to count the SR  SR standard trunnion ball valve as a single block and bleed, because the fluid pressure and the spring load on the downstream seat can provide a single isolation. Due to a higher torque requirement for DIB type valves, the ball could be designed as trunnion mounted even in small sizes such as 200 or 300 . The other reason for having trunnion-mounted ball is to create a DPE, which cannot be created in a floating ball. Valve seat insert Seat insert is applicable only for soft seat ball valves and not metal seat. This is one of the reasons that changing the seat from soft to metal or vice versa requires changing the seat insert. Fig. 1.84 shows a soft seat ring inside the seat retainer in a soft seat ball valve. Metal-seated ball valves are tungsten carbide (TC) coated in contact with the ball, and the whole ball may be TC coated. TC (86%WC-10%CO-4%Cr) requires hardness check, porosity check, salt spray check for corrosion test, and ductility test, which means an elongation check without any crack. Different hard-facing materials are available on the ball of the ball valve, such as: -. -. -. -. -. -.

Stellite Tungsten carbide Chrome oxide Chrome carbide Nickel boron Titanium dioxide

Seat design for particles The other topic is to design a seat in the particle-containing services. The issue with the ballvalve metal seat in dirty services is that the particles can be entered into the seat arrangement.

60

1. Ball-valve applications and design

FIG. 1.84

Seat insert and seat carrier in a ball valve.

FIG. 1.85

Seat arrangement with a seat scraper.

Therefore, either a seat scraper must be applied or a washing valve must be installed on the body of the valve to wash the dirt out of the seat arrangement. Installing a valve wash requires an extra hole on the body of the valve, which is a disadvantage. In addition, there are some space issues to performing a valve wash on valves in small sizes such as 400 and below. A seat scraper could be just an extra sealing ring in PTFE or Viton around the seat to reduce the possibility of particles entering the seat arrangement. A seat scraper of PTFE could be a good option for metal-seated ball valves in dirty services. In the detail in Fig. 1.85, item number 530 is the seat scraper to prevent ingress of particles from the side away from the ball.

61

Ball-valve design consideration

100

11 DRAIN PLUG 150 COA-

14

16

520

522

6

DETAIL A

FIG. 1.86 Seat arrangement.

Seat retainer back springs are inside a cylinder, called a spring guide, to avoid the springs moving out of their places and becoming buckled. The material of the spring guide should be same as the trim material. In addition, a lip-seal retainer plate can be placed at the end of the lip seal. In Fig. 1.86 the spring is guided by two spring guides. Item number 11 is the cylindrical one in forged material that is F51 for a 22Cr duplex body valve, and number 14 is the one in plate A240 Gr. S31803. Number 16 is the lip-seal retainer in plate A240 Gr. S31803. It is recommended that the lip-seal retainer is in metallic material and not soft material such as PTFE. Valve-installation direction affected by seat design It was mentioned earlier that a DIB2 valve is cheaper than a DIB1, and there is no need to make an extra hole on the body of DIB2 valves for PSV installation. Making an extra hole in the body of the valve has the disadvantage of creating an extra leak point. In addition, a PSV on DIB2 valves requires regular maintenance and calibration. DIB1 valves may need higher torque and probably larger actuators and higher force on the ball from both seats (less flexibility of the ball). Therefore, DIB2 valves are the preferred choice of some end users rather than DIB1 valves with two DPE seats. But DIB2 valves with one DPE and one SR are not bidirectional. Therefore, SR and DPE seats are marked on the relevant engineering drawings like piping and instrument diagrams, isometrics, PDMS models, and the body of the valves. The DIB valves body marking according to API 6D was shown earlier in this chapter. There are two possibilities for the gearbox (left or right side) and actuator installation, and two positions for seat direction that create two installation statuses in the model. The requirement for handwheel and gearbox direction for DIB2 valves initiates from the piping layout consideration, based on the operator access requirement. As an example, a handwheel on the right could be interpreted to mean that the operator stands in the line close to the DPE seat and the handwheel stands on the right-hand side. Drain-and-vent plugs/flanges should usually be located on the same side of the gearbox and handwheel. However, drain-and-vent connections may be required to be on the opposite side of the handwheel due to piping layout requirements and ease of pipe routing from or to the drain or vent. This situation should be avoided, and a new valve drain arrangement should be ordered. The drain-and-vent connections may be machined from bosses on the

62

1. Ball-valve applications and design

FIG. 1.87

Bosses on the ball-valve body casting. Courtesy: FCT.

FIG. 1.88

Flange connections on the bosses of the ball-valve cast body. Courtesy: FCT.

body of the valve. Figs. 1.87 and 1.88 illustrate bosses on a body casting to be machined for making cavity flange connections. If the wrong side of the DIB2 valve is machined for cavity flange connection, one solution is to have bosses on both sides of the valves. The disadvantage of this solution is that it increases the cost and delivery time and requires extra machining of two holes, with two extra gaskets and blind flanges. In addition, having the drain-and-vent connections on both sides of the valve introduces additional valve leak paths. Some valve suppliers order the casting with bosses on both sides (symmetrical casting) and it is possible to have drain-and-vent cavity connections on both sides. Changing the cavity drain-and-vent side on a valve could have major cost and delivery impact, especially at a later stage of the project. Therefore, one solution is routing (piping) the drain and vent to the other side of the valve rather than changing the cavity flange drain-and-vent connections side. This may not be an optimal layout design, but it is a good way to avoid cost and delivery time impact. When machining of the drain and vent is done on the wrong side but the body casting is symmetrical, it is possible to add the drain and vent on the other side (correct side). The

Ball-valve design consideration

63

FIG. 1.89 Ball valve with handwheel/vent-and-drain plugs.

consequence is having more holes on the body of the valve and adding two more blind flanges, gaskets, and bolts on the other side of the valve. The reason why SR  SR does not need a handwheel direction requirement is that the SR  SR valve is bidirectional, and if the valve has a handwheel on the right, it can be turned 180 degrees and get the handwheel on the left, since both seats are identical. DIB1 valves with two DPE seats are also bidirectional. Turning the valve 180 degrees to change the handwheel direction in manual valves makes changing the direction of the vent-and-drain plug/flange by 180 degrees. Fig. 1.89 shows a ball valve with a handwheel as well as drain-and-vent plugs facing the reader of the book. Let us suppose an actuated ball valve has two SR seats and a clash between the actuator and a structure. Rotating the vale and actuator 180 degrees can probably solve the clash. But rotating the valve changes the direction of the cavity vent-and-drain connections. The best way is to rotate just the actuator at the valve supplier factory, since it does not have cost impact. Some companies may ask for drain-and-vent connections on the opposite side of the handwheel to avoid clashing the piping connected to the vent in 45-degree upward with the handwheel. However, it is possible to prevent a cavity vent connection piping clash with the handwheel through two solutions: 1. Use elbow or bend after the vent connection to avoid clash with the gearbox and the handwheel. 2. Get the piping branch from the drain instead of the vent. It is important to define the direction of the cylinder and piston sides of the actuator for DIB2 valves. As an example, the SR seat and spring sides of the actuator may be considered

64

FIG. 1.90

1. Ball-valve applications and design

Ball valve with SR seat and piston housing of the actuator on the left side.

FIG. 1.91 Ball valve with SR seat and piston housing of the actuator on the right side and the drain connection at the back of the valve.

on the same side (left side). In that case, the drain connection can be on the side facing the book reader as shown in Fig. 1.90. The spring housing of the actuator is longer than the cylindrical side. Fig. 1.91 shows a DIB2 valve with an SR seat and actuator piston housing on the right. The drain connection is at the back of the valve with a longer piping route. It is more convenient to have the drain connection on the other side of the valve, as it is marked in the figure. However, changing the drain side is not a good solution because of extra machining on the casting, which creates extra cost and delivery time.

Ball-valve design consideration

65

FIG. 1.92 Drain boss on the cast body of a top-entry ball valve. Courtesy: FCT.

The drain and vent of the electrically actuated valves should usually be located on the same side of the electrical actuator handwheel. In conclusion, changing the drain or vent side for a DIB2 ball valve is required to be done at an earlier stage in the project before receiving general arrangement drawings. Some manufacturers may provide bosses on the body of the valve where the plug is inserted or the flange is machined. The boss provides extra thickness on the cast body of the valve. The main advantage of the boss is that there is no requirement to weld a nippo flange to the body and do a nondestructive test. The boss is machined to form the flange face. Some manufacturers may order the cast body with bosses on both sides of the valve (a total of four—two on each side for vent-and-drain connections). Then, it is possible to machine the other side boss in order to change the vent-and-drain directions. However, extra machining on the body casting increases delivery time and cost at the later stage and creates extra leakage points. Therefore, it is better to specify the side of drain-and-vent connections for DIB2 valves earlier. Fig. 1.92 shows the body casting for a 3800 valve including bosses for drain, seat retraction, and sealant (grease injection) on the seats. The vent boss is located on the bonnet. The cast body of the valve is very close to shape with little or no machining. Therefore, extra thickness is required on the cast body for the boss. However, extra machining is required for forging because of extra thickness. So, the bosses should be made during the machining if the body of the valve is forged.

Seat sealant injection design Sealant injection is used for: 1. Temporary maintenance of the seat (seal minor scratches). 2. Loosening the seat in the seat pocket to make them to have good contact with the ball. 3. Cleaning the seat and ball (maybe from particles). However, a separate flushing port can be designed on the seat of the valve for seat cleaning if it was not possible to integrate a flushing port and sealant injection due to size and injection efficiency.

66

1. Ball-valve applications and design

Emergency sealant injections are installed on the soft and metal seats to inject sealant and repair the soft/metal seat ring (restore sealing integrity) as well as postpone the required maintenance on the seat to the prescheduled maintenance time. A soft seat has the first priority for emergency sealant injection, since it is more exposed to risk of damage. Although the metal seat is more robust, with TC hard facing, emergency sealant is usually required for the metal seat valves as well. The particle can be between the ball and the seat while closing the valve, which scratches and damages the ball and seat. Frequent opening and closing of a valve also can damage the seat. Thus, it is proposed to make additional holes on the body for grease injection fittings on the metal seat ball valve. Also, operating the ball valve for throttling is the worst case during which a seat could be damaged. The sealant injection can repair the seat and stop the leakage temporarily. The injection is done during the normal operation condition. Sealant injection on the seat is not preventive maintenance; it is an emergency maintenance action. The location of sealant injection is between two O-ring or two lip seals, or in case of fire-safe design, between the graphite and O-ring or lip seal. A seat sealant injection requirement is based on end-user requirements that could be for sizes 400 and above in high-pressure classes, and 600 and above in low-pressure classes, as an example. However, another recommendation is to use two sealant injections per seat for sizes 300 and 800 , and always use sealant injection for trunnion-mounted ball valves. Using one flushing port per seat for sizes 300 to 800 cannot provide enough sealant injection circulation to repair the seats. The number of sealant injection ports could be higher, such as four in large size valves, considering the fact that the sealant injection is very viscous. Fig. 1.93 shows a viscous orange sealant injection liquid for a ball valve.

FIG. 1.93

Sealant injection liquid.

Ball-valve design consideration

FIG. 1.94

67

1800 CL300 ball valve with two sealant injections per seat on one side and totally four per seat. Courtesy:

FG Valvole.

Size, pressure class, and viscosity of the sealant affect the number of sealant injection ports. It was experienced to have four sealant injections per seat for 2000 and 1800 (two on each side per seat) (Fig. 1.94), and two sealant injections per seat for 1200 (one on each side per seat). One per seat for 600 and 800 valves means one seat injection on one side and nothing on the other side (Fig. 1.95). It was experienced in an offshore site that repairing a seat after injecting the sealant injection reduced the leak from 100% to 60% through one injection point per seat; so, it was recommended to use two sealant (grease) injections per seat for trunnion-mounted valve sizes 300 –800 . The amount of sealant is not necessarily 1 once per inch. It depends on type of seat, the distance of hole inside the body and seat to reach the seat ring, as well as the location of the sealant injection compared to the seat ring (above or under) and the type of damage (using the ball for throttling is the worst case to damage the seat, and not repairable since the seat can be cut). This may seem like many holes on the body, but maintaining flow capacity for sealant injection and solvent is very important. Grease can be injected on the valve seat after dismantling the valve from the line during the maintenance from the sealant injection port. It is proposed to inject the grease on the seat when the valve is closed and then open and close the valve three times. In addition, lubrication during maintenance can be done for bearing, packing, stem threads, and threaded parts of bolts and nuts. Cycling and visual examination are also part of maintenance activities. The emergency sealant injection or the grease or solvent will be pushed all the way from the cavity and back of the seat to the ball and seat contact and the line through the holes on the seat ring. The sealant injection point is done through two-seat sealing as shown in Fig. 1.96.

68

1. Ball-valve applications and design

FIG. 1.95

600 CL150 metal-seat ball valve with one sealant injection per seat. Courtesy: FG Valvole.

FIG. 1.96

Sealant injection on the seat-and-ball through sealant injection.

Fig. 1.97 shows the ball valve seats with some small holes in the seat to be used for grease injection to the valve seat and ball. Stem emergency sealant or grease (lubricant) injection is usually installed between the stem O-rings (the upper O-ring is for weather sealing and the down sealing is for pressure sealing). The stem grease injection may be required for sizes 400 and above as per project specifications. Grease injection on the stem reduces the torque on the stem and increases the ease

Ball-valve design consideration

69

FIG. 1.97 Ball-valve seat arrangements with grease injection holes.

FIG. 1.98 Stem sealing as well as grease injection port.

of valve operation as well as reduction of wearing in the stem (see Fig. 1.98). It is proposed to apply grease injection on the stem for dry gas application twice per year. In the unlikely event that the primary pressure seal fails, the leak will occur in the grease injection fitting. In that case, the grease injection fitting, which has a cap with a 1/800 NPT and is equipped with one or two check valves, prevents the internal leaked fluid to be sprayed out of the valve. At this stage, both stem seals should be removed as soon as possible. The other solution could be injecting the emergency sealant injection to the pressure seal O-ring for temporary sealing before complete failure of the O-ring. To avoid ingress of paint, sand, or old dried sealant into the grease injection fitting and seat or stem arrangement, a cap should be installed on the grease injection fitting. These solid

70

FIG. 1.99

FIG. 1.100

1. Ball-valve applications and design

Stem sealing as well as grease injection port.

Injection port assembly.

contents can also prevent the check valve from functioning properly. The check valve should be installed with vent holes to show the leakage from the sealant injection and warn the operator in case of check valve failure (see Fig. 1.99). As an example, a manufacturer can provide emergency sealant (grease injection) for sizes 600 and above on the seat and stem due to space issues. A manufacturer may integrate the grease injection with a cavity drain connection in a 400 ball valve and not provide a drain or vent plug for 300 ball valve. However, it might be recommended to have two grease (sealant) injections per seat for valve sizes 300 –800 . The sealant injections are equipped with one or two check valves. A check valve has a spring-energized ball to prevent sealant backflow after an injection (see Fig. 1.100). Having two check valves reduces the flow capacity of the grease injection but it also reduces the risk of backflow and adds more safety in case one check valve fails.

Stem design Stem leak prevention expensive solution Leakage from stem sealing as well as the seat could be due to the side dynamic loads on the ball, which leads to movement of ball and stem together. Stem leakage could also be due to wearing and tearing of the stem bearing. One solution is having the integrated ball and stem as a more robust design to avoid ball and stem movement. An integrated ball and stem provides an antiblowout stem design, but it makes the valve more expensive.

Ball-valve design consideration

71

Antiblowout stem Both upper and lower stems should be antiblowout. The upper stem should be antiblowout when the top cover of the ball valve is disassembled. An antiblowout stem is achieved by a thicker stem part in a larger diameter, which is placed under two adapter body parts (side body parts). This stem design requires machining the stem, which is expensive in materials like duplex, titanium, 6MO, etc. Also, the stem has a tee shoulder that seats on the top of the ball. A lower stem (trunnion) should be antiblowout to avoid cutting the finger of the operator during trunnion flange disassembly. The lower stem (trunnion flange) at the bottom of the valve should be supplied with a drain connection to make the lower stem antiblowout. Stem key The stem key shows the direction of the ball hole when the gear is disassembled. The stem key is the connection of the stem to the valve operator such as a gear or actuator. Fig. 1.101 shows the stem and the stem key, which is attached to the stem. Fig. 1.102 shows the stem and stem key from another angle. One to four keys may be fitted between the stem and the valve operator (gear or actuator). Usually, the stem has two key grooves that give the possibility of rotating the gearbox/actuator 180 degrees. However, rotating the gearbox and handwheel 90 degrees parallel to the line is possible for ball valves that have four stem grooves on four sides of the stem. Even just two stem grooves perpendicular to each other is sufficient to rotate the valve operator 90 degrees. By default, a ball-valve gearbox and handwheel is located on the side of the valve. Two stem keys located on 180-degree rotations from each other, or even one, is sufficient for a 180-degree rotation of the actuator or gear box. In addition, the stem key is a mechanical stop to control the ball rotation. The stem key affects the torque capability of the stem (MAST) against the actuator or gearbox torque. Therefore,

FIG. 1.101 Stem key and stem for a ball valve.

72

FIG. 1.102

1. Ball-valve applications and design

Stem key and stem for a ball valve.

some manufacturers may offer materials with high mechanical strength such as 17-4PH or AISI 4140 for the stem key of a 22Cr duplex body valve with 22Cr stem. However, 22Cr duplex or alloy 718 stem key are better materials compared to 17-4PH or AISI 4140. 17-4PH has a high risk of stress cracking corrosion in an offshore environment but it is a good choice of material for stem keys in the onshore industry. AISI 4140 does not have enough corrosion resistance to be used in the offshore industry. In addition, dissimilar materials of stem and stem key in a humid offshore environment lead to galvanic corrosion. Fig. 1.103 shows galvanic corrosion between the stem key in 13Cr-4Ni material and 22Cr duplex stem in offshore environment. A line is machined on the top of stem in Fig. 1.104 shows the ball direction in a ball valve. If the stem has a square shape and is not rounded, there is no need to machine the stem for placing the stem keys. A square stem provides the possibility of multiple orientation of the gearbox without any need to have the stem key as shown in Fig. 1.105. Stem extension Insulation friendly

The stem may be extended for applying the insulation around the valve. For example, rounded couplings in 100 or 120 mm can be installed around the stem to wrap the

FIG. 1.103 Galvanic corrosion of the stem key.

FIG. 1.104 Machined stem with the line on the top showing the ball direction (position).

FIG. 1.105 Square stem drive allowing for multiple orientations.

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1. Ball-valve applications and design

insulation. In some cases, the valve supplier may increase the height of the coupling, depending on the valve size or pressure class. It is possible to install or reinstall the couplings through the bolts or screws connected to the body of the valve. Figs. 1.106 and 1.107 show a ball valve with the stem extension between the valve and gearbox installed to facilitate applying the insulation.

FIG. 1.106

Extended-stem ball valve. Courtesy: LVF.

FIG. 1.107

Extended-stem ball valve.

Ball-valve design consideration

75

FIG. 1.108 Allen screws for fixing the coupling to the valve and the lever.

FIG. 1.109 Extended stem and bonnet ball valves for cryogenic services.

Allen screws are used to fix the coupling adapter to the body of the valve from the bottom and to the lever locking device from the top as shown in Fig. 1.108. Cryogenic services

The stem and bonnet can be extended in cryogenic (very cold) services to keep the sealing away from the fluid and avoid ice formation and malfunction of stem sealing as well as the valve gearbox. An extended stem and bonnet can be used for hot service applications where the operating temperature is above 200–250°C and the proposed stem sealing materials are lip seal and graphite. Graphite does not have the sealing capability of O-rings or lip seal, so it is a good idea to mix the graphite and lip seal for stem sealing. Sometimes, a drip plate can be welded to the extended bonnet to avoid ice moving up externally in cryogenic services. Fig. 1.109 shows the ball valves designed for cryogenic services.

76

1. Ball-valve applications and design BB

H

DD

Ø CC

AA

DRAIN BLEEDER RF

F (BODY) G (FLANGE) °

50

FIG. 1.110

Ball-valve design with bracket.

Case study of stem extension

In one case, another stem extension solution was offered by a valve supplier. A bracket around the rounded coupling was considered in this design, which makes it difficult to apply the coating around the stem as shown in Fig. 1.110. The bracket is not removable and it is designed under the gearbox. As shown in Fig. 1.110 there are three important dimensions related to the valve operator (handwheel plus gearbox). The first dimension, the distance from the center of the handwheel to the center of the gearbox, is called handwheel extension, which is parameter BB in the figure. The handwheel extension is an important parameter since a long handwheel can be extended to the walkways (sideways) on the platforms. The problem is that the sideways should be free from any object, especially in case of emergency. The other parameter is the distance from the center of the gearbox to the center of the valve, shown as parameter DD. The third important dimension is from the center of the gearbox to the end of the handwheel, parameter AA. Fig. 1.111 shows the problem in mismatching between two stem extensions (spindle) parts. The spindle (part number 2) inside the mounting bracket was not machined accurately to match the stem extension (part number 1) covered by the bracket.

Ball-valve design consideration

FIG. 1.111 Mismatching between stem extension parts.

77

78

1. Ball-valve applications and design

More information about valve insulation

In some cases, insulation in the form of an insulation box is wrapped around the valve. It is important that the insulation box does not have any clash with the handwheel. The clearance between the handwheel and the insulation box should be at least 75 mm, as an example. A fire nut is a good alternative way to use an insulation box to save space. In addition, having an insulation box around the valve blocks access to the drain/venting plugs as well as the greasing injection. Fire nuts on the body pieces can cause clashes with the flange bolts in FB valves, even in sizes larger than 400 . Unlike the insulation box, which requires coating (painting) underneath to avoid corrosion under insulation, there is no need to apply paint on the valve when using fire nuts. From a valve management point of view, applying the paint not only increases costs, it also affects the delivery time of the valves. Fire nuts protect the flange connection against fire and blast loads. In addition, they provide protection against corrosion and wearing. Fig. 1.112 shows the fire nuts on the flange bolts and nuts connections.

FIG. 1.112

Fire nuts around the flange connection nuts.

Ball-valve design consideration

79

Lever/handwheel design Smaller and lower pressure class valves usually require lower torque and are operated with a lever. When the lever is parallel to the line, the valve is open. When the lever is perpendicular to the line, the valve is closed. The opening/closing directions can be seen on the lever as shown in Fig. 1.113. Fig. 1.114 shows a half-open lever-operated ball valve during a body pressure test. The open and closed positions are usually not marked on the levers of lever-operated valves as they appear on the lever in Fig. 1.113.

FIG. 1.113 Open/closed marking on the lever of the valve.

FIG. 1.114 Half-open lever-operated ball valve during the body pressure test. Courtesy: LVF.

80

FIG. 1.115

1. Ball-valve applications and design

Gearbox with marking of the closing/opening.

In this case, the valve supplier offered a gearbox and a handwheel for small size underground (UG) valves instead of a lever. Probably, the reason was that the opening and closing status of a UG valve is stated on the gearbox. But the opening/closing positions of the valves are not usually marked on the lever-operated valves. Fig. 1.115 shows a gearbox in stainless steel 316 material with the position indicator on that. UG valves have extended stems, and the stem extensions of UG valves do not increase the torque values for valve operation. Torque depends on the opening/closing force of the valve, which is affected by the valve size and pressure class as well as the lever or hand-wheel diameter. Opening and closing position marking is done on both the handwheel and the gearbox of the valves. As shown in Fig. 1.114, the lever is moving approximately 45-degree upward (e.g., 20 mm) and then extends horizontally. The lever is moved upward to avoid a clash between the lever and the body end flange (in case of no mounting coupling on the valve). In some cases, a flat lever may be selected without being moved upward on the condition that no clash is made between the lever and the body flange. A flat lever design can save some space in a vertical position if the valve is installed horizontally. The connection of the lever to the stem should be strong enough so that two nuts can be selected to connect them together. In this case, the second nut that is sitting on the first nut is called a lock nut. Lock nuts can be fixed with Loctite.

Ball-valve design consideration

81

FIG. 1.116 Normal handwheel (none flat handwheel).

The distance between the center of the handwheel to the center of the ball valve can be different for metal and soft-seat ball valves in the same size and pressure class because a metal-seat ball valve may need a larger gearbox due to higher torque values. The distance from the handwheel to the center of the valve (handwheel extension) may be increased by the supplier by about 10% to cover the insulation space and insulation box. However, this extra length can cause problems by keeping the operators back in the sideway, which should always be clear during an emergency. Having a DIB valve, especially in a metal seat, increases the possibility of the hand-wheel extension to the sideway. One solution is to order a flat handwheel. Fig. 1.116 shows a normal handwheel with some height from the surface that increases the hand-wheel extension, unlike a flat handwheel. Fig. 1.117 shows a flat handwheel with no height from the surface that reduces the handwheel extension. Changing the gearbox to a compact one can save more space when it comes to hand-wheel extension but may be more costly. The other option is a gearbox with a short shaft that can save more space than the flat handwheel. If larger savings are required, the combination of both a flat handwheel and a short shaft gearbox can be selected. The disadvantage of a short shaft is the possibility of the clash between the insulation and the handwheel if insulation is wrapped around the valves.

Vent and drain plug or flanges Vent or drain requirements, as well as size and pressure class, depend on the valve size and pressure classes. Table 1.4 shows vent-and-drain sizes based on valve size and pressure class.

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1. Ball-valve applications and design

FIG. 1.117

Flat handwheel.

TABLE 1.4 Vent-and-drain size and type based on valve size and pressure class. 1 Drain and 1 vent connection

1 Drain and 1 vent connection

1 Drain and 1 vent connection

CL 150 and 300

300 –1000 , Min. 1/200 THD

1200 –2000 , Min. 3/400 FLG + Blinded FLG

2400 and above, Min. 100 FLG + Blinded FLG

CL 600 and above

300 –600 , Min. 1/200 THD

800 –2000 , Min. 3/400 FLG + Blinded FLG

2400 and above, Min. 100 FLG + Blinded FLG

TABLE 1.5 Cavity drain size based on the valve size as per API 6D. Nominal size of valve NPS

DN

Minimum pipe thread/pipe size in. (mm)

½–1 ½

15–40

¼ (8)

2–8

50–200

½ (15)

>8

>200

1 (25)

Usually there is no need to have a cavity vent-and-drain connection for valve sizes less than 300 as shown in Table 1.4. However, API 6D asks for vent-and-drain connection for sizes from ½00 as per Table 1.5. API 6D gives the cavity drain size based on the valve flange size and not the valve bore size. As an example, an RB ball valve 1000  800 has a 1000 flange and an 800 bore. It was a case that a ball-valve supplier considered the valve bore to be the size of the valve. Therefore, for a

Ball-valve design consideration

83

1000  800 RB ball valve, the valve supplier provided a ½00 plug equivalent to an 800 bore. However, the piping outlet of the drain connection was considered 100 since the valve has a 1000 flange size. That means that the ½00 drain plug was not compatible with the 100 pipe. Therefore, a 100  ½00 reducer can be designed on the line to solve the size mismatch. The other important point is about the valve drain/vent connection. That is related to changing the plug to flange connection for the drain/vent cavity connection. In fact, if a valve is ordered by mistake with a plug instead of a flange connection, one solution is to use a nipple with male threads, which is welded to the flange connection for the cavity drain. The male thread can be seal welded. The face of the flange should be welded with Inconel 625. If the face of flange is RTJ and made of carbon steel, that increases the cost and delivery time. The other question is whether it is correct to provide vent and drain on the cavity just for the DPE seat trunnion-mounted ball valves. The answer is that the cavity drain-and-vent connections are not only limited to ball valves with DPE seat(s). The SR seat ball valves should have cavity drain/vent connections. The cavity drain/vent connections are used as ports for cavity relief tests in ball valves, not only for a DPE seat but also for SR seats. The cavity drain/vent connection is also used for online testing of the valves. The second reason to have a cavity drain/vent for SR seat ball valves is that the cavity should be drained completely during the maintenance. The cavity may contain the trapped fluid which does not release from the SR seat. As per API 6D, the fluid pressure should reach to 1.1–1.33 times of the design pressure in order to be released from the cavity. Otherwise, the pressure will be accumulated in the cavity and will not be released. Therefore, the drain and vent is required for an SR seat. In addition, a floating-ball valve requires a ventand-drain connection on the cavity. Vent-and-drain flange connections could be fillet welded to the body or be threaded to the body with a seal weld done after a pressure test. The drain or vent safety plug should not be completely removed. The plug should release the pressure to the atmosphere by unscrewing the heavy hexagonal nut on the plug. Figs. 1.118 and 1.119 show the safety bleed plug with a

FIG. 1.118 Cavity drain safety plug in open position.

84

FIG. 1.119

1. Ball-valve applications and design

Cavity drain safety plug in closed position.

hole in it. Fig. 1.118 shows a safety plug that is open so the fluid can be released from the hole on the body of the plug. Fig. 1.119 shows a safety plug in the closed position. Fig. 1.120 shows the safety plug schematics. The safety plug can be connected to the body through part number 60f, as shown in Fig. 1.121. The drain/vent flange connections can be integrated and cast with the body as the preferred option. The ASME B16.34 standard for valves allows a welding connection from the body for auxiliary purposes like vent and drain. Making the hole in the body should be limited as much as possible to reduce the risk of leakage. The ball valve drawing in Fig. 1.122 shows a cavity drain path through the body that is very narrow, approximately 5–6 mm. The problem is that the drain connection can be clogged by the particles. Drain-and-vent connections are tested with the valve body during the shell test and are considered as the weak points with a greater risk of leakage than the body of the valve. Drain-and-vent connections are used as a port for the body-cavity test on both DPE and SR seats. The advantages of the drain flange to the plug are: 1. A flange connection is more robust and less exposed to damage in case of transportation. 2. A plug connection has a high risk of galling in the threads, unlike a flange connection. Some valves with an emergency shutdown (ESD) function are known as safety critical valves that require a leakage monitoring test once per year. Body-cavity connection should be used for a leakage monitoring test of the valves. The body cavity of the valves should have flange connections due to the frequency of the tests. Opening and closing the plug on a yearly basis would create galling on the threads. For small sizes of ESD valves with a yearly leakage monitoring test, it is practical to have one flange connection on the cavity for both vent-anddrain purposes. The flange connection could be integrated with the body or welded to the body through full penetration weld, and then radiographically test the weld. One

FIG. 1.120 Safety plug schematics.

FIG. 1.121 Schematic of safety plug connected to the body through part number 60f.

86

FIG. 1.122

1. Ball-valve applications and design

Ball valve with small-bore cavity drain connection.

disadvantage of the flange compared to the plug is that the flange connection should be piped to a closed drain or downstream for pressure equalizing, which requires more space and piping cost. Even the connections that should be blinded off with a valve for future piping require a flange instead of a plug connection. If the drain-and-vent connections are flanged and not integrated with the body, then they should be made of forged material grades. A drain plug is installed at the bottom on the trunnion to make the lower stem and trunnion antiblowout. The drain plug can be installed completely under the valve body on the 6 o’clock position, as shown in Fig. 1.123. The drain plug could be designed to lie at a 30- or 45-degree angle to the bottom of the valve to minimize the risk of the drain clash with the deck floor as shown in Fig. 1.124. Regarding Fig. 1.125, the cavity drain flange in red (dark gray in print version) has some angle degree from the bottom flange. This means that the cavity drain flange is not located completely at the bottom of the valve. Another valve supplier had vent-and-drain plugs in the 1 o’clock and 5 o’clock positions. Placing the drain plug in the 5 o’clock position (Fig. 1.126) can mitigate the risk of plug clash with the bottom. A flange connection is larger, so it may be required to be at the 3 o’clock or 4 o’clock position, with the connection to a very low point of the valve to suit drainage.

FIG. 1.123 Ball valve with a cavity drain plug on the bottom. Courtesy: LVF.

FIG. 1.124 Ball valve with a cavity drain plug with some degree from the bottom. Courtesy: FCT.

88

1. Ball-valve applications and design

FIG. 1.125

Cavity drain flange connection. Courtesy: FCT.

FIG. 1.126

Cavity drain plug in the 5 o’clock position.

Ball-valve design consideration

89

FIG. 1.127 Ball-valve cavity-drain flanges with isolation valves.

The drain-and-vent flanges are blinded with the blind flanges and a gasket between. On a carbon steel body valve in a high-pressure class, a stainless steel 316 RTJ gasket can be selected for cavity drain flanges. Fig. 1.127 shows a ball valve with cavity drain-and-vent flange connections that are connected to two modular valves. The modular valves should be open to connect the fluid inside the cavity to the drain. The cavity should be drained during maintenance. As was mentioned before, the disadvantage of having the drain flange is piping the cavity drain to the closed drain and installing the isolation valve, which requires more space and makes it a more costly option. Drain-and-vent plugs will leak if they are not sealed after a pressure test. PTFE seal tape was used in the past, but Loctite is more common nowadays. PTFE tape could be around 0.1 mm thick and should contain a high concentration of PTFE (>99.5%), and it is used for temperatures up to 250°C. Graphoil tape can be used for temperatures above 250°C. Fig. 1.128 shows PTFE tape, and Figs. 1.129 and 1.130 show Loctite sealing for a drain plug (Fig. 1.131). If the valve drain or vent cavity should be piped to the closed drain, then the piping layout engineer should know the drain-and-vent positioning (α) (e.g., 45 degrees to horizontal and downward when the valve is vertically installed) as well as distance from the center of the valve to the drain-and-vent connection (L) in order to be able to model the pipe in PDMS software. Fig. 1.132 shows the α angle and L dimension for the cavity drain of a ball valve.

90

1. Ball-valve applications and design

FIG. 1.128

PTFE tape on the valve drain plug.

FIG. 1.129

Loctite for drain-plug sealing of a ball valve.

In some cases, the valve cavity should be piped because of leakage monitoring. As mentioned earlier, leakage monitoring should be done for safety critical valves, usually with ESD and XSV functions. This test is done to make sure that the valves are not leaking from the seats during the operation. The leakage monitoring connection should be flange type and not drain plug.

Ball-valve design consideration

FIG. 1.130 Loctite for sealing the drain plug.

FIG. 1.131 Sealant on the drain plug of a ball valve.

91

92

FIG. 1.132

1. Ball-valve applications and design

The α angle and L dimension for the cavity drain of a ball valve.

Lifting lug and valve support Ball valves in sizes 600 and above are usually provided with a support to hold the weight of the valve. Support could be a plate connected to the body-piece bolts or a pipe piece welded under the body of the valve, or integrated with the body in TCG valves (as per the API 6D standard). API 6D uses an expression called “support ribs or legs” that refers to a metal structure that provides a stable footing when a valve sits on a fixed base. Item number 15 in Fig. 1.133 shows an integrated support under the TCG valve integrated with the body as per the API 6D standard. This support is used during handling and storage of the valves before installation and maintenance. Some end-users may avoid using the support due to health, safety, and environment (HSE) issues, especially when the valve is installed vertically as shown in Fig. 1.134. Sharp edges of the support can cause injury to workers during the installation. Removal of the support plates shown in Fig. 1.135 requires opening the body-piece bolts and maybe retesting the valve. Generally, sharp edges should not be seen on the valves and their parts with a radius of more than 2 mm in the NORSOK standard. Sharp edges could be found on the gearbox or body of the valves in some cases. In addition, a larger insulation

Ball-valve design consideration

FIG. 1.133 TCG valve with integrated support (number 15) under the body.

93

94

1. Ball-valve applications and design

FIG. 1.134

Support plates on a ball valve.

FIG. 1.135

Support plates on a ball valve. Courtesy: LVF.

box is required in case of insulation if the valve contains sharp edge supports toward the outside when it is installed vertically. If a valve has no supporting plate, the valve manufacturer may use wooden plates or rectangular wooden blocks under the valves to support them, as shown in the series of photographs in Fig. 1.136. The support is not necessary for small-size valves such as 400 and less. However, a valve in 00 4 size but high-pressure class of 1500 and 330 kg requires supports. The supports can be welded to the body as per Fig. 1.137. ASTM A36 can be the material of the supporting plate that is placed under the bolts for body and bonnet connections. ASTM A36 is a structural low-temperature carbon steel plate with good strength and formability. It is possible to have it galvanized (zinc coated).

Ball-valve design consideration

FIG. 1.136 Ball valves with a wooden support underneath. Courtesy: FCT.

95

96

1. Ball-valve applications and design

FIG. 1.137

Ball valves with the welded support.

FIG. 1.138

3800 top-entry ball valve self-supporting. Courtesy: FCT.

The big 3800 riser valves are usually self-supporting and they sit on a big area of approximately 1 m2 underneath the body (Fig. 1.138). A support is placed after the valve on the pipeline or pup piece of the valve in the offshore industry. A lifting lug is provided for sizes 800 and above as per API 6D standard, if it is not agreed to by the supplier. Some suppliers may consider the valve bore to be the size of the valve. For example, if 800  600 is counted as a 600 valve, a lifting lug is not given for this valve by some

Ball-valve design consideration

97

valve suppliers as per API 6D. The Norsok standard (Norwegian Petroleum Standard) specifies permanent lifting lugs for valves above 200 kg, and an instruction for lifting the valve from 25 to 200 kg should be provided by the valve manufacturer. Some valve manufacturers may provide a lifting lug for smaller sizes such as 300 and 400 in high-pressure classes due to the relatively heavy weight of the valves. The temporary screwed-on lifting lugs should be removed from the valves after installation. A silicon or a plastic plug can be placed in the screwed lifting holes inside the valve body to mitigate the risk of corrosion. Corrosion in the screwed lifting lug holes is more risky for carbon steel materials. Sometimes, valve manufacturers cannot apply thick hot dip galvanized (HDG) on the lifting lugs and lifting threads. Applying thick HDG on smaller threads would fill the thread gaps completely; so, it is not possible to screw the lifting lug in. In that case, a thin zinc plate with 5–20 μm should be used for corrosion protection of the lifting lug. The other choice is to change the lifting lug material to stainless steel 316. Considering the fact that the screwed lifting lug should be removed from the valve after installation, there is no need to apply HDG or zinc plate on the lifting lug for corrosion protection. A carbon steel lifting lug can be in ASTM A29 grade material. One example of a threaded lifting lug is using a carbon steel lifting lug on a 6MO body valve. The lifting lug is proposed to be threaded to avoid welding two dissimilar materials of carbon steel and 6MO. Cost is the main reason why a carbon steel lifting lug is proposed for 6MO body valves. A carbon steel lifting lug is cheaper than other materials such as austenitic stainless steel or duplex. There are two different challenges related to the welding of the carbon steel lifting lug to the 6MO body valve. The first issue is that the carbon steel and 6MO are in two different materials. Therefore, a new PQR/WPS is required for welding these two different materials. The other issue is the cross-contamination that could cause a crack on the welded materials, as well as applying NDT on the welding. A threaded carbon steel lifting lug is proposed to be removed from the valve and the hole is filled in with a silicon or plastic cap. Threaded carbon steel lifting lugs could be subject to crevice corrosion even if they are hot dip galvanized. In a welded lifting lug, it might be better to weld SS316L to 6MO instead of carbon steel since both 6MO and SS316L have austenitic properties. 22Cr/25Cr duplex lifting lugs can be welded to the flange connections of the valve body of 22Cr/25Cr duplex as shown in Fig. 1.155. A lifting lug made of materials such as ASTM A516 Gr.70 (plate of carbon steel) or ASTM A29 can also be welded on the body flange of carbon steel body valve. Fig. 1.139 shows a screwed lifting lug made of carbon steel. The other type of lifting lug is a plate that is welded to the body of the valve. Fig. 1.140 shows a lifting lug welded to the body flange of the valve. The first choice of lifting lug could be welded or integrated with the body instead of threaded to avoid making a threaded hole in the body of the valve. A lifting lug could be swiveled (able to be installed laterally) like an eye nut shown in Fig. 1.141. This type of installation is called an articulated lifting lug. Swivel lifting eyes are available to rotate 180 or 360 degrees, as shown in Fig. 1.142. Lifting lugs may be painted with the body of the valve as shown in Fig. 1.143. A lifting lug should have a safety factor regarding the withstanding loads (load capacities). As an example, an end user may need a safety factor of 4 for a lifting lug, which means that the lifting lug should be strong enough to withstand four times the weight of the valve. The lifting lug can be integrated with the cast body or full penetration welded to the body. A welded lifting lug may need 100% visual inspection as well as a magnetic particle test (MPT), liquid

FIG. 1.139

Screwed lifting lug.

FIG. 1.140

Plate lifting lug welded to the body of the valve.

FIG. 1.141

Articulated lifting lug.

Ball-valve design consideration

99

FIG. 1.142 Swivel lifting eye rotation.

FIG. 1.143 Painted lifting lug with the body of the valve. Courtesy: FCT.

penetration (LP), radiography test, or ultrasonic test (UT). However, some manufacturers may deviate in such a way as to avoid volumetric UT on the welded lifting lugs. Applying LP instead of MPT can be the preferred choice of NDT since it is difficult to put probes on the nonflat-shaped body of the valve for MPT in carbon steel material. Fig. 1.140 shows an LP test on the welded lifting lugs in 22Cr duplex material welded to the body flange of the valve. For large size valves such as 2000 and above, the integrated or welded lifting lugs are preferred on the threaded lugs. The valves are relatively heavy, so threaded lifting lugs cannot

100

1. Ball-valve applications and design

FIG. 1.144

Welded lifting lug on the top of a 3800 valve body. Courtesy: FCT.

FIG. 1.145

Actuated ball valve lifting. Courtesy: LVF.

provide the required mechanical strength to support the weight of the valve. Fig. 1.144 shows a 3800 body valve with the welded lifting lugs on the top. Actuator lifting lugs should not be used for lifting the valve and actuators together as per actuator manufacturer instructions. Fig. 1.145 shows an actuated ball valve that is lifted from the valve instead of actuator lifting lugs. However, small-size valves like 200 , 300 , or 400 light butterfly types can be lifted with the actuator lifting lug since they are not heavy. Usually, actuator as well as gearbox lifting lugs can be removed after mounting the actuator or gearbox on the valve. Fig. 1.146 shows lifting lugs in pink color (gray in print version) on the electrically actuated ball valve during the test. Fig. 1.147 shows a ball valve and how it is lifted from two lifting lugs like a cross.

Ball-valve design consideration

101

FIG. 1.146 Actuated ball valve with pink lifting lugs (gray in print version) during the test. Courtesy: ATV.

FIG. 1.147 Lifting a ball valve from two lifting lugs. Courtesy: FG Valve.

Air-breather/overpressure plug An air breather/overpressure plug is installed on the top flange to allow the flow of clean air to and from the closed chamber where balanced atmospheric pressure is required. The air breather ensures that there is no dangerous buildup of the pressurized fluid in a closed

102

FIG. 1.148

1. Ball-valve applications and design

Air breather on the valve top flange.

chamber, which is important during gearbox/actuator installation. Therefore, an air breather is used for cooling and removing the heat created in the valve as well as a safety device to release extra fluid pressure in the valve around the stem. Fig. 1.148 shows an air breather on the valve. The grease injection on the stem is located lower than the air breather/overpressure release plug on the other side of the valve.

Valve and actuator connection A coupling or adaptor spool is usually used between the valve and actuator to ensure the integrity of the valve and actuator together. The adapter spool should be strong enough to withstand the actuator weight and generated loads as well as any blast load (accidental load) based on design accidental load (DAL) specifications. In addition, environmental loads like snow, wind, etc., as well as direction of installation and frequency of operation should be taken into account in the mounting bracket design. Standard API 6DX covers the design and requirements for the adaptor spool between the valve and the actuator. It also covers actuator testing. The ISO 12490 standard covers the actuator sizing and integrity but it is not applicable for control valves. The coupling should withstand 1.1 times of the maximum output torque of actuators including the PSV device load on the control panel and spring force load. The stress in the mounting bracket should not exceed 67% of yield stress in 1.1 times the maximum output torque. Blast load affects the coupling size, and if the coupling is not designed based on the blast load, then the stress and support department would be required to design a large support for the valve like the one shown in yellow color in Fig. 1.149. The lesson learned is that the valve manufacturer should be informed if the valve is installed on the vertical line, since there are more loads on the coupling if the valve is installed

Ball-valve design consideration

103

FIG. 1.149 Support design for a vertically oriented valve with a weak coupling.

vertically. The actuator supplier usually considers the blast, weight, and environmental loads on the coupling design. But the connection of the coupling to the valves and the bolt diameters may not be strong enough. Thus, the bolt diameters on the valve top work cannot be enlarged and strengthened if the valve manufacturer is not informed of the vertical direction of the valve installation until a very late stage. The support shown in Fig. 1.149 has disadvantages such as extra cost, the risk of blocking the tube connections around the actuator, as well as reducing the flexibility and movement of the actuator. The support should not be completely fit around the actuator; a gap is required to avoid restricting the movement of the valve and actuator in any direction. One solution to avoid the structure support around the valve actuator is to change the coupling material to 22Cr duplex instead of stainless steel 316, and the bolting material of the coupling connection to the valve and actuator from 22Cr duplex to 25Cr duplex to strengthen the coupling as well as the connections. It is important to consider that the bolting for the SS316 coupling should be ASTM A193 B8M Cl.2 (SS316), which is relatively high strength due to strain hardening. Strain hardening or work hardening is strengthening of the metal by plastic deformation. L7 HDG (zinc-coated) bolts have higher strength than SS316 bolts, but they are not recommended for SS316 coupling. The contact of zinc in HDG bolts with austenitic stainless steel coupling corrodes the stainless steel coupling, especially in the hightemperature applications. In one situation, the coupling connection to the actuator was not strong enough for a valve installed on the vertical line; so, two supports from the actuator to the flange face were proposed by the valve manufacturer, as shown in Fig. 1.150. It was decided to avoid drilling the hole on the valve body flange due to the following reasons: 1. Making the holes on the flange can create weak points regarding the mechanical strength, especially in cases of dealing with excessive forces on the flanges. 2. The drilling and threading of the flange edge to fasten the actuator support may cause corrosion and future maintenance requirements.

104

FIG. 1.150

1. Ball-valve applications and design

Support design for a vertically oriented valve with a weak coupling.

A better solution is to weld the support to the valve lifting lug instead of making the hole on the flange, and the support material should be lean duplex or stainless steel 316L as per Fig. 1.151. The differential pressure across the valves affects the actuator sizing. In this case, the differential pressure across the valve was changed and the size of the actuator was increased. Increasing the actuator size increases the actuator weight and surface, which results in higher blast load. Thus, the coupling design should be strengthened to withstand the actuator weight load. The coupling is stronger and bigger in the ball valves than the TCG valves. The TCG valve actuator load is concentrated and coming from the vertically oriented actuator. The TCG valve actuator is vertically installed on the top of the valve as shown in Fig. 1.152. The connection of the coupling to the actuator from one side and to the valve from the other side should be strong enough against the loads. In addition to the coupling, contacts between three parts of the actuator—center part to the spring housing, center part to the cylinder part, and center part—should be strong against the blast loads.

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105

FIG. 1.151 Revised support design for a vertically oriented valve with a weak coupling.

An adapter is usually supplied by the actuator supplier. However, it is the valve manufacturer’s responsibility to supply the coupling for top-entry ball valves in which the valve top flange is not given as per ISO 5211. Fig. 1.153 shows top-entry ball valves with pneumatic actuators on the top. The couplings act as supports under pneumatic or hydraulic actuators. However, electrical actuators are lighter and usually have no requirement to design and have a coupling under the electrical actuators unless for insulation purposes or for top-entry ball valves as shown in Fig. 1.154. A coupling may need finite element analysis for large size 3000 or 3800 valves, and it is better to have it as one solid piece. The load on the adapter spool is stronger if the valve is installed on a vertical line. If the adapter spool is made of a pipe that is welded to the flanges from both sides, it should be a full penetration weld rather than fillet weld (fillet weld has 0.75 strength efficiency) and liquid penetration test on the welds is recommended. The material of the adapter spool is usually SS316 at a minimum. Alternatively, painted carbon steel coupling is acceptable for the coupling to reduce the cost.

106

FIG. 1.152

1. Ball-valve applications and design

Vertically installed actuator on the TCG valve. Courtesy: Valvitalia.

An adapter spool (mounting bracket) is always required for hydraulic and pneumatic actuators mounted on both top-entry and side-entry ball valves. However, electrical actuators are directly mounted on the side-entry ball valves’ top flanges without any mounting brackets in case of an insulation requirement. However, top-entry ball valves require adapter spool/ coupling for electrical actuator mounting since they do not have any top flange. As per API 6D, typical quarter turn valve-to-actuator interface is given in ISO 5210/5211. The ball-valve top-flange standards are also ISO 5210/5211. In addition, the dual pin that penetrates both the actuator bottom flange and the coupling is required to avoid coupling bolts and the coupling side movements during the actuator functioning, as per API 6D. If the dual pin is left out, the connected bolts may not withstand the loads. As per API 6DX, it is the valve manufacturer’s responsibility to ensure that the mounting bracket or kit, or coupling bolts to the valve body, are capable of withstanding 1.1 times the torque or trust load from the actuator. Coupling should be rounded for easy wrapping of insulation. The coupling (bracket) should have a vent or drain connection as a means of overpressure protection and releasing pressure build up as per API 6D, like the one shown in Fig. 1.155. The operator, coupling, and other interfaces should be sealed to avoid ingress of external contamination and moisture as per the API 6D standard. Therefore, a gasket is installed between the top flange and the coupling, and silicon is used to seal between the actuator/gearbox and the coupling.

Ball-valve design consideration

FIG. 1.153 Top-entry ball valve with a coupling between valve and pneumatic actuator. Courtesy: ATV.

107

108

1. Ball-valve applications and design

FIG. 1.154

Top-entry ball valve with a coupling between valve and electrical actuator. Courtesy: ATV.

FIG. 1.155

Drain on the coupling between the valve and the actuator. Courtesy: ATV.

Ball-valve flow characteristic The flow characteristic in a ball valve is an equal percentage that is the opposite of the quick opening. That means that when the ball moves from a closed to an open situation, the fluid passes the valve when it is 32%–40% open, as an example. It means that the valve closure

Ball-valve design consideration

109

FIG. 1.156 Ball movement inside the ball valve.

FIG. 1.157 Flow capacity of a ball valve based on the ball rotation.

member does not allow the fluid to be passed quickly while the valve is opening. Thus, there is no flow from the valve below 32%–40% opening percentages. A DIB valve may allow the fluid to pass even more quickly at 40% opening since the ball is reinforced and larger. The stem angle and opening angle are the same. Fig. 1.156 shows the ball movement during the opening of a ball valve. Fig. 1.157 shows a chart of flow capacity based on the stem angle or closure member angle. As shown in the picture, the valve provides flow from a little bit more than a 40-degree opening.

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1. Ball-valve applications and design

Ball-valve cycle test A cycle is defined as the continuous movement of the valve closure member or obturator from a fully closed position to a fully open position and back to a fully closed position, or vice versa. Valve manufacturers usually guarantee valves for a maximum of 1000 cycles. Performing cycling tests 1000 times can wear the valve, and are therefore not required by some end-users. Fluid types can affect the wearing; for example, oil could lubricate and result in minimum wearing compared to dry gas. Cycle tests may be done before the main seat leak measurement to make sure that the sealing is good enough even after cycles. A valve supplier may propose a small number of cycles (e.g., 10 times) before the main seat test or DIB seat test, which can improve the sealing like a lapping process. Fig. 1.158 shows cycle tests for a DIB valve.

Ball-valve torque values Torque values are calculated by valve manufacturers as inputs for the actuator sizing done by actuator manufacturers. There are six torque values: break to open (BTO), break to close (BTC), end to close (ETC), end to open (ETO), opening running, and closing running. Torque values for ball valves are based on the following sequence: BTO  BTC > ETC  ETO > Running to open ¼ Running to close ðfor valveÞ The rule above is usually true for valves. But when it comes to pneumatic and hydraulic actuator torques, the rule is usually different. The torque values depend on the fail open (FO) or fail close (FC) function for the actuated valves. The actuator torque should be larger than the torque produced by the valve due to a safety factor of minimum 150% on actuator sizing. For an FC valve, the torque values could be like this, at least at a normal or high operating air/ oil pressure: BTO > BTC > ETO > ETC > Running FO means that the spring provides torque to open. The BTO is lower than the BTC, which is the air pressure. The reason for this is probably that air pressure should be stronger than the spring torque to open the valve. In this case: BTC > BTO > ETC > ETO > Running However, it could be a case that air with a low pressure of 5.5 barg does not have enough power to close the valve in an FO valve. In this case, BTC is lower than BTO, unlike the normal condition for an FO valve. This can happen if the spring is not designed properly and the spring torque is higher than what it should be. The minimum air pressure and oil pressure are 5.5 and 160 barg, respectively, in pneumatic and hydraulic actuators. The intention is to test the actuator torque with a low air pressure of 5.5 barg in case of a pneumatic actuator, and 160 barg as the lowest pressure of oil in hydraulic actuators, to make sure that even the lowest pressure of air/oil can close the valve in an FO valve and open the valve in an FC valve. In addition, the maximum allowable stem torque (MAST) should be greater than the actuator torque even at the highest oil or gas pressure. Therefore, it is a requirement to test the actuator with 9 barg air or 210 barg oil (maximum air and oil pressure values) to see that

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111

FIG. 1.158 Cycle tests of a DIB valve 3800 Class 1500.

the MAST is sufficient even with high air or oil pressure values. The important point is that the torque table provided by the actuator supplier is higher than the valve torque values given by the valve supplier. The highest torque given by valve supplier is the MAST as per Table 1.6. One important parameter in actuator sizing and measuring the torque values is the differential pressure that the valve should be opened or closed against. A higher differential pressure increases the size of the required actuator.

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1. Ball-valve applications and design

TABLE 1.6 Torque values for a 1600 class 300 actuated valve.

NPS (Ø mm)

Class

Delta Opening P bars break

16” SPE ANSI 51 (385.00 mm) 300 (Metal)

8652

Opening running

Opening end

Closing break

Closing Closing running end

3830

4330

8652

3830

4330

Valve’s stem shear torque (MAST)

Values for 4 P on:

19,150 2 seats (A182 Gr F51)

TABLE 1.7 Torque values for an actuated valve. Valve actuator Tag

Reducer pressure barg

Break to open at 0 degrees Nm

End to close at 0 degrees Nm

Running torque Nm

End to open at 90 degrees Nm

Break to close at 90 degrees Nm

13,454

6730

5960

6730

13,454

7

43,573

25,418

17,436

28,840

31,902

Safety factor

3.23

3.77

2.92

4.28

2.37

5.5

28,640

25,418

11,984

14,432

31,902

9

63,484

25,418

17,436

48,050

31,902

The torque values in Table 1.7 are given by the actuator supplier. The maximum torque in the table is 63,484 N m (highlighted in bold), which gives 73,007 N m by adding a 15% safety factor. The safety factor for actuator sizing has been considered to cover some frictions like stem and packing, seat and ball, etc. The actuator torque is higher than the MAST in this case. One solution is to change the stem material from Duplex to Inconel 725, which will increase the MAST to approximately 40,000 N m. The MAST is still less than the maximum actuator torque, which is 73,007 N m, and the problem is not still solved. The spring force should be higher in the beginning than the end, to push the air/oil back in the piston. So, if the valve is FC, the spring has closed, and the BTC is usually larger than the ETC. In addition, air force is larger in the beginning than the end; to push the spring back means that for the FC valve, the BTO is larger than the BTC. The other point is that spring torque is always constant in different oil or gas pressure; so, if the valve is an FC valve, then the BTC torque on all three values of air or oil pressure (minimum/normal/maximum) should be equal. Also, the BTO for an FO valve (spring torque) should be equal for all the conditions and lower than the BTC. The BC and ETC torques (spring torques) for 7, 5.5, and 9 barg air pressure are 3795 N m and 2392 N m, respectively, and constant, as per Table 1.8. The valve is FC since the spring load closes the valve. In electrical actuators, all four torques are equal. Table 1.9 shows the electrical actuator torque. Regarding the first line, the IQT2000 actuator model produces 2000 N m for all four torques, which are BTO, ETC, Running, ETO, and BTC.

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Ball-valve design consideration

TABLE 1.8

Torque values for an actuated valve.

TABLE 1.9

Torque values for electrical actuated valves. Break to open at 0 degrees Nm

End to close at 0 degrees Nm

Running torque Nm

End to open at 90 degrees Nm

Break to close at 90 degrees Nm

DB 600  4” ANSI 1500

780

330

230

330

780

IQT2000

2000

2000

2000

2000

2000

Safety factor

2.56

6.06

8.70

6.06

2.56

DB 1200  12” ANSI 300

1536

900

790

900

1536

IQ10 F10 B4 + IW5R 280:1

2992

2992

2392

2992

2992

Safety factor

1.95

3.32

3.79

3.32

1.95

DB 1200  12” ANSI 300

1536

900

790

900

1536

IQ10 F10 B4 + IW5R 280:1

2992

2992

2392

2992

2992

Safety factor

1.95

3.32

3.79

3.32

1.95

Valve actuator Tag

Valve max Nm

Max actuator output torque Nm

Check MAST OK/NOK

3910

2000

OK

9390

2992

OK

9390

2992

OK

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1. Ball-valve applications and design

Note: BTO torque can be measured when the seat is energized from both sides by the fluid (DBB) or from one side. The ball movement is fastest in running status compared to open or closed situations. BTO torque is effective in the first 15 degrees of the valve opening. Maybe because after some opening degree, the pressure upstream and downstream will be equalized; so, less force is required to open the valve after some degree of opening. Usually, the BTO torque is measured when the upstream seat is under pressure. The cavity and downstream pressure are zero. So, just upstream is exposed to delta P and one seat is under pressure. When it comes to BTC torque the valve is open, so seat1, cavity, and seat2 are under pressure and delta P on both seats is zero. It means that no seat is under pressure providing that there is a hole in the ball to facilitate communication between cavity and both upstream and downstream. That is the reason why the BTO is higher than the BTC if the ball is drilled. Thus, drilling a hole in the ball is a way to equalize the pressure in the cavity with the upstream and downstream seats. The hole in the ball enables communication between the cavity and the inside bore of the ball. In this case, the pressures in upstream, downstream, and cavity are equal when the valve is open. Therefore, the BTC is very low (almost zero) since no seat is under pressure. The other advantage of the hole in the ball is that the valve body test should not be done with a ball valve in a half-open position. The ball valve should be half-open during the body test with 1.5 times the design pressure to avoid damaging the seat. Thus, the valve with a hole in the ball can be body tested in a fully open position. Fig. 1.159 shows the ball valve with the hole in the cavity. Torque values are higher for DBB valves where two seats are under pressure from both sides and no pressure is in the cavity. In this case, both seats are under pressure in both BTO and BTC and these two values are equal and higher than BTO and BTC when one or no seat is under pressure. However, it seems that DBB with no pressure in the cavity is

START CLOSING

PSEAT 1

PSEAT 2 PCAVITY

FIG. 1.159

Ball valve with a hole in the cavity.

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115

designed for torque measurement and actuator sizing, which could be a case for valves during the operation. Both BTO and BTC are equal for valves designed as DBB with zero pressure in the cavity. The actuator torque values are higher than the torque values specified by the valve supplier such as BTO, BTC, ETO, etc. However, MAST should be 10% or maybe 15% higher than the actuator torque. In Table 1.8, torque values of 1535, 1075, 900, 1075, and 1535 N m are provided by the valve manufacturer. But the values before 7, 5.5, and 9 barg are coming from the actuator manufacturer. The maximum actuator torque in the last column is given as 6055 N and the MAST is 6524 N. Torque or MAST should be more than the actuator maximum torque, and a margin of approximately 15% may be added to make sure that the stem is strong enough. In this example, the safety margin on the MAST is approximately 7% higher than the maximum actuator torque. The safety factor is the ratio of the maximum torque @ 9 barg to the valve torque or to the actuator torque @ 5 or 7 barg. Torque values are affected by the size and rating, seat design, valve differential pressure, seat-and-ball material, and bore design (FB/RB). A DPE seat requires more torque for opening and closing as well as a larger gearbox/actuator due to higher spring torque values, and a special seat design that is pushed more tightly to the ball. Increasing the body-cavity pressure to a maximum 133% of the design pressure in the body cavity increases the valve torque and actuator size as well. As mentioned earlier, finite element analysis is required for DPE seats to make sure that the contacted ball and the DPE seats are not damaged (overstressed) due to high spring forces. Harder metallic seat-and-ball materials such as 22Cr duplex require a higher torque for operation of the valve than soft 316 stainless steel materials. Metallic seat materials require higher torque than soft materials such as PEEK and PTFE. Selecting a trunnion support for ball valves reduces the torque and saves the size of the actuator. The maximum torque value could be 150 N m for operating a hand-wheel-operated valve. If the required torque for opening and closing the valve exceeds the value given above, then it is difficult for the operator to open and close the valve. The first solution is to try opening and closing the valve to reduce the friction between the ball and seat. If this solution does not work, the valve should be disassembled and ball seat surfaces and seats should be lapped to reduce the friction. The other solution is to increase the hand-wheel diameter, which should be checked with the piping layout engineer because of the potential extra space requirement. The hand-wheel diameter depends on the size, pressure class, and bore (RBd or FB). For example, having a 750-mm large handwheel for a small 200 or 300 valve is not logical and the handwheel is too large. One way of reducing the hand-wheel diameter is to increase the gear tooth numbers in the gearbox, which could lead to increasing the gearbox dimension. For example, a 1000 metal-seat ball valve in the pressure class 150 has an M15 gear (15 teeth) and the hand-wheel diameter is 700 mm in one valve supplier design. It is possible to increase the gearbox size to M20 and reduce the hand-wheel diameter to 500 mm for class 300. But in some cases, the gearbox size can be increased without any change to the hand-wheel size. The handwheel diameter can be designated with a capital R in a number like R24, which is 24  25 ¼ 600 mm diameter. Finite element analysis may also be required for metal-seat ball valves. PEEK is a stronger soft material than PTFE; so, higher torque is required for opening and closing the PEEKseated ball valve. PEEK may be filled with PTFE or graphite to be softer and reduce torque values.

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1. Ball-valve applications and design

An actuator manufacturer should know the valve delta pressure to calculate the torque values and size the actuators. The worst case is maximum pipe class pressure@the minimum temperature, which is usually higher than the maximum design pressure. The maximum pipe class pressure should usually be given to the actuator supplier at an earlier stage since accurate process data (design pressure) is not available. Higher torque values are achieved by maximum pipe class pressure. Calculated valve torque values and MAST are a basis for actuator sizing. However, the maximum differential shutoff pressure, which is usually equal to the design pressure, will be used later for the actuator sizing. The stem diameter as well as the MAST should be large enough to withstand the torque coming from the actuator. Upgrading the stem material will not affect the actuator size and torque, but changing the seat from soft to metal will increase the torque, and the stem may be upgraded to increase the MAST. The torque value unit is N m for quarter-turn valves such as ball valves. However, the torque values for gate valves are given based on the unit Newton. If the actuator torque exceeds the MAST, then the first approach is to upgrade the stem material. Using a pressure relief valve on the control panel can reduce the actuator torque and the last solution is to increase the stem diameter. A pressure relief valve can reduce the air torque without reducing the spring torque; so, if the valve is FC, the BTC that is spring torque cannot be reduced by a pressure relief valve. However, the air or oil torque is usually higher than the spring torque. The disadvantage of a pressure relief valve is that it requires yearly maintenance; so, it may not be a favorite choice for an operation company. In one case, the supplier reduced the torque by just adding a pressure relieve valve and the set point was 8 barg. The vendor also upgraded the stem material from 22Cr duplex to Alloy 718 to manage the high actuator torque. However, as discussed earlier, the solution of having a pressure relief valve is not good for the operator due to calibration or maintenance. In addition, in case of pressure relief valve failure, the actuator would experience 9 barg air pressure. An alternative to PSV, an air filter regulator (AFR), which is both filter and air pressure reducer in one unit, can be used on the control panel to reduce the actuator torque. An AFR is not recommended due to the same reasons mentioned for PSV (PRV). Inconel 725 has high strength and is very good material for the stem to increase the MAST and remove the safety relief valve. However, in one case with a small-size ball valve 1 ½00 and 25Cr super duplex body, even updating the stem material from 25Cr duplex to Inconel 725 did not increase the stem torque above the actuator torque. Using an air release valve reduced the air pressure to 6 barg from 9 barg and the MAST, which was 112 N m, became higher than the actuator torque, which was 11 N m. In some cases, increasing the stem diameter slightly within the acceptable tolerance can be helpful to increase the MAST. However, increasing the stem diameter more than tolerances means changing the adapter plates and the bolts, which is a design change. Problems with the MAST can exist even for small-size valves in 1 ½00 and low-pressure class 150 in 25Cr duplex material. The valve torque requirement for a 1 ½00 SS316 body soft seat and 25Cr duplex body soft seat should be the same. However, a 1 ½00 and 25Cr duplex valve receives high torque from the actuator exceeding the MAST. The selected actuator is the smallest possible, but it is still big for the small size valve. It is not possible to select a smaller actuator to reduce the torque on the valve. However, the valve is too small in low-pressure class, so that could be the reason why the MAST is an issue. Selecting a big actuator for a valve could also cause a problem. In this case, a rack and pinion actuator, which is more compact, is

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117

FIG. 1.160 Low torque operated ball valve.

the selected actuator for the valve. The lesson learned is that large size and high-pressure class valves do not necessarily have MAST problems. A very low torque seat ball valve was designed in such a way that the fluid in the connected pipe to the valve is injected to the seats, pushing the seats away from the ball (see Fig. 1.160). Thus, the ball was opened and closed with the lowest torque possible and no friction to the seats. Torque values can be affected by the fluid in terms of being clean or particle containing. Clean fluid creates lubrication on the ball and seat so the torque value can be reduced. In a floating-ball valve, the ball is pushed toward the seat by fluid pressure. In trunnionmounted ball valves, the ball is pushed toward the seat by fluid pressure plus the spring load behind the seat. Higher fluid pressure is pushing the ball stronger toward the seat; the torque value will be increased.

Fire test API 6FA, EN ISO 10497, and BS6755 are applicable fire test standards for both soft- and metal-seat ball valves. API 607 is applicable only for soft-seat ball valves. As per the API 6FA standard, a valve should be fired for 30 min at a temperature between 760°C and 980° C. Two or three thermocouples (in larger sizes) are installed on the body of the valve. The average temperature shown on the thermocouples is counted as the test temperature and none of the thermocouples’ temperatures should be lower than 704°C. Fig. 1.161 shows the valve for the fire test plus the thermocouples installed on the body. Up to seven tests are performed on the ball valves: 1. A high-pressure test is done on the seats when the valve is closed. The test duration is 30 min and the through seat leakage is a maximum of 400 mL/in./min.

118

1. Ball-valve applications and design

1 in. (25 mm)

1.5 in. (38 mm) calorimeter

1 in. (25 mm) from stem seal

1 in. (25 mm)

Flame thermocouples

1.5 in. (38 mm) calorimeters 1 in. (25 mm) 1 in. (25 mm)

FIG. 1.161

Ball valve for fire test.

2. A high-pressure test is done on the body when the valve is closed. The test duration is the burning time (30 min) plus the cooling time (the cooling time to reach 100°C) and the external leakage is a maximum of 100 mL/in./min. 3. A low-pressure test is done on the seat (only for pressure classes 600 and below) and after cool down, the valve is closed. The test duration is 5 min and the through seat leak is a maximum of 40 mL/in./min. 4. A low-pressure test is done on the body (only for pressure classes 600 and below). After cooling down, the valve is closed. The test duration is 5 min and the external leakage is a maximum of 20 mL/in./min. 5. A function test is done to open the valve from the closed position. This test evaluates whether it is possible to operate the valve and the gearbox during the fire test. 6. To test external leakage on body, the valve is opened, and external leak is a maximum of 200 mL/in./min 7. A cavity relief test should be opened for an SR seat at a maximum of 1.33  DP. If a ball valve is fire tested as per the API 6FA standard for a certain size and rating and passes the test, it qualifies at double the size and one rating up. For example, the 800 CL150 fire safety test covers 800 , 1000 , 1200 , 1400 , and 1600 CL150 and 300 of the same design (e.g., side entry) and nonmetallic material. However, qualifying an 800 CL150 could also qualify 2000  1600 CL300, although the size of the valve is counted as the size of the end connection, according to API 6FA. If a 1600 ball valve is fire tested as per API 6FA, it covers all the larger sizes with the same design and the same nonmetallic materials. Changing the nonmetallic materials (e.g., changing a Viton to lip seal for stem sealing) requires a new test. Metallic body material change and bore change (FB/RB) do not require any new additional test as per API 6FA. But material change may require a new test in the ISO 10497 standard. Therefore, 800 FB testing also qualifies an 800 RB that has a smaller bore. An 800  600 RB ball-valve test qualifies a 600 FB ball valve with the same stem and ball design. Fire testing a 200 valve covers the smaller sizes.

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119

As mentioned earlier, a body material change may require a new test in the ISO 10497 standard. Testing the ferrite body valve qualifies austenitic and duplex body materials. L7 bolt testing also covers B8 and B8M bolt materials, but nothing else. Changing the nonmetallic material such as lip seal requires a new test. Changing the bolts from L7 HDG to super duplex does not require any new test. Testing austenitic stainless steel body valves can cover the nickel alloy valves with the same size and pressure class and design. Ball valves can have fire test certificates according to API 6FA or ISO 10497 standards. The fire test certificate is not usually required for gate and globe valves with no soft sealing but can be supplied by some valve manufacturers. A fire test guarantees that the valve functions properly during the fire. ATEX indicates that the valve does not have any source of ignition. Valves with actuators are usually in the ATEX scope of work, because the ATEX directive does not consider the process source of ignition inside ATEX. Only external sources of ignition like actuators with electrical parts make the valve fall inside the ATEX directive. Sometimes a client may require ATEX for the gearbox of manual valves. Figs. 1.162–1.164 show a ball valve during the fire test.

Material selection Body material Valve bodies are made of cast or forge. Forged bodies are usually selected for small-size ball valves such as 200 and below. However, valve bodies can be made from bar instead of forge for sizes up to and including 400 to reduce delivery time. All bars are recommended to have a 100% liquid penetrant or magnetic particle test, a tensile test in both longitudinal and transverse directions, and EN ISO 10204 3-2 certification (full traceability). ASTM A479 is the standard bar material for stainless pressure containing body valves. ASTM A276 is the stainless steel bar material for glands of the gate and globe valves, but it can be used for the body as well. Valves with square-shaped bodies are made of bar material. Bar materials are completely polished and clean like the valve shown in Fig. 1.165, unlike forge and cast materials, which have porosities. A valve supplier can propose replacing a thick 25Cr body valve in 1400 size and class 2500 with a carbon steel body lined with Inconel 625 due to the issue of casting qualification. The fluid is deaerated seawater service with a temperature of less than 20°C. The connected piping to the valve is 25Cr duplex and there is no risk of galvanic corrosion between the pipe and valve in case of valve body material change. However, there are some discussions related to the gasket between the body pieces. The gasket should be an RTJ gasket since the valve is high pressure and softer than the body pieces, to provide an acceptable sealing rate. A 22Cr duplex RTJ gasket can be an acceptable choice for body piece sealing. The body of the valves can be coated in some cases, such as applying insulation to avoid corrosion under insulation or when using them above certain temperature ranges. 22Cr duplex, 25Cr super duplex, or 6Mo body valves should be painted with phenolic epoxy or thermal spray aluminum if they are insulated in the offshore industry. Using 22Cr duplex valves, 25Cr super duplex, and 6MO above 100°C, 110°C, and 120°C, respectively, also requires TSA painting in offshore. Fig. 1.166 shows a nonslam check valve in 22Cr duplex metallized with thermal spray aluminum (TSA).

120

FIG. 1.162

1. Ball-valve applications and design

Ball valve during the fire test.

Ball-valve design consideration

FIG. 1.163 Ball valve during the fire test.

121

122

1. Ball-valve applications and design

FIG. 1.164

Ball valve during the fire test.

FIG. 1.165

Ball valve with the body made of bar.

Fig. 1.167 shows a body flange coated with TSA. The picture shows an area where the painting has been missed. The valve is sand blasted (see Fig. 1.168) before painting to remove the roughness from the body surface of valve and provide good paint adhesion. Carbon steel body valves can be used in temperatures as low as 29°C as per the ASME B31.3, process piping code. As per Figure 323.2.2A of ASME B31.3, the minimum design temperature of a carbon steel body valve or pipe can be increased by increasing the thickness.

FIG. 1.166 Nonslam check valve metallized with TSA. Courtesy: Crain Stockham Valve.

FIG. 1.167 Coating missing on a body flange of a valve.

FIG. 1.168 Sand blasting and surface preparation area before painting. Courtesy: Crain Stockham Valve.

124

1. Ball-valve applications and design

Figure 323.2.2A of ASME B31.3: Minimum temperature limit of carbon steel material without impact testing.

Curve B, which is used for normal carbon steel materials, shows a reduction of the minimum design temperature to less than 29°C when the thickness exceeds 12.8 mm. As an example, valves with body thickness above 12.8 mm and carbon steel material cannot be used for a minimum design temperature of 29°C. The material should be impact tested at 29°C in order to be used for a 29°C design temperature. One way to avoid the impact test is to change the valve body material from normal carbon steel such as ASTM A216 WCB to ASTM A352 LCB or LCC low-temperature carbon steel as well as changing the bolts and nuts to lowtemperature carbon steel. Carbon steel material usage is limited in the offshore industry due to a high risk of rust and corrosion. Fig. 1.169 shows the body of a carbon steel valve which is rusted at the bottom. The upper part of the body has been machined.

Ball-valve design consideration

125

FIG. 1.169 Rusted body ball valve in carbon steel.

Changing the valve body material will not affect the valve dimensions or the face-to-face dimensions. Fig. 1.170 shows ceramic lined body valves, which are suitable for highly corrosive and erosive services. These valves are not common in the oil and gas industry. Ball material Electroless nickel plate (ENP) coating may be selected for the ball to increase the ball corrosion resistance, as shown in Fig. 1.171. For example, ENP thickness could be 75 μm and ENP can be applied on a 316 stainless steel ball to reduce the ball and seat friction as well as required torque. Therefore, ENP is not necessarily applied on the ball for corrosion mitigation. The issue with applying ENP is the high risk of ENP removal from the core and experiencing galvanic corrosion on the ball. Therefore, ENP on the ball could be avoided based on the practices of some EPC contractors and end-users. The ball can be upgraded to a better material (higher strength) to satisfy a higher torque requirement because of actuation. For example, 22Cr duplex, 6MO, and titanium grade 2 balls can be upgraded to 25Cr super duplex, Inconel 625, and titanium grade 5, respectively. The reason for ball upgrade in case of high torque is that the stem force is transferred to the ball; so,

126

1. Ball-valve applications and design

FIG. 1.170

Ceramic-lined body valves.

FIG. 1.171

ENP coating of the ball.

Ball-valve design consideration

127

the ball should be strong as well. The other advantage of upgrading the ball material is to avoid increasing the ball thickness, which can reduce the flow capacity of the valve as well as changing the design pattern. Tungsten carbide should be applied on the whole ball or just the ball contact surfaces with seat to avoid galling between the ball and the seat. Tungsten carbide thickness is different from one end user to another, and the maximum thickness could be between 150 and 400 μm. All parts of the ball in Fig. 1.172 are tungsten-carbide-coated and the surface is like a mirror. Torque values for operating a ball valve with a metal seat and tungsten carbide coating are higher than torque values for a soft seat. However, having tungsten carbide reduces the galling (friction) between the seat and the ball, as well as the wearing of the ball. The ball has contact with the seat on an unlapped area when it is opened. Tungsten carbide is not overlaid on the body material, unlike stellite. Tungsten carbide is sprayed in an overlay through a process called high velocity oxygen flux (HVOF), as it is shown in Fig. 1.173. Therefore, there is no risk of sigma phase formation in applying the tungsten carbide on duplex material, unlike stellite 6 overlay. Stellite 6 overlay on 22Cr duplex can be done through buttering of alloy 625 to minimize or eliminate the risk of sigma phase in duplex. Sigma phase is an embrittlement phase made of chromium and molybdenum, which is formed at high temperature. Stellite 6 is not overlaid on the ball of the ball valves. The ball material of a carbon steel body valve is made of 13Cr or 13Cr-4Ni. Some of the softseat materials may be changed to metal-seat materials in case of particle-containing fluid, high operating temperatures, or high-pressure drop. Tungsten carbide, like stellite, is at the risk of corrosion in seawater service. However, tungsten carbide is not corroded in deaerated (oxygen-free) seawater services. If the seawater is corrosive, then materials like Ultimet (UNS R31233) or Triballoy are proposed for hard facing of the ball. Ultimet has erosion and wear resistance that is as high as stellite, with higher corrosion resistance against pitting and chloride stress cracking corrosion. Laser cladding (weld overlay) provides a better property of overlaying and less delusion of the base material in overlay metal. Laser welding has advantages such as stress-free overlay, low heat input, fine structure, accurate thickness, and fewer passes of welding. Laser welding is not tungsten inert gas (TIG) or gas metal arc welding (GMAW). Fig. 1.174 shows the laser welding of a cobalt alloy on the ball of a ball valve. Fig. 1.175 shows the tool used for applying the laser overlay. Practically speaking, some valve manufacturers cannot provide an Ultimet overlay, or they cannot achieve enough hardness by applying the Ultimet overlay. Chromium oxide or chromium carbide hard facing are alternative materials to tungsten carbide. Valve manufacturers may do function tests after applying chromium carbide or chromium oxide to make sure that the valve is opening and closing properly without any seat leakage. Ceramic balls (see Fig. 1.176) for ceramic-lined body valves can be used in highly erosive and corrosive services. But as mentioned earlier, ceramic-coated valves are not common in the oil and gas industry. ASTM G65 is the standard test method for measuring abrasion, so it can be used for testing abrasion of the hard facing on the ball of the ball valve and seat surfaces. Fig. 1.177 shows a diagram based on ASTM G65, comparing the wearing resistance of different hard-facing materials.

128

FIG. 1.172

1. Ball-valve applications and design

Tungsten-carbide-coated ball. Courtesy: FCT.

Ball-valve design consideration

129

FIG. 1.173 HVOF of tungsten carbide on the ball of a ball valve.

FIG. 1.174 Cobalt coating on the ball valve through laser.

Stem material The stem material for actuated valves can be upgraded to a stronger material instead of increasing the stem diameter to solve the problem of high torque due to actuation. The valve direction of the installation (e.g., installation on the vertical line) will not affect the loads on the stem and stem material upgrade. In fact, the stem should withstand 1.1 times the loads coming from the actuator. Therefore, the actuator load should not exceed 90% of the MAST. The stem is usually forged or machined from the bar. However, the stem is rarely made from casting. Generally, valve manufacturers decide on the method of fabrication for trim of the valves like body, ball, and stem. The stem material that is selected depends on the valve body material. For example, it is very common to select 13Cr or 13Cr-4Ni martensitic stainless

130

1. Ball-valve applications and design

FIG. 1.175

Laser overlay equipment.

FIG. 1.176

Ceramic ball.

131

Ball-valve design consideration

ASTM G 65 abrasion test

Abrasion Comparison

Normalized Wear Resistance

Thermal Spray Coating’s Wear Resistance vs. Hard Chrome Platting, ASTM Normalized G65 Wear Test 6 5 4 3 2 1 0 Hard Chrome platting

Aluminum Oxide Tungsten Carbide

Chromium Carbide

Coating Types

FIG. 1.177 Hard-facing comparison based on ASTM G65.

steel stem materials for carbon steel body valves. 13Cr-4Ni has a UNS S41500 number and the relevant ASTM standard is ASTM A182 F6A for forged stems, and ASTM A217 CA15 for castmade stem material. 13Cr can be selected for a design temperature as low as 29°C without an impact test as per ASME B31.3, Table A. 13Cr can be used for design temperatures of 46° C subject to the impact test at 46°C. 13Cr-4Ni has 4% nickel content, which increases the material toughness and minimum temperature resistance compared to 13Cr. 13Cr-4Ni can be selected for temperatures as low as 46°C without an impact test. 13Cr stainless steel is available in four classes as per Table A1 of the ASME B31.3 code with mechanical properties of (40 ksi, 70 ksi), (55 ksi, 85 ksi), (85 ksi, 110 ksi), and (110 ksi, 130 ksi). The first and second numbers are yield and tensile, respectively. The weak point of 13Cr is the risk of chloride stress cracking corrosion (CLSCC) and painting of 13Cr cannot mitigate the risk of CLSCC in the 13Cr stem material. As mentioned earlier, 13Cr-4Ni (UNS S41500) (A182 F6NM) has more toughness compared to 13Cr and can be used for a minimum temperature of 46°C without an impact test. Adding nickel to 13Cr-4Ni increases the toughness of the material compared to 13Cr but does not increase the corrosion resistance in this case. A 13Cr-4Ni F6NM forged stem has 95 ksi yield and 75 ksi tensile that is stronger than 22Cr duplex. 17-4 PH can be the stem material for carbon steel and low-temperature carbon steel body valves. 17-4PH shall have maximum 33HRC hardness as per ISO 15156 standard to withstand sour services containing hydrogen sulfide. Applying two types of heat treatment, a process called double tempering should be used to reduce the hardness of this material; one is H1150D and the other one is H1150M. The values of tensile and yield through double tempering are given below: H1150M ð115ksi, 75ksiÞ and H1150D ð125ksi, 105ksiÞ (Note: The first number is yield strength and the second is tensile)

132

1. Ball-valve applications and design

17-4PH has a high risk of CLSCC in an offshore environment; so, it is prohibited for use in the offshore industry. However, it is a common stem material for onshore. As mentioned earlier, painting of 17-4PH does not mitigate the risk of CLSCC. Alloy 718 and 25Cr duplex are alternative and stronger stem materials for 22Cr duplex body valves. 22Cr and 25Cr duplex stem materials can be used for maximum 100°C and 110°C operating temperatures, respectively, as per NORSOK standard in an offshore environment. Alloy 718 with 53% nickel content (more than 42%) is immune to CLSCC. Therefore, in conclusion, if 25Cr duplex does not give enough strength for the stem, then alloy 718 is recommended. In addition, if the operating temperature is above 110°C, alloy 718 or alloy 625 can be the stem material options. Nitronic 50 (XM-19) UNS S20910 (22Cr-13Ni-2MO) is a very common stem material for the 316SS body of both ball and butterfly valves. This material has 100 ksi tensile and 55 ksi yield stress, which is much higher than SS316. Inconel 718 could be the upgraded stem material from Nitronic 50 for a 316SS body valve with an actuator.

Valve watch A valve watch can be attached to the body of the valve to measure the leak from the seat and make sure that there is no production loss. The inline leakage monitoring (no need to remove the valve from the line) can be done through an instrument called a valve watch, which is connected on the valve (spool) and does not affect the ordering of the valve. (No need to change the design of the valve because of the valve watch.) In fact, the valve watch is a strain gauge that is connected to the adapter spool (mounting bracket) by glue in the yard, and valve and actuator suppliers should be informed of its requirement. What benefits are achieved by installing a valve watch? Production loss and maintenance cost reduction, increasing safety, and reducing the personnel offshore are significant benefits. Valve watches detect operation problems in both valves and actuators. Valve operation problems can include stem bending, valve leak, overtightening the packing, excessive stem torque, galling, etc. Actuator operation problems include insufficient air supply, undersized actuator, internal corrosion, solenoid damage, actuator leakage, etc. A valve watch could monitor the leak or other problems in the actuator that should be connected to the actuator through a half-inch nominal pipe thread (NPT) plugged connection. The valve watch can measure the leak through acoustic/sound of leakage as shown in Fig. 1.178. A valve watch can be also used for pressure safety valves as a sort of feedback for maintenance or calibration of this valve. There are different sensors for valve watches: 1. A strain gauge is installed directly on the stem and yoke and measures the torque and mechanical force of the valve and actuator. It shows problems such as bending stem and overtightening the packing that makes for stem friction. 2. A static pressure sensor is connected to the actuator to measure the air or hydraulic pressure to the actuator. It shows leakage of supply air and cylinder corrosion. 3. Dynamic pressure sensors are installed on the flow stream (downstream) and the valve body cavity. The sensor converts the flow to the noise.

Valve interlocks

133

FIG. 1.178 Measuring the leak through acoustic sensors (valve watch).

Fig. 1.179 shows the basics of a valve watch, including the sensors mentioned above. The inline testing of the DIB valve with two DPE seats can be made by either of two methods: 1. With the valve pressurized from the upstream side and no pressure downstream, depressurize the cavity and register any pressure buildup in the cavity by the body drain connection. No pressure build up in the cavity indicates that the upstream seat is okay. 2. With the valve pressurized upstream and no pressure downstream, insert 7–10 barg nitrogen pressure into the cavity. If the cavity pressure builds up, the upstream seat is leaking. If the cavity pressure decreases, the downstream seat is leaking.

Valve interlocks Many ball valves, especially those that are located before and after PSVs, should have locking equipment. Interlocks prevent human errors and guide the valve operator through the preferred operating sequence. The main purpose of a valve interlock is to improve process safety by preventing incorrect valve operation. Keys are used to open and close the valves in the right order. An interlock supplier needs valve top work drawings, gearbox spindle length and diameter, and the valve hand-wheel diameter. The interlock supplier should remove the handwheel and install the interlock and a new handwheel to the gearbox. Figs. 1.180 and 1.181

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1. Ball-valve applications and design

FIG. 1.179

Valve watch system.

FIG. 1.180

Interlock with the handwheel.

show an interlock with the handwheel that is installed on the valve. There are two keys in yellow and green colors (gray in print version) in the interlock. The hand-wheel extension could be increased by about 90–150 mm, since the interlock is added on the top or side of the valve. The valve lock, keys, handwheel, and key cabinets should be purchased for an interlock system. Fig. 1.182 shows an interlock ball valve in the plant. The handwheel on the interlock should have the same material and diameter as the original handwheel of the valve. The material of the handwheel is usually selected in stainless steel 316. Fig. 1.183 shows two valves connected with an interlock. The requirement is to make sure that the valve on the left side will be opened before closing the valve on the right side. The operator takes a key from the key cabinet in order to open the first valve on the left, which is usually closed. A key will be released from the first valve on the left, which is used for closing the valve on the right. Fig. 1.184 shows electronic key cabinets and the keys inside.

135

Valve interlocks

FIG. 1.181 Gearbox and its spindle.

FIG. 1.182 Ball valve with the interlock.

Senlce line (Normally closed)

Operation line (Normally open)

Symbol ‘A’ (From control room)

Symbol ‘A’

Symbol ‘C’ (To control room)

Symbol ‘B’

Symbol ‘B’

Symbol ‘C’

Locked closed Locked open

FIG. 1.183 Example of ball valve connections through the interlock system.

136

FIG. 1.184

1. Ball-valve applications and design

Electronic key cabinets. Courtesy: Smith Flow Control.

Some valves have a single lock, which means that they have the same lock as interlock valves but without any sequence of locking changes. A key cabinet could be an electronic type, which has some advantages over a traditional mechanical cabinet: 1. More user-friendly, which means that operators can find the keys from the cabinet much easier and faster. 2. Provide sequence drawings and guidelines on how to use the keys. 3. Provide the details of all the key movements (which operator has which key).

Valve drivers Easy drive An easy drive is a gun that facilitates the opening and closing of a valve. A manual valve maximum limitation for opening and closing is 100 turns or 15 min manually. An

More pictures

137

FIG. 1.185 Easy drive tool. Courtesy: Smith Flow Control.

easy drive tool is one solution to be used on a manual valve instead of changing the manual valve to a motor-operated valve. The gun can work with either 5.5 barg air or electrical supply and up to 950 N m torque can be generated. Different installation options are shown in Fig. 1.185.

Flexi drive A flexi drive tool (see Fig. 1.186) is a cable that enables the operator to operate the valve from up to 30 m away if the valve is located in a hazardous, nonreachable, and remote area.

Torque drive Excessive force of the operator in closing a valve can reduce the life of the seat. A torque drive prevents the operator from using excessive force and equalizes the forces of all the operators with different force. A torque drive can be used with the easy drive.

More pictures See Figs. 1.187–1.201.

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1. Ball-valve applications and design

FIG. 1.186

Flexi drive tool. Courtesy: Smith Flow Control.

FIG. 1.187

Torque tool for fastening the ball-valve bolts.

More pictures

FIG. 1.188 Ball of the ball valves (sitting on the hole). Courtesy: FCT.

139

140

FIG. 1.189

1. Ball-valve applications and design

Electrical-actuated ball valve/electrical actuator. Courtesy: FCT.

More pictures

FIG. 1.190 Vent plug on the valve body. Courtesy: FCT.

FIG. 1.191 Modular valve on the ball valve drain cavity. Courtesy: FCT.

141

142

1. Ball-valve applications and design

FIG. 1.192

Modular valve on the ball valve drain cavity. Courtesy: FCT.

FIG. 1.193

Body of the ball valves after machining. Courtesy: FCT.

FIG. 1.194 Pressure transmitter for pressure test.

FIG. 1.195 Ball valve after assembly. Courtesy: FCT.

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1. Ball-valve applications and design

FIG. 1.196

Actuated ball valve during the pressure test. Courtesy: LVF.

FIG. 1.197

Ball valve with plywood body flange protection. Courtesy: LVF.

More pictures

FIG. 1.198 Electrical-actuated ball valves. Courtesy: LVF.

FIG. 1.199 Gear-operated ball valves. Courtesy: LVF.

145

146

1. Ball-valve applications and design

FIG. 1.200

Torque measurement on ball valves. Courtesy: LVF.

FIG. 1.201

Lever-operated small-size ball valves. Courtesy: LVF.

C H A P T E R

2

Butterfly valve applications and design Valve application examples A butterfly valve (Fig. 2.1) stops, regulates, and starts the flow of fluid. This valve is easily and quickly operated due to 90-degree rotation of the handle and the disk. Butterfly valves possess many advantages over gate, globe, plug, and ball valves including lower cost, less weight, and space requirements. The maintenance cost is relatively low since there are few moving parts and no cavity like ball valves to trap the fluids. Butterfly valves are usually selected for utility liquid and gas services in low-pressure classes such as class 300 and lower. Ball valves are robust, which makes them suitable for high pressure and aggressive process services (e.g., oil and gas) in the offshore industry. However, selecting a ball valve for utility services such as air, water, and seawater services that are not high pressure is usually an unnecessary and expensive choice. Wafer-type butterfly valves (flangeless body) are lighter, more compact, and cheaper than the ball valves. In addition, butterfly valves require less force/torque for opening and closing compared to ball valves, which could save the size and cost of an actuator or gearbox. A butterfly valve disk is lighter than the ball valve closure member (ball) and does not have contact with the seat during its travel. Butterfly valves are either concentric or eccentric (high performance). Butterfly valves should not be selected for use upstream of pressure safety valves (PSVs) if the fluid is not process service. As an example, PSVs can be installed for heat exchangers (see Fig. 2.2) to release the excess pressure of the heating medium. There are two reasons why a butterfly valve is not proposed for use upstream of PSVs. The reduced bore of a butterfly valve cannot release enough flow capacity value (Cv) to the flare, and a butterfly valve is not robust enough to withstand the loads coming from the PSV. Full bore ball valves should be selected for use both upstream and downstream of PSVs. A butterfly valve can also be used for the isolation valves upstream and downstream of the temperature control valve (see Fig. 2.3) as well as for bypass of the control valve, shown highlighted with a red circle (light gray in print version) in the figure. The figure shows a shell and tube heat exchanger in the shape of rectangular box with a half-circle cap on each end. The control valve on the outlet of the heat exchanger is isolated with two gate valves. The fluid service in the control valve and both isolation valves is water.

A Practical Guide to Piping and Valves for the Oil and Gas Industry https://doi.org/10.1016/B978-0-12-823796-0.00017-9

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# 2021 Elsevier Inc. All rights reserved.

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2. Butterfly valve applications and design

FIG. 2.1 Butterfly valve.

FIG. 2.2 Ball valve selection rather than butterfly valve for subflare line.

Valve application examples

149

FIG. 2.3 Heat exchanger arrangement.

It is recommended to change the isolation valves from gate valves to wafer-type butterfly valves (eccentric) to save weight and space. Also, a globe valve has been selected for the bypass of a control valve. It is recommended to change the globe valve to a wafer-type butterfly valve to reduce the risk of cavity and wearing as an operational problem. Changing the globe valve to a butterfly valve is practical for sizes of 400 and above. A wafer-type eccentric butterfly valve is cheaper and lighter than a globe valve. Fig. 2.4 shows another example of a heat exchanger (Tag number A-20HA201), which is the oil stabilizer heat exchanger before the separator in an offshore platform. Two phases of oil and water should be heated up in the exchanger for better separation. The outlet line from the heat exchanger to the control valve contains hot water. Two isolation ball valves have already been selected for upstream and downstream of the control valve. It is recommended to change the ball valves to wafer-type butterfly valves to save weight, space, and cost, considering the fact that the fluid is hot water (utility service). Also, it is a good idea to change the 600 globe valve to a wafer-type butterfly valve on the bypass of the control valve plus the ball valve on the downstream of the globe valve. The choice of seat material for the butterfly valve (soft or metal) depends on the temperature of the hot water. As an example, metal-seated butterfly valves may be required for fluid operating temperatures higher than 150°C. When using a metal seat, it is better to upgrade the metal seat butterfly valve to triple offset to ensure a better seal. It is difficult or unsuccessful to have a metal seat double offset as a bidirectional valve, because the flow on unpreferred pressure direction cannot provide enough sealing between the metal seat and the disk, unlike a soft seat design. A triple offset butterfly valve is metal seated by default.

150

2. Butterfly valve applications and design

FIG. 2.4 Heat exchanger arrangement.

Concentric butterfly valves Concentric butterfly valves are cheaper and simpler than eccentric valves, which make them a good choice for noncontinuous seawater services. Although exotic materials such as titanium and 25Cr duplex are typically selected for piping and valves in seawater services in the Norwegian offshore industry, most concentric butterfly valves for noncontinuous seawater service are manufactured in cheap carbon steel or ductile cast iron with a rubber or PTFE (Teflon) linear. Rubber-line elastomeric materials could be Viton, Buna-N (nitrile rubber), EPDM, natural rubber, etc. Ethylene propylene diene monomer (EPDM) rubber (M-class rubber), a type of synthetic rubber, is an elastomer. Hydrogenized Buna N (HNBR) is probably a better lining than FKM (Viton) in seawater services. The price of FKM and HNBR is almost the same. HNBR has elevated temperature resistance (e.g., 150°C) compared to Buna N, which is 80°C. EPDM is not recommended for hydrocarbon-containing services. EPDM is also black in color like Viton. There is usually a maximum operating temperature associated with butterfly valves material linear such as 150°C. Proposed temperature ranges of soft materials are given in Table 2.1. Fig. 2.5 shows a carbon steel body ASTM A216 WCB concentric butterfly valve with natural rubber (Ebonite), hard rubber liner. The rubber liner sits on the flange body face and acts as a gasket, and prevents direct contact of the corrosive service with the carbon steel body of the valve. When the butterfly valve is concentric with the liner, a gasket should not be used unless recommended by the manufacturer as per API 609, Standard for Butterfly Valves. The liner acts as the flange sealing. The stability of the liner to the body is accomplished by bonding the resilient backing ring in materials such as aluminum or phenolic or even soft Viton ring. Phenolic is probably more applicable for small sizes. The stem sealing area is designed with molded O-rings with threaded grooves as shown in Fig. 2.6. Stem sealing O-rings such as Viton material are designed to prevent leakage behind the liner. The material beneath the O-rings is prone to crevice corrosion type. The holes in Fig. 2.6 look like threaded grooves, but actually the molded O-rings are placed in the grooves.

151

Concentric butterfly valves

TABLE 2.1

Proposed soft materials temperature ranges. Nature of seal material

Elastomeric

Thermoplastic

Designation

Maximum operating temperature range (°C)

(designation as per ASTMD 1418) Nitril rubber (service class A only)

NBR

0 to +80

Hydrogenated nitril

HNBR

40 to +150

Viton GLT

FKM

40 to +180

Chemraz 526

FFKM

20 to +220

Silicon (70 shore A)

VMQ

60 to +220

Fluorinated silicon (70 shore A)

FVMQ

60 to +220

Teflon (Virgin or filled)

PTFE

80 to +200

Kelf

PCTFE

150 to +100

Teflon FEP

FEP

80 to +140

Teflon RFA

PFA

80 to +200

Nylon 12

Polyamide

20 to +100 20 to +100

Devlon V API Peek

Polyether ketone

80 to +160

Turcite 243

Polyether ketone

200 to +250

Vespel SP 21

Polyamide

200 to +260

Courtesy: Total.

FIG. 2.5 2000 Carbon steel body concentric rubber-lined butterfly valve. Courtesy: Center Tech.

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2. Butterfly valve applications and design

FIG. 2.6 Molded stem seal areas for O-rings (stem sealing).

The design of the stem surrounding area includes stem bearings. A stem bearing usually contains a metallic part plus Teflon (PTFE liner) to prevent stem and bearing friction. However, hard nonmetallic materials like PEEK and PTFE reinforced with graphite, glass, or fiber carbon can be selected for a stem bearing. For example, two stem bearings can be designed for the upper stem and one for the lower stem. Nickel aluminum bronze with PTFE liner is a choice of metallic bearing material for concentric butterfly valves in noncontinuous seawater service. Fig. 2.7 shows stem bearings, one for the upper stem and one for the lower stem for a double offset butterfly valve. Fig. 2.8 shows a rubber-lined butterfly valve with the description of each part.

FIG. 2.7 Double offset butterfly valve with the part lists including a bearing for upper and a bearing for lower stem.

Concentric butterfly valves

153

FIG. 2.8 Concentric rubber-line butterfly valve including bill of materials.

Concentric butterfly valves require less opening and closing force compared to eccentric types. The disks of concentric valves consequently are smaller and lighter than the disks of eccentric butterfly valves in the same size and pressure class. The rubber-lined butterfly valve shown in Fig. 2.9 has a special lever (operator) to stop the disk and prevent movement of the disk due to fluid pressure. According to the API 609 standard for butterfly valves, all

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2. Butterfly valve applications and design

FIG. 2.9 Concentric rubber-line butterfly valve with the special lever.

components of butterfly valve operation such as the actuator, the handwheel, the gearbox, as well as the lever shall be equipped with provisions to prevent movement of the disk from the desired set position during the normal operation. Normal operation for a butterfly valve is on-off, but throttling (fluid control) can be used in special cases (e.g., to avoid using a straight pattern globe valve). Concentric butterfly valve internals such as the disk and the stem can be selected in cheaper materials such as 13Cr and coated with rubber/PTFE rather than using exotic and expensive solid materials such as 25Cr duplex and titanium for seawater applications. Fig. 2.10 shows a PTFE-lined concentric butterfly valve with a painted cast iron body. The valve internals (stem and disk) are also PTFE-coated 13Cr stainless steel material. The body of the

FIG. 2.10

800 Cast iron body concentric butterfly valve. Courtesy: Xomox.

Concentric butterfly valves

155

PTFE-lined butterfly valve is in two pieces bolted together to facilitate placing the integrated stem and disk in the body of the valve. The integrated stem with the disk gives antiblowout characteristics to the stem. The valve does not need a packing around the stem since all around the stem is filled with PTFE, which seals the body and the stem. Therefore, the PTFE line could be as thin as 4 mm, which can be measured through a test. The body of the valve is manufactured out of either carbon steel or ductile cast iron ASTM A395, which can be painted with zinc epoxy. If PTFE coating is not done around the disk and stem, the disk and stem material can be 25Cr super duplex on condition that the seawater operating temperature is maximum 20°C per NORSOK standard. Otherwise, if the seawater temperature is above 20°C and no PTFE has been selected for coating of the stem and disk, titanium could be a choice of material. There are two common grades of titanium, grade 2 and grade 5. Grade 5 is harder than grade 2 and is recommended in situations that require a higher maximum allowable stem torque (MAST) for the stem of the valve. Higher MAST may be required in case of valve actuation. In addition to savings on material, the concentric butterfly valves require smaller size actuators and stem diameters compared to double offset butterfly valves. The American Water Work Association (AWWA) C504 can also be referred to for the rubber-lined butterfly valves standard. Some manufacturers do not produce and guarantee concentric butterfly valves for the full pressure rating of CL150 equal to PN20 (PN stands for pressure nominal). Lined butterfly valves may be produced for maximum 16 barg (PN16) by some valve manufacturers. According to the API 609 standard, the valve body pressure should be based on the manufacturer standard. It is possible that fluid is leaked to the area between the liner and the body from stem sealing, so a cycle test is usually required from the final user to test the possibility of leakage. A cycle test includes frequent seat tests plus many opening and closing cycles to check that the valve has enough sealing ability between the stem and the body as well as the body and the liner. Passing the cycle test can qualify one size larger and up to five sizes smaller. Concentric butterfly valves are usually covered by the API 609 standard from sizes 200 to 4800 in pressure class 150, which are known as “category A” butterfly valves. However, butterfly valves are not generally selected for sizes 300 and below due to low Cv in the Norwegian offshore industry. The Cv of butterfly valves is even less than reduced bore ball valves. Having the disk on the flow path reduces the Cv of butterfly valves. Ball valves are the alternative choice to butterfly valves for small sizes of 300 and below, to achieve required V. Concentric butterfly valves do not have a firesafe design. The linear rubber would be melted in case of fire and the valve would leak exceeding the leakage rates given in fire test standards such as API 6FA or ISO 10497. However, these valves as a part of a fire-fighting piping system require delivering the firewater to extinguish the fire. Therefore, a valve supplier can burn a concentric butterfly valve to measure the Cv reduction. Ideally, the Cv and flow reduction of the valve should not be reduced by more than 5% in order to supply sufficient water for fire-fighting purposes. Fig. 2.11 shows concentric butterfly valves in zinc bichromate body in yellow color (light gray in print version) for water application. The zinc bichromate material is similar to nickel aluminum bronze in color.

156

FIG. 2.11

2. Butterfly valve applications and design

Concentric butterfly valves in zinc bichromate body. Courtesy: Center Tech.

Eccentric butterfly valves Eccentric butterfly valves can be either double or triple offset types. Triple offset butterfly valves are metal seated and applicable for either particle-containing fluid services or hightemperature applications, where the usage of soft seat materials is limited. A triple offset butterfly valve is not a better valve choice than a double offset in nonparticlecontaining services and/or high-temperature applications. Triple offset requires a higher opening and closing torque and larger stem diameter, due to a larger disk volume. Larger stem and disk volume make the Cv of the triple offset valve less than the Cv of the double offset and increases the pressure drop. Triple offset butterfly valves are metal-seated valves so they usually cannot provide zero leakage (tight shutoff ), unlike soft seat double offset butterfly valves. In addition, triple offset butterfly valves are more expensive than double offset valves so it is better to avoid selecting triple offset unless they are really required for specific applications. Triple offset butterfly valves with painted bodies are shown in Fig. 2.12. Although triple offset butterfly valves can be selected as alternatives to ball valves in process services where pressure drop and lower Cv are not important, they are not popular in the Norwegian offshore industry due to higher cost, higher torque, and less Cv compared to double offset types. Double offset butterfly valves in exotic materials such as 25Cr super duplex and titanium are very common for continuous or even noncontinuous seawater services (if a concentric butterfly valve is not selected) for sizes 400 and above in Norwegian offshore platforms. Also, double offset butterfly valves in carbon steel or 22Cr duplex in 400 size and above are common for utility services such as freshwater, air, etc., in the Norwegian offshore industry. Butterfly valves can also be used instead of globe valves for throttling (fluid control) in utility and seawater services as a cost effective and lighter choice, and butterfly valves have less risk of cavitation and wearing compared to globe valves.

Eccentric butterfly valves

157

FIG. 2.12 Triple offset butterfly valves. Courtesy: Westad.

Butterfly valve body design A wafer is a design in which the butterfly valve is placed between two flanges and long length bolts are passed through the bolt holes without any thread (guiding lugs) in the valve body or the bolts are passed through threaded lugs (Fig. 2.13). The second design is the wafer with threaded holes on the valve body as per API 609. A butterfly valve with guiding lugs, known as a “wafer-lugged” butterfly valve, cannot be used for the end of the line. The bolt holes are used for mating flanges alignment. Fig. 2.14 shows a butterfly valve with wafer threaded lugs, which can be used for the end of the line.

FIG. 2.13 Double offset butterfly valves with guiding lugs. Courtesy: Westad.

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2. Butterfly valve applications and design

As shown in the photos in Figs. 2.14 and 2.15, the butterfly guiding lugs are larger, including the combination of two holes, which make this design compatible with both classes of 150 and 300. Fig. 2.16 shows a wafer-lugged eccentric butterfly valve 2400 class 300 during the lifting that can be used for the end of the line. A wafer-lugged butterfly valve can be used for the end of the line. Since the valve is connected to the line through sets of bolts from two sides, it is possible to remove the blind flange at the end of the line through loosening one set of bolts and still have the butterfly valve connected to the line. Wafer-lugged double offset butterfly valves are shown in Figs. 2.17 and 2.18 with the threaded holes passing through the body of the valve.

FIG. 2.14 Wafer-lugged butterfly valves with guided lugs suitable for both classes of 150 and 300. Courtesy: Westad.

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159

FIG. 2.15 Wafer-lugged double butterfly valve. Courtesy: Westad.

FIG. 2.16 Wafer-lugged eccentric butterfly valve 2400 Cl300.

It is important that the wafer-type butterfly valve has adequately thick and robust as shown in these figures. The bolt holes are usually completely drilled and tapped through the body of the valve, except for four bolt holes close to the stem in large sizes such as 3000 (Fig. 2.18) or even smaller sizes such as 1000 (Fig. 2.19). The reason could be either clashing

160

2. Butterfly valve applications and design

FIG. 2.17

Wafer-lugged double butterfly valve. Courtesy: Westad.

FIG. 2.18

Wafer-lugged double butterfly valve. Courtesy: Westad.

the bolt with the stem or a very thin part remaining between the bolt holes and the stem, in the case of having these four bolt holes extend all the way through the body. The other wafer lug design is to have just four holes on the valve body as it is shown in Fig. 2.20. The bolt holes are not fully through in this design again due to minimum thickness requirements given in API 609/ASME B16.34. The valve needs bolts from each side, eight bolts in total. The bolt threads up to and including 100 should be unified coarse threads (UNC) and above 100 should be eight UN, meaning eight threads in 1 in. class 2B. ASME B1.1, “Unified Inch Screw Threads,” is the standard for tapped holes on the wafer-lugged butterfly valves.

Eccentric butterfly valves

161

FIG. 2.19 Wafer-lugged butterfly valve 1000 class 150 titanium body material with four threaded lugs on the body.

FIG. 2.20 Bolt holes close to the stem in lugged butterfly valve.

Fig. 2.20 shows why the bolt holes in close positions to the stem hole should not be fully bolted through the hole. In fact, the small pink area is the body thickness if the thread holes are fully going through the body, which is less than the API 609 standard minimum body thickness requirement. Fig. 2.21 from the API 609 standard shows the bolting options for wafer and lugged-type butterfly valves.

162

FIG. 2.21

2. Butterfly valve applications and design

Wafer and lugged-type butterfly valves with bolting options.

A threaded wafer-lugged valve could be designed in a way that the valve body holes are not bolted fully through, so the valve body is bolted from two sides with either a cap screw or stud bolts. However, stud bolts could be a better choice since there would be no need to calculate the length of the bolts specifically. It is possible to adjust the length of the stud bolts inside the threaded lugged holes by leaving threads out of the nuts, unlike the accurate measurements required for cap screws. Hot-dip galvanized (HDG) low alloy steel bolts with zinc coating may not fit inside the lugged holes. It is recommended that a butterfly valve manufacturer provides size and depth of the body holes on the valve drawings to avoid possible bolt mismatching inside the butterfly valve bodies. A threaded wafer-lugged butterfly valve has the advantage of opening the bolts from one side and keeping the valve in place. Each side of the valve can be removed independently without any need to remove the valve and shut

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down the other side. Thus, the threaded lugged type is called an end of line valve. A threaded lug type is a more expensive valve and contains more material compared to a wafer-lugged valve with guiding lugs. But it has better integrity compared to both the wafer and the wafer with guiding lugs. The alternative for lugged valves for end of the line application is a double-flanged butterfly valve, as shown in Fig. 2.22. Valve configurations including double flange, lug, and wafer types should be compatible with ASME and MSS SP standard flanges. ASME flanges could be either ASME B16.5 or ASME B16.47 depending on the size and pressure class MSS SP 44 is the common manufacturer standard for flanges. The double-flanged butterfly valve shown on the left in Fig. 2.23 is short pattern and more compact. The double-flanged butterfly valve can be a short or a long pattern as per API 609. Fig. 2.24 shows both short and long pattern designs as per API 609. This is a case study in which a lugged-type butterfly valve was requested to be at the end of the line blinded with a blind flange. The valve had to be operated when the blind flange was removed, to avoid a clash between the butterfly valve disk and the blind flange and consequent damages. The butterfly valve was the connection port from a temporary firewater supply to the main firewater ring during the commissioning through a flexible hose. But when switching the water supply from the temporary source to another source, the valve had to be closed to avoid drainage and discharge of the whole water system. One solution was to lock the butterfly valve in order to avoid operation before removing the blind flange. The other solution was to use a short pipe spool downstream of the butterfly valve and blind it with a blind flange (Fig. 2.24). The butterfly valve is not end of the line and there is no need to be a lugged type in case of using a spool. However, an additional flange between the butterfly valve and the spool pipe was required. The other advantage of a spool pipe is providing space for ease of supporting the line. Welded body butterfly valves can be designed in a way that a plate ring for the body is welded to two other plates, called the top and bottom covers. This design is not recommended

FIG. 2.22 Double flange butterfly valve in the middle of two wafer lug butterfly valves. Courtesy: Westad.

164

FIG. 2.23

2. Butterfly valve applications and design

Short and long pattern double flange butterfly valves as per API 609.

Blind Flange Spool Pipe

Buerfly Valve FIG. 2.24 Adding a spool piece for an end of line butterfly valve to avoid clash between the valve and the blind flange.

and should be rejected since it is not robust. However, the welded design is cheaper since there is no requirement to cast and machine the bodies of the valves. There are two steps for machining the body of the triple offset butterfly valve in Fig. 2.25 for placing the seat and seat retainer. Butterfly valves with butt weld end connection (see the photos in Fig. 2.26) are common for cryogenic services in liquid natural gas (LNG) plants. This design has a bolted flange from the top like a top entry design. However, it is difficult or impossible to have access to the valve internals from the top, especially in small sizes such as 800 and less. Therefore, this design should not be considered a top entry, since removing the internals such as disk and stem

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FIG. 2.25 Triple offset butterfly valve with two steps on the body for placing the seat. Courtesy: Westad.

FIG. 2.26 Cryogenic butterfly valve for LNG plant with butt weld end connection. Courtesy: Westad.

and seat retainer should be done from the side. Alternatively, this design can be considered side entry. Liquefied natural gas (LNG) contains more volatile gases such as methane and ethane that have been converted to liquid at very low temperatures for ease of storage and transportation.

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2. Butterfly valve applications and design

Cryogenic temperature is different from one project specification to another and could be below 46°C or 80°C or 101°C to minimum 196°C. As shown in Fig. 2.30, the stem is extended to keep the packing and gearbox away from the extremely cold temperature of the fluid. The gearbox is usually filled with grease for lubrication and preservation, so it should be kept away from cold temperatures. The packing material is usually graphite that can withstand wide ranges of temperature, from very cold to very hot. As shown in Figs. 2.27–2.30, the butterfly valve body may be integrated with a travel stop to prevent the disk from over traveling. A triple offset butterfly valve does not have any travel stop, and the disk travel stops by the seat. One reason for having the triple offset butterfly valve with a metal seat is that a soft seat probably cannot stop the disk travel. There is a travel stop on the gearbox, which controls the positioning of the disk toward the seat and provides tight contact.

FIG. 2.27

Cast nickel aluminum bronze body valve with travel stop. Courtesy: Westad.

FIG. 2.28

Cast wafer-lugged double offset butterfly valves. Material: 6MO, CK3MCuN. Courtesy: Westad.

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167

FIG. 2.29 Cast wafer bodies of double offset butterfly valves with guided lugs. Courtesy: Westad.

Butterfly valves disk design There are some connections at the back of the disk used to fasten the disk to the machining equipment. The disk shown in Fig. 2.31 is a cast and very close to shape, so not much machining is required. There are some machining activities on the external area of the disk. These four connections are removed after machining the disk seat surfaces. The size and pressure rating is engraved on the back of the disk. The disk of the butterfly valve does not have any contact and friction with the seat during the opening and closing, which reduces the valve torque. As a design example, a double offset butterfly valve disk is usually cast made and integrated with two holes at the back of the disk and a passage for the shaft, as shown in Fig. 2.32. Two pins are hammered into the stem (Fig. 2.33) for electrical continuity and making the stem antiblowout. Two pins, called cone or hinge pins (Fig. 2.34), can be tack welded

168

2. Butterfly valve applications and design

FIG. 2.30 Cast wafer bodies of double offset butterfly valves with guided lugs before machining the guiding holes. Courtesy: Westad.

FIG. 2.31

Disk of butterfly valves with the shaft hole (passage). Courtesy: Westad.

to the disk. Pins should be as strong as the stem material (e.g., titanium grade 5 for titanium body valves or Monel K500 for NAB body valves in UNS C63000 material). If one pin is corroded, the second pin is the backup. Making a step-through machining a larger diameter stem is an expensive solution to make an antiblowout stem, especially for titanium and 25Cr duplex body butterfly valves. In addition, the connection between the shaft and disk shall be designed in such a way as to prevent loosening and disconnection due to the loads and vibrations as per the API 609 standard (Fig. 2.35). Fig. 2.36 shows how the pins have been passed from the outside of the stem, which is slightly machined.

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169

FIG. 2.32 Butterfly valve disks. Courtesy: Westad.

FIG. 2.33 Cast disks of butterfly valves after machining. Courtesy: Westad.

Sometimes the disk can be strengthened by adding extra thickness (bar shape) shown in Fig. 2.37. The same can be done in dual plate check valves to add extra thicknesses to the disks to increase the strength. The disk of a butterfly valve does not have any contact with the seats during traveling, unlike ball valves. Fig. 2.38 shows Stellite 6 overlays on the disk to avoid galling and wearing the disk from it being in contact with the seat when the valve is closed. Both seat and disk maybe hard faced with Stellite 6 in some cases, to avoid galling. However, hardness differences also help better sealing so it is possible to overlay just the disk with Stellite 6, as shown in Fig. 2.44. Laser weld overlay of stellite increases the advantages of stellite. Stellite can be overlaid on materials such as carbon steel, 13 chromium, and 22Cr

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2. Butterfly valve applications and design

FIG. 2.34

Hammered pins to connect the shaft to the disk. Courtesy: Westad.

FIG. 2.35

Pins are tack welded to the disk. Courtesy: Westad.

FIG. 2.36

Pins contact with stem for an eccentric butterfly valve. Courtesy: Westad.

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171

FIG. 2.37 Strengthened disk through extra thickness. Courtesy: Westad.

FIG. 2.38 Stellite overlay on the butterfly valve disk. Courtesy: Westad.

duplex through laser welding, with advantages such as greater hardness, stress free overlay, low heat input, and fine structure (no stellite fusion in the base metal). Also, using laser results in an accurate thickness without the need for extra machining and with fewer passes of welding. Extra machining on Stellite 21 can be challenging, since it makes the Stellite 21 harder. In case of stellite welding, dilution of base metal in stellite can make the Stellite in the first pass less pure, so a second and third pass increases the quality of the stellite. However, this is not an issue with laser welding, and no dilution may see in Stellite overlay. Laser welding is not tungsten inert gas (TIG) or gas metal arc welding (GMAW). Higher Stellite hardness is desirable to achieve higher lifetime against erosion. However, hardness should be controlled and limited due to the presence of hydrogen sulfide (H2S), as per ISO 15156 standard. Fig. 2.39 shows laser weld overlay equipment.

172

FIG. 2.39

2. Butterfly valve applications and design

Laser weld equipment. Courtesy: Westad.

Butterfly valve stem design The stem and disk for a butterfly valve are separate pieces. The stem can be designed as a square shape to avoid machining the stem on the corners for stem keys to be fitted to the gearbox or actuator. Machining the stem and creating the grooves on the corners for placing the stem key could be considered a weak point by some butterfly valve suppliers. Also, a square stem (Fig. 2.40) allows for multiple orientations of the valve operator (gearbox or actuator) without any need to make grooves on two or four corners of a rounded stem. Therefore, a square stem drive allows the operator to position both a manual and an actuated operator in any 90-degree position without needing a stem key on the stem. On the other hand, the stem can be rounded with machined grooves to place the stem keys. Fig. 2.41 shows a rounded stem with two grooves machined 90 degrees for stem keys. Even the stems shown in Fig. 2.41 can provide multiple operator orientations on every 90-degree position through machined grooves on the stem. The stem in Figs. 2.42 and 2.43 is machined from two areas, one on the top and the other on the bottom. The machining on the bottom part is done for placing the hinge pins or cone pins in connection to the disk. Cone/hinge pins have two roles—providing antiblowout design and providing electrical continuity between the stem and disk to discharge antistatic electricity.

Eccentric butterfly valves

FIG. 2.40 Square stem drive allowing for multiple orientations. Courtesy: Hobbs.

FIG. 2.41 Rounded stems with two grooves 90 degrees.

FIG. 2.42 Rounded stem with machining grooves for stem keys and hinge pin. Courtesy: Westad.

173

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2. Butterfly valve applications and design

FIG. 2.43

Rounded stems with machining grooves for stem keys. Courtesy: Westad.

FIG. 2.44

Testing the stem under stress. Courtesy: Westad.

Fig. 2.44 shows another groove that is machined under the stem key grooves all around the stem. This groove has a critical function. If the stem is broken from the bottom part (cone pins), then the stem would blow out and can injure the operator. Also, if the stem is broken from the top section machined for stem keys, then the top stem can get stuck in the gearbox or actuator. These two conditions are not desirable. Therefore, a valve manufacturer can create the weakest point through machining under the stem key grooves as is shown in Fig. 2.44 to have the stem broken from that part in case of high stress. Fig. 2.50 shows the test on the stem to make sure that the stem is broken from the groove that is machined under the stem key. Stem material used for actuated butterfly valves may need to be upgraded to materials with higher mechanical strength. In fact, higher loads can be placed on the valve stem in case of actuation compared to manual valves. It is not possible or preferable to increase the stem diameter in wafer-type butterfly valves, because there is not enough space on the thin and

Eccentric butterfly valves

175

compact wafer body designed based on the API 609 standard. In addition, increasing the stem thickness would reduce the Cv of the valve. Furthermore, manufacturers may prefer to keep the stem diameter standard to avoid using different sizes of bearings, O-rings, and packings. Stem sealing is usually achieved by packing or O-ring seals in a conventional stuffing box.

Butterfly valve seat design Stopping the flow is achieved by sealing a valve disk against a seat that is on the inside diameter periphery of the valve body. Seat material can be soft (nonmetallic) or metallic in double offset butterfly valves. But triple offset butterfly valves are always metal seated. A metal seat may be selected because of particles, high temperatures, and high delta pressure. If the seat is metallic, it may be a good idea to select a triple offset butterfly valve. The allowable leakage of a metal seat butterfly valve should be same as a metal seat double offset, as per API 609. However, a triple offset metal seat butterfly valve in practice should provide better sealing than a metal seat double offset butterfly valve. Sealing of the metal seat double offset from unpreferred flow (pressure) direction is difficult. The seat is usually placed in a seat retainer. Fig. 2.45 shows a special seat design by a valve manufacturer. The thicker ring on top is the seat retainer. The one in the middle is the rubber seat with a metallic backup ring, and the third ring in the bottom is designed to act as a backup for the soft seat in case of fire or seat damage. The firesafe ring acts as the sealing in case of fire when the soft seat would be melted. The contacts between the seat retainer, the seat ring, and the backup metallic ring are shown in Fig. 2.46. The problem observed was seat deformation, as shown in Figs. 2.47 and 2.48. Moreover, the deformed seat was socked out and cut by the disk during the closing, as shown in Fig. 2.49. This problem was observed during the valve test.

FIG. 2.45 Seat design for a butterfly valve.

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2. Butterfly valve applications and design

FIG. 2.46

A seat design for a butterfly valve.

FIG. 2.47

Butterfly valve soft seat deformation.

The other issue with the seat design shown in Fig. 2.49 is that the retainer ring does not have any curve that improves the seat sealing and placing integrity. To solve these problems, the seat retainer for a butterfly valve should be changed to the design shown in Fig. 2.50. The seat retainer (070) has a curve on its surface in contact with the seat ring (060). The metallic backup ring from the valves was removed, and a new test called a “full flow test” was designed to examine the stability of the seat. In addition, the seat retainer was changed to the one shown in Fig. 2.51. There is probably no need to have the firesafe ring in the seat arrangement since the secondary sealing should be achieved between the valve disk and seat retainer in case of fire when the soft ring would be melted. The test was done through opening and closing the valve very slowly, five to six times, with the normal water velocity of the firewater pump (25,000 L/min), and checking the seat stability (see Fig. 2.51). There was no requirement to open the valve completely since when the valve is slightly open,

177

Eccentric butterfly valves

FIG. 2.48 Butterfly valve soft seat deformation.

FIG. 2.49 Butterfly valve soft seat has been cut.

030

060

010 FIG. 2.50 Seat arrangement for a butterfly valve.

070

178

FIG. 2.51

2. Butterfly valve applications and design

Full flow test.

the flow open area is small and the velocity of the flow is high so the possibility of the seat sucking out is high as well. Figs. 2.52 and 2.53 show the butterfly valve with the seat in place correctly without any damage after the full flow test. The conclusion in this case was to remove the firesafety metallic backup ring to avoid the soft seat being sucked out and other potential damages, in addition to changing the seat design to the arrangement shown in Fig. 2.50. Metal and soft seat rings could be interchangeable in a double offset butterfly valve. However, the seat retainer should also be changed in case of the possible need for changing the soft and metal seat ring. Laminated seat is another type of seat design with a combination of graphite and metal layers for the seat, one between two other layers with each layer working

FIG. 2.52

Butterfly valve seat examination after full flow test.

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FIG. 2.53 No damage on the seat after full flow test.

FIG. 2.54 Laminated seat including layers of graphite and metal.

independently. The laminated seat that is shown in Figs. 2.54 and 2.55 can completely prevent leaks for triple offset butterfly valves. The seat retainer can be bolted to the body using Allen screws because they are not pressure-containing parts. Fig. 2.56 shows the body of a double offset butterfly valve with small holes on it for fastening the seat retainer with Allen screws. The body is lugged type with four bolt holes not drilled completely through the tapered holes. The photos in Fig. 2.57 illustrate a completely assembled valve with the seat retainer screwed to the body of the valve with the metallic surface of the seat retainer is pressed to the body using Allen screws to tighten the seat. If the body of the valve is in 22Cr duplex material, the screw materials to connect the seat and seat retainer can be selected in 25Cr duplex or Inconel 718. The tight seal has been achieved with the seat ring, which could be made of polytetrafluoroethylene (PTFE) or reinforced (RPTFE).

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2. Butterfly valve applications and design

FIG. 2.55

Laminated seat including layers of graphite and metal.

FIG. 2.56

Body of a double offset lugged butterfly valve with Allen screw holes for seat retainer connection.

When it comes to screw materials, Inconel 718 is one option of material to use for 22Cr duplex body valves. Inconel 718 is a strong and hard material. However, these screws are not pressure-containing parts, so 25Cr duplex or 22Cr duplex screws may be sufficiently strong. Fig. 2.58 shows the seat retainer of a triple offset valve with holes to be bolted to the body. A layer of graphoil on the seat is used to provide sealing between seat retainer and the body. Seat and seat retainers in butterfly valves could be renewable or nonrenewable. The seat in the triple offset design shown in Fig. 2.59 has been placed between the seat retainer and the disk, and it is renewable. Fig. 2.59 shows the seat retainer in contact with the seat inside that, which is hard faced with Stellite 6.

Eccentric butterfly valves

FIG. 2.57 Assembled valve with seat retainer connected to the body using Allen screws. Courtesy: Westad.

181

182

2. Butterfly valve applications and design

FIG. 2.58

Seat retainer in a triple offset butterfly valve. Courtesy: Westad.

FIG. 2.59

Seat and seat retainer in a triple offset butterfly valve. Courtesy: Westad.

Fig. 2.60 shows the complete triple offset butterfly valve assembly. The grinding of the seat retainer and the seat is done in five different axes (Fig. 2.61), which are a very important design feature to provide tight sealing. The seat design and material for cryogenic valves can be different. Two seat rings with two layers of lip seal (PTFE + Elgiloy) would be more flexible in expansion or shrinkage during the temperature range with three metal parts (see Fig. 2.62). The seat in a double offset butterfly valve should be flexible, unlike the triple offset, which is the reason why the lip seal (Elgiloy and PTFE) are selected materials for seats. Two lip seals are installed to provide sealing in two different directions, but the valve is still recommended to be installed in the preferred pressure direction. It is noticeable that lip seal provides sealing in one direction. Copper (Cu) is also suitable for the seat of butterfly valves in cryogenic service (as shown in Fig. 2.63). Fig. 2.64 shows a copper seat ring installed in a cryogenic double offset butterfly valve. The inspection is done to make sure that it is seated properly in place. A spring (see Fig. 2.65) is

Eccentric butterfly valves

183

FIG. 2.60 Complete assembly of seat and seat retainer on a triple offset butterfly valve. Courtesy: Westad.

placed inside the copper seat to facilitate the correct placement of the seat ring in the seat retainer.

Stem sealing design Stem sealing design includes layers of packing (e.g., graphite), a gland, and a gland flange. Fig. 2.66 shows the sealing arrangement for a butterfly valve with an integrated gland and gland flange (091) and packing rings (095). Fig. 2.67 shows the integrated gland flange. Layers of packing graphite and lip seals are shown in Fig. 2.68.

Antistatic design (electrical continuity) Antistatic design, or electrical continuity, is a requirement for butterfly valves with soft materials. In fact, it is important to make sure that electrical continuity is established between the shaft, disk, and body to discharge static electricity that can be accumulated in the soft seat and cause fire. As it was explained earlier when discussing stem designs, a hinge pin or cone pin can be welded to the disk and placed between the disk and stem to create electrical continuity. An antistatic test can be implemented to make sure that the resistance of the electrical discharge path is not more than 10 Ω where direct current (DC) power does not exceed 12 V.

Bracket design The bracket is the top of the butterfly valve, under the top flange. A thick bracket design has the advantage of withstanding the weight load of a heaving operator such as an actuator. The top flange is usually installed at the top of the bracket under the gearbox. However, there is a coupling (adapter spool) installed on the top of the bracket without any top flange to provide

184

FIG. 2.61

2. Butterfly valve applications and design

Valve seat ground in five different axes. Courtesy: Westad.

space for insulation of the valve. The same shape of coupling is used under the pneumatic and hydraulic actuators (see Fig. 2.70). There is no need to have a top flange for the butterfly valves shown in Fig. 2.69 since there is a bottom flange on the mounted coupling.

Coupling and top flange design The coupling, also called the mounting bracket, is designed and installed between the valve and actuator to provide support for the actuator. In some cases, coupling can be used between the valve and gearbox to provide space for insulation (Fig. 2.71). The coupling is made of a piece of pipe welded to flanges on both sides. Full penetration weld is the preferred method of welding because fillet welding cannot provide the higher joint efficiency produced by full penetration. Solid coupling with an integrated pup piece

Eccentric butterfly valves

185

FIG. 2.62 Seat design for cryogenic valves in two layers of PTFE and three rings of metal. Courtesy: Westad.

FIG. 2.63 Copper seat inside the seat retainer for a cryogenic butterfly valve. Courtesy: Westad.

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2. Butterfly valve applications and design

FIG. 2.64

Copper seat inside the seat retainer for a cryogenic butterfly valve. Courtesy: Westad.

FIG. 2.65

Copper seat inside the seat retainer energized by the springs. Courtesy: Westad.

and two flanges on both sides is an even better choice compared to welded coupling, providing that the supplier is able to produce it. The coupling should be circular with a drain connection attached to drain the fluid leaking from the packing. However, the leaked fluid from the valve packing in the butterfly valves is open to the environment in this design. Therefore, it is not necessary to apply the drain connection to the coupling located between the valve and actuator. Alternatively, there is a drain connection on the coupling between the ball valve and the actuator, as shown in Fig. 2.72. It is important to note that using coupling affects the valve design in a way to increase the shaft (stem) length. The requirement for having the drain connection on the coupling is based on the API 6D Pipeline Valves standard. The coupling should be strong enough to withstand the weight of the operator (gearbox or actuator) plus the blast loads (accidental loads). The

187

Eccentric butterfly valves

091

095

FIG. 2.66 Stem sealing arrangement for a butterfly valve.

FIG. 2.67 Integrated gland flange. Westad Design.

FIG. 2.68 Graphite packing plus lip seals.

188

2. Butterfly valve applications and design

FIG. 2.69

Bracket design for the butterfly valves. Courtesy: Westad.

FIG. 2.70

Coupling under the pneumatic actuator. Courtesy: Westad.

accidental loads are usually defined in the design accidental load (DAL) specification. If the coupling is not strong enough, then pipe support may be required to be installed between the valve and actuator to prevent movement of the actuator and implementing extra stress on the coupling. The coupling material is usually Stainless Steel 316 (SS316) in the Norwegian offshore industry. Fig. 2.73 shows the coupling for manual valves in nickel aluminum bronze (NAB) valves placed between the valve and gearbox.

Eccentric butterfly valves

189

FIG. 2.71 Coupling between the valve and gearbox for insulation purposes. Courtesy: Westad.

Electrical actuators or manual valves without insulation should be supplied without coupling or mounting brackets. In that case, the valve operator such as a gearbox or electrical actuator will be installed directly on the top flange provided by the valve supplier (Fig. 2.74). Fig. 2.74 shows a wafer-type butterfly valve during the pressure test. The gearbox is colored in red (gray in print version) since the valve is used in a firewater system. In fact, the red color (gray in print version) on the gearbox is marked to give attention to the operator where firewater valves with safety functions are located. Butterfly valves on the fire ring are usually open. Fig. 2.75 shows an electrical actuator installed on the valve top flange. Fig. 2.76 shows the installation of top flanges on triple offset butterfly valves. The stem connection to the top flange is isolated through a Viton O-ring. Actuated and manual valves with insulation contain a bracket (coupling) and stem extension, and there are two options for the stem extension.

190

2. Butterfly valve applications and design

FIG. 2.72

Coupling between the ball valve and actuator and drain connection on the coupling. Courtesy: LVF.

FIG. 2.73

Coupling between the NAB valve and gearbox (SS316 material). Courtesy: Westad.

A removable stem extension (e.g., 100–120 mm) can be removed without any need to retest the valve. Alternatively, the height of the stem can be increased (e.g., 120 mm) and checked with the layout department for space considerations. Fig. 2.77 shows the connection of the gearbox to the top flange. It is important to provide sealing between operator, top flange, and coupling to avoid ingress of external contamination and moisture. Fig. 2.78 shows the silicon sheets between the gearbox and the coupling or top flange. Silicon sheets are yellow in color (light gray in print version). Alternatively, liquid silicon maybe used for sealing the gearbox and the top flange or coupling as shown in Fig. 2.79. A stem extension is useful not only for insulation. Cryogenic valves also have a stem extension to keep the packing and gearbox from the very cold service. Fig. 2.80 shows the stem extension for a cryogenic valve manufactured in stainless steel 316.

Eccentric butterfly valves

191

FIG. 2.74 Gearbox on the top flange. Courtesy: Westad.

Fig. 2.81 shows a butterfly valve for a cryogenic service with the stem extension. Usually, cryogenic valves are butt weld ended to reduce the risk of fluid leakage. Welding has higher joint efficiency than the flange connection. However, the butterfly valve for cryogenic service in Fig. 2.81 is a flanged connection. The reason for having the valve in flange connection is the high frequency of maintenance.

192

2. Butterfly valve applications and design

FIG. 2.75

Electrical actuator on the butterfly valve top flange. Courtesy: Westad.

FIG. 2.76

Top flange installation on the triple offset butterfly valves. Courtesy: Westad.

Eccentric butterfly valves

193

FIG. 2.77 Gearbox installation on the top flange. Courtesy: Westad.

FIG. 2.78 Silicon sheets for sealing the gearbox and coupling or top flange. Courtesy: Westad.

Packing design Butterfly valves are a very common valve selection for seawater services. Graphite packing in seawater services can create stem corrosion such as crevices, pitting, and galvanic faults. Although some end users accept graphite packing for butterfly valves in exotic body and stem materials such as titanium and 25Cr super duplex, other end users may not. This example describes an actual industry case where different a packing design and solution was chosen to avoid graphite packing corrosion. Crevice corrosion is the most common type of corrosion created during packing in seawater services. This type of corrosion can happen if packing is not placed properly in the packing box. The gap between the packing and the stem, as shown in Fig. 2.82, is a weak point where crevice corrosion can happen.

194

2. Butterfly valve applications and design

FIG. 2.79

Liquid silicon for sealing the gearbox. Courtesy: Westad.

FIG. 2.80

Stem extension for a butterfly valve in cryogenic service. Courtesy: Westad.

Pitting corrosion of the stem in which small holes are formed in the metal due to chloride in the seawater is the second corrosion mechanism. Pitting is a form of localized attack that can initiate stress-cracking corrosion. The risk of pitting corrosion is higher for lower grades of stainless steel (chromium-nickel alloys) with a pitting resistance equivalent number (PREN) less than 40, such as 22Cr duplex. According to the ISO 15156, the definition of PREN is “a number developed to reflect and predict the pitting resistance of a corrosion-resistance alloy (CRA) based upon proportions of chromium, molybdenum, and nitrogen in the chemical composition of alloy.” PREN ¼ Cr + 3:3 ðMo + 0:5WÞ + 16N 25Cr super duplex grades UNS S32750 and UNS S32760 have PREN values usually more than 40, which make the risk of pitting corrosion low for them.

Eccentric butterfly valves

FIG. 2.81 Cryogenic butterfly valve with flange connection. Courtesy: Westad.

FIG. 2.82 Risk of crevice corrosion on the packing.

195

196

2. Butterfly valve applications and design

This is an electrochemical corrosion that occurs through an electrochemical process that happens in the presence of electrolytes. By formation of a galvanic chain, the less noble metallic material (lower grades of chromium-nickel alloys) loses electrodes and is corroded as an anode. Graphite packing, on the other hand, is a very noble material that plays the role of a cathode in contact with the metallic stem in the presence of seawater as an electrolyte. The following sections discuss five different solutions regarding the graphite packing selection in seawater service in different projects. High-purity graphite with low impurities The first and easiest solution is using graphite with more than 98% purity, low-chloride content less than 50 ppm, and sulfur content less than 700 ppm, according to some end users’ specifications. The graphite packing internal diameter should be accurately sized and be very smooth (low roughness) to avoid friction with the stem and the potential creation of crevices and leakages.

Flexible graphite packing Using graphite foil or flexible graphite packing (see Fig. 2.83) with low impurities such as chloride and sulfur significantly reduces the chance of crevice and pitting corrosion. One reason for corrosion risk reduction may be the flexibility of graphite foil that can fill in the crevices in the stem and body. Therefore, crevice and consequent pitting corrosion can be prevented.

Teflon PTFE packing PTFE is proposed for packing instead of graphite in seawater services in some projects. However, the butterfly valves with PTFE packing cannot be a firesafe design and successfully pass the fire test based on API 607, API 6FA, or EN ISO 10497 fire test standards. PTFE is not usually recommended for operating temperatures above 150–200°C and in case of fire since it

FIG. 2.83

Flexible graphite (Sigraflex trade name).

Reinforced graphite packing with Inconel 625

197

would be melted. PTFE also cannot provide electrical continuity between the stem and body, unlike graphite. Butterfly valves used in seawater service should be a firesafe design. Although seawater is not the source of ignition and fire, the valve needs to function properly in case of fire, to transport seawater to the ignition source without a high rate of leakage and reduction of Cv. Therefore, PTFE (Fig. 2.84) is not a good choice of packing if a firesafe design and/or fire test is required for the valve.

Reinforced graphite packing with Inconel 625 Graphite packing can be reinforced by Inconel 625 or SS316 in order to have higher pressure and temperature resistance. There is no specific rule for the pressure and temperature limits of graphite. However, graphite could be reinforced (braided) with Inconel 625/ SS316 in operating temperatures above 300°C and high-pressure classes above class 900. The other advantage of graphite reinforcement with Inconel 625 is that a smaller thickness for one ring of braided graphite (see Fig. 2.85) can be achieved. Thus, more numbers of reinforced graphite can be placed in the packing box compared to the pure graphite, and better sealing would be achieved. As an example, four packing rings including two metallic braided rings at the top and the bottom and two nonbraided packings in the middle can be placed in the packing box instead of three nonbraided graphite packing rings. Fig. 2.105 shows braided packing graphite with Inconel 625 wires. Reinforced graphite packing with SS316 or Inconel 625 is not required for butterfly valves in seawater services for two reasons. First, wafer-type butterfly valves are used for lowpressure classes 150 and 300 in which metallic braided graphite packing is not required. Metallic braided graphite is usually used for high-pressure classes of 1500 and 2500 to strengthen graphite packing. Second, graphite is a very noble material and acts as the cathode, and a metallic braided part such as alloy 625 would be corroded as the anode in the presence of an electrolyte like seawater (galvanic corrosion). The other disadvantage of strong braided packing is that it increases the torque requirement and probably the size of the operator (gearbox).

FIG. 2.84 PTFE packing.

198

FIG. 2.85

2. Butterfly valve applications and design

Braided graphite packing with Inconel 625 wires.

Isolation of graphite packing One solution is to isolate the graphite packing rings through a Viton or a lip seal O-ring (Fig. 2.86). The Viton or lip seal is placed at the bottom of the graphite packing rings to avoid seawater contact with the graphite. Fig. 2.87 shows a lip seal made of PTFE and Hastelloy C springs under three rings of graphite. Fig. 2.88 shows graphite packing rings and lip seals made of white PTFE (Teflon) and Hastelloy C springs. The disadvantage of this solution is that an extra groove must be machined on the internal part of the body to place the lip seal, which can increase the delivery time of the valves. In addition, the lip seal groove must be machined with a very low roughness of 0.4 mm to make sure that no leak can occur through the lip seal.

FIG. 2.86

Lip seal made of PTFE seal and springs.

Isolation of graphite packing

199

FIG. 2.87 A layer of white lip seal under three layers of graphite packing. Courtesy: Westad.

FIG. 2.88 Lip seals and graphite rings.

As shown in Fig. 2.89, a valve manufacturer may need to machine an additional groove at the bottom of the valve and above the graphite sealing to protect the graphite used for the sealing of the bottom cover and the body from seawater contact. It might be a good idea to change the graphite sealing at the bottom to a Viton O-ring (Fig. 2.90) or lip seal to avoid extra machining at the bottom part of the body to isolate the bottom graphite sealing. Fig. 2.91 shows leakage from the bottom cover during the factory acceptance test because of a Viton rupture.

200

2. Butterfly valve applications and design

FIG. 2.89

Lugged butterfly valves (Manufactured by Westad, Norway).

FIG. 2.90

Viton O-ring for sealing of bottom cover in the butterfly valve.

Conclusion Although graphite packing is not the predominant sealing in butterfly valves, a correct packing solution to avoid stem corrosion in seawater services should be selected. The most effective way to avoid corrosion is selecting the flexible and low-impurity graphite packing as described earlier in this book. Although isolating the graphite packing through a lip seal or Viton O-ring is also a good approach that can increase the delivery time and cost. Braided

Butterfly valves standards

201

FIG. 2.91 Leakage from the bottom cover during the test.

graphite with Inconel 625 or SS316 is not recommended for the packing in seawater due to the potential for galvanic corrosion between graphite and the wire. Teflon (PTFE) packing is also not a good solution if the valve needs to be firesafe.

Offset definitions in eccentric butterfly valves The first offset is between the disk and the body. The second offset is between the stem and the disk for ease of disk opening and closing (see Fig. 2.92). The third offset is related to the axis on the seat surface and the disk, which causes bubbles tight between the disk and the seat and prevents galling between them. Fig. 2.93 shows all three offsets in a butterfly valve.

Butterfly valves standards The API 609 standard specifies the concentric butterfly valves (category A) for sizes 200 –4800 in pressure class 150. But they are usually used for sizes 400 and above in the Norwegian offshore industry. The disk of a rubber-line butterfly valve is smaller than a double offset, so that may be why it is possible to make a 200 concentric butterfly valve. Concentric butterfly valves require less torque for opening and closing of the valve compared to eccentric butterfly valves. Therefore, the disk and stem in concentric butterfly valves are smaller and more compact than those in eccentric butterfly valves. The larger disk of a double offset does not allow eccentric valves to be made in 200 as per API 609, unlike concentric butterfly valves. Double offset wafer-type butterfly valves are defined from 300 up to and including 2400 and maximum class 600 in API 509. ISO 5752 can be used for larger size butterfly valves, such as the 3000 class 150 shown in Fig. 2.94. Generally, class 600 equal to 100 barg is the maximum pressure class covered by API 609. The 3000 CL150 butterfly valves on the firewater rings were 410 kg, with a gearbox of 145 kg in one project. The gearbox is designed based on the maximum pipe class differential pressure

202

FIG. 2.92

2. Butterfly valve applications and design

Shaft offset toward the disk.

that requires a larger and heavier gearbox than usual. This valve should be electrically actuated for ease of operation according to the end-user criteria. But the 3000 class 150 was not selected with an actuator since the usually open valves are not operated frequently.

Butterfly valve bore Butterfly valves are reduced bore, so the bore of a butterfly valve could be even smaller than the bore of a ball valve.

Face to face Face-to-face values of butterfly valves are given in API 609. Category B (double offset) wafer-type butterfly valves in class 150 are usually 4 mm longer than category A (concentric) wafer-type butterfly valves up to and including 1200 . A category B wafer-type valve is 14 mm longer than a category A wafer-type valve in 1400 and class 150, and both category A and category B wafer-type class 150 valves have the same face to face in sizes 1600 –2400 , as shown in Tables 2.2 and 2.3 (taken from API 609). The face-to-face values for category A lug and wafer types are given only in class 150 in the API 609 standard. The face-to-face values of the double-flanged butterfly valves for category B butterfly valves are given in Tables 2.4 and 2.5 based on long or short pattern design.

Face to face

203

FIG. 2.93 Butterfly valves offsets.

FIG. 2.94 tesy: Westad.

Wafer double offset butterfly valve 3000 class 150 in titanium body for seawater (fire water) service. Cour-

204

2. Butterfly valve applications and design

TABLE 2.2 Face-to-face dimensions for category A (concentric) lugged and wafer butterfly valves CL150 (based on API 609). Face-to-face dimensions Valve size (NPS)

in.

Maximum variance (plus or minus)

mm

in.

mm

2

1.69

43

0.06

1.5

2½

1.81

46

0.06

1.5

3

1.81

46

0.06

1.5

4

2.06

52

0.06

1.5

5

2.19

56

0.06

1.5

6

2.19

56

0.06

1.5

8

2.38

60

0.13

3.3

10

2.69

68

0.13

3.3

12

3.06

78

0.13

3.3

14

3.06

78

0.13

3.3

16

4.00

102

0.13

3.3

18

4.50

114

0.13

3.3

20

5.00

127

0.13

3.3

24

6.06

154

0.13

3.3

30

6.50

165

0.25

6.4

36

7.88

200

0.25

6.4

42

9.88

251

0.25

6.4

48

10.88

276

0.25

6.4

Fire test Usually, there is no requirement to fire test valves to be used in seawater services. But the test might be done to measure the pressure drop and Cv created by the valve during the fire, to make sure that the valve is still capable to deliver the required water volume to extinguish the fire. PTFE-lined butterfly valves in Fig. 2.10 have been fire tested based on API 607, the fire test standard for soft-seated quarter-turn valves, and the result showed that they have just a maximum 5% Cv drop in case of a fire. In addition, there was not much disk deflection on the butterfly valves disk as a result of thermal expansion. It is notable that disk deflection can also create leakage. API 607, ISO 10497, or BS6755 standards can be applied for fire test of the valves. The rubber-lined butterfly valves will have an internal leak in case of a fire, since the lining will be melted. It is possible to use graphite packing instead of PTFE (Teflon) to minimize the external leak from the stem packing. But that is not enough, since the sealing between the valve

205

Installation direction

TABLE 2.3 Face-to-face dimensions for category B (eccentric) lugged and wafer butterfly valves CL150, 300, and 600 (based on API 609). Class 150

Class 300

Class 600

Maximum variance (plus or minus)

Valve size (NPS)

in.

mm

in.

mm

in.

mm

in.

mm

3

1.88

48

1.88

48

2.12

54

0.13

3.3

4

2.12

54

2.12

54

2.50

64

0.13

3.3

6

2.25

57

2.31

59

3.06

78

0.13

3.3

8

2.50

64

2.88

73

4.00

102

0.13

3.3

10

2.81

71

3.25

83

4.62

117

0.13

3.3

12

3.19

81

3.62

92

5.50

140

0.13

3.3

14

3.62

92

4.62

117

6.12

155

0.13

3.3

16

4.00

102

5.25

133

7.00

178

0.13

3.3

18

4.50

114

5.88

149

7.88

200

0.13

3.3

20

5.00

127

6.25

159

8.50

216

0.13

3.3

24

6.06

154

7.12

181

9.13

232

0.13

3.3

and the mating flange (which is achieved through the rubber liner) would be melted in a fire. Internal leakage from the seats may not be a problem since the butterfly valves for a firewater system are usually open in the line. Passive fire protection is another way to minimize leakage from the valves. Fig. 2.95 shows the burnt triple offset valve after a fire test. The valve is fire tested because the seat design was changed, and changing the design of the valves requires new fire testing.

Installation direction Concentric butterfly valves are bidirectional. Double offset and triple offset butterfly valves are also bidirectional but with preferred flow (pressure) direction, such as flow from the stem side. Fig. 2.96 shows the preferred flow direction of a flanged end double offset butterfly valve. Flow direction is marked on the body of the valves refer to Fig. 2.97. Fig. 2.98 shows an example where the actuated butterfly valve was installed in the wrong direction in the construction yard. This butterfly valve installation is wrong because the flow was incorrectly assumed to be in the opposite direction in the piping modeling program (PDMS) as shown in the small picture on the bottom left of Fig. 2.119. Therefore, it was the recommendation from the valve manufacturer to remove the valve from the line, rotate it 180 degrees, and install it in the preferred flow direction. One reason for the valve supplier manufacturer is that the fluid helps in closing the valve in the preferred flow direction, so it is not possible to get fluid sealing force for closing the valve in the opposite flow direction. Even if a butterfly valve has passed the test on the opposite flow direction, the sealing of the valve may not be effective after a period of time.

206

2. Butterfly valve applications and design

TABLE 2.4 Face-to-face dimensions for category B (eccentric) long pattern double flange butterfly valves CL150, 300, and 600, based on API 609. Class 150 Valve class (NPS)

in.

Class 300

Class 600

Maximum variance (plus or minus)

mm

in.

mm

in.

mm

in.

mm

3

8.00

203

11.12

282

14.00

356

0.13

3.3

4

9.00

229

12.00

305

17.00

432

0.13

3.3

6

10.50

267

15.88

403

22.00

559

0.13

3.3

8

11.50

292

16.50

418

26.00

660

0.13

3.3

10

13.00

330

18.00

457

31.00

787

0.13

3.3

12

14.00

356

19.75

502

33.00

838

0.13

3.3

14

15.00

381

30.00

762

35.00

889

0.13

3.3

16

16.00

406

33.00

838

39.00

991

0.13

3.3

18

17.00

432

36.00

914

43.00

1092

0.13

3.3

20

18.00

457

39.00

991

47.00

1194

0.13

3.3

24

20.00

508

45.00

1143

55.00

1397

0.16

4.0

26

22.00

559

49.00

1245

57.00

1448

0.16

4.0

28

24.00

610

53.00

1346

61.00

1549

0.16

4.0

30

24.00

610

55.00

1397

65.00

1651

0.16

4.0

32

26.00

660

60.00

1524

70.00

1778

0.16

4.0

36

28.00

711

68.00

1727

82.00

2083

0.19

5.0

Insufficient sealing of butterfly valve can be intensified due to bearing wear and emergency cases like fire or water hammering. However, to avoid extra jobs in the construction yard and save time, some engineers may recommend leaving the butterfly valve as it is, since the valve is designed to be bidirectional and is tested from both sides in the valve factory.

Layout considerations Operator companies (end users) may prefer to limit usage of the straight pattern globe valves for flow control applications to reduce the risk of cavitation. Therefore, it may be a good idea to use butterfly valves instead of straight pattern globe valves in size ranges from 400 to 1200 , for example, in low-pressure classes 150 (20 barg) and 300 (50 barg). Butterfly valves especially wafer designs are lighter and cheaper than globe valves. Again, there is a risk of cavitation for butterfly valves. Therefore, butterfly valve manufacturers may propose straight pipe requirements upstream and downstream of the butterfly valve selected for flow control to reduce the risk of cavitation, erosion, and wearing. As an example, a butterfly valve manufacturer may propose two or four times the valve size straight run before and after the valve

207

Layout considerations

TABLE 2.5 Face-to-face dimensions for category B (eccentric) short pattern double flange butterfly valves CL150, 300, and 600, based on API 609. Class 150 or Class 300 Valve class (NFS)

in.

mm

Class 300 in.

mm

Class 600 in.

Maximum variance (plus or minus)

mm

in.

mm

3

4.50

114

7.09

180

7.09

180

0.13

3.3

4

5.00

127

7.48

190

7.48

190

0.13

3.3

6

5.50

140

8.27

210

8.27

210

0.13

3.3

8

6.00

152

9.06

230

9.06

230

0.13

3.3

10

6.50

165

9.84

250

9.84

250

0.13

3.3

12

7.00

178

10.63

270

10.63

270

0.13

3.3

14

7.50

190

11.42

290

11.42

290

0.13

3.3

16

8.50

216

12.20

310

12.20

310

0.13

3.3

18

8.75

222

12.99

330

12.99

330

0.13

3.3

20

9.00

229

13.78

350

13.78

350

0.13

3.3

24

10.50

267

15.35

390

15.35

390

0.16

4.0

26

11.50

292

16.14

410

–

–

0.16

4.0

28

11.50

292

16.93

430

–

–

0.16

4.0

30

12.52

318

17.72

450

–

–

0.16

4.0

32

12.52

318

18.50

470

–

–

0.16

4.0

36

12.99

330

20.80

510

–

–

0.19

5.0

38

16.14

410

20.87

530

–

–

0.19

5.0

40

16.14

410

21.65

550

–

–

0.19

5.0

42

16.14

410

22.44

570

–

–

0.24

6.0

48

18.50

470

24.80

630

–

–

0.24

6.0

Note: Due to Class 300 having two sets of dimensions in this table the purchaser shall clearly specify which column is applicable.

to straighten the flow and minimize the risk of erosion and wearing. The other solution to avoid butterfly valves for flow control is to select a smaller size butterfly valve for full flow and add a reducer and expander before and after the butterfly valve, respectively. As an example, if the line is 600 and the butterfly valve should be 70% open for fluid control, it is possible to select a 400 butterfly valve fully open on the 600 line with a 600  400 reducer upstream and a 400  600 expander downstream of the valve. The fluid velocity is another important factor to consider in preventing erosion. It is probably better to limit the fluid velocity to reduce wearing risk. The other point related to installation is that usually the stem of the butterfly valve should not be located below the horizontal line, to avoid fluid movement toward packing. However,

208

2. Butterfly valve applications and design

FIG. 2.95

Fire test of the triple offset valves because of new seat design.

FIG. 2.96

Flanged end double offset butterfly valve with the preferred flow direction. Courtesy: Westad.

a butterfly valve with robust packing solution, including three or four rings of lip seals and graphite (see Fig. 2.107) may be an exception if the valve supplier gives approval. Large size butterfly valves (i.e., 2000 or above) are recommended to be installed horizontally to lower the weight of the valve on the spacers, seats, and bearings (see Fig. 2.99). If the valve is installed on the vertical line with the stem on the horizontal, there is no weight on the spacer, but some loads on the stem bearings. There is a high load on the lower spacer in a horizontally installed butterfly valve in an open position, and high load on the seat ring in closed position. Figs. 2.100 and 2.101 illustrate the spacers for butterfly valves.

Layout considerations

209

FIG. 2.97 Preferred flow direction on the body of the butterfly valves. Courtesy: Westad.

FIG. 2.98 Wrong installation of a double offset butterfly valve in the yard.

The actuator and handwheel directions should be specified on the purchase order for the valve manufacturer. The piston side of the actuator can be positioned upstream or downstream of the valve. If the actuator direction is not correct on the valve, the actuator must be removed and rotated 180 degrees in the yard based on the given procedure from the supplier. If workers in the yard do not perform actuator turning due to lack of a guarantee, after technical services (ATS) will be affected. In that case, the actuator rotation should be done by the valve manufacturer personnel at an additional project cost. If a butterfly valve is selected for the dirty particle-containing services (e.g., triple offset in the mud service), it is recommended to install the valve in a vertical position with the horizontal stem to avoid the accumulation of particles around the stem and body hole as well as lessen the possibility of particle ingress in the body hole. Installation of the butterfly valve in both vertical and horizontal positions will not change the erosion level on the disk.

210

FIG. 2.99

2. Butterfly valve applications and design

Large size butterfly valves installed horizontally.

Torque Torque is a measure of how much force can act on a valve operator to rotate the valve closure member for opening or closing of the valve. Torque can be measured on either stem or gear for gear-operated valves. The torque value should have a limitation that is defined in project specifications (such as 150 N m maximum). The torque on gear is equal to the torque on the stem  gear ratio. Figs. 2.102 and 2.103 illustrate the torque measurement on the gear and stem, respectively. MAST and torque are lower in butterfly valves than the ball valves. Torque should cover the friction of stem and packing (the largest friction value), seat ring friction, and bearing/

Torque

211

FIG. 2.100 Spacers for butterfly valves.

FIG. 2.101 Spacers on a double offset butterfly valve. Courtesy: Westad.

stem friction. Torque value on the stem is higher when the valve is opened against the fluid pressure rather than opening an empty valve. The higher torque provides a higher gearbox ratio if the valve is manual. A higher gear ratio means more torque output and a larger gearbox. A triple offset butterfly valve is a torque-seated valve that requires a higher torque than a double offset butterfly valve for opening and closing. Higher torque requirements for a triple offset butterfly valve result in a thicker stem and a larger disk compared to a double offset butterfly valve. The larger disk in a triple offset butterfly valve causes a higher pressure drop. Therefore, the higher pressure drop in a triple offset butterfly valve reduces the Cv of the triple butterfly valve. The higher pressure drop also increases the wearing and cavitation risk in the triple offset butterfly valve. In addition, a triple offset butterfly valve is metal seated, so it cannot provide zero leakage, unlike a soft seat double offset butterfly valve. Refer to the API

212

2. Butterfly valve applications and design

FIG. 2.102

Torque measurement on the gear of a rubber-lined butterfly valve.

FIG. 2.103

Torque measurement on the stem of a rubber-lined butterfly valve.

598 standard for testing the valves; a metal seat can have a maximum two drops per inch size per minute leakage in a seat hydro test and a maximum of four bubbles per inch size per minute leakage in a low-pressure (4–7 barg) pneumatic test if the valve size is 1400 and above. In the test of a triple offset in case of leakage, it is possible to increase the torque on the seat and retest the valve to see whether the leak has stopped. Like other valves, butterfly valves have five torque values: 1. 2. 3. 4.

BTO: Break to open, which is usually the highest torque. ETC: End to close, which is usually the second highest torque in a butterfly valve. BTC: Break to close Running torque when the disk is between open and closed positions.

Lifting lug

213

5. ETO: End to open, which is usually the lowest torque value If a butterfly valve is installed in the preferred flow direction, the fluid pressure helps with the closing of the valve. If the valve is installed in an unpreferred flow direction, the fluid pressure helps with opening the valve instead of closing. Therefore, higher ETC and lower BTO torque may be required if the valve is installed against the preferred flow direction. The ETC may even exceed the BTO. Hopefully, designing the actuator based on design pressure instead of operating and considering the safety factor will cover the ETC torque that exceeds beyond the usual value.

Locking devices A mechanical locking device could be achieved through a chain or padlock flange on the valves. A padlock flange for locking the valve is shown in Fig. 2.104, applied between the handwheel and gearbox.

Lifting lug Requirements for a lifting lug are different from one project to another. As an example, a lifting lug could be required for valves weighted 200 kg and above. However, some valve manufacturers may provide lifting lugs in 25 kg or above. Lifting lugs could be removed after installation and the holes filled with grease and plugged. Two lifting lugs are placed on the body of butterfly valves in Fig. 2.105, and the thicknesses of the body on lifting lug parts should be increased. Lifting lugs are removed during tests and considered as weak points for leaks during the body leak inspection (Fig. 2.106). Lifting lug threads are electroless zinc plated as per ASTM B633 (5, 8, 12, or 25 μm thicknesses) to achieve a very thin coating. Selecting hot-dip galvanized (HDG) as the thicker coating compared to zinc plate is probably better in an offshore environment. But the screwed in

FIG. 2.104 Padlock flange for locking the rubber-line butterfly valve.

214

2. Butterfly valve applications and design

FIG. 2.105

Additional thickness on the cast body to drill and install lifting lug. Courtesy: Westad.

FIG. 2.106

Butterfly valves with lifting lugs. Courtesy: Westad.

body lifting lugs will most likely be removed from the valve after installation. Bolts are HDG in Norway as per ASTM A153, to achieve higher thickness (perhaps 45 μm on average). Lifting lug material is usually carbon steel ASTM A29. Lifting lugs can be HDG and the other option for coating the fasteners and screws in small size is GEOMET, which is made of zinc and aluminum and more cost effective than zinc plate. Pneumatic and hydraulic actuators are supplied with the lifting lugs. Actuator manufacturers may recommend avoiding the use of the actuator lifting lugs for lifting the assembled

Lifting lug

215

FIG. 2.107 Butterfly valves with lifting lugs.

valve and actuator together. However, it should not be a problem to lift a light valve with the actuator on the top from the actuator lifting lug. Fig. 2.107 shows pneumatic actuators on the ball valves, and the lifting lugs for the actuators have been highlighted. Unlike pneumatic and hydraulic actuated valves, electrical actuators do not have lifting lugs. Therefore, a cloth can be used for lifting the actuator. Fig. 2.108 shows how the electrically actuated butterfly valve has been lifted by a cloth. The valve and actuator have been lifted together since the valve is light and the combined weight of the valve and the actuator is not heavy. A lifting lug may be designed and applied for larger and heavier valve gearboxes, as shown in Fig. 2.109.

FIG. 2.108 Lifting the electrically actuated butterfly valve by cloth. Courtesy: Westad.

216

FIG. 2.109

2. Butterfly valve applications and design

Gearbox lifting lugs. Courtesy: Westad.

Bottom cover A bottom cover can be installed at the bottom of a butterfly valve and connected to the body through bolting. Graphite can be used to seal the bottom cover to the body. If the intention is to isolate the bottom cover graphite from the seawater, then a Viton O-ring can be installed at the top of the graphite. But adding an O-ring requires additional machining to create the sealing groove. Additional O-ring groove machining can cause a delay in delivery time, so an alternative solution is to switch the bottom cover sealing from graphite to a Viton O-ring. Fig. 2.110 shows leakage from the body and bottom cover due to a break in the Viton O-ring. The reason for the leakage is the rupture of Viton O-ring, as shown in Fig. 2.111.

Cv value A butterfly valve has a smaller bore than a reduced bore ball valve with the disk on the way of fluid passage so the Cv of a butterfly valve is less than the Cv of a reduced bore ball valve. Butterfly and axial valves are both choices for a fast-opening valve on the knockout drum outlet line located on the subflare line. Comparing the Cv of these two options, a butterfly valve could have double or even more than double the Cv of an axial valve. The material change does not affect the Cv. First of all, the internal diameter of the valve is constant. The other issue that affects the Cv is that the disk design might be thinner in 22Cr duplex than stainless steel 316. A thinner 22Cr duplex disk leads to higher Cv. In addition, a thinner disk may need a smaller diameter of the stem connection. A smaller diameter stem also increases the Cv. But manufacturers may prefer to standardize the size of the disk and stem for all different materials to avoid design change as well as changing different sizes of O-ring, bearing, packing, and coupling for different materials.

Material traceability

217

FIG. 2.110 Leakage from the bottom cover.

FIG. 2.111 Viton O-ring rupture during the body pressure test.

Material traceability The material traceability based on EN ISO 10204 standard specifies “type of inspection for metallic products. It covers all methods of metallic production such as plates, sheets, bars, forging, casting, whatever their method of production.” Two types of inspection have been defined in the standard. Nonspecific inspection is carried out by the manufacturer in accordance with his own procedures to assess whether products defined by the same product specification and made by the same manufacturing process are in compliance with the requirements of the order. The products inspected are not necessarily the products actually supplied. Specific inspection is carried out before delivery according to the product specification on the products to be supplied or on test units, the products are part of, in order to verify that these products are in compliance of the requirements of the order.

218

2. Butterfly valve applications and design

There are four types of inspection levels identified in the EN ISO 10204 standard. 1. Declaration of compliance with the order “type 2.1” Document in which the manufacturer describes that the products are supplied in accordance with the requirements of the order, without the inclusion of the test results. 2. Declaration of compliance with the order “type 2.2” Document in which the manufacturer describes that the products are supplied in accordance with the requirements of the order, and in which test results are provided based on nonspecific inspection. 3. Inspection certificate of “type 3.1” Document in which the manufacturer describes that the products are supplied in accordance with the requirements of the order, and in which he provides test results. The inspection test certificate of 3.1 provides traceability of the inspected parts. All important butterfly components such as body, stem, seat retainer, and disk contain traceability numbers in the material certificates. 4. Inspection certificate of “type 3.2” Document prepared by both the manufacturer’s authorized inspection representative, independent of the manufacturing department, and the purchaser’s authorized inspector in compliance with the requirements of the order and in which the test results are supplied.

Material selection Body material 25Cr super duplex and titanium are popular materials for the body of butterfly valves in the Norwegian offshore industry mainly for seawater services. However, usage of nickel aluminum bronze (NAB) UNS C95800 as a cheaper choice than super duplex and titanium shall be considered for seawater applications. Fig. 2.138 shows NAB body valves used for seawater services in the offshore industry. NAB valves can be oxidized to provide a corrosionprotective layer on the body of the valve. Super duplex is selected for oxygen-free seawater services with less than 20 particles per barrel or seawater services with maximum 20°C operating temperature in the Norwegian offshore industry. Carbon steel body butterfly valves can be a good option for freshwater services. Fig. 2.112 shows 400 class 150 titanium valves in seawater services. As shown in the photo, titanium is bright and silvery white. This metallic material is the most noble and most expensive one used in the Norwegian offshore industry with no rust and corrosion. Austenitic stainless steels such as SS316 or SS316L (low carbon grade) are good materials for the butterfly valves in cryogenic services with the minimum design temperature of 196°C. Figs. 2.113 and 2.114 show the cast body of a welded end butterfly valve after machining on the ending connections and top flanges, as well as another welded butterfly valve after assembly

Material selection

219

FIG. 2.112 400 CL150 titanium body valves for seawater services. Courtesy: Westad.

FIG. 2.113

Cast body of a butt welded end butterfly valve in SS316 material for cryogenic service. Courtesy: Westad.

that is ready for cryogenic testing. Valves in both pictures are manufactured in SS316 materials. Stainless steel 316 should be impact tested as per Norwegian Petroleum Standard (NORSOK) if it is used for temperatures below 101°C. 316L stainless steel has a low carbon content that improves the material toughness and weld ability. The cryogenic maximum temperature can begin at 46°C or 101°C depending on the project specification (Fig. 2.115).

220

2. Butterfly valve applications and design

FIG. 2.114 Stainless steel 316 weld end butterfly valve for cryogenic application (Ready for test). Courtesy: Westad.

FIG. 2.115

Nickel aluminum bronze valves in seawater services. Courtesy: Westad.

The bottleneck for butterfly valve manufacturers is ordering the body casting, which can take 4 months or longer. Casting of carbon steel, 22Cr and 25Cr duplex, and NAB materials can be weld repaired based on a valve supplier procedure if there are any minor defects from the foundry. Major casting defects should be returned to the foundry for repair. The criticality

Material selection

221

of a casting defect should be defined by the valve supplier based on the relevant ISO standard. Weld repair is not allowed on the titanium by the valve manufacturer. Defects that are found during the visual examination or other NDT methods should be repaired by welding (weld repair) and post-weld heat treatment (PWHT) afterward. Weld repair is done by tungsten inert gas (TIG). A weld procedure specification (WPS) is created based on ASME Sec. IX and it is recommended to be performed by a qualified welder based on the procedure, even if he is qualified based on ASME Sec. IX. Different materials such as carbon steel, stainless steel, and titanium should be kept separate during the storage, machining, and assembly to avoid cross contamination. Cross contamination is defined as the contamination of a starting material, intermediate, or finished product with another starting material or product. Casting can be sandblasted for better quality. Wax casting or replicasting give a higher casting quality without porosity compared to sand casting. Molten metal is put in the wax that is in the clay, and then the wax will be melted in wax casting. Sand casting gives porosity in the cast, which can be revealed or cracked after machining.

Seat and disk materials Seat and disk materials as valve internals should have a material quality equivalent to the body material. Table 2.6 proposes disk and seat materials based on the valve body. Stellite hard facing may be required for all the materials except for NAB and titanium to increase the material resistance to particles, galling, and erosion. Copper (Cu) is a good material for the seat of butterfly valves in cryogenic services since it is a soft material and can make hardness differences with the disk, which could be in 316L/316 SS (see Figs. 2.116 and 2.117). However, it may be lubricated with antifriction material such as MolyKote. It can also be used for temperatures as low as 268°C. Ammonia and H2S are two limitations for copper material. Copper is a chemical element with the symbol Cu and atomic number 29. It is a soft, malleable, and ductile metal with very good thermal and electrical conductivity. This material has a reddish-orange color. Fig. 2.118 shows a copper seat ring inside a seat retainer. The seat design for a cryogenic application could be manufactured in SS316 or SS316L materials. Even a lower grade of austenitic stainless steel such as SS304 can be selected for TABLE 2.6 Proposed seat and disk materials. Body material

Seat/disk material

Carbon steel

13%Cr or 13%Cr-4%Ni or 22Cr duplex

Stainless steel 316

Stainless steel 316

22Cr Duplex

22Cr Duplex or 25Cr super duplex

6MO

6MO, Inconel 625

Nickel aluminum bronze

Nickel aluminum bronze

Hastelloy

Hastelloy

Titanium

Titanium

222

2. Butterfly valve applications and design

FIG. 2.116

Copper seat material. Courtesy: Westad.

FIG. 2.117

Hard-faced copper material. Courtesy: Westad.

cryogenic applications with a low design temperature of 196°C. The other design created by Westad (a Norwegian valve manufacturer) is to create a seat ring by mixing the layers of metal and lip seal. The series of photos in Fig. 2.119 show two seat rings with two layers of lip seal (Teflon plus Elgiloy) between metallic rings, which provide flexibility in expansion and shrinkage during the temperature fluctuations between very cold 196°C and ambient temperature. The reason two lips seals have been used is that lip seal provides sealing in only one direction, so two lip seals should be installed to provide valve sealing in both directions. However, a valve supplier may recommend the valve be installed only in the preferred flow direction. NAB body valves may need more corrosion-resistant internal materials such as Monel (a nickel alloy with copper) for the seat and stem. However, selecting a NAB seat for NAB body

Material selection

223

FIG. 2.118 Copper seat ring in a seat retainer. Courtesy: Westad.

valve should be fine. In one instance, a triple offset butterfly valve supplier asked to upgrade the seat material from 22Cr duplex to Inconel 625 to increase the hardness between the seat and the disk. The disk of the valve was manufactured in 22Cr duplex material. Hardness difference between the disk and seat minimizes galling, wearing, and friction rate. But the friction rate between the disk and the seat is less in a triple offset butterfly valve than it is in a double valve. The other solution is to apply Stellite 6 overlay on both the 22Cr duplex seat and disk, or at least on the disk, to reduce the hardness difference. Soft seat materials could be PTFE (Teflon), Viton, or lip seal for a soft seat butterfly valve. Lip seal can provide sealing in only one direction, so it cannot provide bidirectional isolation in a butterfly valve. Another lip seal should be added to the lip seal in order to provide bidirectional sealing. Fig. 2.120 shows a spring energized PTFE lip seal. It contains a PTFE seal energized with innerspring forces. Viton is a black elastomer sealing, as shown in Fig. 2.121. Elastomer is a natural or synthetic polymer having elastic properties similar to rubber.

Stem material NAB grade UNS C63000 is a very common choice of stem material for NAB body valves. UNS C63000 has a higher mechanical strength than NAB UNS C95800. However, if the stem strength is not sufficient in case of valve actuation, then Monel K500 is the proposed alternate stem material. It is worth mentioning that upgrading the stem material for NAB due to actuation can happen rarely in the offshore industry. There should not be a risk of galvanic corrosion between a Monel K500 stem and an NAB body. The more noble material (Monel K500) has less area so it cannot corrode a large anodic NAB body. If the body of a butterfly valves is in stainless steel 316 (SS316), the same stem material SS316 is proposed for the valve. Nitronic 50 FXM-19 (UNS S20910) or alloy 718 can be selected

224

FIG. 2.119

2. Butterfly valve applications and design

Seat design for cryogenic application. Courtesy: Westad.

Material selection

225

FIG. 2.120 Lip seal.

FIG. 2.121 Viton seat.

alternatively for the 316SS body valves to increase the torque capacity, mainly in case of valve actuation. Alloy 718 is more expensive than Monel K500. 25Cr duplex butterfly valves with 25Cr super duplex stem material and other internals are selected for noncorrosive seawater applications in the Norwegian offshore industry. Usually a 25Cr super duplex stem in a butterfly valve provides enough strength, so there is no need to upgrade the stem material even in case of actuation. However, a titanium grade 5 stem bar with ASTM B348 Gr.5 grade/forge ASTM B381 (tensile ¼ 130 ksi, yield ¼ 120 ksi) is stronger than 25Cr super duplex (tensile ¼ 116 ksi, Yield ¼ 80 ksi). Titanium grade 5 contains aluminum and vanadium, which increase the mechanical strength of the material. Titanium Gr.5 can be

226

2. Butterfly valve applications and design

used for pressure-containing bolts in titanium body valves. There is not much corrosion resistance difference between titanium Gr.2 and Gr.5. They can be used in seawater services in maximum 95°C and low-chloride content, 85°C and medium chloride content, and 80°C and high-chloride content. Titanium plate material is used according to the ASTM B265 Gr.2 or 5 grades.

Bearing material Bearings usually are made of a metallic part to avoid deformation and a soft internal part to avoid friction between the metallic bearing and the stem, metal-to-metal friction, and galling. However, sometimes valve suppliers may use hard-soft materials for bearings such as PEEK or reinforced PTFE without any metallic parts. As an example, two bearings can be used for the upper stem and one bearing for the lower stem. One common bearing material, DU-DRY, contains three layers—copper, carbon steel, and PTFE. A titanium bearing with PTFE lining was requested for a titanium body valve. However, the valve supplier had difficulties in supplying the titanium bearing. Alternatively, Hastelloy C276 was agreed upon for the metallic part of the stem bearing. The valve supplier did spinning tests on the bearing to be sure that there was enough bonding between the PTFE and Hastelloy C276.

Interlock Usually butterfly valves do not have interlocks. But if an interlock is required for a butterfly valve, the interlock supplier must have top work drawings for valves. For example, the interlock supplier should remove the handwheel and install the locking device on the valve that increases the handwheel length by 100 mm.

Position indicator A butterfly valve may be equipped with position indicators. Fig. 2.122 shows the analog position indicator on a butterfly valve.

Spare parts Valve manufacturers can propose packing and bottom cover sealing, which could be Viton or graphite gasket, sealing such as stem sealing (e.g., lip seal), and the seat ring as spare parts.

ATEX ATEX covers equipment for potentially explosive atmospheres. Manual butterfly valves do not fall inside the ATEX scope of work because they do not have any source of ignition. But the valve gearbox is a source of ignition in the manual valves, since it is filled in with the grease. The internal soft materials such as the seat and the lip seal can accumulate static electricity and cause fire and ignition. But internal parts of the valve do not put the valve inside the ATEX scope of work. On the other hand, if a valve contains actuators like electrical

Material selection

227

FIG. 2.122 Butterfly valve with analog position indicator.

actuators, the valve does fall inside the ATEX scope of work since an actuator with electrical parts is a source of ignition.

Transportation Manual butterfly valves are transported with the disk in a half-open position. However, actuated butterfly valves are either fail open (FO) or fail close (FC). FO actuated valves are open in the fail position when the pneumatic air or hydraulic oil has been disconnected. FC actuated valves are closed in the fail position. In this case, fail open actuated valves are transported in an open position, and fail close actuated valves are transported in a closed position.

Packing and preservation Packing and preservation will be described in detail in Chapter 18. Butterfly valves are transported with a disk half-open, so it is not possible to place the plywood directly on the flange face. As it is shown in Fig. 2.123, the valve is placed in a plastic bag and then plywood

228

FIG. 2.123

2. Butterfly valve applications and design

Preservation of the butterfly valves flange face. Courtesy: Westad.

Material selection

229

is placed on black nitride rubber on the valve. But if the valve is FC, then the valve is transported in a closed position. The gearbox of the valve contains grease, so it is a source of ignition. Therefore, aluminum foil as it is shown in Fig. 2.124 is wrapped around the gearbox. Aluminum foil also protects the gearbox against the ingress of sand and particles. Fig. 2.125 shows the inside the gearbox of a butterfly valve almost fully filled with grease.

FIG. 2.124 Aluminum foil for protection of gearbox.

FIG. 2.125 Opened gearbox with almost full grease.

230

2. Butterfly valve applications and design

Vulc tape should be wrapped around the stem and bracket to protect them against external corrosive environment. A rubber hose may be used to cover the stem threads. But butterfly valves, unlike gate and globe valves, do not have stem threads so there is no need to use a rubber hose around them. The stem can be protected just with vulc tape so there is no need to use the rubber hose around the stem. Fig. 2.126 shows the vulc tape around the stem. Vulc tape should be flexible, firesafe, and waterproof.

Tagging and marking Figs. 2.127 and 2.128 show two tags on the bracket of a butterfly valve. One tag is permanent, and the main tag number includes information such as valve manufacturer name, type, serial, year size, material, rating, etc. The temporary tag includes the stock number and valve data sheet (e.g., FHAD21R). The tag numbers are placed on the valve bracket.

More pictures This section includes more pictures of butterfly valves, with explanations (Figs. 2.129–2.148).

FIG. 2.126

Vulc tape around the stem.

More pictures

FIG. 2.127 Tag plates on the butterfly valve bracket.

FIG. 2.128 Details of the permanent tag plate.

231

232

2. Butterfly valve applications and design

FIG. 2.129 400 Class 150 titanium body butterfly valves after a factory acceptance test. Application: Seawater service. Manufacturer: Westad.

FIG. 2.130 400 Class 150 titanium body butterfly valves during factory acceptance test. Application: Seawater service. Courtesy: Westad.

More pictures

FIG. 2.131

233

1800 Class 150 titanium body butterfly valves during factory acceptance test. Application: Seawater service. Courtesy: Westad.

FIG. 2.132 Cast body of the butterfly valves before assembly. Courtesy: Westad.

234

2. Butterfly valve applications and design

FIG. 2.133

Machining equipment. Courtesy: Westad.

FIG. 2.134

Butterfly valve gearboxes. Courtesy: Westad.

More pictures

FIG. 2.135 Butterfly valve with electrical actuator after FAT test. Courtesy: Westad.

FIG. 2.136 Lugged butterfly valve. Courtesy: Westad.

235

236

2. Butterfly valve applications and design

FIG. 2.137

Butt weld end actuated butterfly valve for cryogenic service. Courtesy: Westad.

FIG. 2.138

Pneumatic actuated butterfly valve. Courtesy: Westad.

FIG. 2.139 Butterfly valve seat retainer and PTFE seat ring. Courtesy: Westad.

FIG. 2.140 Places for cryogenic test. Courtesy: Westad.

238

2. Butterfly valve applications and design

FIG. 2.141

Helium capsules for cryogenic test. Courtesy: Westad.

FIG. 2.142

Wafer lug butterfly valve. Courtesy: Westad.

More pictures

FIG. 2.143 Stellite 6 for hard face overlaying on the disk and seat. Courtesy: Westad.

FIG. 2.144 Stellite 21 for hard face overlaying on the disk and seat. Courtesy: Westad.

239

240

FIG. 2.145

2. Butterfly valve applications and design

Liquid penetrant test on the cast body of the butterfly valves after machining the holes for lug. Courtesy:

Westad.

FIG. 2.146

Flanged body butterfly valve with the spacers. Courtesy: Westad.

More pictures

FIG. 2.147 Assembling of a disk inside the butterfly valve disk. Courtesy: Westad.

FIG. 2.148 Butterfly valve disks after machining. Courtesy: Westad.

241

C H A P T E R

3

Plug valve application and design Valve application examples A plug valve is an appropriate choice of valve for on-off or limited throttling applications in abrasive and erosive media as an alternative to metal seat ball valves or through conduit gate valves (Fig. 3.1). Like ball and butterfly valves, this valve is a quarter-turn valve and the closure member rotates 90° from opening to closing and vice versa. Plug valves may be the oldest generation of valve configuration. The valve is very good for operation against high differential pressure but has a bad reputation for sticking. One application of a plug valve is for downstream of a separator-produced water line where jet water is injected to remove sand from the bottom of the separator (see Fig. 3.2). The other option for this application is a through conduit gate (TCG) valve, which is less compact than the plug valve. Fig. 3.3 illustrates both a plug valve (left) and a through conduit gate valve (right as two options for a separator-produced water outlet line). The advantages of a plug valve over a ball valve will be explained later. A plug valve is a better choice than a ball valve for drain piping systems carrying dirty fluids because the seat area in a ball valve is very thin and small compared to a plug valve. The thick seat area of a plug valve (almost the whole plug area) makes this valve more robust against particles and erosion (Fig. 3.4). As a result of the thicker seat sealing area, a plug valve has a rotary cut action. This means particles are cut during the closing or opening of the valve without damaging the body or the closure member in the plug valve. As shown in Fig. 3.5, the seat can be damaged by a particle trapped in a ball valve. Opening against the full delta pressure and throttling for a ball valve is critical, because the flow open area is small and increases fluid velocity, erosion, and damage to the seat. A plug valve has a larger flow open area during closing, which results in lower fluid velocity, less erosion, and less risk of damage to the seat. Fig. 3.6 compares ball-and-plug valves for fluid control purposes. Additionally, plug valves do not have a cavity, unlike ball valves. A cavity is a weak point where high pressure or accumulated particles can damage the seat (Fig. 3.7).

A Practical Guide to Piping and Valves for the Oil and Gas Industry https://doi.org/10.1016/B978-0-12-823796-0.00016-7

243

# 2021 Elsevier Inc. All rights reserved.

244

3. Plug valve application and design

FIG. 3.1 Plug Valve/Plug Configuration.

FIG. 3.2 Application of plug valves in a dirty service (sandy produced water) outlet of separators.

FIG. 3.3 Plug and TCG valves in a dirty service (sandy produced water) outlet of separators.

Plug valve design

245

FIG. 3.4 Seat sealing area comparison between ball-and-plug valves. Courtesy: Serck Audco Valves.

FIG. 3.5 Particle cutting action in ball-and-plug valves. Courtesy: Serck Audco Valves.

Plug valve design The closure member is a cone-shaped element, as shown in Fig. 3.8. The sealing of a plug valve between the closure member and the body can be achieved through a thin film of grease or a polymeric sleeve such as Teflon (PTFE) (Fig. 3.10). Lubricated plug valves can be used for throttling. Lubrication provides sealing between the plug and the body seat, so a lubricated plug valve has a better sealing capacity than a metal-to-metal plug valve. There are two injection points, one on the plug (H) and the other on the stem sealing (G). The sealant injection (grease) on the plug is applied for plug and body sealing. Grease injection should be done regularly as part of a maintenance program. Some operator companies prefer to use through conduit gate valves rather than plug valves so that they do not have to

246

3. Plug valve application and design

FIG. 3.6

Comparison between ball-and-plug valves for controlling fluid. Courtesy: Serck Audco Valves.

perform regular grease injections. Lubrication loses its viscosity at high temperatures such as above 200°C, which disturbs the sealing. There is a check valve on the grease injection port that prevents grease from being ejected backward. The check valve extends from the valve body and has a male end that is screwed into the female end of a plug. Fig. 3.9 illustrates the check valve, which is the smallest part, and the plug, which is the largest part. If there is insulation, the grease injection port should be extended beyond the insulation as far as the minimum insulation thickness. Extension is done through a 100-mm nipple installed between the check valve and the plug, with one female

FIG. 3.7 Body cavity comparison in ball valves compared to plug valves. Courtesy: Serck Audco Valves.

Plug valve design

FIG. 3.8 Lubricated plug valve. Courtesy: Serck Audco Valves.

FIG. 3.9 Check valve and grease injection plug.

247

248

FIG. 3.10

3. Plug valve application and design

PTFE sleeved plug valve.

thread end connected to the male side of the check valve and one male end toward the female side of the plug. A plug valve with a PTFE sleeved plug is a good choice to avoid grease injection on the plug for sealing. A PTFE sleeved plug might not be a good choice in particle-containing services. In addition, PTFE has the risk of sucking out due to a high-pressure drop. This type of plug valve is known as a nonlubricated-type plug valve. One advantage of PTFE sleeved plug valves is that the PTFE sleeve not only reduces the friction between the plug and the body but also reduces the torque values for valve operation. Plug valves can be designed as double block and bleed (DBB) or double isolation and bleed (DIB), as shown in Fig. 3.11. In the valve closed position, two segments around the plug are pushed by the plug to the body for a tight shutoff. The valve is torque seated, which means that continuous rotation of the valve operator, such as with a handwheel, forces the plug downward and the segments outward to seal firmly against the valve body. This movement creates a metal-to-metal sealing on both upstream and downstream areas, providing double isolation or double block. During the valve opening, the segments are retracted from the body, enabling the plug to rotate 90° for opening. A drain plug on the bottom flange is used as a bleeder to discharge the fluid. The valve has metal-to-metal contact through sealing, so achieving a bubble tight shutoff is very difficult. The valve has a top flange or bonnet to allow in-line maintenance by opening the top flange. Fig. 3.12 shows the four sequences involved in the opening and closing of a DBB plug valve. The valve is torque-seated and bidirectional. Torque-seated valve sealing is achieved by using enough torque (stem force) to make and energize an effective sealing in a closed position. Bidirectional means that the valve can be rotated 180° and installed from both ends without any flow direction or installation restrictions.

Body design

249

FIG. 3.11 Double block and bleed (DBB) plug valve.

Body design The best choice for body design is an integrally forged or cast body. Although full penetration butt welding is allowed in the API 599 standard for plug valves, it is not recommended. The dimensions and finishing faces of the flanges for flanged end valves should be based on ASME B16.5 or ASME B16.47 standards for pipe flanges and flanged fittings.

250

FIG. 3.12

3. Plug valve application and design

Sequences of DBB plug valve opening and closing Courtesy: Franklin.

251

Body design

The wall thickness of the valve should be based on the ASME B16.34 standard (Table 3.1) for valves, or in some cases based on the API 600 standard for gate valves (Table 3.2). TABLE 3.1

Minimum body thickness based on ASME B16.34. Minimum wall thickness—tm (mm)

Inside Dia. d (mm) [Note (1)]

Class 150

Class 300

Class 600

Class 900

Class 1500

Class 2500

Class 4500

3

2.5

2.5

2.8

2.8

3.1

3.6

4.9

6

2.7

2.7

3.0

3.1

3.5

4.2

6.5

9

2.8

2.9

3.2

3.4

3.8

4.9

8.0

12

2.9

3.0

3.4

3.7

4.2

5.6

9.6

15

3.1

3.3

3.6

4.2

4.8

6.6

12.0

18

3.3

3.5

3.9

4.7

5.3

7.7

14.3

21

3.5

3.7

4.2

5.2

5.9

8.7

16.7

24

3.7

4.0

4.4

5.7

6.4

9.7

19.0

27

3.9

4.3

4.8

6.3

7.2

11.1

22.2

31

4.3

4.7

5.1

6.6

8.l

12.8

26.1

35

4.6

5.1

5.4

6.9

9.0

14.5

30.0

40

4.9

5.5

5.7

7.2

9.9

16.2

33.9

45

5.2

5.9

6.0

7.5

10.8

17.9

37.9

50

5.5

6.3

6.3

7.8

11.8

19.6

41.8

55

5.6

6.5

6.3

8.3

12.7

21.3

45.7

60

5.7

6.6

6.6

8.8

13.6

23.0

49.6

65

5.8

6.8

6.9

9.3

14.5

24.7

53.6

70

5.9

6.9

7.3

9.9

15.5

26.4

57.5

75

6.0

7.1

7.6

10.4

16.4

28.1

61.4

80

6.1

7.2

8.0

10.9

17.3

29.8

65.3

85

6.2

7.4

8.3

11.4

18.2

31.5

69.3

90

6.3

7.5

8.6

11.9

19.1

33.2

73.2

95

6.4

7.7

9.0

12.5

20.1

34.9

77.1 Continued

252

3. Plug valve application and design

TABLE 3.1 Minimum body thickness based on ASME B16.34—cont’d Minimum wall thickness—tm (mm) Inside Dia. d (mm) [Note (1)]

Class 150

Class 300

Class 600

Class 900

Class 1500

Class 2500

Class 4500

100

6.5

7.8

9.3

13.0

21.0

36.6

81.0

110

6.5

8.0

10.0

14.0

22.8

40.0

88.9

120

6.7

8.3

10.7

15.1

24.7

43.4

96.7

130

6.8

8.7

11.4

16.1

26.5

46.9

104.6

140

7.0

9.0

12.0

17.2

28.4

50.3

112.4

150

7.1

9.3

12.7

18.2

30.2

53.7

120.3

160

7.3

9.7

13.4

19.3

32.0

57.1

128.1

170

7.5

10.0

14.1

20.3

33.9

60.5

136.4

180

7.6

10.3

14.7

21.3

35.7

63.9

143.8

190

7.8

10.7

15.4

22.4

37.6

67.3

151.7

200

8.0

11.0

16.1

23.4

39.4

70.7

159.5

210

8.1

11.3

16.8

24.5

41.3

74.1

167.4

220

8.3

11.7

17.4

25.5

43.1

77.5

175.2

230

8.4

12.0

18.1

26.6

45.0

80.9

183.1

240

8.6

12.3

18.8

27.6

46.8

84.4

190.9

250

8.8

12.7

19.5

28.7

48.6

87.8

198.8

260

8.9

13.0

20.2

29.7

50.5

91.2

206.6

270

9.1

13.3

20.8

30.8

52.3

94.6

214.5

280

9.3

13.7

21.5

31.8

54.2

98.0

222.3

290

9.4

14.0

22.2

32.8

56.0

101.4

230.2

300

9.6

14.3

22.9

33.9

57.9

104.8

238.0

310

9.8

14.7

23.5

34.9

59.7

108.2

245.9

253

Port design

TABLE 3.2

Minimum body thickness based on API 600. Class designation

Nominal valve size (NPS)

150

300

600

900

1500

2500

½

4.6

4.6

5.3

5.3

5.3

5.3

¾

4.6

4.6

6.4

10.2

10.2

10.2

1

6.4

6.4

7.9

12.7

12.7

15.0

1¼

6.4

6.4

8.6

14.2

14.2

17.5

1½

6.4

7.9

9.4

15.0

15.0

19.1

2

8.6

9.7

11.2

19.1

19.1

22.4

2½

9.7

11.2

11.9

22.4

22.4

25.4

3

10.4

11.9

12.7

19.1

23.9

30.2

4

11.2

12.7

16.0

21.3

28.7

35.8

6

11.9

16.0

19.1

26.2

38.1

48.5

8

12.7

17.5

25.4

31.8

47.8

62.0

10

14.2

19.1

28.7

36.6

57.2

67.6

12

16.0

20.6

31.8

42.2

66.8

86.6

14

16.8

22.4

35.1

46.0

69.9

–

16

17.5

23.9

38.1

52.3

79.5

–

18

18.3

25.4

41.4

57.2

88.9

–

20

19.1

26.9

44.5

63.5

98.6

–

24

20.6

30.2

50.8

73.2

114.3

–

Stem and plug design The stem to plug connection should be strong enough to withstand loads, and the connection strength should be verified through a test or calculation method. In addition, the stem should be strong enough to withstand loads coming from a lever, gear, or actuator. Stem roughness is recommended to be less than 32 μin., especially in contact areas with sealing or packing, in order to facilitate better sealing. The surface of the plug should have a maximum roughness of 16 μin. as per the API 599 recommendation.

Port design As per API 599, the port of a plug valve can be a regular, venture, or rounded full-bore type. The regular pattern design has a plug port area larger than the venture type. The venture pattern is a reduced port plug valve with sections changing throughout the body in order to

FIG. 3.13

Full port plug valve.

FIG. 3.14

Venture port plug valves.

Valve standard

255

FIG. 3.15 Closure member (plug) of the plug valve.

produce a venture effect, to increase velocity through the plug valve, which results in a drop in pressure. Fig. 3.14 shows a venture port plug valve. The round full port pattern has a circular port that should not be smaller than the port values given in ASME B16.34 for inside diameter values (Fig. 3.13). The bore diameter as per ASME B16.34 for wall thickness calculation (also called the minimum flow passage area) should not be less than 90% of the basic inside diameter of the valve end. Plug valves are usually reduced bore and nonpiggable. However, full-bore plug valves with a higher flow capacity and CV values are recommended for very dirty services. Full port plug valves are more expensive than standard reduced bore plug valves. The best way to calculate the bore reduction percentage is to ask the valve supplier for the valve flow curve and watch the flow passing the valve when the valve is 100% open. Then the ratio of the valve flow to the connected pipe flow based on the process requirement could provide the percentage of the valve port.

Since Q flow capacity ¼ A ðareaÞ  V velocity ,then, Q Valve @ 100% open=Q pipe ¼ area of the valve plug=area of the pipe: Fig. 3.15 shows the port of a lubricated plug valve. One possible problem for the plug of plug valves is unbalanced pressure in which the pressure runs the plug upward. However, injecting the grease in the plug grooves as shown in Fig. 3.15 can solve this issue. The grooves should be made in a way such that the lubricant will be transmitted to all parts of the system in both open and closed positions.

Valve standard The API 599 standard covers plug valves with flange, welding, or threaded and socket weld ends. This standard covers size ranges from ½” to 2400 for flanged and butt weld end

256

3. Plug valve application and design

TABLE 3.3 Pressure-temperature rating for carbon steel materials in different ASME pressure classes taken from ASME B16.34. A—Standard class Working pressures by class, bar Temperature, °C

150

300

600

900

1500

2500

4500

29 to 38

19.6

51.1

102.1

153.2

255.3

425.5

765.9

50

19.2

50.1

100.2

150.4

250.6

417.7

751.9

100

17.7

46.6

93.2

139.8

233.0

388.3

699.0

150

15.8

45.1

90.2

135.2

225.4

375.6

676.1

200

13.8

43.8

87.6

131.4

219.0

365.0

657.0

250

12.1

41.9

83.9

125.8

209.7

349.5

629.1

300

10.2

39.8

79.6

119.5

199.1

331.8

597.3

325

9.3

38.7

77.4

116.1

193.6

322.6

580.7

350

8.4

37.6

75.1

112.7

187.8

313.0

563.5

375

7.4

36.4

72.7

109.1

181.8

303.1

545.5

400

6.5

34.7

69.4

104.2

173.6

289.3

520.8

425

5.5

28.8

57.5

86.3

143.8

239.7

431.5

450

4.6

23.0

46.0

69.0

115.0

191.7

345.1

475

3.7

17.4

34.9

52.3

87.2

145.3

261.5

500

2.8

11.8

23.5

35.3

58.8

97.9

176.3

538

1.4

5.9

11.8

17.7

29.5

49.2

88.6

valves, as well as size ranges from ½00 to 200 for threaded and socket weld valves. API 599 covers lubricated and non-lubricated plug valve types. This standard does not cover threeway and four-way plug valves. Steel made plug valves in this standard should have a pressure-temperature rating based on the ASME B16.34 standard. As an example, Table 3.3 provides the pressure-temperature rating for carbon steel materials in different pressure classes taken from ASME B16.34. If a fire test has been specified by the end user, the valve should be fire tested based on API 6FA or API 607 (Fire Test for Soft Seated Quarter-Turn Valve). API 607 probably is more applicable for sleeved plug valves.

Material selection

257

Face-to-face standard The face-to-face standard of plug valves is based on the ASME B16.10 standard. The short pattern design is available in pressure classes of 150 and 300 in sizes from 1½00 to 1200 . As an example, Table 3.4 shows the face to face of the flanged end plug valves in class 150 in four types of regular pattern (regular bore), short pattern and regular bore, venture and round full port. Venture pattern is the most compact design. The full port has the longest face to face among other types, but the face to face of the full port design is given up to and including 400 in Table 3.4.

Antistatic design Antistatic springs should be applied between the closure member (ball), stem, and body to provide electrical continuity between these three parts in ball valves (Fig. 3.16). Providing electrical continuity between these parts is not essential for plug valves, but an antistatic design for electrical continuity should be considered for plug valves if the project requirements are based on API 599. In this case, the valve should have electrical continuity across the discharge path with a resistance of not more than 10 Ω from a power source of 12 V Direct Current (DC). There is usually a direct contact between the body, plug, and stem, so an antistatic spring and test are not required.

Material selection Body material A carbon steel body cladded with Stellite 6 or 21 overlay for hard facing is the most common choice of material for plug valves in onshore plants such as refineries. However, it is possible to select just a carbon steel body without Stellite hard facing if the fluid is not very abrasive, such as sulfur. If the fluid is corrosive and not very erosive, Inconel 625 cladding can be done on the carbon steel body, or the body material can be changed to corrosion-resistant alloys (CRAs) such as 22Chromeuim duplex or 25Chromeium superduplex. A plug valve is common for sulfur recovery units in which sulfur is taken out and recovered from H2S. Stellite is a cobalt alloy used primarily for hard facing of valve internals, as well as valve bodies in some cases. 22Chromeuim duplex or 25Chromeium superduplex body plug valves are commonly used in the offshore industry.

Plug material A plug should be overlaid with hard material such as Stellite or tungsten carbide (TC) to mitigate the risk of erosion and galling since the plug valve is normally used for abrasive services. The thickness of Stellite 6 overlay is normally a minimum 1.6 mm, whereas TC thickness could be a maximum 200 μm. TC usually has more resistance to erosion than Stellite 6, so it could be the preferred choice of hard facing material for the plug. Therefore, it is no problem

TABLE 3.4 Face-to-face values of the flanged valves including plug-type valve based on ASME B16.10. 11

12

Nominal valve size

13

14

16

17

18

19

20

21

Class 150 Steel Flanged End (2 mm Raised Face) and Welding End Plug

NPS

15

Regular Pattern, A

Short and Regular Pattern, B

Venturi Pattern, A

Round Port, Full Bore, A

DN

Flanged End

Globe, Lift Check, and Swing Check [Note (1)], A and B

Angle and Lift Check, D and E

Y-Globe and Y-Swing Check, A and B

Welding End Ball

Long Pattern, A

Short Pattern, A

Long Pattern, B

Short Pattern, B

¼

8

…

…

…

…

102

51

…

…

…

…

…

⅜

10

…

…

…

…

102

51

…

…

…

…

…

½

15

…

…

…

…

108

57

140

108

108

…

140

¾

20

…

…

…

…

117

64

152

117

117

…

152

1

25

…

…

…

176

127

70

165

127

127

…

165

1¼

32

…

…

…

…

140

76

184

140

140

…

178

1½

40

…

…

…

222

165

83

203

165

165

190

190

2

50

…

267

178

267

203

102

229

178

178

216

216

2½

65

…

305

…

298

216

108

279

190

190

241

241

3

80

…

330

203

343

241

121

318

203

203

282

282

4

100

305

356

229

432

292

146

368

229

229

305

305

5

125

381

381

…

…

356 (7)

178

…

…

…

…

…

6

150

394

457

394

…

406 (7)

203

470

394

267

457

403

8

200

457

521

457

…

495

248

597

457

292

621

419

10

250

533

559

533

…

622

311

673

533

330

559

457

12

300

610

636

610

…

698

349

775

610

356

635

502

14

350

686

…

686

…

787

394

…

686

381

762

572

16

400

762

…

762

…

914 (8)

457

…

762

406

838

610

18

450

864

…

864

…

978 (9)

…

…

864

…

914

660

20

500

914

…

914

…

978 (9)

…

…

914

…

991

711

22

550

…

…

…

…

1067 (9)

…

…

…

…

1092

…

24

600

1067

…

1067

…

1295 (9)

…

…

1067

…

1143

813

26

650

…

…

…

…

1295 (9)

…

…

…

…

1245

…

28

700

…

…

…

…

1448 (9)

…

…

…

…

1346

…

30

750

…

…

…

…

1524 (9)

…

…

…

…

1397

…

260

FIG. 3.16

3. Plug valve application and design

Antistatic springs design in a ball valve.

to have thinner TC instead of Stellite on the valve plug. The other advantage of TC is that there is no test requirement, unlike the Stellite 6 overlay test required by the NORSOK standard. In addition, applying the TC on the plug is done through a process called high-velocity oxygen fuel (HVOF) coating. HVOF is a thermal spray coating process in which molten or semimolten TC is sprayed onto the surface of the core material. Unlike applying Stellite on duplex material, a coating of TC through HVOF does not pose any risk for duplex core material (e.g., sigma phase formation on the duplex). HVOF has other advantages such as reduced cost, improved performance, improved final properties, etc. Fig. 3.17 shows Stellite overlay on the plug of a plug valve. A thin layer of electroless nickel plate (ENP) on the plug may be applied to reduce the friction between the plug and the body, and to reduce the opening and closing force and torque of the valve. But it may not be a good idea to apply ENP on the plug since it can be removed and cause galvanic corrosion. Generally speaking, applying hard facing materials such as Stellite or TC or ENP or Teflon (PTFE) to avoid friction, erosion, and galling is known as antifriction treatment (AFT).

Stem material The stem material should be strong enough to withstand the loads from operators such as the gearbox and actuator. Hard alloys such as martensitic 13%Cr, 22Cr duplex, 25Cr duplex,

More pictures

261

FIG. 3.17 Stellite overlay on the plug of the plug valve.

and Inconel 718 are common stem materials depending on the valve body material. 17-4pH is a martensitic precipitation hardening stainless steel that provides an outstanding combination of high strength and good corrosion resistance. This material is not proposed for the stem of valves in the offshore industry due to the high risk of external chloride stress cracking corrosion in a marine atmosphere.

Stem bearing material It is very common to use a metallic bearing material with a soft material lining, such as Teflon (PTFE), to reduce friction between the stem and the bearing. However, one plug valve supplier selected polyether ether ketone (PEEK) for the bearing of the plug valve and had a very good experience in the long run without any metallic reinforcement. PEEK as a nonmetallic material is very hard, and can be used in high-pressure and relatively high-temperature applications.

Gasket between body parts The gasket between the main body and the bottom cover of a plug valve is sometimes called the diaphragm. As an example of a diaphragm, a 22Cr duplex gasket with PTFE coating can be selected for a 22Cr body plug valve. The gasket should have less hardness than two joints to provide sufficient sealing. This can be achieved by applying PTFE coating around the 22Cr duplex metal.

More pictures This section contains more pictures of the plug valves (Figs. 3.18–3.21).

FIG. 3.18 Plug of the lug valve (view from the top).

FIG. 3.19

Body of the plug valve.

FIG. 3.20 Body of the plug valve (view from the Top).

More pictures

FIG. 3.21 800 Actuated plug valve.

263

C H A P T E R

4

Through conduit gate valve application and design valve application examples Through conduit gate (TCG) valves are usually available in sizes 200 and above. However, valve manufacturers can produce smaller sizes such as 1½00 . TCG valves are very robust valves, so they are the best option for wellheads in sizes of a maximum 800 based on API 6A. These valves are also designed based on API 6D, “pipeline valve standards.” These valves have the advantages of reliable performance and long life. TCG valves are used for on/off applications in process (mainly particle-containing) services. The valve shown in Fig. 4.1 is a 2400 CL1500 TCG (slab type) with hydraulic actuators for a drilling platform. As shown in Fig. 4.1, the actuated TCG valve occupies large space vertically especially in large sizes and high-pressure classes. The valve shown in Fig. 4.1 is approximately 4–5 m high. Fig. 4.2 shows an example in which very dirty fluid-containing drilling muds coming to the first stage separator. A TCG valve and slab-type valve were evaluated for use in the application shown in Fig. 4.2. However, there was not enough space for the TCG valve (4–5 m high). Therefore, a metal-seated ball valve was selected for installing upstream of the separator. A ball valve occupies less vertical space compared to a TCG valve on the vertical plane when it is installed horizontally, as shown in Fig. 4.3. Since the fluid is relatively dirty and the risk of damage to the valve seats is high, it was proposed to design seat scrapers for ball valves to avoid possible seat damages due to the particles. The issue with the ball valve metal seat in dirty services is that the particles can enter the seat arrangement and damage the seat. Therefore, either a seat scraper should be applied or a washing valve should be installed on the body of the valve to wash out dirt from the seat arrangement. Having a valve wash has the disadvantage of making extra holes in the body of the valve. In addition, it is challenging and not practical to design a valve wash on small valves. Item number 530 in Fig. 4.4 is a seat scraper, which is a soft ring made of Teflon (PTFE) or Viton. This ring prevents the particles from entering the seat arrangement. The seat of the valve is item number 524.

A Practical Guide to Piping and Valves for the Oil and Gas Industry https://doi.org/10.1016/B978-0-12-823796-0.00013-1

265

# 2021 Elsevier Inc. All rights reserved.

266

4. Through conduit gate valve application and design valve

FIG. 4.1 2400 CL1500 TCG valve with hydraulic actuators. Courtesy: Valvitalia.

FIG. 4.2 2400 CL1500 valve selection for upstream of the separator.

TCG valves are very good selections for use in particle-containing services. Metal-seated ball valves are not recommended for very dirty services because the seat has a high risk of getting damaged by particles, especially during the opening and closing of the valve. Very dirty service should be defined in the project documents based on particle sizes and erosion values. For example, fluids that can make 2-mm corrosion allowance for the material could be counted as very dirty services. Erosion allowance is defined as the erosion value per year multiplied by the design life of the plant. Therefore, the value of the erosion allowance depends on the design life of the plant (e.g., 20 or 30 years). A TCG valve is a better choice than a ball valve in the fluid-making scale as well as particle-containing erosive services.

Through conduit gate valve application and design valve

FIG. 4.3 Actuated ball valve installed horizontally.

FIG. 4.4 Seat scraper for seat arrangements.

267

268

4. Through conduit gate valve application and design valve

One application of TCG valves is for downstream of a separator produced water line where jet water is injected into drain to remove sand from the bottom of the separator (Fig. 4.5). The other option for this application is a plug valve, which is more compact. Fig. 4.6 shows both plug and TCG valves as two options for a separator produced water outlet line. A lubricated plug valve is one choice for a separator outlet line. One disadvantage of lubricated plug valves from the end user point of view is that a plug valve requires regular maintenance and lubrication of the plug. Some operators (end users) prefer to select a TCG valve instead of a plug valve to minimize required maintenance. Another option is a 1400 CL1500 valve on the flow lines before chock valves in a very dirty fluid service, where a TCG valve is the preferred choice. However, the valve plus a vertically

FIG. 4.5 Application of TCG valves in dirty service (sandy produced water) outlet lines of separators.

FIG. 4.6 Plug and TCG valves in dirty service (sandy produced water) outlet of separators.

Through conduit gate valve application and design valve

269

FIG. 4.7 Drain arrangement with two wedge gates as blocks and a bleed in between.

installed actuator could be approximately 4.5 M high. In this case, it is necessary to select a more compact (shorter) actuator. A compact actuator design can be achieved by increasing the actuator diameter and reducing the height to approximately 3.5 M. In some cases, there is enough space available for the slab gate valve with the actuator on the top from a layout point of view. However, there is not enough space around the valve for moving other equipment as well as actuator dismantling from the valve. It may be possible to change an arrangement including two wedge gate valves in series with a bleed wedge gate valve in between, as shown in Fig. 4.7, for draining purposes using a slab gate with two double piston effect seats or an expanding gate valve. Having one slab gate valve saves weight and space on the drainage compared to two gate valves in series. However, the challenge is how to remove the TCG gate valve from the line during maintenance without any isolation valve. One solution is to have a gate valve upstream of the TCG valve for isolation purposes. A double block and bleed with two wedge gate block valves (Fig. 4.8) in one body could be an option to save weight and space.

270

4. Through conduit gate valve application and design valve

FIG. 4.8 Double block and bleed gate valve. Courtesy: LVF.

TCG valve design TCG valves have two common types of design, slab gate (Fig. 4.9), and expanding. Expanding gate valves can be produced as either single expanding or double expanding (Fig. 4.10). A double expanding valve has two half disks and it is used for isolation of the piping system or a component when it is closed. What is the difference between single expanding and double expanding gate valves? A double expanding wedge is expanded in both open and closed positions, and the two seats are sealed in both open and closed conditions. A single expanding wedge is expanded only in the closed position and the two seats are sealed. Thus, fluid enters the cavity in the open position in a single expanding gate valve, but the cavity is not filled in either open or closed positions for a double expanding gate valve. Double expanding gate valves can guarantee zero leaks to the cavity in both closing and opening conditions. One advantage of a double expanding valve is that this valve contains two half wedges with more disk flexibility in high temperatures due to thermal expansion. Double expanding is the preferred choice of valve for very dirty services in high temperature ranges above 200°C.

FIG. 4.9 Slab gate valve. Courtesy: Orion valve.

FIG. 4.10 Double expanding gate valve. Courtesy: Orion valve.

272

4. Through conduit gate valve application and design valve

TCG valves are not recommended for fluid control (throttling) since prolonged usage under throttling will result in quick damage to the seats of the valves as well as internal valve components. The main parts of the double expanding and slab gate valves are body, bonnet, wedge (gate) halves, seats, and stem. The body and bonnet are the main pressure-containing parts. The disk(s) are positioned by the stem to block the flow or open the fluid path. The wedge assembly in a double expanding gate valve includes two halves, one male and the other female, which are coupled together, usually with springs. A slab gate valve, also called a single disk, is designed to provide isolation of the piping system or a component when it is in a closed position. This type of valve is also not suitable for fluid control (throttling). Just as the double expanding gate valves, prolonged usage of a slab gate valve under a throttling operation will result in wearing and damage of the seats and internal components. The main parts of a double expanding and slab gate valve are body, bonnet, wedge (gate), seats, and stem. The body and bonnet are the main pressure-containing parts. The seats are usually floating-type seats with the springs at the back to ensure proper tightness between the gate and seats. A double expanding valve is two wedge gate valves in series with one bleed gate valve between. A double expanding valve can be as much as 50% more expensive on average than a slab gate valve in small sizes and 25%–30% more expensive in larger sizes. Single expanding valves are usually less expensive than double expanding. Single expansion is a good choice if a more robust option than a slab gate valve is required, and the valve is most often in the closed position. Comparing the metal seat ball valve with a TCG valve, both slab and expanding are more expensive in large sizes such as 3000 and 3600 . In some cases, a ball valve in smaller or medium sizes could be more expensive than a TCG valve. For example, a 1200 Class 1500 ball valve with API 6D design could be more expensive than a slab gate valve in the same size and pressure class and API 6D design. One way to estimate the relative cost of the valves is to compare their weights. As an example, a 300 slab gate valve in class 300 was compared to a ball valve with the same size, pressure class, and material. The slab gate valve was almost twice as heavy as the slab gate valve. Of course, the weight of a valve is different from one supplier to another one. A double expanding gate valve is not necessarily a better valve than a slab gate type. But double expanding is a more robust valve since less friction and wearing happens between the seat and the disk during disk traveling. In addition, less fluid is accumulated and pressurized into the cavity so double expanding has a longer packing life compared to the slab gate valve. However, the actuation of a double expanding valve is challenging because this valve is a torque-seated type and over-torquing the valve could damage the disk. Therefore, extra attention should be paid to sizing and selecting the actuator for a double expanding gate valve to avoid over-torquing. The wedge is expanded at the top (open) and bottom (closed) points in a double expanding gate valve. Expansion of the wedge toward the seats by the mechanical stem force and sealing pressure between two halves provides tight sealing with two seats in both directions. Tight contact of the wedge with the seats at open and closed positions increases the breakaway torque in both closed and open situations, which increases the actuator sizes. For this reason, an end user may avoid selecting a double expanding valve to prevent having a larger actuator. As mentioned earlier, over-torquing an actuated double expanding gate valve can damage the seat, wedge, and stem. Slab gate valves are not torque-seated so there is no risk of damage to valve components due to over-torquing.

Disk (wedge) design

273

Body and bonnet design TCG valves usually have a flanged body and bonnet design bolted together (Fig. 4.11). Sealing between the body and bonnet is achieved with gaskets such as spiral wound and ring-type joint (RTJ) gaskets. RTJ gasket types are common in high-pressure classes such as Class 600 and above. Spiral wound gaskets are a common choice of gasket used for low-pressure classes.

Disk (wedge) design Double expanding gate valves contain two wedges (halves), one male and one female, with sealing between. A slab gate has only one wedge, resulting in friction with the seat as it travels, unlike a double expanding gate valve. The disk assembly in a slab gate valve is retained between two floating (spring energized) seats (Fig. 4.12). Seat skirts or guiding rails are plates that are installed between the wedge and the seats to protect the seats from particles in the fluid. Seat skirts can make the TCG valves as good as plug valves in dirty services. Seat skirts can be a default manufacturer design or they can be requested in a purchase order at extra cost. Special attention to the thickness of the guiding rails is required if the valve is installed vertically to withstand the weight of the valve and the wedge. Seat skirts are usually welded to the body to withstand the weight of the gate in lateral installation, usually in large size valves. A wedge is a very expensive part of slab and expanding gate valves that require lapping and tungsten carbide coating. The wedge in a slab gate valve has friction with the floating seats during the seat travel. However, a double expanding wedge valve has a fixed seat

FIG. 4.11 Bolted body and bonnet design. Courtesy: Orion valve.

274

FIG. 4.12

4. Through conduit gate valve application and design valve

Slab gate valve seat and disk design. Courtesy: Orion valve.

and therefore does not have any friction with the seats during the travel. Some manufacturers may lubricate the wedge before installation to reduce friction. Fig. 4.13 shows half wedges of a double expanding valve. Wedges for expanding and slab gate valves are placed inside the valve between seats with special tools. In fact, the wedge in a slab gate valve is floating, and the connection of the stem to the gate should be flexible as well to move freely, as shown in Fig. 4.14. The stem collar has a larger diameter (connection of the stem to the wedge as shown in Fig. 4.9). As a result, the collar stops the stem on the travel stops or location of back seat bushing to make the stem design an “anti-blow out” stem. The T shoulder (T-shaped slot connection) on the wedge and stem connections (Fig. 4.14) also contributes to the anti-blow out design. Fig. 4.13 shows a T shoulder on the female wedge. The double expanding gate valve shown in Fig. 4.9 does not have the back seat bushing feature. The gate travel is limited by the travel ends and not the stem collar, so back seat bushing would not be activated.

Seat design The seat design of slab gate valves can be either fixed (welded, pressed, or threaded) or floating (spring loaded). Slab gate valves with fixed seats cannot be considered double isolation and bleed (DIB) valves since the wedge is not pushed strong enough to the downstream seat. But the slab gate with two floating self-relieving seats could be counted as DIB2 (DIB type 2) since the wedge and the downstream seats are forced strongly together toward springs. However, a valve supplier confirmed that a slab gate valve with two floating unidirectional (self-relieving) seats is not even DIB2. The manufacturer stated that the slab gate valve would be DIB2 if the downstream seat is double piston effect (DPE) and the upstream

Seat design

FIG. 4.13 Double expanding gate valve half disks design. Courtesy: Orion valve.

FIG. 4.14 Stem and wedge connection.

275

276

4. Through conduit gate valve application and design valve

seat is self-relieving (SR) or DIB1 if both seats are double piston effect type (DPEXDPE). Definitions of DIB1, DIB2, SR, and DPE seat types are explained in Chapter 1 based on the API 6D standard. A TCG valve with two floating SR seats is usually considered DIB2. Most valve manufacturers confirm that a slab gate valve with two floating unidirectional (self-relieving) seats is DIB2 but cannot be DIB1 since the gate (wedge) is pushed tightly just to the downstream seat. If two seats are DPE in a slab gate valve, then one cavity relief line or a plug with an isolation valve and an automatic relief valve are usually required for condensate services (Fig. 4.15). In some cases, a DIB1 or DIB2 valve cavity can be piped upstream or downstream. A check valve plus an isolation valve are located on the connected piping line to the upstream or downstream part of the valve. Fig. 4.16 shows a cavity drain line connected to the piping header for a DIB valve.

FIG. 4.15

Drain plug and automatic release valve on the body of a DIB1 TCG valve. Courtesy: ATV.

277

Seat design

Valve cavity vent connection

Valve body

CSO

gate valve Flanged check valve

FIG. 4.16 Cavity drain line on a DIB TCG valve.

Fig. 4.17 shows a TCG valve with a line from the cavity drain to upstream of the valve. A dual plate check valve and a modular valve are located on the line. The dual plate check valve prevents backflow of the line to the valve. The modular valve provides double isolation between the valve cavity and the line, so it should be as compact as possible. Fig. 4.18 shows a slab gate valve with two SR seats. The forces derived from upstream working pressure push the gate tightly against the downstream seats when the valve is in the closed position. This makes upstream sealing to be pushed by spring to the wedge through fluid working pressure. Overpressure in the body cavity makes a piston force to move the seat away from the gate. When the valve is open, forces again make the gate pushing against upstream and downstream seats, like in the closed position. The sealing function through seat and wedge contact is completely different for a double expanding gate valve. Because a double expanding valve is a torque seated valve, it provides sealing through mechanical stem force and not inline fluid pressure (see Fig. 4.19). The assembly of two disks travels up and down between open and closed positions. Two stops (travel limits) stop the male sector of the wedge while the stem exerts the force on the wedge, enabling the gate to close against both seats at the same time. This provides a double isolation or double block effect in double expanding gate valve in both open and closed positions. As shown in Fig. 4.20, the female section of the disk (green, gray in print version) stops at the bottom body of the valve. The male section (yellow, light gray in print version) can stop on the travel stop (see Fig. 4.9) or back seat bushing. Single expansion provides the same double isolation effect through the stem force in the closed position.

278

FIG. 4.17

4. Through conduit gate valve application and design valve

Cavity drain line on a DIB TCG valve.

Bore (port) design It is possible to have either full bore or reduced bore design for TCG valves. However, since TCG valves are popular for very sandy services, full bore valves are recommended. The fullbore design has a very small pressure drop, almost the same as a connected pipe. Another important consideration for TCG valves is the type of port design in the wedge, which can be a normal port or reverse port. Fig. 4.21 shows a normal port wedge, meaning that the hole in the wedge is located at the bottom.

Bore (port) design

279

FIG. 4.18 Seat and sealing in a slab gate valve with two floating self-relieving seats.

If the slab or expanding gate valve is pneumatic or hydraulic actuated with a fail closed function, the port should be a reverse port wedge, meaning that the hole is located at the top. In a reverse port design (Fig. 4.22), actuator air or oil pressure pushes the stem down and the valve becomes open. The reason this design is called a reverse port is that valves are usually closed when the stem is moving downward. However, in this design, the valve is open when the stem moves down. The valve is closed if there is no air or oil on the actuator, and the stem moves upward. Fluid helps the reverse port TCG valve to be closed with a fail close (FC) action, but it cannot completely close the valve. The fluid force to close the valve should not be taken into account in actuator sizing. The TCG valve with an electrical actuator such as the one shown in Fig. 4.6 is a normal port.

280

4. Through conduit gate valve application and design valve

Stem

Segment

Gate

FIG. 4.19

Wedge sealing mechanical forces through the stem force.

End stop

Downstream Skirt

Upstream Skirt

Segment Gate

FIG. 4.20

Expanding gate valve disks.

Back seat design Back seat or back seat bushing (item number 4 shown in Fig. 4.23) is a seating arrangement typically designed for the body of gate and globe valves. This component provides a seal between the stem and bonnet and prevents the fluid pressure from building against the valve packing.

Back seat design

281

FIG. 4.21 Normal port wedge design.

FIG. 4.22 Reverse port wedge design.

Some valve manufacturers may not provide back seat bushing for a double expanding gate valve. The cavity in a double expanding gate should be almost free from the fluid as a result of strong contact between the disk and seat. As a result, there is not much chance of fluid entrance into the packing arrangement. However, it is possible to have back seat bushing for a double expanding gate valve. Single expanding and slab gate valves require back seat

282 FIG.

4. Through conduit gate valve application and design valve

4.23 Typical stem sealing

arrangement.

bushing to avoid pressure buildup in the packing area. The fluid enters the cavity during the valve operation in slab and single expanding gate valves. One design for double expanding is without back seat bushing. The stem collar is seated on the back seat bushing. The other design provides the travel stops where the stem collar touches, and the back seat is not activated. The male half sits at the bottom when the stem and wedge move down, as shown in Fig. 4.9. The design shown in Fig. 4.9 contains both back seat bushing and a travel stop. On the other hand, the female part of a double expanding gate valve sits at the bottom when the stem and wedge move down, as shown in Fig. 4.20.

Cavity design A double expanding gate valve requires an automatic relief valve on the cavity in condensate services in addition to a drain or vent plug/flange because the double expanding gate is counted as a DIB type one (DIB1) valve. A slab gate valve with at least one unidirectional (selfrelieving) seat does not require any automatic relief valve on the cavity since the trapped fluid in the cavity can be released through the self-relieving seat. Fig. 4.24 shows an electrical actuated TCG valve that is installed with two body cavity flange connections on the top (vent) and one on the drain (bottom) to release the cavity. The body cavity of the valve should be released before maintenance, as a safety precaution.

Packing design

283

FIG. 4.24 TCG valve (slab type) with electrical actuator including drain cavity flanges. Courtesy: Valvitalia.

Packing design Packing is maintenance free in a double expanding valve, unlike the floating seat in a slab gate valve. The double expanding is a DIB type 1 valve with a two double piston effect seat design, with very little risk of leakage into the body cavity. For this reason, the valve is sometimes not supplied with a back seat bushing and the stem collar sits on the bonnet instead of the back seat bushing. On the other hand, the body cavity will be filled in a slab gate valve during the operation, which increases the leakage toward the stem packing (packing design is item number 3 in Fig. 4.23, including layers of graphite). It is important to avoid overtightening the packing because it can cause wearing of packing, high stem friction, and finally leakage. Overtightened packing cannot provide proper sealing. Stem packing leakage can be solved by either tightening the packing with gland flange bolts (item number 1 in Fig. 4.23) or changing the packing. Changing the packing should be done by opening the bolts of the gland flange and removing the gland (item number 2 in Fig. 4.23) to have access to the packing. Packing can be supplied with emergency sealant injection (Fig. 4.25) for the injection of sealant to repair the packing in an emergency. The injection of a sealant is done through a narrow area called a lantern ring. Sealant injection on the packing is not a preventive maintenance. In some cases, if the packing is damaged, it is not possible to provide packing sealing by tightening it with gland flange bolts. The sealant can be injected from one side with a relief provided on the opposite side to flush the lantern ring and make sure that space is filled with a sufficient amount of sealant.

284

4. Through conduit gate valve application and design valve

FIG. 4.25 Emergency sealant injection on the stem.

Packing is the most important part of maintenance in a slab gate valve. As explained earlier, emergency sealant injection is recommended during the normal operation for packing maintenance. Bearing, stem threads, visual inspection, and function tests of the valve are also parts of maintenance exercises.

Sealing capability Slab and expanding gate valves have better sealing capacities than metal seat ball valves. However, both ball and TCG valves may have equal leak rates, such as leak rate B as per BS5208 standard, which is the valve pressure standard with both air and water. Making a sealing between two flat sealing surfaces of wedge and seats in a TCG valve is easier than making a sealing between spherical contacts of a ball and seats in a ball valve. In addition, a TCG valve is a better choice than a ball valve in frequent cycling applications. Some manufacturers claim that it is possible to achieve leak rate A (zero leakage) for a seat test with air and water in a double expanding gate valve, and leak rate B for a seat test in a slab gate valve as per BS 5208 standard. A ball valve seat is also leak rate B as per BS5208 with air and water. It is difficult to claim leak rate A with low-pressure air and also high-pressure water for a metal-seated valve, even a double expanding gate valve. Emergency sealant injection can be designed on valve seats to repair the seats in an emergency and postponing the valve seat sealing function until the next maintenance program by the end user. Fig. 4.26 shows the seat sealant injection points on a TCG valve body.

285

Face-to-face standard

FIG. 4.26

Emergency sealant injection

on the seats.

Valve standard These valves could be designed based on API 6D or ISO 14313, which are both standards for the pipeline valves. The valves could be designed based on API 6A if they are located on the wellhead. The flange face is based on ASME B16.5 or ASME B16.47 standards for piping flanges and flanged fittings, and the face-to-face dimensions of the valve are based on the ASME B16.10 standard.

Face-to-face standard Face-to-face dimensions of TCG valves can comply with the ASME B16.10 standard. Manufacturers can comply with ASME B16.10 face-to-face dimensions for a DIB design or make a longer face-to-face dimension in some cases. Fig. 4.27 shows that there is not enough space for the mating flange nut at the bottom during testing the valve. It can be a requirement to have a minimum of 2 bolt threads out of the nut as per the NORSOK standard. Fig. 4.27 shows that no bolt is threaded out of the nut on the bottom, highlighted with a red (gray in print version) arrow. One solution is to machine the valve body flange and reduce the thickness. Machining the body flange is the practical solution if the body flange thickness is more than the value given in the ASME B16.5 standard that covers flange and flanged fittings. It is important to apply a nondestructive test (e.g., liquid penetrant) after machining the extra thickness and applying a pressure test on the body of the valve. Grinding the body is also a solution if the body is thicker than what is specified in the standard. It should be ensured that there is enough space for the mating flange nut in the construction yard during the valve installation. The height of the nut in Fig. 4.27 was measured and compared to the bolt diameter. The nut is called a heavy hexagonal nut if the height of the nut is equal to the bolt diameter. Fig. 4.28 shows a heavy hexagonal nut, and parameter H is the height of the heavy hexagonal nut. The heavy hexagonal nut is covered by the ASME B18.2.2

286

4. Through conduit gate valve application and design valve

FIG. 4.27

Lack of space for body flange nut in a TCG valve during the test.

FIG. 4.28

Heavy hexagonal nut.

standard, nuts for general applications. There is a question as to why the height of the heavy hexagonal nut was measured. It is possible that the heavy head nut shown in Fig. 4.27 during the test is shorter than the bolt diameter (e.g., the thickness of 70% of the bolt diameter). In that case, using heavy hexagonal nuts during the installation creates a problem of nut lack of space in the yard.

Flow direction Both slab and expanding gate valves are bidirectional. However, a slab gate valve with one DPE seat and one SR seat is not bidirectional. In some cases, a DPE seat may be considered for the downstream side. However, a DPE seat may be considered on the side where maintenance takes place. Also, some TCG valve manufacturers may consider flow direction for a double expanding gate valve from the half-male side. The flow direction should be engraved on the valve body or indicated on the valve tag. Stainless steel 316 tag plates and rivets are proposed in the offshore industry.

287

More photographs

More photographs This section contains additional photographs of TCG valves (Figs. 4.29–4.54). FIG. 4.29

Actuated TCG valve. Courtesy: ATV.

FIG. 4.30 Manually operated TCG valve in high-pressure class. Courtesy: ATV.

288

4. Through conduit gate valve application and design valve

FIG. 4.31

Manually operated TCG valve. Courtesy: ATV.

FIG. 4.32

Manually operated TCG valve in high-pressure class during a test. Courtesy: ATV.

More photographs

FIG. 4.33 Casting body of a TCG valve.

FIG. 4.34 800 Class 1500 TCG valve. Courtesy: Vitas.

289

290

4. Through conduit gate valve application and design valve

FIG. 4.35

TCG valves with electrical actuators. Courtesy: Vitas.

FIG. 4.36

TCG valves with electrical actuators 400 Class 300 body Duplex. Courtesy: Vitas.

More photographs

FIG. 4.37 Wedge and seat of a TCG valve. Courtesy: Vitas.

FIG. 4.38 Testing the wedge and seat of a TCG valve after leakage. Courtesy: Vitas.

291

292

FIG. 4.39 valve.

4. Through conduit gate valve application and design valve

Opening and closing time measuring of an electrical Rotork actuator installed on a 400 Class 300 TCG

More photographs

FIG. 4.40 2400 Class 1500 TCG valve preparation for the test. Courtesy: Vitas.

293

294

4. Through conduit gate valve application and design valve

FIG. 4.41

2400 Class 1500 TCG valve. Courtesy: Vitas.

FIG. 4.42

Cavity flange connection, ½00 , class 300 and 22Cr duplex forge.

More photographs

FIG. 4.43 TCG valve during the test. Courtesy: Vitas.

295

296

FIG. 4.44

4. Through conduit gate valve application and design valve

Body flange measurement of a TCG valve. Courtesy: Vitas.

More photographs

FIG. 4.45 Electrical actuator sizing installed on a TCG valve. Courtesy: Vitas.

FIG. 4.46 TCG valve face to face measurement. Vitas.

297

298

FIG. 4.47

4. Through conduit gate valve application and design valve

TCG valve during a hydrotest. Courtesy: Vitas.

More photographs

FIG. 4.48 2400 Class 1500 TCG valve. Courtesy: Vitas.

299

FIG. 4.49

Testing the electrical actuator of a TCG valve 400 Class 300. Courtesy: Vitas.

FIG. 4.50

Tagging plate on electrical actuator installed on a TCG valve. Courtesy: Rotork and Vitas.

301

More photographs

FIG. 4.51 Testing the electrical actuator of a TCG valve 400 Class 300. Courtesy: Vitas.

FIG. 4.52 Testing the pneumatic actuator reverse port TCG valve. Courtesy: Vitas.

302

4. Through conduit gate valve application and design valve

FIG. 4.53

Pneumatic actuator reverse port TCG valve control panel. Courtesy: Vitas.

FIG. 4.54

Position indicator on the pneumatic actuators.

C H A P T E R

5

Modular valve applications and design Modular valve applications Modular or combination valves are usually made of two ball valves with a needle valve (bleed) to drain the fluid trapped between the valves. They have different applications, including isolation of the following: – Instrument pressure gauges or differential pressure transmitter connections to pipes or pressure vessels (Fig. 5.1). – Vessel level gauge or transmitter connections. – Orifice flange tapping points and drainage (Fig. 5.2). – Sampling of high-pressure or hazardous fluid, as well as isolation of chemical injection tubes to the main header with high-pressure or hazardous fluid. – Draining or venting of high-pressure or hazardous fluid through a conduit gate or ball valve cavities (Fig. 5.3). – Chemical injection lines to main pipeline connections. The method of getting connection from the orifice flange is to use tapping points on the flange’s outer rings and connect the tapping points to two of the modular valves. Modular valves are usually used in high-pressure classes above CL300 or in hazardous services such as toxic H2S-containing fluids to provide double and safer isolation in case of instrumentation to be dismantled for maintenance. Instrument gauges should be disassembled from the lines or the vessels, so that it is safer for the operator to have double isolation from high-pressure or toxic fluid containing pipes or vessels through double block and bleed (DBB) modular valves. If the valve cavity is depressurized in advance through a safety relief system such as DIB1 type valves in condensate services, it is more practical to use only a gate valve for draining the cavity instead of a modular valve, to save on cost and required space. Modular valves are commonly designed for small size pipe or tube connections, usually a maximum of 200 –300 and manufactured in flange, butt weld, hub, compact flange, threaded, or different end connections for the inlet and outlet. Although large size integrated two ball

A Practical Guide to Piping and Valves for the Oil and Gas Industry https://doi.org/10.1016/B978-0-12-823796-0.00006-4

303

# 2021 Elsevier Inc. All rights reserved.

304

5. Modular valve applications and design

FIG. 5.1 Modular valve for isolation of pressure gauges on vessels in high-pressure classes.

valves with a bleed valve in between (in sizes 300 –1600 ) (Fig. 5.4) are available in the market, their application is limited in the Norwegian offshore industry. One typical application of these large size modular valves is for upstream of pressure safety valves (PSV) in highpressure classes of 600 and above. Some valve manufacturers can produce modular valves up to 2400 .

Modular valves design The modular valve design is usually based on a manufacturer standard in addition to the ASME B16.34 valve standard requirements. The minimum bore of the valve is also based on a manufacturer standard if it is not defined by the valve purchaser, and it does not comply with standards such as API 6D Pipeline Valves. In fact, the bore of the valve is much smaller than the bore values given in API6D. The face-to-face dimension in a modular valve is approximately 1.3 times more than that in a single ball valve. Full or reduced bore as well as floating or trunnion affect the face-to-face dimension of a modular valve. Changing the floating ball to a trunnion design in order to reduce the opening and closing torque, and overcoming the metal to metal seat and ball friction increase the face-to-face dimension of the valve. In one scenario, a ¾00 CL1500 floating ball valve had a problem with the opening and closing of the valve during the test. A trunnionmounted valve requires less force for opening and closing than the floating ball. However, the valve was not changed to trunnion-mounted to avoid increase in the face-to-face dimension. Instead, the ball and seat were lapped more to facilitate opening and closing of the floating design ball valve.

305

Modular valves design 45.0° MAX (TYP.)

45.0° MAX (TYP.) ORIENTATION OF TAPS FOR LIQUID SERVICE

ORIENTATION OF TAPS FOR GAS AND VAPOUR SERVICE PIPING

INSTR

0.50° RTJ FLANGE

PIPING FULL PENETRATION WELD AT BOTH ENDS

0.50° NIPPLE BBE 100 MM LONG

FLOW

INTERNAL WELD BEADS TO BE GROUND FLUSH WITH PIPE WALL INSTRUMENT PIPING

ANSI B16 36 RTJ WN FLANGE BORED TO MATCH NOMINAL INTERNAL DIAMETER OF CONNECTING PIPE 0.50° COMBINATION VALVE BALL/NEEDLE/BALL ONE END FLANGED ONE END THREADED 0.50° NPT FEMALE NOTE 5

FIG. 5.2 Modular valve for orifice flange connection.

A needle valve has better flow control characteristics compared to a globe valve of small sizes. A bleeder is a needle valve (swivel plug) of size ½00 and 5 mm bore, for example, with a drain plug. The operator should open the needle valve to release fluid through the bleed plug. Small modular valves may need a small drain connection such as ½00 . Some manufacturers may propose a minimum 7/800 size bleed valve/plug as a more robust connection with less chance of breaking. A needle valve should be a swivel plug in which the plug is rotated freely in all directions to avoid concentrated galling and wearing between the plug and seats (Fig. 5.5).

306

5. Modular valve applications and design

FIG. 5.3 Modular valves on the vent and drain of ball valve body cavities.

FIG. 5.4 Large size integrated two ball valves with a bleed valve in between.

The needle valve, including the valve stem and bonnet plus the drain plug, could be extended in case of insulation through a 100-mm nipple, as an example. An alternative would be to avoid applying insulation on the needle valve and drain plug through having a window hole for the insulation on the needle valve as well as the drain plug. The stem should be an antiblowout design that can be thicker in the middle where body adaptors are connected, making the stem antiblowout. The stem to lever connection should be strong and should be fastened through double nuts (Fig. 5.6). Strength can be ensured by fixing the double nut in place with Loctite. Alternatively, one nut can be installed below the stem

Modular valves design

307

FIG. 5.5 Modular valve with a one end flange and the other end threaded with a needle valve and drain plug. Courtesy: Bonney Forge.

FIG. 5.6 Modular valves including a stem extension, double nut, and Allen screws. Courtesy: Bonney Forge.

extension on the stem and the other one installed on the lever to stem extension connection, in case of a removable stem extension. The stem extension is like a bonnet connected to the body through Allen screws (Fig. 5.6). If a modular valve does not have a stem extension, the lever is connected to the stem on the body (Fig. 5.7). Sometimes it is difficult to use hot-dip galvanizing (HDG) on the small bolts and nickel plating may not be thick enough for coating the bolts. Stainless steel 316 bolting on the coupling may not be corrosion-resistant enough in an offshore environment containing chloride. However, stainless steel 316 screws probably could be used for the coupling since they are not

308

5. Modular valve applications and design

FIG. 5.7 Modular valve without a stem extension. Courtesy: Bonney Forge.

in contact with the fluid. Some end users may accept nickel alloy bolts for a minimum 10 mm size bolting and ASTM A453 Gr.660 (25% nickel and 15% chromium) that is cheaper than Inconel 625. Some end users may reject A453 Gr.660 bolts in the offshore industry. These bolts are sometimes used to fill in the lifting lugs on gearboxes when they are removed from the gear box after installation on the valve. However, the cheaper option is to fill in the holes in the gear box with silicone or plastic plugs. Because the valves are small, alloy 625 overlays on seat pockets, sealing areas, and ring type joint (RTJ) flange grooves of carbon steel body materials for modular valves can be avoided. Seat pocket overlay is applicable only for trunnionmounted modular valves that contain seat retainers. Modular valves for pressure gauge connections can be a ¾00 flange  ½00 bore nominal pipe thread (NPT). Modular valves can be a 200  100 FLG for unclean service or a 100 FLG full bore for clean services, for example, if the pressure gauge is in a remote seal area. Remote seal area pressure gauges require flange connections, so the connected modular valve should have the flange end connected to the remote seal area pressure gauge. Modular valves that are used for insulation of the remote seal area delta pressure transmitters should be 300 because of higher sensitivity of the delta and its requirement to have a higher flow rate. Some of the modular valves are a 300 FLG  200 FLG on the vessel trim where 200 is connected to the vessel and 300 is used to connect to delta pressure remote seal transmitters for better sensitivity. The bore of the valve is 200 , as illustrated in Fig. 5.8. Lip seal is used for three places in a modular valve: stem sealing, seat retainer and body sealing, and body adapters and main body sealing. Modular valves can be designed with two gates in series rather than two balls. Fig. 5.9 illustrates a type of modular gate valve design in which the body and bonnet connection of gate valves are connected with fillet weld. That design has a shorter face-to-face dimension and less weight. One gate valve is on the opposite side of the other one since there is no space to keep both together facing the same direction. But if it is necessary to operate both valves from one side, then the face-to-face dimension should be increased. Two gate valves on both sides make the valve higher.

Compact design

309

FIG. 5.8 Modular valves for a delta pressure transmitter installed on the equipment.

Insulation-friendly design Insulated modular valves should have an insulation-friendly design that allows installation of insulation boxes around the valves. A stem extension and adapter spool is usually included in the specification. The adapter should preferably be circular and nonrotating and have an average height of 100 mm (between 70 and 150 mm approximately). The height of the stem extension depends on the insulation thickness. Some suppliers can give a minimum of 65 mm stem extension. The preferred solution is a removable stem extension and adapter stool, which can be disassembled on-site without retesting the valve, as shown in Fig. 5.10. The adapter stool material is 316SS and unpainted. The removable stem extension does not affect the stem strength.

Compact design The main challenge in modular design is to keep the face-to-face dimension, height of the valve, and lever length/arrangement as compact as possible to minimize the chance of

310

5. Modular valve applications and design

90°

200 ~ (Closed) RUN=18

ø140 1 6 7 8 11 10 12 13 17 16 15 2

VALVE 1

14 9

18

f 13

FLOW

VALVE 1

VALVE 2

26

3

VALVE 1

65 245

4 5

18 ARRANGEMENT FOR LOCKING DETAIL

FIG. 5.9 Modular gate valves (welded body and bonnet connection). Courtesy: LVF.

FIG. 5.10

Stem extension solution for insulation purposes (Bonney Forge Design).

GATE VALVES POSITION INDICATOR & PROTECTION STEM

Compact design

311

FIG. 5.11 Modular valve lever clash with an adjacent pipe during installation.

clashes with adjacent pipes or equipment during installation. Fig. 5.11 illustrates the clashing of the blue (light grey in print version) lever of the modular valve with the pipe, making it impossible to open the valve fully. The problem was solved by changing the direction of the clashed lever 180° to the top of the other lever. Therefore, it is important to define the lever arrangement during the design phase in the 3D model to avoid clash problems. The other important point is it is not acceptable to select a gate valve instead of a modular valve in high-pressure classes to save space and avoid clashes. Making a modular valve reduced bore is an important evaluation to reduce valve body dimensions, reduce the face-to-face dimension and height of the valve, weight and material, cost, torque value, and lever length, and possibly remove the need for a gearbox. The modular valve bore usually is not important, and the bore of a modular valve is smaller than the bore values given in API 6D. Changing the bore from full bore to reduce the size of the bore will not change the ball valve face-to-face dimension. For example, a 300 flange end full bore ball valve and a reduced bore, 300  200 , have the same face-to-face dimensions. Modular valves, unlike ball valves, may have different face-to-face dimensions due to reducing the bore size if the reduction changes the valve from trunnion to floating. Changing the valve from trunnion to floating reduces the height for both ball and modular valves. Levers of modular valves can be installed on either side, 180° apart, or one above the other one. Manufacturers may ask for the lever length to be increased, to increase the torque instead of changing the lever operation to the hand wheel gearbox operation. Such a request should be checked with the layout engineer to be sure enough space is available and increasing the lever length will not result in any clash. Suppose that the lever of a modular valve clashes during installation. Reducing the lever length increases the force required for opening and closing the valve to 450 N, which is higher than the maximum allowable 350 N force required by the project. In this case, it is not a good solution to reduce the lever length. Assuming that all the modular valves have the same size and pressure class, the modular valve lever length in a 22Cr duplex body valve with a duplex

312

5. Modular valve applications and design

ball and seat can be longer than 316SS or 6MO ball and seat materials, because duplex is a harder material and more torque is required to open and close the valve in duplex internals.

Integrated modular valve with check valve and quills Modular valves are sometimes integrated with a small spring-loaded check valve in chemical injection lines such as monoethylene glycol (MEG), antifoam, and other injection lines such as those used upstream of separators in oil field development units (Fig. 5.12). The purpose of the check valve is to avoid backflow from the header to the injection lines. The ball (Item No.20A) and spring (Item No209C) in Fig. 5.12 are the main parts of the check valve. Two ball valves are located between the check valve and the piping header where the chemical is injected. Check valves are used only for chemical injection and not sampling. An integrated modular valve with a check valve is sometimes referred to as a combination valve. One operation problem of combination valves is that when the ball of the check valve is pushed far away when the valve is fully open, the ball can block the flow of fluid through the seating at the downstream end part of the spring. The fluid condition is usually not given to the supplier, so the spring could have a very low torque. The solution is that the fluid passes the ball in the area where the spring is located (as shown in Fig. 5.13) through proper valve design as well as spring torque. Fig. 5.14 shows the combination valve (modular valve plus an integrated check valve) on the chemical injection line that is a 1 ½00 FLG  3/400 THD with a ¾00 bore. The combination of 603

G

201 602C 801 212

D

111

F

C

352C 209C 20A 312D

øB

1 20 6 352B 312C 21A

F1

RELIEF HOLE

FOR THE FLANGE FINISH SEE THE REFERENCE TABLE

21B THREADED CLOSURE LOCKED WITH LOCTITE 222

FLOW

21C

A

FIG. 5.12 Integrated modular valve with a spring-loaded check valve for the chemical injection line (Bonney Forge Design).

Integrated modular valve with check valve and quills

313

FIG. 5.13 Integrated modular valve with a spring-loaded check valve for chemical injection, proper solution.

two ball valves and one check valve avoids backflow of the main line to the chemical injection. Sometimes due to additional safety, another check valve may be added with a different mechanism than the first one, to avoid concurrent failure of two check valves. Modular valves are the only valves with different sizes on ends (e.g., 1 ½00  ¾00 ). If the process changes the tube

314

5. Modular valve applications and design

Tubing

Modular valve Size 1 1/2"

pecial 1 1/2" nozzle see PDS TW01 1/3 of pipe Dia - max 100

FIG. 5.14

D

Flow direction

L = See PDS TW01

Note 3

Combination valve for a chemical injection line.

size from ¾00 to 1 ½00 , that could change the 1 ½00 from the tube to the pipe to make the other side of the valve a flange connection. Some manufacturers such as Bonney Forge are able to integrate the modular valve and the check valve with the injection quill by welding or threading the injection quill to the bore of the valve (Figs. 5.15 and 5.16). Check and modular valve integration saves space, weight, and cost. The combination valve can be a 1 ½00 FLG  ¾00 female threaded from the tube side. Unlike gate valves, which have the check valve close to the header, the check valve in the combination valve is located farther away from the header, past two ball valves.

Pressure and function tests Modular valves are tested according to the API 598 or BS5208/ISO 12266 requirements. There are four high-pressure hydrostatic leakage tests (1.1  design pressure) done on two seats of each ball valve in both directions. More importantly, one high-pressure hydrostatic leakage test (1.5  design pressure) on the shell (body) shall be done. In addition, the bleeder (needle valve) function to bleed the trapped fluid between two ball valves should be tested after the body test. Fig. 5.17 shows a modular valve during the seat test where the ball valve at the bottom is closed, the top valve is open, and the fluid is downward. In this case, the upstream seat of the bottom valve is under the pressure test. The allowable leakage from the soft seat is

Trunnion and gearbox requirements

315

FIG. 5.15 Combination valve for chemical injection integrated with an injection quill.

FIG. 5.16 Oliver valve and Alco valves.

zero. The allowable leak test for metal-seated valves including ball in sizes 200 and less is also zero, as per API 598. No leakage is allowed from the body of the valves. If a modular valve is 300 in size (greater than 200 ), the maximum allowable leakage with water for a seat test is 12 drops per minute, as per the API 598 standard. API 598 covers valve inspection and testing. Fig. 5.18 shows a modular valve during the body test when two ball valves are half open.

Trunnion and gearbox requirements It can be difficult or almost impossible to open and close full bore and floating modular valves after assembly, especially those with a metal-seated and lever operation, because more

316

5. Modular valve applications and design

FIG. 5.17

Modular valve seat test. Courtesy: Bonney Forge.

FIG. 5.18

Modular valve body test. Courtesy: Bonney Forge.

317

Trunnion and gearbox requirements

force/torque is required to overcome the friction between the metal surfaces of balls and seats. Therefore, the valves should be disassembled and the seats or balls should be lapped to reduce the roughness and provide smoother contact surfaces. This action increases the assembling or testing time considerably, so it is better to design the valves with trunnions or gearboxes to reduce the force/torque requirement from the operator. The trunnion is a bearing shaft supporting installed below the ball depending on the size, pressure rating, and seat material to support the ball in place and reduce the opening and closing force/torque values. As per the Norwegian Petroleum Industry Standard (Norsok), the maximum force requirement for lever operated valves should be 350 N, and the single hand force on the hand wheel for gearbox operated valves should be limited to 200 N. Tables 5.1 and 5.2 show the proposed trunnion and floating ball range selection for modular valves in both soft and metal seats, based on bore size and pressure class, necessary to comply with the force requirements stated earlier. The selection may be different from one vendor to another and is dependent on the project specification. Tables 5.3 and 5.4 present the gear/lever operated range for soft and metal-seated modular valves based on bore size and pressure class. Again, the gearbox selection range is different from one manufacturer to another and is dependent on the project specification. TABLE 5.1

Modular valves floating and trunnion range (soft seat). Class

Bore

150

300

600

900

1500

2500

F

F

F

F

F

F

0.75

F

F

F

F

F

F

00

F

F

F

F

F

F

1.5

F

F

F

F

F

T

00

F

F

F

F

F

T

00

F

F

F

T

T

T

00

0.5

00

1

00

2 3

TABLE 5.2

Modular valves floating and trunnion range (metal seat). Class

Bore

150

300

600

900

1500

2500

F

F

F

F

F

F

0.75

F

F

F

F

T

T

00

F

F

F

F

T

T

1.5

F

F

T

T

T

T

00

F

F

T

T

T

T

00

T

T

F

T

T

T

00

0.5

00

1

00

2 3

F: Floating/T: Trunnion.

318

5. Modular valve applications and design

TABLE 5.3 Modular valves gear/lever range (soft seat). Class Bore 00

0.5

0.75

00

00

1

00

150

300

600

900

1500

2500

L

L

L

L

L

L

L

L

L

L

L

L

L

L

L

L

L

L

L

L

L

L

L

G

00

L

L

L

L

G

G

00

L

L

L

G

G

G

1.5 2 3

TABLE 5.4 Modular valves gear/lever range (metal seat). Class Bore 00

0.5

0.75 00

1

00

00

150

300

600

900

1500

2500

L

L

L

L

L

L

L

L

L

L

L

L

L

L

L

L

L

L

L

L

L

G

G

G

00

L

L

G

G

G

G

00

L

G

G

G

G

G

1.5 2 3

It was proposed to use a PEEK seat instead of a metal seat for modular valves in connection to pressure transmitters in dirty services, to have more compact design in face to face and height as well as avoiding gear operation. The pressure gauges are installed at a 45° angle to the horizontal plane on a high point in an effort to keep dirt from getting stuck in the valve. But this idea may not work, since if the fluid has high pressure, it can force the dirt toward the valve.

Support consideration The valve illustrated in Fig. 5.19 has two supports, which are used during valve storage and transportation. However, they may not be favorable from an end user point of view due to clashes during construction, a larger insulation box requirement, and Health Safety and Environmental (HSE) issues if they are installed on vertical lines. The support is connected to the body with two bolts. Two bolts on each side must be removed to take out the support, so the pressure test certificate for the body may no longer be valid. Therefore, the valve may need to be retested. Fig. 5.20 illustrates the locking plates on a gearbox with operated modular valves for locking the hand wheels.

Support consideration

FIG. 5.19 Modular valve with support plates. Courtesy: LVF.

FIG. 5.20 Modular valve with locking plates. Courtesy: LVF.

319

320

FIG. 5.21

5. Modular valve applications and design

Bracing on a modular valve mating flange.

Some zinc coating has been removed from the nuts during the bolt tightening. The valves in Fig. 5.20 are in Class 4500 for the offshore industry. Class 4500 ASME pressure classes can be used in high-pressure applications to avoid using API 6A valves. The valves in the Figures appear to be hub ended. Some modular valves 200 in size are installed close to the header connection, which should be braced to the line from the flange connection. It is not possible to brace the hub ended valves on the hub, since the hub is covered by a clamp. Fig. 5.21 illustrates bracing of a modular valve flange connection installed on the branch.

Conclusion Modular valves, which are also called double block and bleed or combination valves, can be selected for double isolation purposes such as instrument connections with high-pressure or toxic fluid services. The valve end could be an ASME B16.5 flange, hub end, compact flange, threaded end, butt weld, or different ends for the inlet and outlet. Having a compact design to save space and minimize possible construction clashes is always a challenge for modular valves. One ball check valve in case of a chemical injection application can be integrated at the inlet of a modular valve to avoid backflow from the main header to the injection lines. Removable extended stems and spools are proposed for an insulation-friendly design that can be disassembled easily without any need to retest the valves. In addition, a selection of trunnion and gearbox for ease of opening and closing of the valves should be considered during the engineering design. It is important to keep the bore as small as possible and practical. This will reduce valve body dimensions and operational forces.

C H A P T E R

6

Wedge gate valve applications and design Valve application and selection As discussed in API 615, Valve Selection Guidelines, a gate valve is a common type of block valve for on/off services. The gate valve closure member (gate) moves out of the flow stream perpendicular to the flow path. A wedge gate valve is a common type of gate valve in which upon closing the gate to effect shutoff, the two faces of the gate engage the matching angle of the valve body seats. Turning the handwheel forces the disk firmly into the seats which, assisted by the line pressure, shuts off the flow. The API standards covering gate valves are API 600, 602, and 603. A gate valve is not recommended for throttling due to disk chattering and seat erosion. Gate valves should not be used for dirty services in horizontal lines because particles accumulate in the pocket at the bottom of the body, interfere with closing the wedge, and perhaps damage the seat as well. However, the fluid may wash out the particles when the valve is closed due to higher velocity of the fluid. Alternatively, the valve can be tilted to an angle to increase the fluid velocity and avoid stocking the particles in the pocket. Gate valves are torque-seated like the double-expanding conduit gate, globe, plug, and eccentric butterfly valves. A wedge gate valve (see Figs. 6.1 and 6.2) could be expensive and heavy in large sizes and maybe more expensive than ball valves due to heavy yoke and relatively high height. In sizes larger than 1200 , the valve is so high that a platform is required for providing access to the operator. Also, the gate valve is metal-seated and not as tight as a soft-seat ball valve. Wedge gate valves have more operational problems than ball valves, such as disconnection between the steam and the disk. These are the reasons why wedge gate valves are not popular in sizes larger than 200 in the Norwegian offshore industry. The wedge gate valve is relatively robust, with linear movement of the closing member. Wedge gate valves have the advantage of low-pressure drop. As with through conduit gate valves, the actuation of a wedge gate valve is challenging because it is a torque-seated valve and over-torquing the valve could damage the wedge, seat, and stem. Therefore, extra

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321

# 2021 Elsevier Inc. All rights reserved.

322

6. Wedge gate valve applications and design

FIG. 6.1 Wedge gate valve.

attention should be paid to sizing and selecting the actuator for a wedge gate valve like a double-expanding gate valve. Wedge gate valves in small sizes 200 and below may be more expensive than floating ball valves. The yoke arrangement as a part of the bonnet, as well as the taller height of a gate valve, could make this valve heavier and more costly compared to ball valves in small sizes. Gate valves up to and including 400 or 600 in low-pressure classes have the same face-to-face dimensions as ball valves, but they are taller. Wedge gate valves are common for drain, vent, instrument connections, etc., in offshore, refineries, and petrochemical plants. Ball valves have the advantage of quarter-turn operation (ease of operation) in comparison to gate valves. Unlike plug, ball, and butterfly valves, which are quarter-turn from an operational point of view, gate and globe valves require multiturn handwheel operation. But it is possible to have quick-opening globe and gate valves with a lever (see Fig. 6.3). Also, the same design is possible for a dead-man valve in which the valve is closed automatically when the operator releases the handle. In this design, the operator must hold the lever to keep the valve open. If the operator lets go of the lever or walks away, then the valve will be closed automatically.

Valve application and selection

323

FIG. 6.2 Wedge gate valves.

Gate valves for on/off application in drain and vent connections are normally defined up to and including 200 or 300 in the Norwegian offshore industry. Wedge gate valves are not often used for larger sizes because of excess weight and height issues. Alternatively, ball and butterfly valves are the options for fluid on/off application in larger sizes in the Norwegian offshore industry. Ball valves are more robust valves compared to wedge gate valves and are easier to operate. A wedge gate valve with a rubber/PTFE (Teflon) lining for noncontinuous seawater may not be practical since the internals should also have a coating and the wedge in the closed position would cut the rubber/PTFE. However, some valve manufacturers may claim to make the gate valve with a PTFE coating on the wedge without any pocket on the body bottom, so the PTFE would not be cut when closing the gate (wedge). The seat of the valve can be integrated with the body and covered by PTFE so having PTFE reduces the wearing between seat and disk, and enables tight shutoff and better resistance to fatigue. Normal vent and drain connections are 100 or 200 (for header sizes above 1200 ) or ¾00 (for header sizes 1200 and smaller) gate valves with flanged ends, with a reducing (100 or ¾00 )  ½00 flange that is blinded with a ½00 safety plug (see the example in Fig. 6.4). The safety bleed plug should be removed after a pressure test to drain the line and then it will be sealwelded. On/off valves for drain connections in 300 or 400 can be soft, or metal seated ball valves, especially in dirty services where a gate valve is not suitable. A gate valve for a drain or vent located on the vessel can be 200 with a 200 reducing flange and ½00 bore that is plugged. An alternative solution to Fig. 6.4 is shown in Fig. 6.5, in conditions where enough space is not available vertically between the deck and bottom of the valve.

324

6. Wedge gate valve applications and design

FIG. 6.3 Wedge gate valve with a lever. Courtesy: Bonney Forge.

Figs. 6.6 and 6.7 illustrate a gate valve in 100 for drain and vent connections. A less expensive and more compact solution for vent and drain gate valves is to have one end of the valve as a female threaded connection instead of a flange that is directly connected to the bleed plug. In this case, there is no need to apply a reducing flange between the gate valve and the bleed plug. As an example, a 100 or ¾00 flange  threaded gate valve can be connected to a ½00 safety plug through a ¾00 male threaded bushing  ½00 female threaded. ½00 The safety plug can be directly connected to the threaded end of a ½00 valve flange  female threaded. Bushing is not required if the gate valve and the bleed plug have the same size. The other way to save weight and space for vent and drain gate valves is to select a wedge gate valve with one end threaded and the other end flangeless (Fig. 6.8). This solution is the least expensive for high-pressure classes. Two wedge gate valves in series with a bleed wedge gate valve between can be applied for the drain connection. The solution shown in Fig. 6.9 with three flanged end gate valves requires more space compared to changing the valves to wafer type, at least for high-pressure classes. This change has the advantage of saving weight and cost in addition to space. Therefore, the upstream valve in the arrangement shown in Fig. 6.10 can be selected as a wafer gate valve. But the second one, with a spectacle blind on the upstream, should have a flange

325

Valve application and selection

Class 150 - 2500 l

2" wedge gate valve flanged both ends

min. 300

2" x 1/2" reducing threaded flange

Deck

Seal weld after pressure test 1/2" bleed plug

FIG. 6.4 200 Wedge gate valve arrangement for vent and drain connections.

Alternative layout 2" wedge gate valve flanged both ends 2" x 1/2" reducing threaded flange

1/2" bleed plug Seal weld after pressure test

FIG. 6.5 2 Wedge gate valve arrangement for vent and drain connections (alternative solution). 00

Class 150 - 2500

1" flanged wedge gate valve

Deck

min. 300

1" x 1/2" reducing threaded flange Seal weld after pressure test 1/2" bleed plug

FIG. 6.6 100 Wedge gate valve arrangement for vent and drain connections.

326

6. Wedge gate valve applications and design

Alternative layout 1" flanged wafer wedge gate valve

1" x 1/2" reducing threaded flange

1/2" bleed plug Seal weld after pressure test

FIG. 6.7 1 Wedge gate valve arrangement for vent and drain connections (alternative solution). 00

connection to avoid dropping down the wafer gate valve when the spectacle blind is removed. The wafer gate valve has long-length bolts between two mating flanges around the valve, so losing the bolts would make the valve fall down. However, a flanged body gate valve has two series of bolts connected to each flange side. Losing the flange bolts on the spectacle blind side is not an issue, since the valve is connected to the flange on the other side through different sets of bolts. The bleeder gate valve can be changed to one end flangeless and the other end threaded or socket weld. As was described in Chapter 5, two wafer gate valves may be proposed instead of a modular valve to save face-to face-space. Gate valves for isolation of the pressure gauge in low-pressure classes can be threaded on one end and flanged on the other end, or flanged on both ends. The end on the side of the pressure gauge could be either flanged or threaded, depending on the instrument engineer requirements. Instrument pressure gauges with a remote seal (chemical seal or diaphragm seal) require flanged connections (see Fig. 6.11). A gate valve can be selected for isolation of a sample or injection quill arrangements in lowpressure 150 and 300 classes (see Figs. 6.12 and 6.13). Chemical injection is a general term for injection processes that use special chemical solutions to improve oil recovery and separation, FIG. 6.8 Gate valve with one end female thread for vent and drain connection.

1" flanged x 1" NPT wedge gate valve

min. 300

1" x 1/2" red. bushing

Deck

1/2" bleed plug

Valve application and selection

327

FIG. 6.9 Drain arrangement with two wedge gate as blocks and a bleed between.

reduce or inhibit corrosion, upgrade crude oil, or address crude oil flow-assurance issues. Injections can be administered continuously, in batches, in injection wells, or at times of production. Chemical injection in this case is used for separation of water emulsions from the crude oil. Fig. 6.13 shows a gate valve for isolation of a sample connection. Sample connections are used for accurate sampling of the fluid in the header line. Unlike a chemical injection line, there is no check valve in a sample connection. A check valve is used only for injection, to avoid returning the fluid in the header back to the injection branch. The check valve is located close to the header when the gate valve is installed. The other application of gate valves is for isolation of vacuum break and air release valves (Fig. 6.14). Vacuum breakers and air release valves are special valves with two separate functions. While the system is flowing and under pressure, the valve continuously and automatically exhausts the small quantities of air that would otherwise collect at system high points. Air traps in the pipe during the water pump should be released to avoid water hammering and excessive pipeline damage. In fact, the air release function of the valve protects the pipe from surge pressure, water hammering, and other possible damages. In the vacuum break mode, the pumped liquid is drained to avoid damage to the pipe.

328

6. Wedge gate valve applications and design

ÆB

fC

BEVEL GEAR ORENTATION AT 90⬚

FOR THE FLANGE FINISH SEE THE GENERAL NOTES

A

FIG. 6.10

Wafer-type wedge gate valve. Courtesy: Bonney Forge.

Unlike a globe valve, a gate valve does not have any flow direction and can be installed on both flow directions (bidirectional).

Wedge gate valve standards The API 602 standard covers gate, globe, and piston check valves 400 and below, up to and including CL1500 but usually used for sizes up to and including 200 . ASME B16.34 is the standard for gate, globe, and piston check valves 200 and below in CL2500. API 602 gate valves in process plants may be threaded or socket-welded in the special class of 800. Flanged end and butt weld connections are available where using the socket weld or threaded ends are not desired. Figs. 6.15, 6.16, and 6.17 illustrate typical API 602 bolted body bonnet gate valves one with socket and the other threaded end.

Wedge gate valve standards

329

FIG. 6.11 Remote diaphragm seal pressure gauge with flanged end.

API 600 covers gate valves in 2400 and below and all pressure classes including CL2500 with weld ends and flange connections. API 600 was developed for refinery applications to provide a robust, heavy wall design suitable for fluid services up to 538°C. The pressuretemperature rating of these valves is given in the ASME B16.34 standard for the listed materials. The body and bonnet wall thicknesses given in API 600 are greater than the wall thickness values given in ASME B16.34. Fig. 6.18 shows a typical flanged gate valve bolted body bonnet based on the API 600 standard. API 603 was developed to provide a lower cost alternative to API 600 valves in corrosive and lower pressure class services. API 603 provides a lighter weight, corrosion-resistant design made of stainless or nickel alloy with a thinner body wall than API 600 valves. The wall thickness values given in API 603 are comparable with ASME B16.34 wall thickness values. These valves are available in flange and butt weld end connections in sizes from ½00 to 2400 and in pressure classes of 150, 300, and 600. Fig. 6.19 shows a typical bolted body bonnet wedge gate valve based on API 603.

330

6. Wedge gate valve applications and design

Tubing

nged/NPT Female gate valve

1 1/2” flanged check valve

L = See PDS TW01

Note 3 1 1/2” nozzle see PDS TW01 1/3 of pipe Dia - max 100

Chemical injection arrangement with the isolation gate valve.

Sample in (Note 3)

Class 150 - 300

1 1/2" flanged wedge gate valve (3/4" NPT one end) Special 1 1/2" nozzle - see PDS TW01 1/3 of pipe Dia - max 100

Instrument Piping

L=See PDS TW01

FIG. 6.12

D

low direction

D

Flow direction

FIG. 6.13

Sample connection with the isolation gate valve.

331

Wedge gate valve standards

FIG. 6.14 Vacuum breaker and air release valves.

1 2 Key 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

handwheel identification plate handwheel nut stem nut stem gland bolting gland flange gland packing bonnet bolting bonnet gasket seat ring gate body

3 4 5 6 7 8 9 10 11 12 13 14 15

FIG. 6.15 Typical API 602 bolted body bonnet gate valve (socket welded).

332

6. Wedge gate valve applications and design

1 2 3 4 5 6 7 Key 1 jam nut 2 identification disc 3 handwheel 4 yoke nut 5 bearing ring for yoke nut 6 yoke 7 gland bolting 8 packing gland 9 packing 10 stem 11 bonnet 12 solid wedge 13 body 14 seats

8 9 10 11 12 13

14

FIG. 6.16

Typical API 602 bolted body bonnet gate valve (female threaded end).

Body bonnet design According to API 600 and 602, the body and bonnet of the gate valves should be secured through one of the following methods: – – – –

Bolting (see Fig. 6.20). Welding (see Fig. 6.21). Threaded with a seal weld. Threaded union nut for pressure classes of maximum 800.

Welded body and bonnet gate and globe valves (Fig. 6.22) have less chance of leakage and they are more compact (shorter). But there is no access to the valve internals, so the entire valve must be replaced in case of internal failure. End flanges should comply with the dimensional requirements given in ASME B16.5 and ASME B16.47. Flange faces can be raised face, ring-type joint, and flat face. The recommended end and bonnet flange connections are integrated forge or cast with the body.

Face-to-face standard Face-to-face dimensions for flanged end valves should be based on the ASME B16.10 standard, “Face-to-Face and End-to-End Dimensions of Valves.” The purpose of this standard is to assure installation interchangeability for valves of a given material, type, size, rating class,

Bore design

333

HANDWHEEL NUT FIG. 6.17 Typical API 602 bolted body bonnet gate valve (female threaded end). NAME PLATE HANDWHEEL YOKE SLEEVE GLAND NUTS GLAND FLANGE PACKING GLAND GLAND STUDS BONNET PACKING BOLTS STEM GASKET WEDGE SEAT RINGS BODY

and end connection. As per ASME B16.10, a tolerance of 2 mm should be allowed on face-toface and end-to-end dimensions of valves of 1000 and smaller, and a tolerance of 3 mm should be allowed for 1200 and larger. The expression “end-to-end” is used for those flanged valves where the gasket contact surfaces are not located at the extreme ends of the valve, such as ring-type joint gaskets shown in Fig. 6.23.

Bore design API 602 gate valves can be either full bore or standard bore (reduced bore). Both full bore and standard bore gates have minimum bore diameters less than the nominal valve. Wedgetype gate valves in the standard bore can be defined for bore sizes 200 and below in all pressure classes except for CL2500 as per API 602. Gate valves have equal thicknesses and minimum bore diameters (both for full bore and standard bore) in all pressure classes 150, 300, 600, and 800 as per API 602. The minimum bore diameter is larger for a gate valve than for globe and piston check valves in CL1500 in API 602. The bore diameters for gate valves in CL2500, as well as API 600 gate valves, are according to ASME B16.34. The minimum bore diameter

334

6. Wedge gate valve applications and design

1 2 24

3

23

4

22

5 6 7 8 9

21

10 11 Key 1 handwheel nut 2 handwheel 3 stem nut 4 stem 5 gland flange 6 gland 7 stem packing 8 lantem ring 9 plug 10 wiper packing 11 backseat bushing 12 bonnet 13 bonnet gasket

12 14 15 16 17 18 19 20 21 22

bonnet bolts and nuts gate seat ring body raised face butt-welding end valve port gland lug bolts and nuts gland bolts or gland eyebolts and nuts 23 yoke bolting 24 yoke

13 14 15 16 20 17

18

19

FIG. 6.18

Typical API 600 bolted body bonnet gate valve.

(flow passage) is 90% of the inside diameter of the valve end as per ASME B16.34. Table 6.1 presents the minimum diameter of flow passageway for full bore gate, globe, and check valves based on the API 602 standard. It is not possible to inspect the inside bore diameter for gate, globe, and check valves in small sizes. For example, a 200 CL1500 standard bore gate valve has a 50-mm bore at body flange connections that are reduced to 34 mm per API 602. It is not possible to measure a bore reduction of 34 mm. Table 6.2 presents the minimum diameter of flow passageway for standard bore gate, globe, and check valves based on API 602 standard.

335

Wall thickness

7 8 2

Key 1 butt-welding end 2 yoke 3 yoke bolting 4 gland bolts or gland eyebolts and nuts 5 valve port 6 face to face 7 handwheel nut 8 handwheel 9 stem nut 10 stem 11 gland 12 stem packing 13 plug 14 lantern ring 15 backseat 16 bonnet 17 bonnet gasket 18 bonnet bolts and nuts 19 gate 20 separate or integral seat 21 body

9 10

3 11 4

12 13 14 15 16 17 18 19

5

20

1

21

6

FIG. 6.19 Typical API 603 bolted body bonnet gate valve.

Wall thickness The body and bonnet wall thicknesses given in API 600 and API 602 are greater than the wall thickness values given in ASME B16.34. The wall thickness values given in API 602 (see Table 6.3) are applicable for the body and bonnet of gate and globe valves, as well as check valve covers. Class 900 is not given in the tables since that is not a common pressure class for a piping system. In addition, class 900 and 1500 flanges are the same for small sizes 200 and below. Therefore, all the valves in class 900 and sizes 200 and below are ordered in class 1500. In Fig. 6.24, the blockage shown by a red star on the header causes overpressure in class 150 usually open wedge gate valves. Therefore, the design pressure of the gate valves exceeds 20 bar pressure nominal (PN) which is equal to class 150. The valves should be changed to the higher pressure class, which is class 300 equal to PN 50 barg. The small 3/400 pipe thickness has been selected in schedule 40 based on the ASME B36.19 standard for piping that can withstand the pressure class 300. One solution is changing the pipe routing to avoid overpressure due to blockage. The other solution is to change the valves from class 150 to class 300. Although 3/400 class 150 and 300 valves have the same thickness, as per API 602 standard, the

336

FIG. 6.20

6. Wedge gate valve applications and design

Bolted body and bonnet gate valve.

class 150 and 300 flange connections are not fit together. However, flanged wedge gate valves in class 300 and 600 as well as class 900 and 1500 in small sizes up to and including 200 are fit together. The ASME B31.3 process piping code allows overpressure exceeding not more than 33% of the design pressure for just 10 h at a time and not more than 100 h per year.

Wedge design Wedge gate valves can be split wedge (Fig. 6.25), flexible, or solid one piece (Fig. 6.26). Wedge gate valves in sizes 200 and below are normally solid wedge, perhaps because it is difficult to machine the wedge in small sizes 200 and below. The flexible and split wedge designs provide a small amount of angular deflection of the disk faces to provide for a better engagement with the body seats. The flexible/split wedge design expands or shrinks easily in thermal cycles, which creates less galling between the wedge and seat and prevents the seat from getting stuck to the wedge. Flexible or split wedge gate for larger sizes can be used for high-pressure steam for on/off applications and globe valve for throttling. In high-temperature steam applications where a temperature fluctuation is expected, a flexible wedge gate is the first choice and a split parallel is the second choice. The wedge gate outer seating surfaces should be free from sharp edges to prevent damages to seat surfaces during opening and closing.

Seat design

337

FIG. 6.21 Welded body and bonnet gate valve.

It is very common to apply hard-facing materials such as Stellite to avoid wearing and erosion on the wedge. The minimum required weld overlay thickness as per relevant API standard should be 1 mm. The wedge is an internal part of the valve “trim” that should have, at a minimum, the same material as the body of the valve. As an example, 13Cr stainless steel or 316 stainless steel materials are common trim materials such as wedge for carbon steel body valves. Wedge (disk) sealing surfaces should be carefully machined for better sealing, less torque requirement, and longer design life. The stem connection should be designed to prevent the stem from turning or from becoming disengaged from the gate while the valve is in service. The stem connection to the gate should be in the form of a “T,” as shown in Fig. 6.27.

Seat design Seat design can be integral or renewable. In an integral seat design, the seat and the body are constructed from the same material. Renewable seat ring construction provides seats that are made of different materials and are either threaded into position or pressed and sealwelded to the valve body. It is very common to select small, forged gate valves with hardfaced seats pressed into the body. Standard seat design by some of the manufacturers could be the integral type. Seat repair can be performed by a cold repair, lapping with diamond

338

FIG. 6.22

6. Wedge gate valve applications and design

Welded body and bonnet wedge gate valve.

paste and lapping plates, if the seat defect depth is less than 0.8 mm and the size is larger than 100 . However, for more serious defects, the valve should be removed from the line and sent back to the vendor shop for weld repair. Before placing the seats in the valve body, ensure that all the surfaces on the body and seats are clean and free of foreign matter that may have been created during maintenance. Body seating surfaces should not have sharp corners with an edge that may cause damage in conjunction with a gate or disk-seating surfaces. The inside

FIG. 6.23

Ring-type joint gaskets.

TABLE 6.1 Minimum diameter of equivalent flow passageway for full bore gate, globe and check valves based on API 602. Minimum diameter in. (mm) Class 150, Class 300, Class 600, Class 800

Class 1500

NPS

Gate, globe, or check valves

Gate valves

¼

¼ (6)

¼ (6)

⅜

⅜ (9)

⅜ (9)

½

½ (12)  11 16 ð17Þ  15 16 ð22Þ

½ (12)

¾ 1 1¼

⅝ (15) ⅞ (22)  1 1 16 ð26Þ

1½

1 ⅛ (28)  1 7 16 ð35Þ

1 ⅜ (34)

2

1 ¾ (44)

1 ½ (38)

2½

2 (50)

1 ⅞ (47)

3

2 ¾ (69)

2 ½ (63)

4

3 ¾ (95)

3 ⅝ (92)

Globe or check valves  3 16 ð4Þ  5 16 ð7Þ ⅜ (9)  16 ð14Þ  13 16 ð19Þ 9

DN 8 10 15 20 25

1 (25)  1 1 16 ð26Þ

32

1 ⅜ (34)  1 11 16 ð42Þ  2 5 16 ð58Þ  3 7 16 ð87Þ

50

40

65 80 100

TABLE 6.2 Minimum diameter of equivalent flow passageway for standard bore gate, globe and check valves based on API 602. Minimum diameter in. (mm) Class 150, Class 300, Class 600, Class 800

Class 1500

NPS

Gate, globe, or check valves

Gate valves

¼

¼ (6)

¼ (6)

⅜

¼ (6)

¼ (6)

½

⅜ (9)

⅜ (9)

¾

½ (12)  11 16 ð17Þ  15 16 ð23Þ

½ (12)

1 1¼ 1½

⅝ (15) ⅞ (22)  1 1 16 ð27Þ

2

1 ⅛ (28)  1 7 16 ð36Þ

1 ⅜ (34)

2½

1 ¾ (44)

1 ½ (38)

3

2 (50)

1 ⅞ (47)

4

2 ¾ (69)

2 ½ (63)

Globe or check valves  3 16 ð5Þ  3 16 ð5Þ  5 16 ð8Þ ⅜ (9)  9 16 ð14Þ  13 16 ð20Þ

DN 8 10 15 20 25 32

1 (25)  1 1 16 ð27Þ

40

1 ⅜ (34)  1 11 16 ð42Þ  2 5 16 ð58Þ

65

50

80 100

340

6. Wedge gate valve applications and design

TABLE 6.3 Minimum wall thickness for gate, globe, and check valve bodies, bonnets, and check valves based on API 602. Minimum wall thickness in. (mm)

FIG. 6.24

NPS

Class 150, Class 300, Class 600, Class 800

Class 1500

DN

¼

0.12 (3.1)

0.15 (3.8)

8

⅜

0.13 (3.3)

0.17 (4.3)

10

½

0.16 (4.1)

0.19 (4.8)

15

¾

0.19 (4.8)

0.24 (6.1)

20

1

0.22 (5.6)

0.28 (7.1)

25

1¼

0.23 (5.8)

0.33 (8.4)

32

1½

0.24 (6.1)

0.38 (9.7)

40

2

0.28 (7.1)

0.47 (11.9)

50

2½

0.33 (8.4)

0.56 (14.2)

65

3

0.38 (9.7)

0.65 (16.5)

80

4

0.47 (11.9)

0.84 (21.3)

100

Case study of changing a wedge gate valve.

Stem design

341

FIG. 6.25 Flexible and split wedge design.

Solid Wedge Gate FIG. 6.26 Solid wedge design.

diameter of the body seat flow passageway should be in accordance with API 600 and 602 standards. Special care should be taken to provide a hardness difference between seat and wedge to avoid wearing and galling. Machining on the seat sealing should be controlled to ensure a perfect sealing.

Stem design Stems are designed as either inside screw or outside screw. Gate valves are normally outside screw and yoke (OS&Y) with a rising stem and either a rising or a nonrising handwheel. If the stem is rotating, then the handwheel can be rising or nonrising. If the yoke sleeve/stem nut is extended to the area between the stem and the handwheel—which makes the stem rise through the handwheel—then the handwheel is nonrising. In both cases, more torque is required and less packing life is achieved due to rotating stem action. A nonrising handwheel (Fig. 6.28) may be required to avoid changing the access of the operator to the handwheel.

342

6. Wedge gate valve applications and design

FIG. 6.27 Solid wedge connection to stem. Courtesy Bonney Forge.

For the nonrising stem gate valve, the stem is threaded on the lower end into the gate. This design is also called inside screw and yoke (Fig. 6.29). As the handwheel on the stem is rotated, the gate travels up and down on the threads while the stem remains vertically stationary. Nonrising stem gate valves are not commonly used in the oil industry since the stem threads are created in the pressure boundary with a high risk of crevice corrosion due to contact with the fluid. On the other hand, rising stem gate valves are designed in a way that stem is raised out of the flow path when the valve is open. Fig. 6.30 shows an OS&Y gate valve with a rising stem and the stem threads coming out of the handwheel. The threads in contact with the corrosive offshore environment are at the risk of corrosion. Therefore, a plastic cap, as shown in Fig. 6.31, can be installed on the handwheel and its nut. The plastic cap is installed on the valve handwheel primarily for indicating the position of the valve (position indicator). The rising stem moves up during the opening and moves down during the closing inside the cylinder so it is possible to determine how much the valve opens or closes. The stem should be a one-piece design and no fabricated welding is permitted. The stem surfaces should be less than 32 μin. as per API 600 and 602 standards, especially in contact with the packing, to avoid packing and stem friction. Therefore, fine surface finish of the stem is necessary, especially in the area of the packing. Figs. 6.32 and 6.33 illustrates rising stem and OS&Y gate valves in both open and closed positions. Gate valves have a rotating stem and rotating stem design that increases the torque of the valve by 15%–25%. The torque is increased because there is more friction between the packing and rotating stem than there is between the packing and nonrotating stem. Fig. 6.34 illustrates the design supporting a stem in a gate valve through two bolted plates, which prevent stem rotation and improve the packing life.

Stem design

FIG. 6.28 Rising and nonrising handwheel.

FIG. 6.29 Nonrising stem in a wedge gate valve (inside screw and yoke design).

343

344

6. Wedge gate valve applications and design

FIG. 6.30 Rising stem and OS&Y gate valve. Courtesy: Bonney Forge.

Yoke design Although API 600 allows the yoke to be a separate part of the bonnet, it is common to have an integrated bonnet and yoke made of the same material, as shown in Fig. 6.35. The yokes are on the left side of the box, and there are handwheels on the right side. Figs. 6.36 and 6.37 show the yoke sleeve (stem nut) with the grease injection port. The yoke sleeve (stem nut) should be lubricated since it is in contact (friction) with the stem and exposed to the high-temperature produced between the bonnet, yoke, and stem during the valve operation. The yoke sleeve or stem nut is an internally threaded nut that is placed at the top part of the yoke, where the stem passes through it. The yoke nut has threads that engaged with the stem threads to facilitate the yoke nut traveling up and down the stem. Although the nut is lubricated, it is usually made from low-friction material like nickel aluminum bronze (NiAlBr) to reduce galling and friction with the stem as much as possible. Lubrication of the yoke sleeve is done through a grease nipple on the yoke made from 316 stainless steel materials. The grease nipple should be protected with a plastic cap. The internal thread in the stem nut, yoke sleeve, or stem bushing should be constructed in accordance with relevant ASME or ISO standards.

Back seat design The back seat, or back seat bushing (item #4 in Fig. 6.38), is typically designed for the stem sealing arrangement in gate and globe valves. Back seat is the seating arrangement in the body. This component provides a seal between the stem and bonnet and prevents fluid pressure from building up against the valve packing. The advantage of back seat bushing is in minimizing the leak through the stem if there is something wrong with the packing and the valve is off-seat.

Packing design

345

FIGS. 6.31 Rising stem gate valves with position indicator. Courtesy: Bonney Forge.

Packing design A gland (item #2 in Fig. 6.38) should be provided for packing compression. The gland can be either a selfaligning gland or an integral part of the gland flange (item #1 in Fig. 6.38). Item #1, 2, 3, and 4 in Fig. 6.38 are gland flange, gland ring, packing, and back seat respectively. Gland flange

346

FIG. 6.32

6. Wedge gate valve applications and design

Rising stem and OS&Y gate valves in both open and closed positions.

FIG. 6.33 Rising stem and OS&Y gate valves. Courtesy: Bonney Forge.

bolts can be eyebolts, stud bolts, or studs. Gland flange bolts may be supplied with springs or Belleville washers to provide a constant force on the gland and avoid gland loosening and maintain the packing load over the time. Packing is usually layers of graphite rings (Fig. 6.39) used between the stem and bonnet to prevent leakage from the stem and maintain the sealing. Packing also forms a seal between the valve internal parts and outside when the stem is up and the valve is open. Valve packing must be properly compressed to prevent loss and damage to the

Packing design

347

FIG. 6.34 Supporting the valve nonrotating stem.

FIG. 6.35 Integrated bonnets and yokes. Courtesy: Bonney Forge.

valve stem. If the packing is too loose, the valve will leak. If the packing is too tight, it will damage the stem, cause friction, and increase the possibility of leakage. Packing should be replaced (Fig. 6.40) if there is still leakage from packing even after excessive tightening of the gland bolts. Some operator companies never trust back seat bushing during packing replacement, especially in high-pressure classes when the valve is in service. The MSS SP 42 standard for corrosion-resistant gate, globe, angle, and check valves does not recommend repacking the valve when the valve is in service. It is recommended to isolate and depressurize the valve during the repacking and is not required to take the valve out of the line during simple repacking. Repacking the gate and globe valve includes removing gland bolts and nuts, lifting the gland flange, and gland out of the stuffing box, removing the old packing rings, cleaning

348

6. Wedge gate valve applications and design

ØC

Grease Injection

Yoke Sleeve

ØB

H (OPEN)

603B 103 602 210 803 105 603A 102 217 101 201 330 108 107 2 601 307 5

A

FIG. 6.36

3 1 6

Yoke sleeve and grease injection.

Stem

Handwheel Yoke Yoke bushing

FIG. 6.37

Detail of yoke bushing for a rising stem gate valve.

Packing design

349

FIG. 6.38 Typical stem sealing arrangement.

the stem, and stuffing box, examining them to ensure there is no damage, and finally installing the new packing rings. Tightening the gland bolts compresses the packing rings and stops the leakage. The risk is overtightening the gland bolts with torque values exceeding the values given in the Installation, Operation, and Maintenance (IOM) manual provided by the valve supplier. Overtightening creates high stem and packing friction and packing leakage. Loosening the gland bolts to decompress the packing and reduce the stem friction leads to constant packing leakage. According to Section 5.9.3.1 of ASME B31.3, Process Piping, leakage through stem seals during the shell test should not be a cause for rejection. Gate and globe valves may leak from the packing during the shell test or hydro test after installation. Overtightening of the gland bolts to compress the packing not according the torque procedure locks the valve. Loosening the gland flange bolts or applying grease leads to constant packing leakage. Repacking could be one solution. Torque values for tightening the body and bonnet bolts as well as gland flange bolts with lubrication for gate valves are given in the IOM manual with plus and minus 10% tolerance. A2–70 bolts need a higher torque compared to L7 and B8M bolts. 75% of bolt torque values should be applied for bolts in high-temperature applications 400°C and above. Tightening the gland packing bolts provides packing compression through the gland. Fig. 6.41 provides spring-loaded gland flange (Figs. 6.42 and 6.43). The packing area should be lubricated by grease that is injected to the packing spacer through the lantern rings. Gate and globe valves have risen outside screw (threaded) stems that create friction between the packing and the stem. It is proposed to lubricate even flexible

350

FIG. 6.39

6. Wedge gate valve applications and design

Layers of packing graphite.

graphite packing, which creates less friction to the stem compared to graphite packing. An emergency sealant can be also injected through the sealant/grease injection fitting (Fig. 6.44) to repair the packing temporarily if the leak from the packing cannot be fixed by tightening the gland bolts. A relief plug can be installed on the other side of the bonnet (opposite from the lantern ring) to make sure that lubrication or sealant injection lubricates

FIG. 6.40

Packing replacement.

351

Packing design

FIG. 6.41

Spring-loaded gland flange. Courtesy: Bonney Forge.

the packing completely. Double-packing with an injection point containing two nonreturn ball check valves is possible for very corrosive or toxic services. A bellows stem sealing gate valve (Fig. 6.45) has a very strong stem sealing property where a bellows is welded to the stem from one side and to the bonnet from the other side. Bellows seal valves do not require a back seat test. It is common to have welded body and bonnet for the gate and globe valves with bellows sealing to reduce the leak of fugitive and dangerous

FIG. 6.42 Gland flanges. Courtesy: Bonney

Forge.

352

FIG. 6.43

6. Wedge gate valve applications and design

(A, B) Gland flange and gland flange bolt installation on the yoke. Courtesy: Bonney Forge.

Packing design

PLUG

INJECTOR

FIG. 6.44 Plug and injector on packing of a gate valve.

FIG. 6.45 Bellows stem sealing gate valve.

353

354

6. Wedge gate valve applications and design

fluids. In some cases, bellows is a better design for fugitive emission services than conventional packing design.

Locking design A locking device (Fig. 6.46) can be a padlock or a chain lock as mechanical locks or key lock. The locking device can be welded to the yoke, and the chain passed through the locking and fastened around the handwheel. Figs. 6.47 and 6.48 show how to use the locking facility at the top to install the chain.

Insulation-friendly design Gate valves are insulation-friendly if the insulation is to be extended to the packing area. The packing box is located at the bottom of the yoke arrangement. However, if insulation is required to cover the entire yoke area, a stem extension may be required since the shape of the yoke is not circular and insulation-friendly. In Fig. 6.49, the irregular shape of the yoke is covered by two half circles to facilitate the insulation. However, this solution with two half circles

FIG. 6.46

Locking pads welded to the yoke of gate valves.

Insulation-friendly design

FIG. 6.47 Locking devices.

FIG. 6.48 Locking chains.

355

356 FIG.

6. Wedge gate valve applications and design

6.49 Insulation-friendly

gate

valves.

is not applicable for gate valves in all projects. Gate valves are insulation-friendly without any requirement to cover the yoke in many cases.

Valve operation A gate valve is gearbox operated in sizes 800 and above in pressure classes 150 and 300, 600 and above in CL600, 400 and above in CL900, 300 and above in CL1500, and 1 ½00 and above in CL2500, as an example. Fig. 6.50 shows a gear-operated wedge gate valve. FIG. 6.50

Gear-operated wedge gate valve.

Valve lifting, transportation, and installation

357

The alternative way of operation is through a handwheel without any gear (Fig. 6.51). A bar connected to the handwheel of the gate and globe valves is called a quick lever (Fig. 6.52). Gate and globe valves are closed by rotating the handwheel in a clockwise direction and are opened by rotating the handwheel in a counter clockwise direction. Opening and closing directions are shown on the handwheel. Opening and closing directions are also marked on the gearbox of the valves (Fig. 6.53). Some suppliers can provide a flange at the top of the valves for actuator installation even if the valve is not quarter turn. The image on the left in Fig. 6.54 shows a top flange design for a wedge gate valve for electrical actuator installation on the top. The image on the right shows an electrical actuator to be installed on the top flange. When it comes to pneumatic and hydraulic actuation of the gate valves, the actuators are installed vertically on the top of the valve, which increases the height (Fig. 6.55).

Valve lifting, transportation, and installation Gate valves should be transported in a closed position. Gate valves do not usually have lifting lugs. Gate and globe valves are lifted by using a cloth wrapped around the body and bonnet connection under the yoke, as shown in Fig. 6.56. Gate valves should not be installed with their stem below the horizontal line. If they are, complete drainage is not possible and solids will accumulate in the bonnet that can affect the operation and service life of the valve (increasing the possibility of packing damage). Both positions of installation for gate valves shown in Fig. 6.57 are acceptable since the stems are not below the horizontal line.

FIG. 6.51 Handwheel-operated wedge gate valve (top view). Courtesy: Bonney Forge.

FIG. 6.52 Handwheel/gearbox operated valves with a quick lever on the handwheel. Courtesy: Bonney Forge.

FIG. 6.53

Handwheel/gearbox operated valves with opening/closing instructions on the gearbox. Courtesy: Bon-

FIG. 6.54

Top flange design for a wedge gate valve for placing the actuator.

ney Forge.

Valve lifting, transportation, and installation

FIG. 6.55 Wedge gate valve actuation, vertically mounted actuator.

359

360

6. Wedge gate valve applications and design

FIG. 6.56

Wedge gate valve lifting. Courtesy: Bonney Forge.

FIG. 6.57

Wedge Gate Valve installation in both vertical and horizontal directions.

C H A P T E R

7

Globe valve applications and design Valve application and selection Unlike ball, plug, and gate valves, which are used to stop and start the flow of fluid in piping systems, globe valves are used for regulating the flow. API RP 615, Valve Selection Guide, states that globe valves may be used for blocking the flow of fluid. Fig. 7.1 shows a globe valve and its part lists. Usually globe valves should not be used for less than a 20% opening for throttling. Opening the valve less than 20% increases the wear and load concentration on the seat and plug. However, the disk and plug of a globe valve are exposed to wearing and erosion due to pressure drop and other operational problems such as cavitation, so these valves are not recommended for blocking fluid. One typical example of the use of a globe valve is for bypass of control valves. A bypass with a hand-operated control valve permits continuous operation with some degree of regulation when a control valve is taken out of service for maintenance. Fig. 7.2 shows a manual globe valve highlighted with a red circle (gray in print version) in the bypass of a control valve. Fig. 7.2 shows a shell and tube heat exchanger in the shape of a rectangular box with two half-circle caps on the ends. The control valve on the outlet of the heat exchanger is isolated with two gate valves. The fluid service in the control valve and both isolation valves is water. The highlighted manual globe valve has been selected for the bypass of the control valve. Some end users may try to minimize using straight pattern globe valves for throttling. One approach is to replace straight pattern globe valves with butterfly valves in utility services. Changing the valve selection from globe to butterfly has the advantage of saving cost and weight, in addition to mitigating the risk of cavitation. Bypass of a control valve can be accomplished by using a globe valve in process lines that should have a Cv value close to but not exceeding the control valve. One solution is selecting a control valve for the bypass line and ordering from the control valve manufacturer. A second approach is to order a manual globe valve with a special bore; a third option is applying a restriction orifice downstream of the bypass globe valve to reduce the Cv value (if the bypass globe valve has a larger Cv value than the control valve). Face-to-face dimensions of control valves should be as per ASME B16.10 standard. It can be a case that a globe valve for a bypass

A Practical Guide to Piping and Valves for the Oil and Gas Industry https://doi.org/10.1016/B978-0-12-823796-0.00005-2

361

# 2021 Elsevier Inc. All rights reserved.

362

7. Globe valve applications and design

FIG. 7.1 Globe valve with the part list.

PSV

VENT NOTE 1 TV

NOTE 2 VENT RS RS

RS

TT

CSV

2” LC MAIN CSV

RS

DRAIN

FIG. 7.2 Heat exchanger arrangement including a manual globe valve on the bypass of a control valve.

line should have a special bore (larger than a standard bore) to have a higher Cv value close to the control valve. Since the intended process usually determines the size of the bypass equal to the control valve, it is best to avoid increasing the size of the bypass and instead increase the bore of the valve to achieve the required Cv value. It is also possible to increase the size of the bypass as well as the bore to have higher Cv values. Globe valves are used for throttling (flow control). The most common type of globe valve has a T-pattern body (see Fig. 7.3). The flow reaches the center of the valve where the trim (seat and plug) is located. Then the flow makes a 90-degree turn toward the seat, followed by

363

Valve application and selection

Actuator force

Seals Bonnet Body Valve plug Fluid flow - Pressure P1

Pressure P2 Valve seat

Differential pressure (DP)

FIG. 7.3 Flow path in a T-pattern globe valve.

another 90-degree turn to the outlet port. These two 90-degree flow turns plus the narrow flow path in the center of the valve below the plug create a substantial pressure drop in the valve. There is a narrow area (vena contracta) in the center of the valve where the pressure is minimal and the velocity is at a maximum. The pressure at the narrow area below the plug can drop below the vapor pressure of the liquid in a globe valve used in liquid services. This causes an effect called flashing, where the bubbles of the gas are vaporized from the liquid. The bubbles will recover the pressure and collapse firmly in a way that they create pressure waves. Consequently, the pressure waves cause damages to the seat, plug, and body of the valve. This phenomenon is called cavitation. In addition, the stop check globe design (Fig. 7.4) work like a globe valve with the added ability to open or close the flow inside the piping system. It also shuts automatically if there is a pressure drop in the line and prevents backflow in the same manner as a check valve. Stop check globe valves are usually available in sizes from ½00 to 2400 and all the ASME pressure classes. A stop check globe valve has the same figure as a globe valve, which can be made in a T-type, V-type, or angle type. This design has been accomplished by changing the stem-to-disk attachment. During operation, the disk is guided by the stem and the stem can push the disk closed but not pull it open. Then the disk is opened by the force of the fluid flow. When pressure drop occurs and the flow of the liquid reverses, the disk falls down to close the valve. This design is more complicated than making a conventional globe valve. An angle globe valve (Fig. 7.5) is a globe valve with just 90 degrees of fluid rotation. This valve was originally designed for a boiler’s outlet where the steam line comes out vertically

FIG. 7.4 Stop check globe valve.

365

Valve application and selection

HANDWHEEL STEM BONNET

DISK

SEAT

FIG. 7.5 Angle globe valves.

366

7. Globe valve applications and design

from the boiler and needs to be rotated 90 degrees. Using this valve eliminates the need for using an elbow to change the piping route. Fig. 7.6 illustrates the simulation of the flow passage from an angle globe valve. Needle valves (Fig. 7.7) are similar to globe valves, but they are specialized for throttling and flow control in small sizes. The closure member is a needle-shaped disk and the stem and disk are usually in one piece. The distinguishing characteristic of a needle valve is the long, tapered needle that acts as a disk. The valve is usually available in screwed and socket weld ends, with various types of tube connections. The main disadvantage of this valve is that it can cause a high-pressure drop since it is small in size and has a great risk of clogging due to the entrance of solids into the flow of fluid. The main advantage of needle valves is that they are suitable for applications where a very precise flow regulation is required. Globe valves have some disadvantages: 1. Flow passage is only in one direction from under the disk. Reverse flow can cause wearing and mechanical damage. 2. The pressure drop through a fully open globe valve is much higher than a gate valve. 3. A globe valve does not perform well in dirty services. 4. A globe valve is larger and heavier than most other types of the valves. 5. The required force and torque for opening and closing a globe valve are relatively high. Also, globe valves are torque-seated valves and cannot achieve a tight shutoff (TSO) in the closed position. Globe valves that are designed for throttling may not be excellent for on/off purposes. The seat and disk can become unevenly eroded so they will not provide good sealing together. However, if the erosion on the seat and disk are equivalent, it may be

FIG. 7.6 Flow simulation in an angle globe valve.

Globe valve operation problem: Cavitation

367

Handle • Is available in black aluminum bar, stainless steel bar, and block phenolic knob.

Locking Nut • prevents packing bolt from loosening.

Stem Threads • are rolled and hard chrome - plated for maximum service life

Metal Seal Bonnet - to - body Construction • Ensures safety.

Rugged Body • is available with straight and angle pattern.

Back Sealing • provides anti - blow out of stem.

Variety of End Connections • Include Ve - Lock tube fittinfs, Male / female NPT threads, Male / female ISQ threads, and socket weld Ends.

Variety of Orifice Sizes • Include 4.0mm (GBI series), 6.4mm (GB2 series), 11.0mm (GB# series).

Variety of Stem Tips • include non - rotating Vee(standard) non - rotating boil, non - rotating soft seat, and regulating tip.(optional)

FIG. 7.7 Needle valve.

possible to use globe valves for on/off applications. But excellent sealing cannot be expected, and the leak rate is as per API 598 standard. The allowable leakage rates based on API 598 are higher than most of the leakage rates given in ISO 5208. There is an arrow on the body of a globe valve indicating the preferred flow direction from under the disk in which the valve is intended to be installed. Flow direction above the disk in a globe valve creates more pressure drop and reduces Cv value by 20%, which increases the cavitation risk. A blowdown globe valve (angle valve) in which the pressure drop is not an issue may have flow direction from the top of the disk. A continuous blowdown globe valve is an angle valve. The other consequences of the above-the-disk flow direction include more stress on packing, higher torque value required to open the valve, and a greater risk of the stem and disk disconnection.

Globe valve operation problem: Cavitation Cavitation can create irregular pits and erosion in the trim (seat and plug), the body of the globe valves, and downstream piping. Fig. 7.8 shows the cavitation damage in the form of small pits very similar to the corrosion damage in the plugs of globe valves. Cavitation intensifies the effect of corrosion, which could be called “cavitation corrosion.” Fig. 7.9 shows a major cavitation attack in the form of pits on the plug-sealing areas in a globe valve. The valve has lost its sealing capability when the plug is sitting on the seat due to cavitation.

368

7. Globe valve applications and design

FIG. 7.8 Cavitation damage in plugs of the globe valves.

FIG. 7.9 Cavitation attack to a globe valve plug on sealing areas.

Cavitation can produce excessive noise and vibration and create localized stresses (loads) on the valve bodies in addition to pit, corrosion, and erosion. Vibration and noise due to bursting the bubbles reduce the globe valve efficiency. Vibration and noise are considered as secondary concerns of cavitation after material damage. Cavitation does not necessarily create damage. The severity of the cavitation damage depends on the following parameters: 1. Pressure drop: A higher-pressure drop increases the cavitation effect. T-type globe valves and high-pressure class valves are severely exposed to cavitation because of the high value of pressure drop. For example, the maximum pressure drop of a class 150 globe valve is 20 barg, whereas pressure class 600 can give a maximum pressure drop of approximately 100 barg. 2. Leakage: Leakage is the movement of the fluid from the high-pressure area to the low-pressure area. This pressure drop intensifies the cavitation risk, especially when the valve is closed. 3. Material: Harder materials are less vulnerable to cavitation damage. 4. Valve size: Cavitation can be more severe in larger size valves. 5. Trim design: “anticavitation” or “multistep” trim design reduces the cavitation effect. 6. Flow Regime: Turbulent and high-velocity flow increases the risk of erosion and cavitation.

Globe valve operation problem: Cavitation

369

There are some solutions to reduce the risk of cavitation: 1. Anticavitation trim: There are different anticavitation trim designs offered by major valve suppliers including Fisher, Bonney Forge, etc. A multistep trim design creates pressure drop in two or more stages to avoid a high-pressure drop in one stage. The other advantage of the multistep trim design is to have high-pressure drop away from the seat-and plugsealing areas. A multistep trim design in globe valves significantly reduces the effect of cavitation and noise on the trim (seat and plug) (see Fig. 7.10). 2. Hard trim materials: Hard trim materials such as Stellite 6 (UNS R30006) or Stellite 21 as a form of solid or overlay and 13% chromium martensitic stainless steels including UNS S41000 or 415000 have higher resistance against cavitation. Stellite 6 or 13Cr stainless steel is not recommended for corrosive seawater services, so Ultimet or Tribaloy hard facing should be applied. Free oxygen seawater service is categorized as noncorrosive. 3. New globe valves standard: American Petroleum Standard (API) has released the first edition of the new globe valve design standard (API 623) to control and avoid operation problems in globe valves such as cavitation, vibration, and leakage. The API 623 standard has specified hard facing on both seat and plug and guided disk, especially for high-pressure classes (see Fig. 7.11). Stem diameter in API 623 follows the principles of API 600, “Cast Steel Gate Valves Standard,” with different values. The stem diameter values in API 623 are larger than other globe valve standards like BS 1873, to avoid stem and plug separation (breaking). API 602 and ISO 15761 cover globe valves for sizes up to and including 400 . BS 1873 is the globe valve standard.

FIG. 7.10 Multistep trim design.

FIG. 7.11 Guided disk globe valve.

370

7. Globe valve applications and design

4. Alternative Valve Selection: More costly Y-pattern globe valves (Fig. 7.12) or axial on-off/ control valves (Fig. 7.13) are good alternatives or traditional T-type globe valves. An axial on/off valve is operated manually and an axial control valve is actuator operated. Y-pattern globe valves provide much less pressure drop compared to conventional globe valves due to a more streamlined flow path, and they create less cavitation risk.

FIG. 7.12

Y-type globe valves.

FIG. 7.13

2800 CL1500 Axial control valve ASTM A352LCC body valve (Manufacturer: Petrol Valve).

Body/bonnet design

371

An operator company such as Statoil selects Y-type globe valves for 300 size and less for throttling purposes instead of a T-type globe valve. A Y-type pattern globe valve has more Cv value compared to a straight pattern globe valve and can be used in both flow directions. Y-type globe valves have a different direction of operator access from 45 degrees, unlike the standard 90-degree access of straight pattern globe valves. However, Y-type globe valves may not be a good option for throttling in larger sizes because they have a higher cavitation risk. Axial valves are good replacements for globe valves with no chance of cavitation. Axial valves (Fig. 7.13) are anticavitation because of the following reasons: Low-pressure drop. Short stroke for opening and closing in order to achieve high flow and quick closing. No contact between disk and seat during opening-closing stroke. Sealing is not directly exposed to throttling that gives long life tight seal. Pressure balance disk or piston (equal pressure across the disk or piston) reduces the torque and time of opening and closing for operating the valve. 6. Axial on-off valve especially with the metal seat can be opened against full delta P without any problem with socking out of the seat. 1. 2. 3. 4. 5.

Regarding the working principle, valve disk slides to open or close by means of 90-degree rack transmission (piston rod housing) between the piston rod and stem through teeth on both the stem and the piston rod. The teeth have high tolerance so there is no play between the valve stem and piston rod. The expected leak rate of these valves is low and could be leak rate B as per BS5208 standard as an example. Fig. 7.14 shows the rack and pinion design for axial valves. Axial on-off valves are more expensive than globe valves but can save some money since they have high Cv and makes size reduction. In conclusion, cavitation is the major operational problem in conventional T-type globe valves. Selecting hard trim materials such as Stellite, anticavitation trim such as multistep type, and applying API 623 standard are recommended for designing the T-type globe valves. However, selecting better valves such as Y-type globe or axial valves (Fig. 7.15) are also good solutions to reduce or avoid cavitation risk. Axial on-off valves are manually operated with a fast closing and opening actions which makes them suitable options for fast opening applications. Unlike axial and butterfly valves, ball and through conduit gate valves are not suitable for fast opening applications. Axial valves are bidirectional that are produced up to maximum 4800 and pressure class 2500 by some manufactures. Axial control valves are like axial on-off valves with actuator operation with on/off functions. The actuator is linear spring return hydraulic or pneumatic. The valve has split body construction, as shown in Fig. 7.16. The other example of the axial control valve (axial valve with an actuator) is the bypass of a control valve where very quick opening (e.g., 0.3 s) is needed as shown in Fig. 7.17. The bypass valve is just used for on-off purpose since the axial control valve cannot do throttling.

Body/bonnet design The body, sometimes called shell is the preliminary pressure containing part of the valve. The body of the valve is the main part of a valve assembly because it is the framework that

372

FIG. 7.14

7. Globe valve applications and design

Axial valve rack and pinion design developed by Goodwin.

holds all the other parts together. Body should be strong enough with adequate thickness to withstand fluid pressure loads coming from the connecting piping. The valve bodies should be integrated and either casted or forged. Forged body valves (Fig. 7.18) are common for small size valves. However, forged body valves can be selected for the larger size valves. Some manufacturers may use an open-die forging manufacturing method for gate and globe valves, which makes gate valves more expensive. Open-die forging is a process in which the forged component is partially forced between two dies. The die pressure increases the length and reduces the cross-section of the component. Die forging is required more often for longer components such as the shaft and bonnet of gate and globe valves. It improves the microstructures and strength. Open-die forging requires a high amount of machining, which

Body/bonnet design

373

FIG. 7.15 Axial on-off valve internals. Courtesy: Mokveld.

FIG. 7.16 Axial control valves.

makes this process costly. Forging by press or hammering applies high forces in different directions to the material microstructure, which makes the forging material stronger than casting. Rounded, square, and hexagonal bar stock/billet is usually formed in one direction, so it is not as strong as forging. When bar stock is forged or rolled, it could result in further forming in other directions and achieving the same strength as forging.

374

7. Globe valve applications and design

FIG. 7.17

Control valve and axial bypass.

FIG. 7.18

Forged body valves. Courtesy: Bonney Forge.

The common assumption that “high strength of forging increases its resistance against stress cracking corrosion (SCC) and fatigue compared to bar and cast” is incorrect. Having a higher stress level above the stress threshold of the material does cause SCC. However, controlling and limiting the hardness is one of the SCC risk reduction precautions. Bar material for the body of the valve as a pressure-containing part is considered and may be applied for

Body/bonnet design

375

rush delivery orders. Bar material should be tensile strength tested in both longitudinal and transverse directions based on end user requirements. Forging is more expensive than bar and casting. Casting (Fig. 7.19) requires less machining than forging, so there are a faster delivery time and lower cost. Casting is possible for more complex shapes than forging (see Fig. 7.20). Fig. 7.21 shows a nondestructive test (NDT) called liquid penetrant inspection (LPI) on the valve body after machining. Testing is done after machining or welding. There are three liquids used in a LIP. The first one is a red color that is called a penetrant. The second one is the

FIG. 7.19 Casted body valves.

FIG. 7.20 Body of the valves after machining. Courtesy: Bonney Forge.

376

7. Globe valve applications and design

developer in a white color that reveals the cracks. The last one is cleaner. The LPI is applied according to ASTM E 165 standard. The bonnet is the covering of the valve body open part. The bonnet is usually the second pressure-containing part. The bonnet is cast or forged with the same material as the body. Fig. 7.22 shows the assembled bolted body/bonnet together in duplex material. The body of valves can be created from bar material (Fig. 7.23) in some cases. For example, valves can be made from bar instead of forge for sizes up to and including 400 to shorten the delivery time. All bars should have a 100% LPI or magnetic particle test, tensile test in both longitudinal and transverse directions, and be EN ISO 10204 3-2 certified (full traceability). The American Society of Test and Materials (ASTM) creates high quality, market-relevant international standards used around the world to improve product quality. ASTM A479 is

FIG. 7.21

Liquid penetration test on the valve body after machining. Courtesy: Bonney Forge.

FIG. 7.22

Body/bonnet assembly. Courtesy: Bonney Forge.

Body/bonnet design

377

FIG. 7.23 300 Class 150 Gate valve (body made of bar). Courtesy: Bonney Forge.

the standard bar material for stainless pressure-containing body valves. ASTM A276 is the stainless steel bar material used for gland of the valve. Valves with square-shaped bodies are usually made of bar material. According to API 600 and 602, the body and bonnet of gate valves should be secured through one of the following methods: -. -. -. -.

Bolting (Fig. 7.24) Welding (Figs. 7.25–7.27) Threaded with a seal weld Threaded union nut for pressure classes of maximum 800

Welded body-and-bonnet globe valves, like gate valves, have less chance of leakage and are more compact (shorter). But there is no access to the valve internals and the valve should be replaced in case of internal failures. Body-and-bonnet bolts for gate and globe valves can be stud bolts with one hexagonal head nut on one side or a machine bolt. The bolt does not need to pass completely through the body-and-bonnet holes, provided that the bolt length is at least 7/8 the length of the bolt diameter, as per ASME B31.3. Machine bolts can be used for gate and globe valve body-andbonnet connections (see Fig. 7.28A–C). But corrosion wise, it is a good idea to fill the hole in with silicon to avoid external corrosion of the valve in the offshore industry. End flanges should comply with the dimensional requirements given in ASME B16.5 and ASME B16.47. Flange faces can be raised face, ring type joint, and flat face. The recommended end and bonnet flange connections are integrated forge or cast with the body.

378

7. Globe valve applications and design WHEEL NUT HAND WHEEL

STEM NUT

GLAND FLANGE GLAND BUSH GLAND PACKING BACK SEAT BOLT-NUT BONNET GASKET STEM DISC NUT DISC

SEAT BODY

© www.jdvalves.com

FIG. 7.24

Bolted body-and-bonnet globe valve.

FIG. 7.25

Welded body-and-bonnet globe valve.

Body/bonnet design

FIG. 7.26 Welded body-and-bonnet globe valve.

FIG. 7.27 Welded body-and-bonnet globe valves. Courtesy: Bonney Forge.

379

380

FIG. 7.28

7. Globe valve applications and design

(A–C) Lack of body-and-bonnet bolting engagement in a globe valve. Courtesy: Bonney Forge.

381

Face-to-face standard

MANUAL BLOW DOWN VALVE

SPEC BREAK FLARE

LOW TEMP. SYSTEM TO BE BLOWN DOWN

FIG. 7.29 Manual blowdown for maintenance purpose.

There are cases in the offshore industry on manual blowdown valves (for example) in which the pressure drop in the globe valve causes the temperature to drop below 46°C, and the 22Cr duplex material is not suitable for this application. In that case, the globe valve and downstream part to the gate valve should be constructed in 6MO material, as illustrated in Fig. 7.29. In some cases, the class break is not on a flange, so 6MO will be welded to the duplex material. Carbon steel body valves in Class 600 and above, with a ring-type joint flange face and sizes 400 or 600 and above, are overlaid with alloy 625 on the flange face grooves, seat, and stem seal pockets to avoid crevice corrosion. Ring-type joint, body, and bonnet connections in pressure class 600 as a minimum in carbon steel material are also overlaid with alloy 625. The reason why the smaller sizes 300 and below are not overlaid is that they are not economically worth the cost of applying weld overlay. In addition, applying weld overlay on smaller sizes is more difficult. For example, in one project to change the materials of ball valves to 22Cr duplex from carbon steel for sizes 300 and below, it was more difficult and expensive to apply Inconel 625 on carbon steel than to simply change the material to duplex. In cases such as this, valve internals (trim) should be upgraded to duplex. If the seat is pressed and not welded, the weld overlay on the seat and closure member, as well as alloy 625 overlay on the seat and seal pockets and RTJ flange grooves in carbon steel body materials, are the only welds on gate and globe valves. The other welding is welding repair on casted bodies. Weld repair is not accepted on the forging body of the valves.

Face-to-face standard Face-to-face dimensions for flanged-end valves should be based on the ASME B16.10 standard for “face-to-face and end-to-end dimensions of valves.” The purpose of this standard is to assure installation interchangeability for valves of any given material, type, and size, rating them by class and end connection. The classification “end-to-end” is used for those flanged valves where the gasket contact surfaces are not located at the extreme ends of the valve, such as raised face flange end (Fig. 7.30) and ring-type joint flanges (Fig. 7.31). As per ASME B16.10,

382

7. Globe valve applications and design

FIG. 7.30

Raised face flange end bolted body-and-bonnet globe valve.

FIG. 7.31

Ring-type joint flange face globe valve.

a tolerance of 2 mm should be allowed on the face-to-face and end-to-end dimensions of valves of 1000 and smaller, and tolerance of 3 mm should be allowed for 1200 and larger. The end-to-end/face-to-face dimensions for piston check, swing check, and globe valves are equal. Face-to-face measurements of globe valves are defined up to and including 1600 in pressure class 150 and up to and including 1200 in pressure class 300 in ASME B16.10. Some vendors may give face-to-face dimensions of a swing check valve for the globe valves in sizes and pressure classes not covered by ASME B16.10.

Wall thickness

383

FIG. 7.32 Face-to-face measurement of a globe valve during inspection. Courtesy: Bonney Forge.

Fig. 7.32 shows the face-to-face measurement of a globe valve in a forged 22Cr duplex during the inspection.

Bore design API 602 Gate valves can be either full-bore or standard bore (reduced bore). Both full and standard bore have minimum bore diameters less than the nominal valve size. Wedge-type gate valves in the standard bore can be defined for bore sizes 200 and below in all pressure classes except for CL2500, as per API 602. Gate valves have equal thicknesses and minimum bore diameters (both for full bore and standard bore) in all pressure classes of 150, 300, 600, and 800, as per API 602. The minimum bore diameter is larger for gate valves than globe and piston check valves in CL1500 in API 602. The bore diameters of gate valves in CL2500 as well as API 600 gate valves are according to ASME B16.34. The minimum bore diameter (flow passage) is 90% of the inside diameter of the valve end as per ASME B16.34 standard. Table 7.1 gives the minimum diameter of the flow passageway for full-bore gate, globe, and check valves based on the API 602 standard. It is not possible to inspect the inside bore diameter of gate, globe, and check valves in small sizes. As an example, a 200 CL1500 standard bore gate valve has a 50 mm bore at body flange connections that are reduced to 34 mm as per API 602. It is not possible to measure a bore reduction of 34 mm. Table 7.2 gives the minimum diameter of flow passageway for standard bore gate, globe, and check valves based on the API 602 standard.

Wall thickness The body-and-bonnet wall thicknesses given in API 600 and API 602 are greater than the wall thickness values given in ASME B16.34. The wall thickness values given in API 602

384

7. Globe valve applications and design

TABLE 7.1 Minimum diameter of equivalent flow passageway for full bore gate, globe, and check valves based on API 602. Minimum diameter in. (mm) Class 150, class 300, class 600, class 800

Class 1500

NPS

Gate, globe, or check valves

Gate valves

¼

¼ (6)

¼ (6)

⅜

⅜ (9)

⅜ (9)

½

½ (12)  11 16 ð17Þ  15 16 ð22Þ

½ (12)

¾ 1 1¼

⅝ (15) ⅞ (22)  1 1 16 ð26Þ

1½

1 ⅛ (28)  1 7 16 ð35Þ

1 ⅜ (34)

2

1 ¾ (44)

1 ½ (38)

2½

2 (50)

1 ⅞ (47)

3

2 ¾ (69)

2 ½ (63)

4

3 ¾ (95)

3 ⅝ (92)

Globe or check valves  3 16 ð4Þ  5 16 ð7Þ ⅜ (9)  9 16 ð14Þ  13 16 ð19Þ

DN 8 10 15 20 25

1 (25)  1 1 16 ð29Þ

32

1 ⅜ (34)  1 11 16 ð42Þ  2 5 16 ð58Þ  3 7 16 ð87Þ

50

40

65 80 100

TABLE 7.2 Minimum diameter of equivalent flow passageway for standard bore gate, globe, and check valves based on API 602. Minimum diameter in. (mm) Class 150, class 300, class 600, class 800

Class 1500

NPS

Gate, globe, or check valves

Gate valves

¼

¼ (6)

¼ (6)

⅜

¼ (6)

¼ (6)

½

⅜ (9)

⅜ (9)

¾

½ (12)  11 16 ð17Þ  15 16 ð23Þ

½ (12)

1 1¼ 1½

⅝ (15) ⅞ (22)  1 1 16 ð27Þ

2

1 ⅛ (28)  1 7 16 ð36Þ

1 ⅜ (34)

2½

1 ¾ (44)

1 ½ (38)

3

2 (50)

1 ⅞ (47)

4

2 ¾ (69)

2 ½ (63)

Globe or check valves  16 ð15Þ  3 16 ð15Þ  5 16 ð8Þ 3

⅜ (9)  16 ð14Þ  13 16 ð20Þ 9

DN 8 10 15 20 25 32

1 (25)  1 1 16 ð27Þ

40

1 ⅜ (34)  1 11 16 ð42Þ  2 5 16 ð58Þ

65

50

80 100

385

Seat design

TABLE 7.3 Minimum wall thickness for gate, globe, and check valve bodies, bonnet, and check valves based on API 602. Minimum wall thickness in. (mm) NPS

Class 150, class 300, class 600, class 800

Class 1500

DN

¼

0.12 (3.1)

0.15 (3.8)

8

⅜

0.13 (3.3)

0.17 (4.3)

10

½

0.16 (4.1)

0.19 (4.8)

15

¾

0.19 (4.8)

0.24 (6.1)

20

1

0.22 (5.6)

0.28 (7.1)

25

1¼

0.23 (5.8)

0.33 (8.4)

32

1½

0.24 (6.1)

0.38 (9.7)

40

2

0.28 (7.1)

0.47 (11.9)

50

2½

0.33 (8.4)

0.56 (14.2)

65

3

0.38 (9.7)

0.65 (16.5)

80

4

0.47 (11.9)

0.84 (21.3)

100

(Table 7.3) are applicable for the body and bonnet of gate and globe valves plus covers of check valves. Class 900 is not given in the tables since that is not a common pressure class for a piping system. In addition, class 900 and 1500 flanges are the same for small sizes 200 and below. Therefore, all the valves in class 900 and sizes 200 and below are ordered in class 1500.

Seat design Seat design can be integral or renewable. Integral seat design means that the seat is integrated with the body and made from the same material. This design is the standard seat design of many manufacturers. Renewable seat ring construction provides seats that are either threaded into position or pressed and seal-welded to the valve body. Integral seats have the same material of construction as the valve body. On the other hand, the pressed or threaded seats are made from different materials compared with the valve body. It is very common to select small, forged gate valves with hard-faced seats pressed into the body. Repairing the seat can be a cold repair through lapping with diamond paste and lapping plates if the seat defect depth is less than 0.8 mm and the size is a minimum of 100 or larger. However, the valve should be removed from the line and sent back to the vendor shop for weld repair for more serious defects. Before placing the seats into the valve body, it is essential to be sure that all the surfaces on the body and seats are clean and free of foreign matters during maintenance. Body seating surfaces should not have sharp corners with an edge that may

386

7. Globe valve applications and design

cause damage in conjunction with gate or disk seating surfaces. The inside diameter of the body seat flow passageway should be in accordance with API 600 and 602 standards. Special care should be taken to provide hardness difference between the seat and the wedge, to avoid wearing and galling. Machining on the seat sealing should be controlled to ensure perfect sealing. Fig. 7.33 shows the seat and disk (plug) contact design in a globe valve. A swivel plug or a free-rotating plug avoids having contact between the plug and the seat at one point all the time. Contact between the plug and the seat in different areas can reduce the damage and erosion of the plug. Erosion can be distributed in the plug evenly, which reduces the leakage over time. The wedge/disk and the seat of gate and globe valves should have different harnesses to avoid galling between seat and closure members as well as to provide better sealing. Hardness difference is not required if both seat and wedge are hard faced with a material such as Stellite. Common seat materials for valves in the offshore industry are 13Cr for a carbon steel body, 316SS for a stainless steel body, 22Cr duplex for a 22Cr duplex body, and alloy 625 for a 6MO body. Stellite 6 overlay on 22Cr duplex can be done through buttering of alloy 625 to avoid sigma phase. Stellite 6 overlay on 6MO is challenging because nitrogen in 6MO can produce nitrogen carbide when applying Stellite 6. Thus, alloy 625 instead of 6MO can be selected for the seat and closure members of 6MO body valves. In the Norwegian offshore industry, 25Cr super duplex body valves with 25Cr super duplex trim are used in seawater services with operating temperatures below 20°C and also in seawater services with oxygen less than 20 parts per billion as per Norsok M-001, Material Selection Standard. First, applying Stellite 6 on 25Cr super duplex is risky due to the high risk of sigma phase formation without an alloy 625 buttering layer. Second, Stellite 6 corrodes in seawater services. The first solution to these problems is to avoid hard facing on 25Cr super duplex since it is a hard material. The second solution is to apply Ultimet hard facing (54%Cb-26%Cr-9%Ni-5%MO) or Tribaloy 800 (50%Cb-30%Mo-20% Cr). Nitride is applied on a titanium seat and closure member for hard facing. An alternative solution is making the seat from harder titanium grade (Gr.5) and the closure from titanium in grade 2.

PLUG (Spherical seating surface)

SEAT RING (Conical seating surface)

FIG. 7.33

Seat-and-plug design in a globe valve.

387

Stem design

Stem design Stems are designed as either inside screw or outside screw. Globe valves are usually outside screw and yoke with a rising stem and either a rising or nonrising handwheel. If the stem is rotating, then the handwheel can be rising or nonrising. Extending the yoke sleeve/stem nut to the area between stem and handwheel makes the stem rise through the handwheel, so the handwheel is nonrising. In both cases, more torque is required and less packing life is achieved. A nonrising handwheel is designed to avoid changing the operator’s access to the handwheel. Fig. 7.34 illustrates an OS&Y rising stem globe valve in open and closed positions. Disk (lock) nut or bushing is usually used to lock and connect the stem to the disk for globe valves in sizes above 200 that have trim material. The disk is threaded internally and connected to a threaded stem nut. The other weaker stem-to-disk connection without a stem nut is created with wires. The disk nut or bushing, or guided disk, ensures that the disk will not deflect and causes uneven seat wear and leakage as well as the removal of the disk from the stem, which can completely close the flow path or cause the disk to be removed from the flow path. A disk nut or guided disk avoids stem bending as well. In Fig. 7.34, the disk (lock) nut is

13

14

12

10

11 9 2 7

8 6

5

4 3

1 Rising stem “closed”

FIG. 7.34 OS&Y rising stem globe valve.

Rising stem “opened”

388

7. Globe valve applications and design

number 5 and the stem nut or yoke sleeve is number 13. The yoke design including the yoke sleeve will be explained later in this chapter. The combination of a stem T-shoulder and disk nut on the tee shoulder and threaded to the disk creates a robust connection of stem to disk. For the nonrising stem globe valve, the stem is threaded onto the lower end into the disk. This design is also called “inside screw and yoke.” As the handwheel on the stem is rotated, the disk travels up and down on the threads while the stem remains vertically stationary. A nonrising stem globe valve (Fig. 7.35) is not common in the oil industry since the stem threads are created in the pressure boundary with a high risk of crevice corrosion due to contact with the fluid. On the other hand, rising stem globe valves are designed in a way that the stem is raised out of the flow path when the valve is open. Fig. 7.36 shows an OS&Y globe valve in 400 class 300 for manual operation on the bypass line of a control valve.

FIG. 7.35

Nonrising stem in a globe valve.

FIG. 7.36

Rising stem OS&Y globe valve.

Stem design

389

The threads in contact with the corrosive offshore environment are at high risk of corrosion. Therefore, a plastic cap (shown in Fig. 7.37) can be installed on the handwheel and its nut. The plastic cap is mainly installed on the valve handwheel for indicating the position of the valve (position indicator). The rising stem goes up during the opening and moves down during the closing inside the cylinder so it is possible to distinguish how much the valve opens or closes.

FIG. 7.37 Position indicator on the globe valves. Courtesy: Bonney Forge.

390

7. Globe valve applications and design

The stem (Figs. 7.38 and 7.39) should be a one-piece design, and no fabricated welding is permitted. The stem surfaces should be less than 32 μin. roughness as per API 600 and 602 standards, especially in contact with the packing to avoid packing and stem friction. Therefore, a fine surface finish of the stem is necessary, especially in the area of the packing. A rotating stem design on a globe valve increase the torque of the valve by 15%–25%. The reason is that there is more friction between the packing and a rotating stem than that between the packing and a nonrotating stem. Fig. 7.40 shows how supporting a stem in a globe valve through two plates that are bolted prevents stem rotation and improves the packing life. A nonrotating stem can increase the packing lifetime and provides a better design for fugitive emission purposes. Fugitive emission is done more often for valves in H2S services, but perhaps 60% of the fugitive emissions are related to rotating stems and rising handwheels.

FIG. 7.38

A globe valve stem. Courtesy: Bonney Forge.

FIG. 7.39

A globe valve stem passing through the yoke. Courtesy: Bonney Forge.

Yoke design

391

FIG. 7.40 Supporting the valve nonrotating stem.

One disadvantage of a rising stem for linear movement of a globe valve is that the stem THDs can become corroded in the atmosphere, especially if the valve remains open for a long period of time. The threaded parts of the stem in an OS&Y globe valve will be in contact with a marine atmosphere that could be subject to crevice corrosion. Stem extension (e.g., 300 or 400 mm height from the center of the valve to the handwheel nut) could be required for gate and globe valves in order to provide access levels to the handwheel of the valves. But extension coupling around the stem was required in one project for gate and globe valves due to not having a circular yoke arrangement. (More information will be provided in “Insulation-Friendly Design” section, later in this chapter.) 17-4 PH martensitic stainless steel can be used as the stem material for carbon steel body valves, mainly in the onshore industry. However, this material is avoided in offshore due to the risk of external stress cracking corrosion, although there is a small stem area that is exposed to the marine environment. Alloy 718 is the alternative stem material with the highstrength property. F6NM (UNS S41500) 13Cr-4Ni stainless steel stem material should be fine for an external chloride-containing environment for carbon steel body valves. 17-4 PH in sour services should have a maximum of 33HRC hardness as per ISO 15156 standards. The tensile and yield values in KSI through double tempering heat treatment to satisfy ISO15156 requirements are: H1150M Heat Treatment (115Ksi Tensile, 75Ksi Yield) H1150D Heat Treatment (125Ksi Tensile, 105Ksi Yield) Valves in 6MO body materials can have a stem in a bar shape of ASTM A479 UNS S31254. However, the seat and closure member can be upgraded to Alloy 625, ASTM B446 UNS N06625, to be easily overlaid by Stellite 6.

Yoke design Although API 600 allows the yoke to be a separate part of the bonnet, it is common to have an integrated bonnet and yoke made from the same material as shown in Figs. 7.41 and 7.42.

392

7. Globe valve applications and design

FIG. 7.41

Yoke design.

FIG. 7.42

Yoke of globe valves. Courtesy: Bonney Forge.

As with gate valves, the yoke sleeve (stem nut) should be lubricated since it is in contact (friction) with the stem and exposed to the high temperature produced between the bonnet, yoke, and stem during valve operation (see Fig. 7.43). A yoke sleeve or stem nut is an internally threaded nut that is placed at the top part of the yoke where the stem passes through it. The yoke nut has threads engaged in stem threads, which facilitate traveling up and down of the stems. Although it is lubricated, it is usually made from low-friction material such as nickel aluminum bronze to avoid galling the stem. Lubrication of the yoke sleeve is done through a grease nipple on the yoke made from 316SS material. The grease nipple should be protected with a plastic cap (see Fig. 7.44).

393

Back seat design Stem

Handwheel Yoke Yoke bushing

FIG. 7.43 Detail of yoke bushing.

FIG. 7.44 Grease injection nipple plastic cap in red color (gray in print version). Courtesy: Bonney Forge.

Back seat design Back seat or back seat bushing is typically designed for gate and globe valves (item number 4 shown in Fig. 7.45). The back seat is the seating arrangement in the body of the valve. This component provides a seal between the stem and bonnet and prevents fluid pressure from building against the valve packing. The advantage of back seat bushing is minimizing the leak through the stem if there is something wrong with the packing and the valve is off seat.

394

FIG. 7.45

7. Globe valve applications and design

Typical stem sealing arrangement.

Packing design A gland should be provided for packing compression (illustrated as item 2 in Fig. 7.45). The gland can be either a self-aligning gland or an integral part of the gland flange. Gland material should be made from the same material as the trim. It could be made of stainless steel bar as per ASTM A276 standard—for example, used for a carbon steel body valve in a refinery or petrochemical plant. The gland flange is item number 1 in Fig. 7.45. Gland flange bolts (Fig. 7.46) can be eye bolts, stud bolts, or studs. Gland flange bolts may be supplied with springs (Fig. 7.47) or Belleville washers to provide constant force on the gland, to avoid gland loosening, and to

FIG. 7.46

Gland flange.

Packing design

395

FIG. 7.47 Spring-loaded gland flange.

maintain the packing load over time. Gland flange material is not in contact with the fluid, but it should be made from the same material as the body material (e.g., 22Cr duplex for 22Cr duplex body valves). API 603, the standard for gate valves in nickel and stainless steel (corrosion-resistant alloys), specifies 316 stainless steel for gland flange material or the same as the shell. API 603 covers the valves for sizes 2400 and below and maximum pressure class 600. A SS316 gland flange may be accepted for a nickel aluminum bronze (NAB) body gate and globes valve with an NAB gland flange in onshore plants. Galvanic corrosion should not happen since the NAB gland forms aluminum oxide that protects the NAB gland. Packing is usually layers of graphite rings (Fig. 7.48) used between the stem and bonnet to prevent leakage from the stem and maintain the sealing. Packing also forms a sealing between the valve internal parts and outside when the stem is up and the valve is open. Valve packing must be properly compressed to prevent loss and damage to the valve stem. If the packing is too loose, the valve will leak. If the packing is too tight, it will damage the stem, create friction, and increase the leakage possibility. Packing should be replaced (Fig. 7.49) if there is still leakage from the packing even after the excessive tightening of the gland bolts. Some operator companies never trust back seat bushing during packing replacement, especially in high-pressure classes when the valve is in service. The MSS SP 42 standard for the corrosion-resistant gate, globe, angle, and check valves does not recommend repacking the valve when the valve is in service. It is recommended to isolate and depressurize the valve during the repacking, and not advised to take the valve out of the line during simple

FIG. 7.48 Layers of packing graphite.

396

FIG. 7.49

7. Globe valve applications and design

Packing replacement.

repacking. Repacking a gate or globe valve includes removing gland bolts and nuts, lifting the gland flange and gland out of the stuffing box, removing the old packing rings, cleaning the stem and stuffing box, examining them to ensure there is no damage, and finally installing the new packing rings. Tightening the gland bolts compresses the packing rings and stops the leakage. The risk is overtightening the gland bolts with torque values exceeding the values given in the installation, operation, and maintenance (IOM) manual provided by the valve supplier. Overtightening causes high stem and packing friction and ultimately packing leakage. Loosening the gland bolts to decompress the packing and reduce the stem friction leads to constant packing leakage. According to section 5.9.3.1 of ASME B31.3, “Process Piping,” leakage through stem seals during the shell test should not be a reason for test rejection. Gate and globe valves may leak from the packing during the shell test or hydro test after installation. Overtightening of the gland bolts to compress the packing, which is not according to the torque procedure, locks the valve. Loosening the gland flange bolts or injecting grease into the packing rings leads to constant packing leakage. Repacking could be one solution. Torque values for tightening the body-and-bonnet bolts as well as gland flange bolts with lubrication for gate valves are given in the IOM manual with plus and minus 10% tolerance. A2-70 bolts need higher torque compared to L7 and B8M bolts. 75% of bolt torque values should be applied for bolts in high-temperature applications 400°C and above. Tightening the gland packing bolts provides packing compression through the gland. The packing area should be lubricated by grease that is injected into the packing spacer through the lantern rings. Gate and globe valves have a rising and outside screw (threaded)

Packing design

397

stem that makes friction between packing and the stem. It is proposed to lubricate even flexible graphite packing, which creates lower friction to the stem compared to graphite packing. The emergency sealant can be also injected through the grease injection fitting (see Fig. 7.50) to repair the packing temporarily if the leak from the packing cannot be fixed by tightening the gland bolts. A relief plug can be installed on the other side of the bonnet (the opposite side of the lantern ring) to make sure that lubrication or sealant injection lubricates the packing completely. If the service is very corrosive or toxic, it is possible to have double packing with an injection point that contains two nonreturn ball check valves. Bellows stem sealing gate valves have a very strong stem sealing property in which bellows are welded to the stem from one side and to the bonnet from the other side. Bellows stem sealing valves do not require a back seat test (the only exception for back seat testing). It is common to have welded body and bonnet for gate and globe valves with bellows sealing to reduce the leaking of fugitive and dangerous fluids. Bellows (Fig. 7.51) is a better design for fugitive emission services. Graphite packing has a risk of pitting and crevice corrosion of the stem, especially in 25Cr duplex in seawater services because graphite is a noble material. Therefore, graphite packing should be avoided for valves in titanium and 25Cr duplex body materials in seawater services. However, some end users may accept graphite as packing for seawater since it is not the primary sealing material. One alternative packing material is PTFE (Teflon). However, valves with PTFE packing are not a fire-safe design. The alternative solution is isolating the graphite packing rings from the seawater service by a PTFE packing ring or lip seals installed at the bottom, which provides a fire-safe packing design. Some manufacturers propose using graphoil as a flexible and corrosion-resistant graphite in the seawater services. Flexible graphoil has less friction with the stem and less chance of crevice and pitting corrosion of the stem. Bolts in sizes smaller than 10 mm (mostly applicable to gland flange bolts) with operating temperatures above 60°C are prone to external stress cracking corrosion in the offshore industry, so it is better to make bolts of nickel alloy 625. Valve suppliers have proposed nickel alloy ASTM A453 Gr.660 bolts, which are 25%Ni and 15%Cr, dark gray in color, and nonmagnetic. However, API RP 14E does not recommend these bolts for the offshore environment. ASTM A453 Gr.660 is also a material selected for nuts, the same as bolts. Zinc coating (hot dip galvanizing) of small bolts is also difficult.

PLUG

INJECTOR

FIG. 7.50 Plug and injector on the packing of a globe valve.

398

FIG. 7.51

7. Globe valve applications and design

Bellows stem sealing.

Locking design Locking devices can be padlocks or chain locks, as either mechanical locks or key locks. Locking devices can be welded to the yoke (see Figs. 7.52 and 7.53) with the chain passing through the lock and fastened around the handwheel. The concept is the same as that explained in the earlier discussion of gate valves.

FIG. 7.52

Padlock welded to the yoke of a globe valve for locking. Courtesy: Bonney Forge.

Valve operation

399

FIG. 7.53 Padlock welded to the yoke of a globe valve for locking. Courtesy: Bonney Forge.

Layout considerations Globe valves may have a straight pipe requirement upstream and downstream to streamline the flow of fluid. As an example, four pieces of pipe diameter straight pipe can be taken into account at least on the upstream side of the valve. Straight pipe downstream of the valve may also be as important, or even more important, than an upstream straight pipe requirement due to the pressure recovery of possible gas bubbles that create pressure waves downstream of the valve. Just like gate valves, globe valves should not be installed with a stem below the horizontal line. Complete drainage is not possible and solids will accumulate in the bonnet that can affect the operation and service life of the valve (possibility of packing damage).

Valve operation The gear box requirement for globe valves depends on the size and rating. For example, a globe valve is gear box operated in sizes 800 and above in pressure classes 150, 600 and above in CL300, 400 and above in CL600, and 1 ½00 and above in CL1500 and CL2500. The gear box for the gate and globe valves is a bevel type and not spur. (The gear box operation will be explained in detail in a future chapter.) The handwheel in nongear box operated gate and

400

7. Globe valve applications and design

globe valves stands on the top of the valve (see Fig. 7.54). When adding a gear box, the handwheel will be located on the side of the valve as illustrated in Fig. 7.55. The gear box material could be either painted cast iron ASTM A536 or SS316 (the preferred choice in the offshore industry). The handwheel opening and closing direction is marked on the handwheel of the valves including globe valves (Fig. 7.56). The handwheel is in the form of spoke and rim. The number of rims can be three pieces in 100 size, four pieces in 1.500 size, or six pieces in larger sizes. Valve manufacturers can provide a top flange at the top of the valve for actuator installation even if the valve is not quarter turn. Fig. 7.57 at the right shows the electrical actuator installation on a globe valve with a top flange.

FIG. 7.54

Handwheel operated globe valves (handwheel on the top of the valve). Courtesy: Bonney Forge.

FIG. 7.55

Handwheel orientation for gear box operated gate/globe valves.

Valve operation

401

FIG. 7.56 Handwheel operated globe valves with opening/closing directions marked on the handwheel (Manufacturer: Bonney Forge).

FIG. 7.57 Top flange of a globe valve for electrical actuator installation. Courtesy: Bonney Forge.

402

7. Globe valve applications and design

Insulation-friendly design Gate and globe valves are insulation-friendly if the insulation is required up to the packing. The packing box is located under the yoke arrangement. However, if the yoke needs to be insulated, a stem extension may be required, since the shape of the yoke is not circular and insulation-friendly. However, some end users do not require any stem extension for gate and globe valves.

Quality control The quality control department carries out dimension check, hardness test, flatness test, roughness test, positive material identification (PMI) test (see Figs. 7.58 and 7.59), and threads checking. A PMI test is done on the valve parts to make sure that the materials have correct chemical compositions based on the certificates. Positive material identification (PMI) testing is done by some valve manufacturers on 100% of the materials, even titanium (ASTM B381 F2), including the body, bonnet, and trim received from forge masters or foundries, to make sure that the material chemical compositions are correct and based on the project requirements. The PMI tool is calibrated regularly. PMI low-stress identification is stamped on the parts after the PMI test (see Fig. 7.60). PMI extend is specified in the project specification (e.g., 20% for 316SS, 50% for 22Cr duplex, 25Cr duplex and 6MO, 100% for 25Cr duplex and 6MO in seawater, and no PMI for titanium in the offshore industry). PMI testing can be done for just pressure-containing parts (body and bonnet) or also for trim parts. PMI can be repeated after assembly of the valve on the body and bonnet to make sure that there has been no material mismatching during manufacturing and assembly. Trim materials can be PMI tested again before assembly. (There is no access to trim materials for testing after assembly.)

FIG. 7.58

PMI testing on the body of the valve. Courtesy: Bonney Forge.

Quality control

403

FIG. 7.59 PMI testing on the body of the valve. Courtesy: Bonney Forge.

FIG. 7.60 6MO body globe valve with the stamp of PMI on the right side of the valve. Courtesy: Bonney Forge.

In flatness testing (Fig. 7.61), the vertical tool touches the face of the metal and measures the location correlations. If the examined faces of the metal have the same height correlation, this means that the face of the metal is flat. The roughness test (Fig. 7.62) is done on the flange face of the valve to make sure that it is based on ASME B16.5 standard requirements. The roughness of the flange face based on ASME B16.5 is 125–250 μin. AARH (average arithmetic roughness height) equal to 3.2–6.4 μm for flat and raised face flanges. It is 64 μin. equal to 1.6 μm for ring-type joint flanges. The hardness test (Fig. 7.63) is usually performed by making a small indention in a noncritical area of a part like the flange OD and by measuring the amount of force required to make the indention. There are also NDE techniques that utilize other methodologies that do not leave indentions. The purpose of the hardness test is to ensure that the specified material and hardness as well as yield strength have been provided, and heat treated properly.

404

7. Globe valve applications and design

FIG. 7.61

Flatness testing. Courtesy: Bonney Forge.

FIG. 7.62

Roughness test.

Quality control

405

FIG. 7.63 Hardness test.

Fig. 7.64 illustrates testing the thread end of the valve with the black tool to make sure that it is based on the ASME B1.20.1 standard, “pipe thread.” A magnet is used on the bonnet flange to make sure that the body of the valve is made of 22Cr duplex (see Fig. 7.65). 22Cr duplex has magnetic properties that should attract the magnet. On the other hand, stainless steel 316 and 6MO have nonmagnetic properties and do not attract the magnet. Carbon steel has stronger magnetic properties than duplex. 22Cr duplex and SS316 are bright, unlike dark gray colored low-temperature carbon steel A352 LCC material. The bright color of 22Cr and SS316 is caused by acid pickling that is done to improve and stabilize the Cr2O3 protective layer on stainless steel. Stainless steel acid pickling is done using phosphate or submerging in nitric acid. The acid pickling should be done after machining. The Cv value is given in gal/min and the Kv value is in m3/h. Cv ¼ 1.17  Kv. Size, rating, possible material, end connection, and direction of installation affect Cv values. The Cv value is higher for socket weld and threaded connections than for flange connection valves. Valve manufacturers always give unique Cv values for the valves installed in vertical and horizontal directions. However, the flow capacities of the valves are different in horizontal and vertical directions. Fig. 7.66 shows the facilities for Cv value testing of a globe valve. The first globe valve on the left side of the photograph regulates the flow to values corresponding to 1 psi pressure drop. There are three lines for the test—one small, one medium, and one large size, with three flow meters installed on each line. The flow meters

406

7. Globe valve applications and design

FIG. 7.64

Thread end evaluation.

FIG. 7.65

Body material test with the magnet.

Quality control

FIG. 7.66 Cv test facilities and tested valve for Cv value measurement. Courtesy: Bonney Forge.

407

408

7. Globe valve applications and design

are those with blue squares (gray in print version) on the top. There is a globe valve on the yellow line (light gray in print version), which is tested to measure its Cv value. Fig. 7.67 shows the Cv value of the valve corresponding to 1373 barg equal to 20 psi approximately. The computer screen shows 0.593 gal/min Cv value or flow capacity. But the pressure should be reduced from 20 psi to 1 psi to get the correct Cv value. Therefore, the globe valve on the left side is closed gradually until the screen shows 0.067 barg equal to approximately 1 psi pressure differential across the valve. The Cv value is 1.21 gal/min.

FIG. 7.67

Cv value measuring screen. Courtesy: Bonney Forge.

Pressure and fugitive emission tests

409

Pressure and fugitive emission tests A pressure test certificate (e.g., API 598 test certificate) is no longer valid after opening the valve for maintenance (e.g., changing the gasket or packing and unscrewing the bolts). Thus, the valve should be retested. For example, in one situation all the body-and-bonnet bolts for gate and globe valves had to be changed due to incorrect material selection. The valve test certificate may not be superseded if body bonnet bolts are unscrewed and changed one by one. Gate and globe valves should be fully open during the pipe hydro test (Fig. 7.68). If the valves are not completely open, high pressure will accumulate on the packing rings and leakage may occur. Tightening the gland bolts compresses the packing rings and stops the leakage. The risk is overtightening the gland bolts with torque values exceeding the values given in the manufacturer’s IOM manual. This results in high stem and packing friction and ultimately packing leakage. Loosening the gland bolts to decompress the packing and reduce the stem friction leads to constant packing leakage. Leakage from the body and bonnet of gate and globe valves during the shell test could be caused by gasket damage, loose bolt and nuts, or cracks in the body and bonnet. As an example, test water has a 3% corrosion inhibitor, and it is between 5°C and 50°C with a maximum 30 ppm chloride content. A high-pressure gas test on the valve body and seat is not required for gate and globe valves. BS1873, the standard for globe valves, refers to BS6755 for a valve testing standard which is superseded to EN ISO12266. EN ISO12266 defines leakage rates such as rate A, B, C, D, E, F, and G that is similar to ISO 5208. ISO12266 and ISO 5208 define more restrictive leakage rates than API 598, and leakage rates in API 598 are close to Leak rate E in ISO12266. For a valve such as a globe valve, there is no need to refer to EN ISO12266; API 598 is the correct test standard. ISO 5208 and EN ISO 12266 are the standards for the pressure testing of metallic valves. The gate and globe valve test duration depends on the valve size. Table 7.4 presents the test duration and maximum allowable leakage for gate and globe valves as per API 598. The back seat test is required for all valves, except for bellows seal valves.

FIG. 7.68 Testing a gate valve as per API 598. Courtesy: Bonney Forge.

410

7. Globe valve applications and design

TABLE 7.4 Testing duration and allowable leakage as per API 598, applicable for gate and globe valves. Size

Liquid test (drop per minute)

Gas test (bubbles per minute)

Shell/seat/back seat duration (s)

2

0

Less than 1 bubble

15-15-15

2 ½00 –600

12

24

60-60-60

800 –1200

20

40

120-120-60

2 drops per minute per size

4 bubbles per minute per size

300-120-60

12

00

Fugitive emission testing is done to make sure that the emission from packing is within the accepted limit. The test fluid can be helium, which is the second most volatile gas, after hydrogen. High-pressure hydrogen is explosive and it is not used for the test. The maximum allowable packing leakage is 46 ppm, as an example. Air has 4 ppm helium, so it is allowed to measure maximum of 50 ppm helium packing leakage. A fugitive emission test includes 1510 mechanical cycles and 5 thermal cycles as per API 622 Edition 2. The fugitive emission is applicable for H2S-containing fluids and it was recently updated by API 624 to use methane instead of helium for testing. ISO 15848 is the other fugitive testing standard. Tests for fugitive emissions are not part of the regular functional and pressure testing of valves. Fig. 7.69 shows a sniffing sensor placed around the packing to detect the amount of leakage.

Inspection All valves are tested by the manufacturer in advance. The inspector may witness up to 10% of each valve category during the factory acceptance test (FAT). FAT is done prior to sandblasting and painting. A dimensional check done after FAT includes valve face to face (Fig. 7.70), height of the valve, flange bolt circle and pitch diameter, flange thickness (Fig. 7.71), flange diameter, bolt diameter, handwheel diameter, ring groove depth, and width.

FIG. 7.69

Fugitive emission test.

Inspection

411

FIG. 7.70 Valve face-to-face measurement. Courtesy: Bonney Forge.

FIG. 7.71 Valve face-to-face and flange thickness measurement. Courtesy: Bonney Forge.

Materials are inspected and certificates are checked after FAT. The height of gate and globe valves is measured from the center of the bore to the top of the stem when the valves are open. The stem is rising and the handwheel is nonrising. The handwheel should not be rising to avoid changing the access of operator to the handwheel. The height of the check valve is measured from the center of the bore to top of the cover bolt.

412

7. Globe valve applications and design

The ring-type joint flange faces have a ring number that depends on size and rating between 11 and 105. The ring number is engraved on the outside surfaces of connected valve body flanges. Male threaded tools in different sizes are inserted into the female threaded valve ends to make sure that the threads meet the ASME B1.20.1 standard. The material grade (e.g., L7) is also engraved on the head of hexagonal head bolts. The heat number is engraved on the valve bodies (Figs. 7.72 and 7.73), which are traceable in the material certificates.

FIG. 7.72

Material grade, heat number, and PMI marking on the valve cover. Courtesy: Bonney Forge.

FIG. 7.73

Material grade and heat number marking on the body of the valve. Courtesy: Bonney Forge.

Tagging and marking

413

ATEX and fire test requirements Gate and globe valves can have fire test certificates according to API 6FA or ISO 10497 standards. The fire test certificate is not usually required for gate and globe valves with no nonmetallic parts. A fire test guarantees that the valve will function properly during a fire. ATEX is the European regulatory framework for manufacturing, installation, and use of equipment in explosive atmospheres. ATEX certification indicates that the valve does not have any source of ignition, which is applicable for equipment in potentially explosive atmospheres. Valves with actuators are usually in the ATEX scope of work because the ATEX directive does not consider the process source of ignition inside ATEX. Only external sources of ignition such as actuators with electrical parts make the valve fall inside ATEX.

Coating Coating in the forms of painting or metallizing is applied after assembly and hydro test. Therefore, it is possible that the areas underneath nuts may be left unpainted. Some manufacturers believe that painting covers the nuts completely and prevents air from entering under the nut and causing corrosion. The other solution is applying primer beneath nuts prior to the valve assembly and hydro test. The primer is thin, so it cannot hide possible leakage through the bolts during the hydro test. It is not proposed to have paint beneath the nut, since the paint might be removed during the bolt tightening, and then removal of the paint will affect the bolt torque and can also cause corrosion. Thermal spray aluminum (Norsok M-501 System 2A) can be used for the metallizing of duplex and super duplex body valves in 200 μm thickness. Thermaline 4700 (Silicon) in 50 μm thickness is used to fill the porosities in 50 μm. The total thickness of Thermaline 4700 and TSA should not be less than 200 μm. A standard paint inspection tool cannot measure the TSA and Thermaline thickness on duplex and super duplex accurately due to the double ferrite-austenitic structure of duplex material. But one solution is to cut a piece of paint and measure the thickness by a paint inspection gauge (Fig. 7.74). That cut piece should be touched up in a vendor shop. Carbon steel body valves can be made from phosphate as a sort of corrosion protection prior to painting. All the insulated materials should be painted to avoid corrosion under insulation. Since it is difficult to distinguish which valves will be insulated, one solution is to paint all carbon steel, SS316, Duplex, and 6MO materials, which increases the cost and delivery time (Fig. 7.75). The other solution is to order all the valves unpainted and those that require painting will be painted by the fabricator in the construction yard.

Tagging and marking A stainless steel 316 (SS316) temporary tag plate containing valve data including size, material, end connection, pressure class, and manufacturing stock number is fastened around the stem with SS316 wire for gate and globe valves (see Figs. 7.76–7.78). A name plate in

414

7. Globe valve applications and design

FIG. 7.74

TSA coating thickness measurement on the valve. Courtesy: Bonney Forge.

FIG. 7.75

Coating inspection (TSA Coating) on a duplex body valve.

FIG. 7.76

Temporary and permanent tag plates installed on valves. Courtesy: Bonney Forge.

Transportation

415

FIG. 7.77 Temporary tag plate around the valve yoke. Courtesy: Bonney Forge.

FIG. 7.78 Sample permanent tag plate. Courtesy: Bonney Forge.

316SS material is attached through SS316 on the handwheel around the stem in gate and globe valves. Handwheels and handwheel nuts are usually made of 316SS.

Transportation Globe valves should be transported in the closed position. Globe valves do not usually have lifting lugs. A globe valves, like a gate valve, is lifted using a cloth wrapped around the body flanges (Fig. 7.79) or through the body flange under the yoke (Fig. 7.80).

416

7. Globe valve applications and design

FIG. 7.79

Lifting a globe valve through both end flanges. Courtesy: Bonney Forge.

FIG. 7.80

Lifting a globe valve through body flange under the yoke. Courtesy: Bonney Forge.

More photographs

417

Spare part requirements Usually, there is no spare required for gate and globe valves smaller than 200 . Extra valves are usually ordered for valves in sizes 200 and below. Packing and body/bonnet gaskets are provided as spare parts for gate and globe valves 200 and above.

Maintenance The following steps should be done in order to remove the gate and globe valves from the line for maintenance: 1. Open the valves to depressurize and drain the line (the valve should not be removed from the line in the closed position). 2. The valve should be closed and opened (cycled) to relieve the pressure trapped in the body cavity. 3. The valve should be cycled several times after removal and before disassembly. Maintenance to gate, globe, and piston check valves includes repacking, gasket replacement, packing and stem threads lubrication, opening and closing (cycling) of the valve (function test), and visual inspection to make sure that there is no leak from the valve body.

More photographs See Figs. 7.81–7.88.

FIG. 7.81 Globe valve during the test. Courtesy: Bonney Forge.

418

FIG. 7.82

7. Globe valve applications and design

Globe valves ready for the test. Courtesy: Bonney Forge.

More photographs

FIG. 7.83 Globe valve in stainless steel 316 body. Courtesy: Bonney Forge.

FIG. 7.84 Face-to-face measurement of the globe valve. Courtesy: Bonney Forge.

419

420

FIG. 7.85

7. Globe valve applications and design

Wrapping vulc tape around the globe valve yoke (preservation). Courtesy: Bonney Forge.

More photographs

FIG. 7.86 Plastic position indicator on the top of the valve. Courtesy: Bonney Forge.

421

422

7. Globe valve applications and design

FIG. 7.87

Fugitive emission test. Courtesy: Bonney Forge.

FIG. 7.88

PMI test on the body of globe valve. Courtesy: Bonney Forge.

C H A P T E R

8

Piston check valves General applications Piston check valves are usually selected for small pipe sizes (maximum 2–300 ). Fig. 8.1 shows piston check valves, which are used to prevent backflow to the line. Fig. 8.2 shows the internal components of a piston check valve. The design can be with or without springs. In some cases where pressure drop is important, the valve may be designed without a spring to minimize cracking pressure and pressure drop. Cracking pressure is defined as a pressure of the fluid that opens the valve. However, where the valve is installed in the vertical line, the design may include a spring behind the closure member. A piston check valve can be also called a lift check valve. The flow enters from under the disk, lifts the disk, and passes. When the pressure drops, the seat falls down and closes the valve so there is no reverse flow to the upstream side. The closing action is done through a spring force and/or the weight of the closure member. In some cases, a ball instead of piston is energized toward the seat in this type of valve. In that case, the valve is called a ball lift check valve (Fig. 8.3). Piston check valves are cheaper than ball lift check valves, probably because a ball lift check valve requires more machining on the ball. Piston check valves are very common for 200 nitrogen purging lines to the equipment illustrated in Fig. 8.4. The check valve is located downstream of the gate valve and flange-to-flange connection. The reason for having a check valve on the purge line is that a hose with nitrogen content is connected to the pipe, and it is not desirable to have any hydrocarbon entering the nitrogen line. The reason for using a gate valve instead of a modular valve is that the pressure is low. Purging means replacing the atmospheric fluid inside the vessel with an inert and nonatmospheric fluid such as nitrogen. Piston check valves are installed on the chemical injection lines in sizes 100 , 1.500 , or 200 . In some cases, the valve located close to and upstream of the isolation modular valve can be integrated with the modular valve. But the one located on the chemical injection line in the lowpressure class is downstream or upstream of the gate valve. Fig. 8.5 shows a 1½00 piston check valve on the chemical injection upstream of a gate valve to prevent backflow from the main line (Fig. 8.6).

A Practical Guide to Piping and Valves for the Oil and Gas Industry https://doi.org/10.1016/B978-0-12-823796-0.00011-8

423

# 2021 Elsevier Inc. All rights reserved.

424

8. Piston check valves

FIG. 8.1 Piston check valves.

FIG. 8.2 Piston check valve internals. VALVE STEM SPRINGS VALVE BONNET

SPACERS

CAGE

SEATING SURFACES

MAIN PLUG VALVE SEATING SURFACES

FIG. 8.3 Ball lift check valve. Courtesy: Bonney Forge.

Bolt Bonnet Gasket Spring Ball Body

425

General applications 2" x 1/2" reducing threaded flange 2" wedge gate valve flanged both ends

1/2" bleed plug & 1" x 1/2" bushing

2" x 1" reducing threaded flange

2" check valve 2" wedge gate valve flanged both ends

2" wedge gate valve flanged both ends 2" x 1/2" reducing threaded flange 1/2" bleed plug

FIG. 8.4 Piston check valve on a nitrogen purging line.

FIG. 8.5 Piston check valve on the chemical injection line upstream of the gate valve. 1½" RF x ¼" NPT(F) Reducing Flange/Plug

Header Piping Class

Branch Piping Class

1½" RF Check Valve

1½" RF Gate Valve 1½" N poflange Or 1.5" connection per branch table for header sizes =< 4" According to Piping Class, Node 3 Flow direction

P=1/3xD D

Fig. 8.7 illustrates a modular valve integrated with a check valve on the upstream part where flow enters. This valve was previously discussed in Chapter 5, Modular valve design and applications. In one instance, a manufacturer was asked to make a hole in a piston check valve closure member to provide a small backflow of the water, to avoid frost due to stagnant water on the

426

8. Piston check valves

FIG. 8.6 Piston check valve on the chemical injection line upstream of the modular valve.

Header Piping Class

Branch Piping Class

1½" RTJ x ¾" NPT (F) Modular valve Check/Ball/Needle/Ball Configuration

1½" N poflange Or 1.5" connection per branch table for header sizes =< 4" According to Piping Class, Node 3 P=1/3xD

Flow direction

D

603

G

201 602C 801

D

212

111

F

1 20 6 352B

352C 209C 20A 312D

C

F1

RELIEF HOLE

312C

ØB

21A

FOR THE FLANGE FINISH SEE THE REFERENCE TABLE

21B THREADED CLOSURE LOCKED WITH LOCTITE 222

FLOW

21C

A

FIG. 8.7 Modular valve integrated with a check valve. Courtesy: Bonney Forge.

downstream side of the piston check valve. However, the fluid downstream from the piston check valve (illustrated in Fig. 8.8) could move downward after passing the valve closure member and therefore had no risk of remaining stagnant. Therefore, there was no need to make a hole inside the check valve closure member.

427

Layout requirement

2

5

3

8

4

7

1

6

FIG. 8.8 Piston check valve.

Standards Piston check valves are manufactured in the maximum 200 size as per API 602, in pressure classes of 150, 300, 600, and 800. ASME B16.34 covers the valves in pressure class 2500 since class 2500 is not covered by API 602. They are usually standard (reduced) bore, but can be produced in full bore (nominal full bore, not true full bore). The minimum diameters of check valves for standard and full bore are given in API 602, as shown in Tables 8.1 and 8.2.

Wall thickness The minimum wall thickness of a piston check valve body (Table 8.3) has the same specifications as the gate and globe valves, as given in API 602.

Layout requirement Some straight-line length should be considered for check valves such as dual plate and non-slam types, to straighten the flow of fluid and avoid erosion of the valve internals. On the other hand, a piston check valve can have a flange-to-flange connection to a ball valve without a straight run requirement. The reason is that piston check valves do not have internal pins and keepers like dual plate check valves which are exposed to erosion damage. But even a full bore piston check valve is not actually full bore, and bore reduction could create flow turbulence. However, since the piston check valve is used in small pipes sizes 200 and

428

8. Piston check valves

TABLE 8.1 Minimum bore diameter for reduced (standard) bore check valves API 602. Minimum diameter in. (mm) Class 150, Class 300, Class 600, Class 800 NPS

Gate, globe, or check valves

¼

¼ (6)

⅜

¼ (6)

½

⅜ (9)

¾

½ (12)  11 16 ð17Þ  15 16 ð23Þ

1 1¼ 1½ 2

1⅛ (28)  1 7 16 ð36Þ

2½

1¾ (44)

3

2(50)

4

2¾ (69)

Class 1500 Gate valves  1 4 ð6Þ  1 4 ð6Þ  3 8 ð9Þ  1 2 ð12Þ  5 8 ð15Þ  7 8 ð22Þ  1 1 16 ð27Þ  1 3 8 ð34Þ  1 1 2 ð38Þ  1 7 8 ð47Þ  2 1 2 ð63Þ

Globe or check valves  3 16 ð5Þ  3 16 ð5Þ  5 16 ð5Þ  3 8 ð9Þ  9 16 ð14Þ  13 16 ð20Þ 1 (25)  1 1 16 ð27Þ  1 3 8 ð34Þ  1 11 16 ð42Þ  2 5 16 ð58Þ

DN 8 10 15 20 25 32 40 50 65 80 100

TABLE 8.2 Minimum bore diameter for full bore check valves API 602. Minimum diameter in. (mm) Class 150, Class 300, Class 600, Class 800

Class 1500

NFS

Gate, globe, or check valves

¼

¼ (6)

Gate valves  1

⅜

⅜ (9)

 3

½

½ (12)  11 16 ð17Þ  15 16 ð22Þ

¾ 1 1¼ 1½

1⅛ (28)  1 7 16 ð35Þ

2

1¾ (44)

2½

2 (50)

3

2¾ (69)

4

3¾ (95)

(6)

4

(9)

8

1



(12)

2

 5

(1 5)

8

 7

(22)

8

1

1

 16

 13 8  11 2  17 8  21 2  35 8

ð26Þ

(34) (38) (47) (63) (92)

Globe or check valves  3 16 ð4Þ  5 16 ð7Þ  3 8

 9

16

 13

DN 8 10

(9)

15

ð14Þ

20

16

ð19Þ

1 (25)  1 1 16 ð26Þ  13 8 (34)  1 11 16 ð42Þ  2 5 16 ð58Þ  3 7 16 ð87Þ

25 32 40 50 65 80 100

429

Installation problems

TABLE 8.3 Minimum wall thickness for piston check valves as per API 602. Minimum wall thickness in. (mm) Class 150, Class 300, Class 600, Class 800

Class 1500

NFS ¼

0.12 (3.1)

0.15 (3.8)

8

⅜

0.13 (3.3)

0.17 (4.3)

10

½

0.16 (4.1)

0.19(4.8)

15

¾

0.19 (4.8)

0.24 (6.1)

20

1

0.22 (5.6)

0.28 (7.1)

25

1¼

0.23 (5.8)

0.33 (8.4)

32

1½

0.24 (6.1)

0.38 (9.7)

40

DN

2

0.28 (7.1)

0.47 (11.9)

50

2½

0.33 (8.4)

0.56 (14.2)

65

3

0.38 (9.7)

0.65 (16.5)

80

4

0.47 (11.9)

0.84 (21.3)

100

below, the bore reduction compared to the pipe is not significant. Also, the flow pattern in the piston check valve is not straight. A piston check valve could be connected to tubing with one end threaded.

Installation problems Frequent disk opening and closing (chattering) can happen during operation of the valve if flow (fluid pressure) cannot keep the disk open constantly. This chattering causes vibration and results in valve malfunction. This problem could be due to over-sizing of the valve by a process engineer (e.g., 200 size instead of 100 ). Minimum flow rate (upstream pressure) should be given to the piston check valve manufacturer to be taken into account for the disk design. Some piston check valves with this issue were changed to swing check valves in low weight plastic (high-density polyethylene) disks that require less flow force (pressure) for opening. The other cause of frequent opening and closing of the disk may be wrong spring selection. Process data (e.g., fluid phase) and installation direction affect the required spring torque. Those data should be provided to the manufacturer to select the correct spring. Changing the spring to a lower torque may be a solution for ease of valve opening. As mentioned earlier, piston check valves can be designed without springs to solve the chattering problem. But if a valve is installed vertically, a spring is needed to keep the valve closed. A spring may also be required for the horizontal line to close quickly against the reverse flow, since just relying on the weight of the piston may not be a guarantee for fast closing. Check valves must be fitted in horizontal pipe runs with the cover facing upward. Variance to either side of the vertical axis must not exceed 5° (Fig. 8.9). Swing check valves and

430

8. Piston check valves

spring-loaded check valve designs allow for additional positioning, such as vertical upward flow. Valves must not be installed in vertical downward flow pipe runs or in horizontal pipe runs with the cover not facing upward vertically. It might be possible to install a piston check valve in the vertical line and downward flow if the water column above the closure member is no higher than 150–200 mm. Otherwise, the check valve would be always open and would not function properly in the vertical downward flow. Figs. 8.10–8.19 contain a variety of images of piston check valves and their specifications. Fig. 8.12 shows the marking of the ring-type joint (RTJ) grooves on the flange. Fig. 8.14 shows the cover of a piston check valve in ASTM A182 F51 (forged duplex) which has been marked during a PMI test (positive material identification).

FIG. 8.9 Maximum variance of the check valves (5°).

FIG. 8.10 Piston check valve after assembly and before painting. (Forged body in ASME A350 LF2 lowtemperature carbon steel). Courtesy: Bonney Forge.

431

Installation problems

FIG. 8.11 Piston check valve. Courtesy: Bonney Forge.

FIG. 8.12 Piston check valve RTJ ring number marking on the flange. Courtesy: Bonney Forge.

FIG. 8.13 Bonney Forge.

200 Class 1500 piston check valve. Courtesy:

432

8. Piston check valves

FIG. 8.14 PMI test on the bonnet (cover) of a piston check valve. Courtesy: Bonney Forge.

FIG. 8.15 Piston check valve during the test. Courtesy: Bonney Forge.

FIG. 8.16 Piston check valve during the test. Courtesy: Bonney Forge.

Installation problems

433

FIG. 8.17 Cast body of a piston check valve. Courtesy: Bonney Forge.

FIG. 8.18 Packed and preserved piston check valves. Courtesy: Bonney Forge.

FIG. 8.19 Piston check valve ready for the test. Courtesy: Bonney Forge.

C H A P T E R

9

Dual plate check valves Valve application examples Generally, check valves prevent undesirable backflow to the upstream part of a valve. One typical example is to prevent the flow reverse to a pump and compressor when it is shutting down. However, dual plate check valves are not recommended for downstream of pumps and compressors, as explained in the next chapter. Compared to the swing check valve, a dual plate check valve has the advantage of smoother closing, which results in a less slamming effect. Slamming occurs when the check valve closes abruptly by suddenly slamming the disk toward the seat or body of the valve. Slamming of the disk produces water hammering, the generation and effect of shock waves in incompressible fluids such as liquids. Water hammering produces undesirable operation problems such as vibration, stress, and noise that can damage piping systems. Slamming is discussed in detail in Chapter 10. A swing check valve (illustrated in Fig. 9.1) is an economical choice of check valve for nonreturn applications. However, the valve has a high slamming effect because the disk of the valve closes with a relatively high weight force. A swing check valve opens in response to fluid pressure. This valve is fully closed when the flow reaches zero to prevent backflow. The pressure drop and turbulence in this valve are low. Fig. 9.2 from API 594 illustrates a swing check valve in open and closed positions. Alternatively, the closing action of a dual plate check valve is done through two plates and sets of springs. The distribution of weight on two plates, and more importantly the spring force, reduces the disk slamming effect in a dual plate check valve. Fig. 9.3 compares the principle of closing in swing and dual plate check valves. Fig. 9.4 shows a dual plate check valve with the part list. The valve is opened by fluid pressure assistance and overcomes the spring forces (see Fig. 9.5). The valve is closed (Fig. 9.6) when the fluid rate decreases until the spring force overcomes the fluid pressure and keeps the plates closed. A dual plate check valve can be categorized as a low-to-medium slamming check valve. For that reason, this valve is not recommended for use in downstream of pumps and compressors. In addition, the closing time of a dual plate check valve is not as short as nonslam

A Practical Guide to Piping and Valves for the Oil and Gas Industry https://doi.org/10.1016/B978-0-12-823796-0.00014-3

435

# 2021 Elsevier Inc. All rights reserved.

436

9. Dual plate check valves COVER

SMOOTH OPERATION THICK UNIFORM BODY

STREAMLINED PORTS VALVE

SEAT RING

DISC WITH WELDED-ON FACING

FIG. 9.1 Swing check valve.

check valves such as axial flow nozzle check valves (Fig. 9.7). Nozzle check valves, as explained in Chapter 10, have more advantages than dual plate check valves, such as lowpressure drop and high resistance against loads and vibrations coming from the upstream pump and compressor. Fig. 9.8 illustrates the jet water injection line into the separator for cleaning and sand removal in a preliminary oil treatment plant. The water jet is injected into the separators to wash out the sand and particles accumulated at the bottom of the separators. There is a dual plate check valve coupled flange-to-flange with a full-bore ball valve. Why should the ball be a full bore? Usually, a dual plate check valve requires a minimum of 2D (2 times the width of the pipe diameter) upstream and 5D (5 times the width of the pipe

FIG. 9.2 Swing check valve opening and closing. Source: API 594 standard.

437

Valve application examples

Conventional “Swing check” valve principle

HINGE FORCE (F)

WEIGHT (W1)

“Dual Plate” check valve principle

SPRING FORCE (Fs)

HINGE

FORCE (F)

WEIGHT (W2)

FIG. 9.3 Comparing the closing of a swing check valve vs a dual plate check valve.

diameter) downstream straight line to avoid flow turbulence and erosion inside the dual plate check valve. Therefore, it is not a good idea to couple a reduced bore ball valve with a dual plate check valve. Dual plate check valve disk clearance shall be taken into account when the check valve is installed upstream of the ball, to avoid a check valve disk clash with the ball valve flanges. Fig. 9.9 shows the half circle that the disk can rotate and how it may clash with the ball.

438

9. Dual plate check valves INDEPENDENT SPRINGS Independent plate closing action LIGHTWEIGHT PLATE DESIGN • Increased seating & operation efficiency

HINGE SUPPORT SLEEVE • Reduces friction • Independent plate suspension

LONG-LEG SPRING ACTION • No seat scrubbing at opening & closing

FIG. 9.4 Dual plate check valve with parts list. Courtesy: Crane Stockham valve.

The maximum disk travel out of the body in a dual plate check valve (called protrude) depends on the size and pressure class of the valve. One valve supplier gave the value of 100 equal to 25.4 mm for a 400 class 300 dual plate check valve installed on a water injection line (as shown in Fig. 9.8).

Valve limitations Dual plate check valves are not good for very dirty services. Alternatively, a swing check valve should be selected for very dirty services. The swing check valve standard is either BS1868, or API 6D if the valve is selected for the pipeline system.

Terminology Cracking pressure On the initial opening and start-up, upstream pressure is applied to the front of the disks/ plates. This pressure can open the valve when it overcomes the spring torque and any downstream pressure acting on the back of the plates. The pressure differential between upstream and downstream where the valve becomes open is called cracking pressure. When the pressure differential exceeds the cracking pressure, the valve plates/discs are “cracked open” and the media can flow.

Terminology

(A)

(B) FIG. 9.5 Opening of a dual plate check valve. Courtesy: Crane Stockham valve.

439

440

9. Dual plate check valves

FIG. 9.6 Closing of a dual plate check valve. Courtesy: Crane Stockham valve.

spring

Resting Pressure Back to Ambient Pressure spring

FIG. 9.7 Nonslam axial flow check valve.

FIG. 9.8 Jet water injection line to separator.

Plates design

441

FIG. 9.9 Dual plate check valve with half circle disk travel.

Critical velocity The check valve should be fully open during operation. Otherwise, it has high-pressure drop and CV value is no longer valid since it is for a fully open valve. The velocity of the fluid that can fully open the valve, which is dependent on the spring torque, is called critical velocity. For valves installed vertically and upward in fluid, the fluid velocity must be sufficient to overcome the weight of the disk in addition to the spring force. For example, the maximum size of a valve installed on a vertical line with the fluid upward is 1200 .

Body design The body of a dual plate check valve is usually cast before machining of the flange faces and other parts. Machining the hard materials such as duplex requires extra man-hours. The photos in Fig. 9.10 show part of the factory where the body castings of dual plate valves have been received from the foundry for quality control checking. Quality control includes material checking (such as chemical composition and mechanical properties), dimension check, hardness check, PMI, etc. Each dual plate check valve will be machined (Fig. 9.11) after a visual examination and preliminary quality control. Valve manufacturers should have established criteria for accepting or rejecting a body casting based on the location, depth, and extension of the defects. Fig. 9.12 shows a sample of criteria for accepting the body casting. Nondestructive testing (NDT) is done after machining on the body of the valve to make sure that there is no crack or material imperfection on the machined faces. Fig. 9.13 shows a liquid penetration test as a type of NDT done on the body of a dual plate check valve. The first liquid used in NDT is a red liquid called penetrant. The white color is the second liquid used in NDT, and it is called developer. The developer reveals any cracks or material defects.

Plates design A dual plate check valve does not have a seat and the plates sit directly on the body of the valve when the valve closes. The disks are fixed and moving around a pin called a hinge pin.

442

9. Dual plate check valves

FIG. 9.10 Dual plate check valve cast bodies from the foundry.

There is another pin behind the hinge pin called the stop pin. The stop pin stops the disks when the valve is fully open and prevents the plates from touching each other. Designs that do not use stop pins have consequences such as plates contacting each other and cause plate flutter. The springs behind the plates keep the plates closed when the fluid pressure reduces and stops. Fig. 9.14 shows the disks, plates, pins, and springs of a dual plate check valve. Fig. 9.15 shows an open dual plate check valve with plates, pins, and springs, viewed from the top, based on Crain Design. The plate could be very large, for a valve larger than 10000 with six springs behind the plate for closing action. Fig. 9.16 shows the large plates that are installed inside the valve body. The valve is 4200 class 150 in cast carbon steel. Fig. 9.17 shows where the specifications of the valve are engraved on the valve body.

Plates design

443

FIG. 9.10, CONT’D

Fig. 9.18 shows two plates of a dual plate check valve with two squares installed as additional thickness on each plate that will be drilled and screwed for lifting lug installation. The plates of a dual plate check valve can be provided with additional thickness at the back to enhance the strength of the plates, as shown in Fig. 9.19. Diamond compounds such as diamond paste are used for providing a smooth surface finish and removing the roughness on the surfaces of a dual plate check valve disk (shown in Figs. 9.20 and 9.21). Fig. 9.22 illustrates a liquid penetration test on the disks of a dual plate check valve after machining. White and red colors are two liquids, called penetrant and developer respectively, used for the liquid penetration test. Fig. 9.23 illustrates a dual plate check valve in carbon steel body with a ring-type joint flange face and class 600 equal to pressure nominal 100Barg. The spring is in Inconel 625

444

9. Dual plate check valves

FIG. 9.10, CONT’D Courtesy: Crain Stockham valve.

material and the pins are 22Cr duplex UNS S31205. The plates were originally selected in 22Cr duplex with an overlay of Stellite 6. However, there are some risks associated with weld overlay on duplex, such as sigma phase or brittle phase formation, identified by material engineers. Therefore, the plates were changed to solid Stellite 6 (UNS R30006) to eliminate the risk of sigma phase formation. There are some machining activities required on the plates of a dual plate check valve, so NDT should be applied afterward to discover possible material defects.

FIG. 9.11

Machining the dual plate check valve body. Courtesy: Crain Stockham valve.

445

Plates design

FIG. 9.12 Criteria for accepting a defect on the dual plate check valve body casting. Courtesy: Crain Stockham valve.

FIG. 9.13 NDT on the body of a dual plate check valve. Courtesy: Crain Stockham valve.

446

9. Dual plate check valves

FIG. 9.14

Disks, plates, pins, and springs of a dual plate check valve. Courtesy: Goodwin.

FIG. 9.15

Disks, plates, pins, and springs of a dual plate check valve (view from top). Courtesy: Goodwin.

Spring design There are different choices of spring with different torque values. The choice of spring affects the valve response time. Higher torque springs give a valve a shorter response time for closing. However, they make higher force against the inlet fluid to open the valve. As an example, the spring torque for an inlet fluid of gas should be less than the spring torque when the fluid is liquid. The valve direction of installation also affects the spring torque. If the valve is installed vertically with the upward fluid, the spring torque should be less than when the valve is installed horizontally. Selection of the proper spring is one of the reasons why engineering companies should provide valve manufacturers with valve data sheets. In conclusion, the spring of the valve should be selected carefully, containing correct torque values. The direction of installation (vertical or horizontal), fluid condition (gas or

Spring design

447 FIG. 9.16 Large size plate with six springs behind. Courtesy: Crain Stockham valve.

FIG. 9.17 Installation of large plates inside the valve

body. 4200 class 150 WCB Body. Courtesy: Crain Stockham valve.

448

9. Dual plate check valves

FIG. 9.18 Dual plate check valve plates with additional thickness for lifting lugs. Courtesy: Crain Stockham valve.

FIG. 9.19 Dual plate check valve plates with additional thickness. Courtesy: Crain Stockham valve.

FIG. 9.20

Diamond paste on a dual plate check valve disk. Courtesy: Crain Stockham valve.

Spring design

449

FIG. 9.21 Diamond paste for lapping. FIG. 9.22 Dual plate check valve disks machining after NDT (liquid penetration).

450

FIG. 9.23

9. Dual plate check valves

Dual plate check valve after assembly with internals. Courtesy: Crain Stockham valve.

liquid), and fluid pressure all affect the spring torque. High spring torque may not lead to opening the disk of the valve in gas service. The minimum upstream pressure or flow should be given to the check valve supplier. Otherwise, the spring will be selected just for the normal flow or pressure, which will not be able to open the disk in minimum or low pressure (flow) condition. The disk would be subject to fluctuations between open and closed positions. Surprisingly, the plates of a large dual plate check valve have six springs for closing the valve, as shown in Fig. 9.24. There is one lifting lug per plate to facilitate the lifting. Inconel X750 is a very common spring material for valves, providing very good hardness and resistance against fatigue corrosion. Alternatively, Inconel 625 and Elgiloy (UNS R30003) are recommended for sour services with a high amount of H2S and seawater services. It has been experienced that Inconel X750 springs have been corroded in sour and seawater services. Elgiloy is a Cobalt alloy with approximately 40% cobalt and 20% chromium.

FIG. 9.24

Six springs for closing.

Weld overlay

451

Installation direction There is no size restriction for installation of dual plate check valves in the horizontal line. But there are size restrictions for spring-loaded disk check valves, including dual plate and nonslam axial flow check valves, in the vertical line. The downward fluid in the vertical line can keep the disk open all the time, especially in large size valves with relatively heavy disks. Therefore, some valve manufacturers may recommend spring-loaded check valves for sizes 800 and less. In fact, the fluid column pressure and the weight of the disk keep the valve open in sizes larger than 800 . The challenge with valves in the vertical line with the fluid upward is that the fluid pressure may not be sufficient to open the valve and overcome the weight of the valve disk, especially in large sizes. This is the reason why some manufacturers may recommend using spring-loaded check valves (Fig. 9.25) in the vertical line with the upward fluid for a maximum 1200 size.

Weld overlay The disk and body contact with disk surfaces in dual plate check valves should be hard-faced and weld overlaid with Stellite 6 to avoid galling and contact between metal to metal. In all, 22Cr duplex has the risk of brittle sigma phase in high temperatures due to applying weld overlay. The risk of sigma phase is higher in the smallest and thinnest parts. Therefore, the supplier may offer the solid disk in Stellite 6 instead of overlaying the 22Cr duplex with Stellite, to avoid the risk of sigma phase for sizes up to and including 800 . Alternatively, it is possible to apply Stellite 6 overlay on 22Cr duplex material providing that the temperature is controlled to low values not higher than 150 °C. Another technique is applying Inconel 625 buttering on the duplex and then applying Stellite 6 weld overlay on the Inconel 625. Is it really required to apply Stellite 6 on the disk of an axial flow check valve made of 22Cr duplex? 22Cr duplex is a hard material, there are challenges associated with applying Stellite on duplex and more importantly, the disk travel distance is short and there is no rotation on the disk. It may be possible to avoid duplex overlay with Stellite 6 considering other parameters’ influence the erosion, such as fluid velocity, fluid sand content, pressure drop value, fluid regime, and turbulence. Fig. 9.26 shows a weld overlay of Stellite 6 on the body of a dual plate check valve.

FIG. 9.25 Spring-loaded valves in the vertical line.

452

9. Dual plate check valves

FIG. 9.26 Stellite overlay on the body of a dual plate check valve.

Lapping Grinding and machining usually provide adequate sealing between the disk and the body seat, which is 3 cc/in./min for both dual plate and nonslam check valves according to API 598 standard for testing. Lapping on the seat and disk can be done for more critical valves such as cryogenic valves as well as valves for high-pressure gas tests based on the customer requirement. Cryogenic valves have less leakage rate requirement according to the API 598 standard, which could be 700 cc/in./min.

Valve design standard The design, body wall thickness, and face-to-face measurement of dual plate check valves are according to API 594, the standard for check valves. API 594 gives higher body wall

Dual plate check valve with stem override

453

thickness compared to ASME B16.34, the standard for valves. Dual plate check valves are wafer, lug, or double flanged in API 594, same as butterfly valves in API 609 standard. Figs. 9.27–9.29 illustrate different body designs of dual plate check valves.

Two cases related to manufacturing and installation problems The first case is related to a dual plate check valve with additional wall thickness that clashed with the long length bolts for the flange connection. The problem was experienced during the valve installation, so the valve was sent back to the valve manufacturer. The manufacturer machined the body to remove the extra thickness. NDT was done afterward to make sure that there was no material defect created after machining. The valve pressure test on the body was carried out after machining to assure that the valve was not leaking. The valve was sent back to the construction yard afterward. Another problem experienced during valve manufacturing was encountered when drilling the holes inside the body of the valve for hinge and stop pins. One hole was bigger than the other, so a good solution was to enlarge the smaller hole equal to the larger one, and then use larger hinge and stop pins as well as retainers.

Dual plate check valve with stem override A conventional dual plate check valve does not have an override function. For this reason, gate valves should be applied to drain the downstream part of the dual plate valve in order to

FIG. 9.27

Wafer-type dual plate check valve. Courtesy: Crain Stockham design.

454

9. Dual plate check valves

FIG. 9.28 Lug-type dual plate check valve. Courtesy: Crain Stockham design.

prevent the accumulation of stagnant media. Stagnant media can damage the piping system due to frost formation and expansion, as well as enabling bacteria growth and corrosion. Fig. 9.30 shows a piece of pipe that was damaged by microbial corrosion. The valve in Fig. 9.31 is a dual plate check valve with an OS&Y stem like a gate valve and a handwheel or actuator at the top. The handwheel can lift up the dual plates, which leads to full flushing through the valve. One other benefit of an override check valve is related to the body test of the valve. Unlike a standard check valve, the disk of this type of check valve is lifted up during the body test.

FIG. 9.29

Double flange dual plate check valve. Courtesy: Crain Stockham design.

Dual plate check valve with stem override

455

FIG. 9.30 Corrosion of pipe due to bacteria effect.

FIG. 9.31 Override check valve.

456

9. Dual plate check valves

FIG. 9.31 CONT’D Courtesy: Hi Flo AS.

The pressure test on the body should be applied on the conventional valve from the upstream side. However, this restriction to apply the pressure test from a specific side does not exist for an override check valve. Fig. 9.31 shows an override dual plate check valve containing a stem and handwheel, unlike a conventional check valve. The body of the valves in the photos are made of a bar for a shorter delivery time. Fig. 9.32 shows an override check valve during disassembly. An override check valve has a rising stem plus a bolted body and bonnet connection like gate and globe valves. The bolted body and bonnet design allow maintenance of the valve without any need to remove the valve from the line. Usually, a drained gate valve is installed downstream of the check valve to drain the line. The drain connection is a combination of a welded nippo flange, a gate valve, and a bleed plug. It would probably be cheaper to replace the standard dual plate check valve and the connected drain connection, with a rising stem override dual plate check valve. The other advantage of this valve is that it is a top-entry design, which makes it suitable for cryogenic services or high-pressure gas services. Top entry valves welded to the pipe have a shorter leak path compared to side entry valves. A shorter leak path is critical for hazard services like cryogenic or high-pressure gas. The valve has a seat that can be repaired or changed by bonnet removal. Applicable code and standards are presented in Table 9.1.

Dual plate check valve with stem override

FIG. 9.32 Override check valve during disassembly. Courtesy: Hi Flo AS.

TABLE 9.1

Override dual plate check valve applicable standards.

PED 97/23/ec

General requirement

ATEX

General requirement

API 594

Valve design

ASME B16.5

Body flange design

API 598

Inspection and testing

API 607

Fire safe

API 6D

Valve design

ASTM & ASME Section

Material

Yoke & Stem Design

API 600, 602 & 603

ASME Sec. VIII

FEA analysis

457

458

9. Dual plate check valves

FIG. 9.33 Override dual plate check valve with pneumatic actuator.

The body of the valve may be forged or cast, depending on the size of the valve. A forged body is common for smaller size valves and a cast body is selected for larger size valves. The operation of the valve could be actuated with all types of pneumatic, electrical, and hydraulic actuators with fail close function. The valve contains a back seat and yoke sleeve, like gate and globe valves. The yoke sleeve is in nickel aluminium bronze to avoid stem friction. Fig. 9.33 shows a pneumatic actuated override dual plate check valve with a vertically mounted actuator.

FIG. 9.34

FEA analysis on the body of an override dual plate check valve. Courtesy: Hi Flo AS.

Additional pictures

459

Fig. 9.34 illustrates a finite element analysis as per ASME Section VIII div. 2 in which the body of the valve is Class 300 (PN ¼ 50) tested with 1.5  design pressure. This test was done on relatively weak material, austenitic stainless steel SS316 CF8M, in order to qualify the stronger materials.

Additional pictures See Figs. 9.35–9.53. FIG. 9.35 Body and plates of dual plate check valves after machining and NDT. Courtesy: Crain Stockham valve.

FIG. 9.36 Body flange flatness test. Courtesy: Crain Stockham valve.

460

9. Dual plate check valves

FIG. 9.37 Dual plate check valve pressure test/pressure test equipment. Courtesy: Crain Stockham valve.

FIG. 9.38 Dual plate check valves in duplex and nickel aluminium bronze body materials after assembly. Courtesy: Crain Stockham valve.

Additional pictures

461

FIG. 9.39 Dual plate check valves in duplex body material after test. Courtesy: Crain Stockham valve.

FIG. 9.40 Dual plate check cast body after machining. Courtesy: Crain Stockham valve.

FIG. 9.41 Drying a dual plate check valve after hydrotest. Courtesy: Crain Stockham valve.

462

9. Dual plate check valves

FIG. 9.42 Coated dual plate check valve with thermal spray aluminium in a small size plus permanent tag plate. Courtesy: Crain Stockham valve.

FIG. 9.43 Dual plate check valve in duplex body material with temporary tag. Courtesy: Crain Stockham valve.

FIG. 9.44

Dual plate check valve after assembly and test. Courtesy: Crain Stockham valve.

Additional pictures

463 FIG. 9.45 Dual plate check valves sand blasting. Courtesy: Crain Stockham valve.

FIG. 9.46 Preservation of a dual plate check valve with plywood. Courtesy: Crain Stockham valve.

FIG. 9.47 Preservation of a dual plate check valve in a cardboard box. Courtesy: Crain Stockham valve.

FIG. 9.48 Lifting of a dual plate check valve. Courtesy: Crain Stockham valve.

FIG. 9.49 Box for packing a dual plate check valve. Courtesy: Crain Stockham valve.

Additional pictures

465

FIG. 9.50 Dual plate check valve in the packing box. Courtesy: Crain Stockham valve.

FIG. 9.51 Lugged butterfly valves. Courtesy: Crain Stockham valve.

FIG. 9.52 Rubber lining on the body/disk surface for better sealing. Courtesy: Crain Stockham valve.

466

9. Dual plate check valves

FIG. 9.53 After machining of the flange bolt holes of a dual plate check valve. Courtesy: Crain Stockham valve.

C H A P T E R

10

Nonslam check valves Introduction Nozzle check valves, also called axial flow check valves, are very important for nonreturn fluid purposes with nonslamming and fast-closing characteristics. Fig. 10.1 shows several different axial flow check valves. They are usually installed downstream of rotating equipment to protect the expensive mechanical equipment from possible damages due to backflow. Although they are a costly option compared to other alternatives such as swing-and-dual plate check valves, they can save a lot through safe protection of costly rotating equipment and lower pressure drop. These valves are widely used in different sectors of the oil and gas industry such as top site offshore platforms, subsea, refineries, pipelines, liquefied natural gas, and petrochemical plants. Slamming can have the same effect as surge pressure. It happens when the valve is closed after the pump stops and the forward fluid decelerates, reverses, and accelerates back toward the pump. Reverse fluid liquid induces pressure in the downstream line. The check valve must close quickly before the reverse velocity gets high, in order to minimize the surge pressure and protect the line. Surge is related to fast flow reversal that causes noise, vibration, increased fluid temperature, and damage to the upstream equipment. Advantages and design considerations of these valves are described in the following section.

Advantages of nonslam check valves Quick closing and easy opening disk The short axial disk travel to the seat, spring-assisted design (Fig. 10.2), and low-mass disk make the nozzle check a fast-closing valve, which is an advantage in critical lines with fast reversing flow. The fast-closing response reduces the possibility of equipment damage due to backflow and provides good protection for expensive mechanical facilities. Low static pressure behind the disk in the venture area causes a pressure differential over the disk, providing easy opening of the disk as well.

A Practical Guide to Piping and Valves for the Oil and Gas Industry https://doi.org/10.1016/B978-0-12-823796-0.00010-6

467

# 2021 Elsevier Inc. All rights reserved.

468

10. Nonslam check valves

FIG. 10.1 Axial flow nonslam check valves.

It is even easy to move the disk of a 2000 axial flow check valve by hand and open the valve.

Robust structure and zero leakage The robust body structure of the valve (Fig. 10.3) gives more resistance associated with vibration coming from upstream equipment (pumps and compressors) compared to dual plate and swing check valves. The integrated body without a bolted body-bonnet design (Fig. 10.4)

Advantages of nonslam check valves

469

FIG. 10.1, CONT’D

reduces the risk of leakage through the body to zero. As a result of zero emission body characteristic, these valves are also used in subsea applications.

Low-pressure drop and high flow capacity A high-pressure drop means there is a possibility of higher wearing and erosion in the valve as well as more expensive pumps or compressors needed to provide higher head and lower friction loss. The pressure drop for the valve is low and usually less than 0.1 barg. In addition, the smooth flow pattern through the valve as a result of the venturi effect associated with the nozzle design (bore reduction) avoids flow turbulences, minimizes erosion problems, and maximizes flow capacity as well as easy opening of the disk (Fig. 10.5). To sum up, this valve has advantages from both process and mechanical points of view. Also, the only moving part in the valve is the disk, which reduces the risk of erosion and galling.

470

10. Nonslam check valves

FIG. 10.2

Spring-assisted and low-mass disk of axial flow check valve. Courtesy: Crain Stockham.

FIG. 10.3

Robust design, integrated body, ribs, and axial nozzle cast together. Crain Design.

FIG. 10.4

Integrated body nonslam check valves (no bolted bonnet). Crain Design.

Advantages of nonslam check valves

471

FIG. 10.5 Smooth flow in axial flow check valve and venture (bore reduction) effect.

Long valve life Nonslam check valves have very minimal maintenance requirement from an operational point of view. Having the disk as the only moving part, which travels a very short distance to the seat, makes wearing in the disk and the valve as minimum as possible. The spring is exposed only to an axial load, unlike the springs in dual plate check valves, which increases the life and reduces the wearing. The valves are sometimes sent back to the manufacturers for examination and possible maintenance after quite a long time of operation from 7 to 10 years. Usually, these valves are opened and examined, the seat is greased and pressure tested, and they are sent back to the operator without any major maintenance required (Fig. 10.6).

FIG. 10.6 Seat is greased on the valve sent back to Crain for maintenance. Courtesy: Crain Stockham valve.

472

10. Nonslam check valves

Nonslamming Although the disk closing speed is fast, the disk closing action does not produce slamming against the seat due to a short stroke and spring-assisted design, which minimizes water hammering and valve slam in liquid services. Water or liquid hammering is a possible operation problem in which a pressure wave is caused by the fluid service due to sudden closing or slamming of the valve. This can create noise, vibration, and/or piping collapse due to additional piping loads. Water hammering is the generation and effect of high-pressure shock waves in relatively incompressible fluid when the fluid stops abruptly. Consequences such as noise, flange break, and equipment damage are associated with water hammering. Fig. 10.7 shows how the fluid movement after closing the valve can result in water hammering.

Shorter straight pipe run requirements Ideally, check valves should have 5 diameters of straight pipe both upstream and downstream of the valves. Insufficient straight pipe before the dual plate and axial flow nonslam check valves, especially when the fluid velocity is higher than 4.5 m/s, causes significant wear in the valve and reduces its design life. Practically, achieving five-dimensional (5D) of straight pipe due to layout space limit is very challenging and sometimes not possible. However, the special geometry of the nozzle in an axial flow check valve causes a venturi effect and smoother flow characteristic, as mentioned earlier, so that just two-dimensional (2D) or three-dimensional (3D) of straight pipe upstream and downstream is enough (Fig. 10.8). This saves material, cost, and especially space, which are critical parameters in offshore platforms and FPSOs. It is important to note that the value of the straight pipe requirement is different from one valve supplier to another.

FIG. 10.7

Water hammering due to closing the valve.

Advantages of nonslam check valves

473

FIG. 10.8 Straight pipe up and down of nonslam check valve.

Tight shutoff Axial flow check valves are tight shutoff, although they are metal seated. Even an erosive fluid cannot disturb the sealing since the valves have a robust design. They are usually pressure tested according to the requirements of API 598, in which the leak through the seat should be a maximum of 3CC (equal to 48 drops) per size in inch per minute. However, zero or a very small amount of leakage is usually observed from the valves. Clients rarely ask for high-pressure gas tests on the seat if the valve is installed in high-pressure gas services. Fig. 10.9 shows an 1800 titanium body valve in class 150, cast body during the pressure test. The observed leakage from the valve seat was negligible.

Different end-to-end designs (flexibility in end-to-end resign) Although the manufacturer design (short pattern, Fig. 10.10) is commonly selected for the valves, the compact design and ASME B16.10 (API 6D) (long pattern, Fig. 10.11) end-to-end designs are also available in the market. Compact nozzle check, which meets requirements of API594 in end-to-end design, can provide higher pressure loss and more wearing internally compared to the manufacturer end-to-end design. Unless space is an important consideration, the compact design is not recommended. ASME B16.10 or API 6D (long pattern) design types could cause pressure loss, more or less the same as the short pattern manufacturer standard. However, it is possible to order a new valve to replace the old valve with long pattern design from different nonslam manufacturers (in case of maintenance) considering that manufacturer end-to-end design should be replaced by another valve from the same manufacturer. The compact pattern design has the disadvantage of a shorter stem design that has a higher load distribution. Another disadvantage of the compact pattern design is the lower

474

FIG. 10.9

FIG. 10.10

10. Nonslam check valves

1800 Class 150 titanium body nonslam check valve during the pressure test. Courtesy: Crain Stockham.

Crain end-to-end (short pattern) design.

Valve applications

475

FIG. 10.11 Compact nozzle check valve.

CV value (flow capacity) and higher pressure drop. The compact design could be based on manufacturer design in addition to API 594 standard for dual plate wafer check valves. In conclusion, selection of a suitable check valve in pump and compressor discharge is an essential parameter in the mechanical equipment system design. The challenge is that the valve should be opened easily with low-pressure loss to make movement of the flow smooth, and the valve should be closed gently and fast to avoid flow return to the nonoperated mechanical equipment. Nonslam axial flow check valves are the best choice of valve selection in this application because they provide high-energy saving and safe equipment protection.

Valve applications There are usually two check valves after pumps and compressors that sometimes have to be different types, such as dual plate and nonslam (Fig. 10.12). The reason for different types is that if one fails, the other dissimilar one works. However, sometimes both valves are selected as nonslam check valves, since they are more robust choices. Nonslam check valves can withstand more generating vibration from equipment, and the force on the spring is in just one axial direction unlike dual plate check valves, so the risk of spring fail is lower. When selecting two different valve designs, the one used after the pump and compressor should be a nonslam type. The same schematic representation shown in Fig. 10.12 can be used for compressors. Fig. 10.13 illustrates the piping arrangement after a compressor including two nonslam check valves. Two nonslam check valves after compressor in Fig. 10.14 are proposed to minimizing the leak toward the pressure safety valve (PSV) downstream of the compressor. Having nonslam

FIG. 10.12 Two different check valve types after pumps.

476

10. Nonslam check valves

FIG. 10.13

Two nonslam check valves after compressor.

FIG. 10.14

Small size 2 1/1600 nonslam axial flow check valve for wellhead facilities. Courtesy: Crain Stockham.

check valves instead of dual plate-type check valves minimizes the leak toward the PSV valve located downstream (after) the compressor. Less leakage possibility from the nonslam check valves affects sizing the PSV in a way that a smaller PSV valve might be selected. The other important point is that the compressor should provide enough fluid pressure for full opening of the nonslam check valve, and then the semiopen nonslam check valves are subject to a high rate of tearing and wearing. It is possible to select a dual plate check valve after pumps and compressors if the check valve is in operation for a short period of time, such as 5 or 6 times a year. Nonslam axial flow check valves are usually found in size ranges from 600 to 1800 in a typical offshore platform. However, smaller sizes such as 2 1/1600 can be produced in the factory for wellhead facilities with high API pressure classes such as 15,000 psi. Nonslam check valves in 2400 (Fig. 10.15) and 2800 size, for example, can be selected for use in pipelines after pumps and compressors. The body of the valve is integrated with two pup pieces at both ends that will be welded to the pipe later in the construction yard. The pup piece length

Valve applications

FIG. 10.15

477

2400 Welded body nonslam axial flow check valve installation after compressor in pipeline. Courtesy:

Crain.

should be suitable and sufficient based on the valve size to prevent the transfer of welding to the valve internals. There are sealings inside the valve that may be melted due to high temperature of welding. The design standard of the valve is API 6D instead of ASME B16.34, since the valve is installed on the pipeline (API 6D covers pipeline valves). The end of the valve pup piece should not be painted due to welding the valve end to the line later in the yard. Instead of paint, primer and rust inhibitor can be used to avoid external corrosion of the valve pup piece. Fig. 10.16 shows a welded nonslam axial flow check valve in class 900 and ASTM A352 LCC body (low-temperature carbon steel). The pressure (flow) direction is marked on the body of the valve. The valve should be sandblasted before painting. Abrasive sandblasting involves propelling a stream of abrasive materials such as sand on the valve body surface excluding flange

FIG. 10.16 Welded body nonslam axial flow check valve. Courtesy: Crain Stockham valve.

478

FIG. 10.17

10. Nonslam check valves

Valve sandblasting prior to painting. Courtesy: Crain Stockham valve.

faces (areas that will be painted) to smooth a rough surface and remove surface contamination. Compressed air is typically used to propel the sand onto the steel surface. Sandblasting helps significantly to improve adhesion of the coating on the steel surface. Fig. 10.17 illustrates the sandblasting operation.

Valve limitations Nonslam check valves are not good for very dirty services. Alternatively, swing check valves should be selected for very dirty services. The swing check valve standard is either BS1868, or API 6D if the valve is selected for a pipeline system.

Terminology Cracking pressure On the initial opening and start-up, upstream pressure is applied by pressure to the front of the disks/plates. This pressure can open the valve when it overcomes the spring torque and any downstream pressure acting on the back of the plates. The pressure differential between upstream and downstream where the valve becomes open is known as cracking pressure. When the pressure differential exceeds the cracking pressure, the valve plates/discs are “cracked open” and the media can flow.

Critical velocity The check valve should be fully open during operation. Otherwise, it has a highpressure drop and the CV value is no longer valid, since it is for a fully open valve. The velocity of the fluid that can fully open the valve, which is dependent on the spring torque,

Body design

479

is known as critical velocity. For valves installed vertically and in upward fluid, the fluid velocity must be sufficient to overcome the weight of the disk in addition to the spring force. Therefore, for example, the maximum size of the valve installed on the vertical line with the fluid upward is 1200 .

Body design Usually the minimum size of axial check valves for a typical offshore platform is 600 . But 2 1/1600 is applicable for subsea section. The minimum size in API 6D is 200 . Nonslam check valves are based on API 6D, Pipeline Valves, if they are installed on the pipeline. Otherwise, ASME B16.34, Standard for Valves, can be referred to for nonslam check valves. Finite element analysis is done on the body and other main valve components to ensure design integrity. Flow modeling should be applied on the valve to optimize pressure drop characteristics. Fig. 10.18 shows FEA on the body of an axial flow nonslam check valve. The bodies of nonslam check valves are usually cast before machining on the flange faces and other parts. Machining the hard materials such as duplex requires extra man-hours. Fig. 10.19 shows part of a factory where the body castings of dual plate and nonslam check valves have been received for quality control checking. Quality control includes material checking (chemical composition and mechanical properties as examples), dimension checks, etc. The integrated casting of the body with the axial nozzle and the connecting ribs, shown in Fig. 10.20, is an advantage from a valve design point of view. This design is robust with almost no chance of internal parts disassembling. Fig. 10.21 shows the machining of the end flange body face of a nonslam axial flow check valve.

FIG. 10.18 FEA analysis on the body of an axial flow check valve.

480

FIG. 10.19

10. Nonslam check valves

Cast bodies of dual plate and nonslam check valves. Courtesy: Crain Stockham valve.

NDT is done after machining on the body end flanges to make sure that there is no crack or material imperfection on the machined faces. Fig. 10.22 shows a liquid penetration test as a type of NDT on the flange face after machining. The white color on the flange faces is the second liquid (developer), which is used in NDT. The developer reveals any cracks or material defects. The body of the axial flow check valves after machining and NDT should be ready for assembly, as shown in Fig. 10.23.

Disk and seat design The disk of the valve is pushed against the seat primarily through the spring force, as well as back pressure. When the inlet fluid pressure is greater than the spring force, the disk will move off the seat and the valve becomes open (Fig. 10.24). It is important that the fluid pressure opens the valve completely. The valve would be subject to a high amount of wearing and erosion if the disk is not completely open. The higher flow rate provides a higher force for opening the valve. The venturi area between the body and the disk diffuser or axial nozzle provides a streamline flow and lowpressure drop. When the inlet fluid flow and pressure decreases, the disk will be pushed against the seat, again with the aid of spring. The disk should be closed quickly (Fig. 10.25) to avoid flow return to the upstream equipment. Sizes from 100 to 1000 can be solid disk (Fig. 10.26) and sizes 1200 and above can be ring disk (Fig. 10.27) based on the Goodwin design.

Disk and seat design

481

FIG. 10.20 Cast body of nonslam axial flow check valve. Courtesy: Crain Stockham valve.

There are a few additional things to note regarding other design types of the nonslam check valve. For example, Fig. 10.28 illustrates two nonslam check valves with different designs including some disadvantages. Misalignment in the disk causes a higher pressure drop than normal, as well as noise. The pressure drop in case of disk misalignment can increase from 0.1–0.5 barg to 4–5 barg. Fig. 10.29 shows the comparison between two rib design types inside the body of a nonslam check valve. The low-mass disk of nonslam axial flow check valve was discussed earlier as an advantage. Fig. 10.30 shows the connection of the disk to the stem in a nonslam check valve.

482

FIG. 10.21

10. Nonslam check valves

Machining of axial flow nonslam check valve body flange face. Courtesy: Crain Stockham valve.

The connection is threaded. The threaded connection between the stem and disk can be sealed with sealants such as PTFE tape such as Furmanite or Loctite (Fig. 10.31). The other option is to provide a dry seal between the stem and disk threads. In fact, if the application is more critical in terms of pressure and temperature, the sealing compound may fail. Therefore, dry seal threads are recommended based on the ASME B1.20.3 standard, pipe threads, inch, dry seal. The thread type is different in dry seal from standard nominal pipe thread (NPT). Fig. 10.32 illustrates the differences between normal thread and dry seal thread. The peak and crest points have been truncated in dry seal so that the male and female threads are fitting together completely and provide better sealing. The disk is machined to provide accurate sealing on the valve seat. NDT is done after machining to make sure that there is no defect on the material. Fig. 10.33 shows the liquid penetration (LP) test on the valve disk after machining. There are three liquids in the LP test. The

Disk and seat design

FIG. 10.22

483

Liquid penetration test on axial flow nonslam check valve body flange after machining. Courtesy: Crain

Stockham.

FIG. 10.23 Axial flow check valves body after machining and NDT.

FIG. 10.24 Axial flow check valve in the open position. Courtesy: Crane Stockham valve.

484

FIG. 10.25

10. Nonslam check valves

Axial flow check valve in closed position. Courtesy: Crane Stockham valve.

first one is a red color (gray in print version) that is called penetrant. The second one is the developer in a white color that reveals the cracks. The last one is the cleaner. The LP test is applied according to the ASTM E 165 standard. This is why the valve disks are colored in red (gray in print version). Fig. 10.34 shows the three liquids used for the LP test. The disk contact surfaces with the body should be hard faced through weld overlay. Stellite 6 is a very common overlay material used on disk and body contact surfaces to avoid erosion and galling. Fig. 10.35 shows hard facing on the disk surface. More information will be provided later in the section titled, “Weld Overlay.” The seat of the valves can be cast and machined afterward to fit the body of the valve. The seats are threaded inside the body as shown in Fig. 10.36. An NDT test should be done on the seat after machining to make sure that there is no material defect. The body internal threads are for screwing the threaded seat inside the body. Fig. 10.37 shows the trash collected during machining of the internal threads on the body of the valve. Fig. 10.38 shows the seat of a nonslam check valve that was manufactured with the casting method and has arrived from the foundry. Some quality control activities such as visual examination should be done on the seat before machining and applying an NDT test. The NDT test is usually an LP test on duplex and a magnetic particle test on the carbon steel materials. Fig. 10.39 shows the seat of a nonslam check valve in nickel aluminum bronze material during the machining activity in the valve manufacturer shop. Nickel aluminum bronze body valves are common for sea water services as an alternative to super duplex and titanium, with the advantage of cost saving. Fig. 10.40 shows the seat of a nonslam axial flow check valve in 22Cr duplex material after machining. It is common to apply an LP test on the machined areas of 22Cr duplex material, as shown in Fig. 10.41.

Spring design

485

FIG. 10.26 Solid disk design. Courtesy: Goodwin.

Spring design There are different choices of spring with different torque values. The choice of spring affects the valve response time. Higher torque springs give the valve a shorter response time for closing. However, they create a higher force against the inlet fluid to open the valve. For

486

FIG. 10.27

10. Nonslam check valves

Disk ring design. Courtesy: Goodwin.

487

Spring design

Disc sealing on two contacts Risk of misalignment

Single bolt holding

Ribs located at the back end (offset from the center of the masses) Ribs pressure sealed or threaded

FIG. 10.28 Nonslam check valve alternative designs with disadvantages.

example, if the inlet fluid is gas, the spring torque should be less than when the fluid is liquid. The direction of valve installation affects the spring torque. If the valve is installed vertically with the fluid upward, the spring torque should be less than if the valve is installed horizontally. Selecting the proper spring is one of the reasons why engineering companies should provide valve manufacturers with the nonslam valve data sheets. In conclusion, the spring of the valve should be selected correctly containing correct torque values. The direction of installation (vertical or horizontal), fluid status (gas or liquid), and fluid pressure all affect the spring torque. High spring torque may not lead to opening the disk of the valve in a gas service. Minimum upstream pressure or flow should be given to the check valve supplier. Otherwise, the spring will be selected for just the normal flow or pressure, which may not open the disk in minimum or low-pressure (flow) condition. The disk would be subject to fluctuations between open and closed conditions.

488

10. Nonslam check valves

Supporting ribs better positioned to reduce bending

Ribs located at the back-end (offset from center of the masses) and generating large bending stresses in these ribs due to the cantilever effect of supporting both the disc and the guide housing

FIG. 10.29

Comparison between two rib design types.

Installation direction There is no size restriction for the installation of nonslam check valves in the horizontal line. But there are size restrictions for spring-loaded disk check valves including dual plate and nonslam axial flow check valves in the vertical line. The downward fluid in the vertical line can keep the disk open all the time, especially in large size valves with relatively heavy disk. Therefore, some valve manufacturers may recommend spring-loaded check valves for sizes in a maximum of 800 . In fact, the fluid column pressure and the weight of the disk keep the valve open in sizes larger than 800 . The challenge with valves in the vertical line with the fluid upward is that the fluid pressure may not be sufficient to open the valve and overcome the weight of the valve disk, especially in large sizes. This is the reason why some manufacturers may recommend the spring-loaded check valves in the vertical line (Fig. 10.42) with the upward fluid for a maximum 1200 size.

Weld overlay

FIG. 10.30 Disk and stem connection in a nonslam check valve.

489

(Continued)

Weld overlay The disk and seat contact surfaces in an axial flow nonslam check valve should be hardfaced and weld overlaid with Stellite 6 to avoid galling and contact between metal and metal. 22Cr duplex has the risk of brittle sigma phase in high temperature and applying weld

490

10. Nonslam check valves

FIG. 10.30, CONT’D

overlay. The risk of sigma phase is higher in the smallest and thinnest parts. Therefore, the supplier may offer the solid disk in Stellite 6 instead of overlaying the 22Cr duplex with Stellite, to avoid the risk of sigma phase for sizes up to and including 800 as an example. Alternatively, it is possible to apply Stellite 6 overlay on 22Cr duplex material on the condition that the temperature will be kept lower than 150°C. Another technique is to apply Inconel 625 buttering on the duplex and then apply Stellite 6 weld overlay on the Inconel 625. Fig. 10.43 shows the weld overlay on the seat of an axial flow check valve. Is it really required to apply Stellite 6 on the disk of an axial flow check valve

Lapping

491

FIG. 10.30, CONT’D

made of 22Cr duplex? 22Cr duplex is a hard material, and there are challenges associated with applying Stellite on duplex. More importantly, the disk travel distance is short and there is no chance of disk rotation. Therefore, it is probably possible to avoid duplex overlay with Stellite 6 considering that other parameters influence the erosion such as fluid velocity, fluid sand content, pressure drop value, fluid regime, and turbulence. Fig. 10.44 shows the weld overlay on the whole seat area of a nonslam check valve, which is not an economical solution. As mentioned earlier, weld overlay is applied only on the seat contact surface with the disk.

Lapping Grinding and machining, called “lapping,” usually provides adequate sealing between the disk and the body seat, which is 3 CC per inch per minute for both dual plate and nonslam

492

10. Nonslam check valves

FIG. 10.31

Loctite for sealant.

FIG. 10.32

Dry seal and normal thread comparison.

check valves as per API 598 standard. However, lapping on both the disk and the body seat may be required based on a customer’s request in some cases, such as cryogenic services and for valves with high-pressure gas test requirements. Diamond compounds such as diamond paste are used for providing a smooth surface finish and removing the roughness on the surfaces. Fig. 10.45 shows diamond paste used for lapping.

CV value The CV value in a nonslam check valve is approximately half, or even less than half, of the CV value of a butterfly valve. The same rule could be applicable for an axial on/off valve that has the same structure as nonslam axial flow check valves.

Flow open area The flow open area affects the pressure drop and the flow capacity of the axial valve. The flow open area on an axial flow check valve may be specified as a minimum of 70% in the venturi part (narrowest part) according to the end-user requirement. However, some manufacturers may deviate from this requirement and provide a smaller flow opening to achieve a higher pressure drop and increase the velocity behind the disk. Increasing the fluid velocity

Body Wall thickness

493

FIG. 10.33 Liquid penetration test on the nonslam check valves disk after machining.

helps the fluid to push the disk harder and provide more force for opening the valve. The accepted pressure drop from an axial flow check valve should be given to the valve manufacturer in valve data sheets. Accepted pressure drop is calculated and given from the process department and could be 0.1 barg, as an example.

Body Wall thickness The body wall thickness of axial flow check valves is based on ASME B16.34, “Standard for Flanged, Threaded and Welding End Valves.” Table 10.1, based on the standard, gives the minimum wall thickness for different internal diameters and pressure classes.

494

FIG. 10.34

10. Nonslam check valves

Liquids that are used in the LP test.

Hard facing on the disk

FIG. 10.35

Hard facing on the disk.

Valve face to face ASME (American Society of Mechanical Engineers) B16.10 standard for “Face-to-Face Dimensions of Flanged Valves,” as well as API 6D standards for “Pipeline Valves,” include faceto-face dimensions of the valves. Face-to-face dimensions given in API 6D are equal to the face-to-face dimensions given in ASME B16.10. If API 6D does not cover the face-to-face for a specific size and pressure class, ASME B16.10 is the correct reference. A tolerance of 2 mm should be allowed on the face-to-face and end-to-end dimensions of valves with sizes of 1000 and smaller, and a tolerance of 3 mm should be allowed for valve sizes of 1200 and larger, as per ASME B16.10.

Valve face to face

495

FIG. 10.36 Nonslam check valve with internal threaded body for seat assembly. Courtesy: Crain Stockham valve.

FIG. 10.37 Trash collected from machining the internal threads of a nonslam check valve.

FIG. 10.38 Nonslam check valve cast seat arrived from foundry. Courtesy: Crain.

496

FIG. 10.39

10. Nonslam check valves

Machining of the seat of a nonslam check valve in nickel aluminum bronze material.

Lifting Lifting of the axial flow check valves is done using lifting lugs, which can be integrated with body casting or screwed inside the body. A lifting lug requirement is provided by the valve purchaser in the project specifications. For example, valve sizes 800 and larger or valves heavier than 200 kg may need lifting lugs, based on end-user requirements. API 6D, the standard for pipeline valves, has mentioned that “if the valve manufacturer is responsible for the supply of the valve and operator assembly, the valve manufacturer should verify the suitability of the lifting points for the complete valve and operator assembly.” However, verification of lifting lug capacity can be required only for very large size and heavy valves in practice. Fig. 10.46 shows a nonslam check valve that has lifting lugs integrated with the cast body. Fig. 10.47 illustrates a temporary integrated lifting lug that is screwed into the body of the valve.

Lifting

FIG. 10.40 Seat of a nonslam check valve in 22Cr duplex material after machining. Courtesy: Crain.

FIG. 10.41 LP test on the seat of an axial flow check valve after machining. Courtesy: Crain.

497

FIG. 10.42

Spring-loaded valves in the vertical line.

FIG. 10.43

Weld overlay on the seat contact surface with the disk of an axial flow nonslam check valve. Courtesy: Crain Stockham valve.

FIG. 10.44 Weld overlay on the whole seat of an axial flow nonslam check valve. Courtesy: Crain Stockham valve.

499

Lifting

FIG. 10.45 Diamond paste for lapping. TABLE 10.1

A valve body minimum wall thickness, tm, mm. Minimum wall thickness – tm, mm

Inside dia. d, mm [Note (1)]

Class 150

Class 300

Class 600

Class 900

Class 1500

Class 2500

Class 4500

3

2.5

2.5

2.8

2.8

3.1

3.6

4.9

6

2.7

2.7

3.0

3.1

3.5

4.2

6.5

9

2.8

2.9

3.2

3.4

3.8

4.9

8.0

12

2.9

3.0

3.4

3.7

4.2

5.6

9.6

15

3.1

3.3

3.6

4.2

4.8

6.6

12.0

18

3.3

3.5

3.9

4.7

5.3

7.7

14.3

21

3.5

3.7

4.2

5.2

5.9

8.7

16.7

24

3.7

4.0

4.4

5.7

6.4

9.7

19.0

27

3.9

4.3

4.8

6.3

7.2

11.1

22.2

31

4.3

4.7

5.1

6.6

8.1

12.8

26.1

35

4.6

5.1

5.4

6.9

9.0

14.5

30.0

40

4.9

5.5

5.7

7.2

9.9

16.2

33.9

45

5.2

5.9

6.0

7.5

10.8

17.9

37.9

50

5.5

6.3

6.3

7.8

11.8

19.6

41.8

55

5.6

6.5

6.3

8.3

12.7

21.3

45.7

60

5.7

6.6

6.6

8.8

13.6

23.0

49.6

65

5.8

6.8

6.9

9.3

14.5

24.7

53.6

70

5.9

6.9

7.3

9.9

15.5

26.4

57.5

75

6.0

7.1

7.6

10.4

16.4

28.1

61.4

80

6.1

7.2

8.0

10.9

17.3

29.8

65.3 Continued

500

10. Nonslam check valves

TABLE 10.1 A valve body minimum wall thickness, tm, mm—cont’d Minimum wall thickness – tm, mm

Inside dia. d, mm [Note (1)]

Class 150

Class 300

Class 600

Class 900

Class 1500

Class 2500

Class 4500

85

6.2

7.4

8.3

11.4

18.2

31.5

69.3

90

6.3

7.5

8.6

11.9

19.1

33.2

73.2

95

6.4

7.7

9.0

12.5

20.1

34.9

77.1

100

6.5

7.8

9.3

13.0

21.0

36.6

81.0

110

6.5

8.0

10.0

14.0

22.8

40.0

88.9

120

6.7

8.3

10.7

15.1

24.7

43.4

96.7

130

6.8

8.7

11.4

16.1

26.5

46.9

104.6

140

7.0

9.0

12.0

17.2

28.4

50.3

112.4

150

7.1

9.3

12.7

18.2

30.2

53.7

120.3

160

7.3

9.7

13.4

19.3

32.0

57.1

128.1

FIG. 10.46

Lifting lugs integrated with the cast body. Courtesy: Crain Stockham.

FIG. 10.47

Temporary integrated lifting lug.

Additional photographs

501

Temporary screwed lifting lugs should be removed from valves after installation. If corrosion is a risk in screwed threads after removing the lifting lug, silicon or a plastic plug should be placed in the lifting lug holes. Corrosion in the screwed-in lifting lug holes is more risky for carbon steel materials. The lifting lug should have a safety factor regarding withstanding loads. For example, an end user may need a safety factor of 4 for a lifting lug, which means that the lifting lug should be strong enough to withstand 4 times the valve weight. Applying thick hot-dip galvanized on smaller threads fills the thread gaps completely so it is not possible to screw the lifting lug in. In that case, a thin zinc plate with 5–20 μm should be used for corrosion protection of the lifting lug. Alternatively, the lifting lug material can be changed to stainless steel 316. Considering the fact that the screwed lifting lug should be removed from the valve after installation, there is no need to apply HDG or zinc plate on the lifting lug for corrosion protection. A carbon steel lifting lug can be in ASTM A29 grade material.

Additional photographs See Figs. 10.48–10.56.

FIG. 10.48 Nonslam check valves during the body test. Courtesy: Crain Stockham valve.

FIG. 10.49 High-pressure class nonslam check valves during the test with the mechanical joint. Courtesy: Crain Stockham valve.

FIG. 10.50

Nonslam check valve during the test, 1800 titanium body. Courtesy: Crain Stockham valve.

FIG. 10.51

Nonslam check valves after assembly. Courtesy: Crain Stockham valve.

FIG. 10.52

Nonslam check valves. Courtesy: Crain Stockham valve.

Additional photographs

FIG. 10.53 Nonslam check valves with the tag plates. Courtesy: Crain Stockham valve.

FIG. 10.54 Nonslam check valve cast body received from the foundry. Courtesy: Crain Stockham valve.

503

504

10. Nonslam check valves

FIG. 10.55

Nonslam check valve cast body after visual examination. Courtesy: Crain Stockham valve.

FIG. 10.56

Nonslam check valve coated with zinc epoxy (LCC body). Courtesy: Crain Stockham valve.

C H A P T E R

11

Pipeline valves General information Pipeline valves, also called riser valves in the offshore industry, are usually top entry and actuated valves connected to the pipeline through butt weld pup pieces from both sides. Fig. 11.1 shows a top entry ball valve 2800 class 900. Top entry design has the following advantages: 1. Maintenance (such as seat repair) can be performed online from top of the valve by removing the valve bonnet without having to shut down the plant. 2. Because of its one-piece design, the top entry design has more mechanical resistance than a split body design against pipeline loads, according to finite element analysis results. The choices are between the ball valve and through conduit gate (TCG) valve. TCG valves in larger sizes such as 3800 are more expensive than top entry ball valves. In applications that require frequent operation, a TCG valve probably provides longer life and better sealing. 3. A top entry design has less risk of leaking. The valve is welded to the line instead of a flange connection, having one bonnet connected to the one-piece body. A side entry design has a two- or three-piece body and perhaps a two-piece adopter bonnet. It is possible to have a 600 ball valve in a high-pressure gas service as top entry to reduce the possibility of leakage from the valve. Also, cryogenic valves are recommended to be top entry and welded to the pipe to reduce the risk of leakage. 4. There is greater flexibility in stem design and size in a top entry ball valve, which allows the stem to be thicker for high torque and large actuator requirements. Side entry ball valve stem enlargement requires additional engineering due to design changes and special products, from the manufacturer’s point of view. Stem enlargement in a side entry ball valve may increase the face-to-face design. Fig. 11.2 shows a comparison of top entry and side entry (split body) valve designs. One solution to avoid stem enlargement is to limit the inlet pressure through installation of a pressure regulator or PSV (pressure safety valve) on the control panel of the actuated valves. But this solution is not accepted by instrument or operation companies due to yearly calibration and maintenance.

A Practical Guide to Piping and Valves for the Oil and Gas Industry https://doi.org/10.1016/B978-0-12-823796-0.00002-7

505

# 2021 Elsevier Inc. All rights reserved.

506

11. Pipeline valves

FIG. 11.1

Actuated ball valve 2800 CL900 (Flow Control Technology).

FIG. 11.2

Top entry and split body valve design comparison.

The stem should be enlarged because actuated valves create a high amount of torque exceeding the maximum allowable stem torque (MAST). One way to increase the MAST is to increase the stem diameter. Increasing the stem diameter leads to a design change for side entry ball valves, so it is recommended to increase the stem diameter within the manufacturing tolerance. Upgrading the stem material to higher mechanical strength is another way to increase the MAST. For example, a 22Cr duplex body valve can be supplied with 22Cr stem material. The stem material can be upgraded to 25Cr super duplex to increase the MAST. Inconel 718 (130,110) has a higher mechanical strength than 25Cr super duplex (116, 90). The first number in parenthesis is tensile strength and the second is yield strength. In conclusion, a 22Cr duplex stem can be upgraded to 25Cr super duplex or Inconel 718 for increasing the MAST. The ball of the valve should also be upgraded in the same way as the stem.

507

General information

TABLE 11.1

Upgrading the valve stem material due to actuation.

Body material

Stem material

Upgraded stem material

Carbon steel

13Cr/13 Cr-4 Ni/22Cr Duplex

25Cr Super duplex—Inconel 718

Low-temperature carbon steel

13 Cr-4 Ni/22Cr Duplex

25Cr Super duplex—Inconel 718

Stainless steel 316

Stainless steel 316

Nitronic 50/Inconel 718

22Cr Duplex

22Cr Duplex

25Cr Super duplex—Inconel 718

25Cr Duplex

25Cr Superduplex

Inconel 718

25Cr Duplex in seawater

25Cr Superduplex

Titanium grade 5

6MO

6MO

Inconel 625/Inconel 718

6MO in seawater

Inconel 625

Inconel 625

Titanium grade 2

Titanium grade 5

Titanium grade 5

Note: The pipeline valve body can be manufactured in carbon steel or low-temperature carbon steel materials.

Table 11.1 shows the alternative (upgraded) stem materials for different valve bodies because of actuation. Top entry ball valves should be ordered earlier because they will require longer fabrication activities on-site and a longer delivery time. The fabrication activity on-site includes welding of the valve pup pieces to the line. Top entry valves are typically used after the pig launcher in the offshore industry. Fig. 11.3 shows three of these valves on the platform after the pig launcher.

Replaced valve

Water at 135 bar Gas at 75 bar

FIG. 11.3 Top entry riser valves (quantity ¼ 3).

508

FIG. 11.4

11. Pipeline valves

Assembly of the body/bonnet top entry ball valve. Courtesy: FCT.

Fig. 11.4 shows assembly of the body/bonnet of a 3800 Class 2500 top entry ball valve in the factory. The bodies of these valves are usually made of carbon steel or low-temperature carbon steel. The valve could be top entry with one end having a compact flange or hub and the other end butt welded (Fig. 11.5), provided that the valve is directly connected to the pig launcher. However, having a compact flange, hub, or flange connection on one side of the riser valve does not necessarily increase the valve weight; rather, it increases the leakage possibility. A top entry ball valve is heavier than a side entry ball valve due to having a heavier bonnet. For example, a valve supplier stated that a 2000 Class 1500 top entry ball valve weighed 11 tons while a side entry valve of the same size and pressure class was estimated to weigh

509

Valve design and weight reduction

FIG. 11.5 Top entry ball valve with one end having a flange and one end with a pup piece.

approximately 9 tons. Using a top entry ball valve helps engineers avoid having two flange body connections on the valve, but there are pup piece and transition pieces as well as a large top cover (bonnet) that increases the weight of top entry valves.

Valve design and weight reduction There are some ways to reduce the weight of top entry valves. The first one is to calculate the body wall thickness based on ASME Section VIII Div.02 instead of ASME B16.34. Thickness reduction reduces the end-to-end measurement, height, and weight of the top entry ball valves. Table 11.2 lists the thickness, end to end, height, and weight reduction of a 3000 CL1500 top entry ball valve through wall thickness calculation according to ASME Sec. VIII. Fig. 11.6 compares top entry ball valves in the 3000 and class 1500 design based on the codes and standards mentioned earlier. Valve suppliers require loads such as axial, bending, torsion, wave, and axial from the EPC contractor company in order to calculate the wall TABLE 11.2 Weight and dimension comparison for a 3000 Class 1500 top entry ball valve based on ASME B16.34 and ASME section VIII for valve thickness calculation. 3000 CL1500, TE ball

Thickness (mm)

End to end (mm)

Height (mm)

Weight (tons)

ASME B16.34

158

2540

2340

34

ASME Sec.VIII

135

2320

2253

25

Saving

23

220

87

9

510

11. Pipeline valves

FIG. 11.6 Valve dimensions comparison between top entry ball valve design based on ASME B16.34 and ASME Section VIII, Dev.02.

thickness based on ASME Section VIII. Figs. 11.7–11.10 illustrate axial, bending, torsional, and accidental loads, respectively. The weight of top entry valves of the same size and pressure class installed on the pipeline could be different, because pipeline loads (axial, bending, etc.) are different for various pipeline valves in different locations. Valve manufacturers may prove the mechanical strength of a valve to withstand loads through a bending test. The bending test is a test performed by applying forces (bending moments) to the body of the valve using connecting pistons on the pup pieces, which are shown

FIG. 11.7

Axial load on the top entry ball valve.

Valve design and weight reduction

511

FIG. 11.8 Bending load on the top entry ball valve.

FIG. 11.9 Torsional load on the top entry ball valve.

FIG. 11.10 Wave load.

in Fig. 11.11. Sensors (strain gauges) installed on several critical areas of the valve body can show the possibility of body elastic deformation due to the loads. Body deformation externally can cause seat leak, and body deformation internally may damage the seat or ball and body or cause the seats to get stuck in the body.

512

FIG. 11.11

11. Pipeline valves

Valve bending moment test.

A bending test is a proof on validation of the finite element analysis (FEA) report. Fig. 11.12 shows the FEA on the body of a pipeline valve with a top entry design. The bending test may be avoided if an FEA report is provided by the manufacturer. The bending test can be done with design and accidental loads when the body and bonnet are all together. This test can be repeated with the maintenance load when the bonnet is off during maintenance and the valve is more fragile against the loads. The spool pieces are usually used during the bending (load)

Valve design and weight reduction

513

FIG. 11.12 Finite element analysis on the body of the valve.

test at the ends of the valve pup piece to increase the length of the valve and get sufficient bending moment. The applied load to the valve is limited, so increasing the length through spool pieces is the solution to get a higher bending moment. The maintenance test could create body ovality in a way that the bonnet cannot be assembled on the valve body easily. Fig. 11.13 shows the bending test on a pipeline valve including the strain gauges. In addition, cylindrical nuts are used for valve body/bonnet connection instead of ASME B18.2.2 standard heavy hexagonal nuts to save the weight of the pipeline valve. Fig. 11.14 shows a pipeline valve 3800 Class 1500 with circular nuts. Cylindrical nuts have the same diameter as standard hexagonal nuts, but without the corners (see Fig. 11.15). This design allows having more bolts on the same circle because adjacent nuts can be located much closer than with hexagonal nuts. This design also saves some centimeters outside the diameter of the body and bonnet and the weight. The valves are heavier than 1 ton, so a weight certificate should be issued for them. A special tool for bolt tensioning of large size valves is required with hydraulic power. The bolt sizes in Fig. 11.15 are larger than 100 , so a tensioning tool should be used for the body and bonnet bolts, tightening as shown in Fig. 11.16. A bolt tensioning tool is purchased as a special tool. The estimated torque for fastening the bolt is between 87,687 N.M. and 131,530 N.M. for a 3800 Class 1500 valve with L7 bolts and one double piston effect seat. The required tension force to achieve that is 7200 kN, the maximum bolt tension before plastic deformation is 9238 kN, and the maximum bolt tensioning of the tool is 8505 kN with 150 barg hydraulic force.

514

11. Pipeline valves

FIG. 11.13

Valve bending moment test including the strain gauges. Courtesy: FCT.

FIG. 11.14

3800 Class 1500 top entry ball valve with cylindrical nuts. Courtesy: FCT.

Body design/material Carbon steel plus 3-mm corrosion allowance is usually suitable for noncorrosive oil and gas services in export pipelines. However, 22Cr duplex could be the better choice of material for export oil and gas offshore pipelines (designed as per ASME B31.3 code) in order to save the weight of the pipeline. 22Cr duplex has no corrosion allowance and it has higher mechanical strength than carbon steel. Therefore, pipe wall thicknesses, weight, welding electrode

Body design/material

FIG. 11.15 Hexagonal nuts based on ASME B18.2.2 Standard.

515

516

FIG. 11.16

11. Pipeline valves

Bolt tensioning tool.

consumption, and perhaps the number of supports are saved by selecting 22Cr duplex material for the offshore pipeline. The valve bodies could be made in ASTM A105 or ASTM A216 WCB/WCC or A352 LCB/LCC. Therefore, the valve in carbon steel material may be welded to different pipeline material in 22Cr duplex. There are two main reasons why pipeline valves are made of carbon steel and not 22Cr duplex. The first reason is that changing the valve from carbon steel to duplex makes the valve much more expensive. Not only the body but also the trim of the valve must be upgraded to 22Cr duplex material. In addition, making a large size thick duplex valve has problems related to heat treatment. Quenching of the thick 22Cr duplex valve can be unsuccessful since the core may not cool down rapidly and achieve the required mechanical strength. Some engineers may prefer forge ASTM A105 material as a preferred solution, since it is stronger and has less change of defects compared to the casting. The delivery time is also shorter for forged material. Although the forging process is usually more expensive than

Body design/material

517

casting, forging is more cost effective compared to casting. Weld repair is allowed only for cast and not forged materials. When the body of the valve is ordered with casting, it has less thickness since casting is close to the final shape. But when it comes to forging, the thickness of the body is greater, so a lot of machining is required to make the forging close to the shape. Fig. 11.17 shows the cast body of a top entry ball valve of 3800 size and 1500 pressure class in low-temperature carbon steel material. The bosses on the valve are for drain (seat retraction) that will be explained later. The body casting inspection includes mechanical tests (tensile and yield), hardness test, elongation test, and charpy test in the body casting foundry. It is recommended to apply a radiography test (RT) in addition to the magnetic particle test on a large size and high-pressure class ball valve such as Class 1500 and 3800 size. Sometimes it might be difficult for the supplier to apply an RT test on the body casting of a riser valve due to its special shape and thickness variations. In that case, an ultrasonic test (UT) may be proposed instead of an RT. In fact, some areas are not accessible, so an RT test is not possible. RT should be done for welded pup pieces and transition pieces. A magnetic particle test and visual examination in addition to UT should be applied. Fig. 11.18 shows complex top entry ball valve body casting areas. Tests done in the foundry for row material such as casting or forging include heat treatment, test sampling, mechanical and chemical composition test, and perhaps dimension check and NDT. The ASTM A991 standard is the standard test method for conducting temperature uniformity of the furnace used for heat-treating the steel product. Tensile and impact tests are both done based on ASTM A370. Some casting blocks are molded for the mechanical test. Carbon steel material’s lowest design temperature is 29°C as per the ASME B31.3 Process Piping Code. That temperature restriction can be increased due to thickness, as per ASME B31.3 Fig. 323.2.2A. The temperature curve in Fig. 11.19 for carbon steel is curve B. The minimum temperature can be reduced to a value below 29°C if the thickness of the pipe or valve exceeds 12.7 mm. The carbon steel material should be impact-tested at 29°C in order to be used for a minimum temperature of 29°C. The other choice to avoid the extra cost of the

FIG. 11.17 Cast body of a 3800 class 1500 top entry ball valve.

FIG. 11.18

Complex-shaped areas on a top entry ball valve body casting.

Nominal Thickness T, in. [Note (6)] 0

1.0

0.394 0.5

1.5

2.0

2.5

3.0 130

50

120 110

40

100

Design Minimum Temperature, °C

30

eA

te [No

v Cur

(2)]

90 80 70

20

)]

ve B

(3 ote

60

[N

Cur

10

50

0

ve C

te [No

40

(3)]

30

Cur

20

–10

10 ve D

0

Cur

–20

Design Minimum Temperature, °F

Note (1)

–10 –20

–30

–30

Note (4)

–40 Note (5)

–48 –50 0

10

20

30

40

–55 –60 50

60

70

Nominal Thickness T, mm. [Note (5)]

FIG. 11.19

Minimum temperature without impact test for carbon steel material based on ASME B31.3.

Welding

519

impact test is to select a low-temperature carbon steel body valve, such as a valve made in LCB/LCC casting materials. In such a case, the bolting should be changed to low-temperature carbon steel L7. Low-temperature carbon steel can be used for a minimum design temperature of 46°C without applying any impact test.

Welding Welding of a transition piece to the valve body as well as welding the pup piece to the transition piece is done prior to putting valve internals in the body so there is no possibility of internal damage during these welding activities. The pup piece should be long enough to avoid soft material damage inside the valve as well as ball valve sealing disturbance due to the heat of welding between the valve pup piece and the pipeline at the construction yard. Fig. 11.20 shows a top entry ball valve body with the connected pup pieces and transition pieces on a welding machine. The end to end of the valve was increased 50 mm on each side of the casting due to a welding issue. The roller was placed on a 50-mm long groove on each side of the casting. The purpose of the roller under the valve was to facilitate rotation of the valve during welding. Fig. 11.21 shows the welded pup piece and transition piece to the body of a top entry ball valve. In addition, butt weld and post weld heat treatment temperature of the valve pup piece and the pipeline in the yard should not exceed 200°C to melt the lip seal in the seat pocket. One way to avoid high temperature could be circulation of cold water in the body cavity during the welding. The pup piece is not painted by the manufacturer since the paint will be damaged due to the welding. Tectyl may be applied internally to the pup piece as a means of corrosion and rust prevention. The pup piece is welded to a blind cap (ASTM A694 F52) to be used during the pressure test of the valve at the manufacturer’s site. The cap is cut after the test and the pup piece is beveled again according to either ASME B16.25 or narrow gap welding (7° as an example) and keeping the duplex welding temperature to a maximum of 150°C.

FIG. 11.20 Top entry ball valve on the welding machine.

520

FIG. 11.21

11. Pipeline valves

Top entry ball valve connection to the pup piece and transition piece. Courtesy: ATV/FCT.

Fig. 11.22 shows post-weld heat treatment on the welding of the valve body to a transition piece. The valve in carbon steel material (e.g., A352 Gr.LCC) is connected to the duplex pipe through a carbon steel transition piece and a duplex pup piece (ASTM A182 F51) as illustrated in Fig. 11.23. The transition piece and pup piece are welded to the body of the valve and transition piece, respectively. Item number 18C provides both welding and hub connection, and enables the valve manufacturer to pressure test the valve with the blind hub. The other approach to blind the end of the valve during the pressure test is to weld a cap to the pup piece as shown in Fig. 11.24. Some suppliers may prefer to test the valve with the blind hub at the end of the pup piece to avoid welding and cutting the cap. The large size valve should be fastened to the machine for cutting the cap, which is difficult and time-consuming. Fig. 11.25 shows a blind hub specially made for the end of a top entry ball valve during the pressure test.

521

Welding

FIG. 11.22 Post-weld heat treatment on the valve body welding to the transition piece.

SEE DETAIL D 800 18a

18c

A352 Gr. LCC

A694 Gr. F52

A182 F51

FIG. 11.23 Body valve connection to the pipeline through the pup piece and transition piece.

522

11. Pipeline valves

FIG. 11.24

Cap welded to the transition piece for the pipeline valve pressure test. Courtesy: ATV.

FIG. 11.25

Special blind hub custom-made in the factory for pressure test of the valve. Courtesy: FCT.

Welding

523

Welding of a 22Cr duplex pipe to a carbon steel body valve is done through a 22Cr (F51) pup piece. The pup piece 22Cr duplex is not directly welded to a carbon steel valve in larger sizes (e.g., 2000 and 3800 ) where there is a significant thickness differential between the carbon steel valve and the 22Cr pup piece. For example, if the pipe is of 60 mm thickness and the valve is 103 mm, the thickness differential is more than 50%. In that case, a transition piece (F52 usually) is required between the carbon steel valve and the 22Cr duplex pup piece in order to join the two different materials and thicknesses. Welding a 22Cr pup piece to a carbon steel valve creates a lot of heat input and there is a risk of sigma phase in welding such a high thickness of two dissimilar materials. In addition, welding carbon steel to 22Cr in thickness above 19 mm requires buttering of Alloy 625 on the carbon steel material and it is very difficult to apply buttering on a thick carbon steel valve thicker than 100 mm. The heat affected zone (HAZ) of the welding between the F52 transition piece and the F51 pup piece should be within the buttering of Alloy 625 (shown on the right side of Fig. 11.26) and not extended to the F51 pup piece (shown on the left in the figure). If HAZ is located on the F51 pup piece, an impact test should be required for both F52 and F51 after the welding. In this case, HAZ is extended on both F52 and F51 as well as the buttering layer of Alloy 625. It could be possible to weld the carbon steel valve to a 22Cr pup piece without a transition piece in smaller sizes (e.g., 1200 ) where the thickness offset between the valve and the pipe is less, and the heat input of welding is low. Fig. 11.27 shows the testing of a pneumatic actuated valve during the test in vertical position without any transition piece. The pup piece is directly connected to the valve. The valve is tested vertically because it is going to be installed in the vertical line.

FIG. 11.26 HAZ of welding between the transition piece and pup piece.

524

FIG. 11.27

11. Pipeline valves

Top entry ball valve without any transition piece between the valve and pup piece. Courtesy: ATV.

Fig. 11.28 shows another top entry ball valve with a hub connection and a pneumatic actuator. The body of the valve is directly connected to the pup piece without a transition piece, since the valve is not very large. The picture shows the valve during the pressure test. Hub end valves are tested with the hub profile in most cases, upon request by the end user. Welding of the carbon steel transition piece to the 22Cr duplex pup piece is challenging due to the post-weld heat treatment (PWHT) requirement for carbon steel if the thickness exceeds 19 mm as per ASME B31.3, the process piping code. PWHT is not recommended for 22Cr duplex material, so carbon steel should be buttered with Alloy 625 and then PWHT is applied. Afterward, a filler of Alloy 625 should be used to weld the carbon steel to 22Cr duplex. Carbon steel is preheated at 100°C before buttering by Inconel 625. Fig. 11.29 illustrates the welding of the carbon steel transition piece to the duplex pup piece through buttering with Inconel 625 as well as Inconel 625 filler. The other option is buttering on both the carbon steel and the duplex side (Fig. 11.30). 100% volumetric NDT (RT or UT) should be applied on the buttering layer. Alloy 59 is the better choice of filler and buttering compared to Inconel 625 since it does not have Niobium

Welding

525

FIG. 11.28 Top entry ball valve without any transition piece between the valve and pup piece. Courtesy: ATV.

FIG. 11.29 Welding of a 22Cr duplex pup piece to a carbon steel transition piece.

FIG. 11.30 Welding of a 22Cr duplex pup piece to a carbon steel transition piece through double buttering.

526

FIG. 11.31

11. Pipeline valves

Connection of the top entry valve to the DNV pipe.

unlike Alloy 625. Niobium can cause welding defects. The welding temperature of the duplex should not go above 150°C to avoid sigma phase formation. Welding of the cap to the pup piece and the pup piece to the transition piece can be done with tungsten inert gas with 99% argon shielding, or by using the submerged arc welding (SAW) process. Sand (powder) is used in SAW to avoid ingress of the oxygen to the weld. The pup piece of the pipeline valve is in carbon steel if the valve is connected to a riser pipe in DNV code as shown in Fig. 11.31. The code break between ASME and DNV in this figure is at the end of the pup piece. Fig. 11.32 shows a more detailed view of the code break between DNV and ASME. The 694 F65 pup piece that is welded to the DNV pipe in Fig. 11.32 is equivalent to an API 5L X65 pipe and should be thicker than the DNV pipe. The DNV pipe is pressure tested with 1.2 times the design pressure and the ASME pipe is tested with higher pressure than the DNV test—1.5 times of the design pressure. The end part of the pup piece, F65 material, in ASME code, has been reduced to 45 mm to match the thickness of the DNV pipe. The end part of the pup piece does not have the test pressure since it is blinded with the blind flange (hub) during the test and this narrow part is located downstream of the blind flange. At least one additional pup piece should be ordered for the valve in the boundary of ASME and DNV code. The additional pup piece(s) should be made with the same heat number to the foundry that made the pup piece welded to the transition piece on the valve. The additional pup piece(s) will be used as the test ring in the yard prior to the welding of the valve pup piece to the pipeline, in order to qualify that weld. The extra pup piece(s) could be made in ASTM A694 F65 and 300 mm long, as an example. The connection between the pup piece in duplex and the transition piece in carbon steel material should be radiography tested (RT test). The carbon steel transition piece is buttered with Inconel 625. Cobalt is a good X-ray with better penetration property. In some cases, welding of a carbon steel valve to a downstream low alloy subsea riser line (DNV pipe equivalent to API 5L X65) may be done without a transition piece. This can be

527

Welding

Code Break ASME B31.3 DNV-OS-F101

WELD

FIG. 11.32 Code break between the top entry valve and the DNV pipe.

done when two materials of pipe and the connected valve pup piece are the same with a small thickness offset. In this case, the pup piece could be ASTM A 694 F65, for example, and it may be directly welded to the carbon steel valve from one side and to the API 5L pipeline from the other side. A transition piece is not required if the ratio of valve thickness/pup piece thickness < 1.5 (less than 50% offset between two thicknesses) that can happen in smaller sizes such as 1200 or 1400 . Otherwise, a transition piece ASTM A694 F52 should be welded to the valve from one side and to the pup piece from the side, as illustrated in Fig. 11.31. There are five weld types on the riser valves: 1. Tungsten carbide spray—high velocity oxygen fuel (HVOF) overlay, maximum 200 μm on the ball seat surfaces and seats. Tungsten carbide can be even thicker, but could be porous. However, some end users may propose tungsten carbide hard-facing even in 400 μm. The pipeline valves are metal-seated, which is a robust option. 2. Alloy 625 weld overlays on the seat, seal, and grooves of the body and bonnet connections as well as drain and vent flange grooves. In addition, the body and bonnet sealing areas with RTJ connections, the seat retraction sealing area, and flushing ports should have an Inconel 625 overlay. An Inconel 625 overlay is applicable only for carbon steel body valves to avoid crevice corrosion. Fig. 11.33 shows the areas of the top entry valve that should have an Inconel 625 weld overlay. 3. The valve internal body in carbon steel could be overlaid with Inconel 625 to protect the valve from corrosion during shipment and storage. 4. Casting weld repair. 5. Welding between the pup piece, the transition piece, and the cap (circumferential welds). The weld overlay of alloy 625 could be 5–6 mm initially. However, the thickness will be reduced to 3 mm after machining, as an example. The welding method is tungsten inert gas weld. The filler is Inconel 625 material that is melted by tungsten. The low amount of delusion and slow welding are very important in this type of welding. Fig. 11.34 shows the Inconel overlay on the facing (contact surface) of the ring (the intermediate body piece) of the ball valve that may be cast through centrifugal casting to be very smooth.

528

11. Pipeline valves B

C

VOIR DETAIL E

VOIR DETAIL A

E

E VOIR DETAIL C

VOIR DETAIL B

B

C

FIG. 11.33

Areas of a carbon steel valve with an Inconel 625 overlay.

FIG. 11.34

Inconel 625 weld overlay on carbon steel casting. Courtesy: FCT.

Bonnet design The bonnet is a heavy part of a top entry ball valve. Fig. 11.35 shows the bonnet during machining. There is a hole in the bonnet to reduce the weight of the bonnet and the entry ball valve. As mentioned earlier, it is very important to reduce the weight of pipeline valves as much as possible. Also, there is a step (male/female) on the body and bonnet of the valves for mechanical stop and better seating of these two pieces together. Fig. 11.36 shows the step on the bonnet of the valve.

Bonnet design

529

FIG. 11.35 Bonnet during machining.

FIG. 11.36 Step on the bonnet of a top entry ball valve.

There is sealing (lip seal) between the body and bonnet of the valve, as illustrated in Fig. 11.37. The machining action on the bonnet is called “turning.” The bonnet (the piece under machining) is rotating while the machining tool is fixed. Another machining action is called “milling.” It means that the machining tool is moving and the piece being machined is fixed. Milling happens when machining the bolt holes and flange faces. Fig. 11.38 shows the bonnet and body assembly through the long bolts after finalizing the machining on the bonnet.

530

11. Pipeline valves

FIG. 11.37

Sealing between the body and bonnet.

FIG. 11.38

Body and bonnet assembly.

Ball design The valves may have one double piston effect seat. Therefore, the balls for double isolation and bleed (DIB) valves with one or two double piston effect seats can be larger and heavier than a ball for a standard ball valve with self-relieving seats. The reason is that more loads during the FEA can be experienced on the ball of the DIB valve from special double piston effect seats and the spring. Fig. 11.39 shows an FEA on the ball of a 3800 Class 1500 valve.

Seat design

531

FIG. 11.39 FEA on the ball of a 3800 Class 1500 pipeline valve.

Fig. 11.40 shows an FEA on the seat and ball contact areas of a 2000 class 1500 top entry ball valve. The seat in contact with the ball is a double piston effect type. The red (grey in print version) lines on the right side of Fig. 11.40 indicate that the stress level between the ball and the DPE seat exceeds the limit. Therefore, the ball should be strengthened by adding thickness, which affects the weight of the valve and possibly the face-to-face dimension. Fig. 11.41 shows the ball of a 3800 Class 1500 ball valve. Fig. 11.42 shows the top of the ball in contact with the stem.

Seat design The seat is usually metallic even if the service fluid is clean oil or gas and the temperature is less than 150°C. One reason for having a metallic seat could be a high frequency of pig running that increases the opening and closing frequency for one valve downstream of the pig launcher. To avoid the risk of seat damage, a more robust metallic seat is a better choice than a soft seat. Another reason to select a metal seat could be a high-pressure drop during the opening of large size ball valves. A high-pressure drop increases wearing, risk of cavitation, and soft seat socking out and damage. In addition, the debris from welding and grinding can damage the seat during the hydrotest and commissioning if the valve is soft seated.

532

11. Pipeline valves

FIG. 11.40

Ball/DPE seat FEA for a top entry 2000 CL 1500.

FIG. 11.41

Ball of a 3800 Class 1500 pipeline valve. Courtesy: FCT.

Seat design

533

FIG. 11.42 Top of the ball in contact with the stem. Courtesy: FCT.

The seat may be equipped with flushing ports. The oil that lubricates the ball and seats is clean. Flushing ports enable cleaning and flushing of the seat in case the valve does not seal properly between the seat and ball. As an example, wax formation from the oil may become stuck in the seat area and become harder over time. It interferes with functioning of the seat arrangement and disturbs the tightness of the seat to the ball. Thus, it may be proposed by the valve manufacturer to install flanged connection flushing points (ports) on the seat for solvent injection on the seat arrangements. As an example, two flushing ports per seat (a total of four ports) are designed on a 3800 class 1500 ball valve for pipeline application with four modular valves for the isolation of flushing ports. The flushed solvent is injected into the body cavity at the back of the seat and the seat and ball contact afterward through the multiple holes (e.g., 12 holes) drilled in the seats for sealant injection. Fig. 11.43 shows a seat with flushing port holes.

534

11. Pipeline valves

FIG. 11.43

Seat with the holes for flushing. Courtesy: FCT.

FIG. 11.44

Top entry ball valve with the modular valve used for isolation of the flushing port. Courtesy: FCT.

Flushing and sealant injection ports are probably integrated to reduce the number of holes on the body of the valve. But the sealant injection port may not be large enough to be used for a flushing port. A flushing port from the sealant inject port can create extra holes and potential leakage points on the valve cavity, so it may not be desirable from a valve design point of view. Due to the risk of leakage from the flushing port, it might be a good idea to have an integrated flushing port with the body instead of welding a nippo flange to the body of the valve. It is recommended to seal the flushing ports with the modular valves. Fig. 11.44 shows a top entry ball valve 3800 class 1500 with modular valves installed on the flushing ports.

Seat design

535

FIG. 11.45 Sealant injection in orange. Courtesy: FCT.

A DPE seat requires more flushing than an SR seat. The maximum pressure of flushing should not be more than the valve design pressure. Fig. 11.45 shows the sealant injection fluid in orange color. The sealant injection is a viscous component and perhaps four ports per seat have been considered for sealant injection on the pipeline valves. Emergency sealant injections are installed on soft and metal seats to inject the sealant and repair the soft/metal seat ring (restore sealing integrity) as well as postpone the required maintenance of the seat. A soft seat has the first priority for emergency sealant injection since it is more exposed to the risk of damage. Although a metal seat is more robust with a tungsten carbide hard facing, an emergency sealant is usually required for the metal seat as well. The injection is done during normal operation. Sealant injection on the seat is not preventive maintenance. The sealant injection can repair the seat and stop the leakage temporarily. As an example, a 3800 top entry ball valve can be equipped with two opposite flushing ports per seat within a relatively large area to allow high flow for efficient cleaning. These holes are 100 class 1500 RTJ flanged on the external surface of the body and plugged by modular valves to keep them isolated from the environment so as to avoid leakage. The injected flushing fluid should be channeled through the holes drilled inside the seats. The crude oil (pipeline fluid) entrapped at the back of the seat should be dissolved in the flushing fluid and pushed inside the pipe. The injection flow and pressure rate should be forceful enough to create effective cleaning. The flow or pressure values are dependent on the gravity and viscosity of the flushing fluid. A higher flow rate increases the cleaning efficiency. Fig. 11.46 shows three top entry ball valves after the pig launcher. All of them have one seat in a double piston effect (DPE) toward the pig launcher. A DPE seat provides tighter sealing

536

11. Pipeline valves

Oil Export Pumps Cavity Thermal relief

DP

Pig Launcher

SR

XV0811 38”

DP

SR

XV0812 38”

DP

ESV0817 38”

SR

Oil Export pipeline

Trapped incompressible fluid

FIG. 11.46

Pipeline valves after pig launcher.

compared to the self-relieving (SR) seat toward the pig launcher, which needs to be opened for pig launcher maintenance. A DPE seat is bidirectional, which provides better isolation and minimizes the risk of leakage from the body cavity. The DPE seat is pushed more tightly against the ball than a unidirectional SR seat, due to the higher torque containing a spring and/or the special seat design with two lip seals instead of one. Fig. 11.46 shows a condition in which two valves after the pig launcher are closed by mistake. Therefore, the pressure shown in blue color (dark grey in print version) is built up between two valves. There was a proposal to have DPE seats on both sides of the first valve after the pig launcher, since the cavity can be over-pressurized through the built-up pressure in the line between two valves. However, the best design is to install a pressure safety valve (PSV) on the line between two valves after the pig launcher in order to release the excess pressure. Having two DPE seats on a valve requires an extra hole on the cavity for PSV installation and there is more risk of leakage. The PSV on the body cavity requires regular maintenance, which is not a preferred solution from an operational point of view. There are usually two to four pieces of valves installed on a 3800 pipeline (Fig. 11.46). The first one (XV0811) is located just downstream of the pig launcher, and isolates the launcher in case of maintenance. This valve could be a ball or TCG type and it is usually closed and electrically actuated. Since the first valve might be opened and closed frequently due to pig running, a pressure equalizer line from the cavity to the suction may be required in order to reduce the wearing of the valve. The second valve (XV0812) is the backup and the same as the first valve with an electrical actuator and it is always open. The reason to have a backup is that the first one needs to be opened and closed frequently, which exposes it to wearing and maintenance. The second valve is usually open to avoid frequent opening and closing for the pig running. The last ball valve (ESV 0817) isolates the ASME B31.3 design code offshore line from the DNV design code subsea riser pipeline. It is usually an open Emergency shutdown (ESD) valve with a hydraulic actuator. This valve is closed in case of failure occurrence through a signal from the ESD system. The code break between ASME and DNV is usually on the weld between the valve pup piece and the pipe. Since the code break is on the toe of the weld of the pup piece, the pup

537

Seat design

piece should be made of material based on both DNV and ASME codes. Support may be needed on a long-length pup piece, and its material should be according to ASME code. When it comes to marking DIB valves, the SRXDPE seat should be written on P&IDs and isometrics, and should be highlighted in the Plant Design Management System (PDMS) model. The construction yard personnel need to know the correct directions of DP and SR seats. The SR and DP could be hammered onto the body of the valve toward each seat. However, it may not be clear (readable) after painting, so hammering is not recommended. API 6D provides the marking of DPEXSR through a plate that is connected to the body through the rivet illustrated in Fig. 11.47. The material of the plate and rivet are in Inox (SS316). Sometimes the marking could be done on the flange edge. The arrangement of the PSV installation on the DIB1 valve illustrated in Fig. 11.48 requires an isolation valve, which is a wedge gate valve for low-pressure class valves or a double block

FIG. 11.47

Typical identification plate for valve with one seat unidirectional and one seat bidirectional based on

API.

Min. 1/2" relief valve Bracing to main valve

Min. 1/2" piping

Valve cavity vent connection

Valve body 2 pcs. flanged wafer wedge gate valve

FIG. 11.48 PSV installation on the valve body for high-pressure class.

538

FIG. 11.49

11. Pipeline valves

One DPE seat and one SR seat for a 3800 Class 1500 ball valve. Courtesy: FCT.

and bleed valve for high-pressure class valves. The isolation gate valve should be locked open and closed only in case of PSV maintenance and calibration. A tee is required to have two connections, one for pressure release through PSV and the other one for a manual vent. The PSV is usually ¾00 for sizes up to and including 1200 and 100 for sizes above 1200 . Fig. 11.49 shows the two types of seats for a 3800 Class 1500; one is SR and the other one DPE. The DPE seat is longer (higher) than the SR seat and located at the back of the picture.

Special bore diameter The bore of the valves should be equal to the pipeline internal diameter due to the pig running. Although the valves are designed based on API 6D, the minimum bore diameters given in API 6D are not necessarily piggable. The bore of the valve is usually less than the internal diameter of the pipe, especially when the pipe is in 22Cr duplex with no corrosion allowance and less thickness. Fig. 11.50 shows a drift test after manufacturing and assembly of a riser ball valve by passing a tool (1-m long bar with three circular shape plastic plates on both ends and the middle) to make sure that the internal diameter of the valve is suitable for running the pig.

Valve maintenance

539

FIG. 11.50 Drift test on a top entry ball valve. Courtesy: ATV.

Cycling A cycle is defined as the continuous movement of the valve closure member or obturator from the fully closed position to the fully open position and back to the fully closed position, or vice versa. Valve manufacturers usually guarantee valves to operate for a maximum of 1000 cycles. A cycling test for 1000 times can wear the valve down, and is not required by some end users. Fluid types can affect the wearing in a way that oil could lubricate and result in minimum wearing as compared to dry gas. A cycle test may be done before the main seat leak measurement to make sure that sealing is good enough even after cycles. The valve supplier may propose a small number of cycles (for instance, 10 times) prior to the main seat test or DIB seat test, which can improve the sealing, like lapping. Fig. 11.51 illustrates a cycle test for a DIB valve.

Valve maintenance One type of valve design is to have seat retraction tools on the body of the valve to move the seats away from the ball. When the bonnet is completely removed, the stem and ball can be removed from the body completely. In the final step, one seat after the other can be removed for maintenance and repair purposes. There are threaded holes on the ball, stem, and bonnet for removal and lifting. Fig. 11.52 illustrates seat retraction tools on the top entry ball valve body. Fig. 11.53 shows details of the seat retraction tool.

540

FIG. 11.51

11. Pipeline valves

Cycle test of a DIB valve 3800 Class 1500.

The retraction tool includes extension, eccentric, gear box, flange, and sealing, as illustrated in Fig. 11.54. The blind flange connection (number 13) is connected to the gear box (number 12: through lip seal) and graphite (number 14). The lip seal seating surface on the flange should be overlaid with alloy 625. Figs. 11.55 and 11.56 show a top entry valve body with seat retraction tool flanges on the body.

Valve maintenance

FIG. 11.52 Top entry ball valve with seat retraction tools on the body. Courtesy: FCT.

541

542

11. Pipeline valves

Details of the seat retraction tool on the top entry ball valve body. Courtesy: FCT.

SEAT RETRACTED

SEAT IN CONTACT AGAINST THE BALL

FIG. 11.53

FIG. 11.54

10 - EXTENSION 11 - ECCENTRIC 12 - GEAR BOX 13 - FLANGE 14 - SEAL

10 11 12 14 13

Details of the seat retraction tool on the top entry ball valve body. Courtesy: FCT.

Valve maintenance

FIG. 11.55

543

Cast body of a top entry ball valve with bosses for machining the seat retraction tools. Courtesy: FCT.

FIG. 11.56 Seat retraction flanges on the body of the valve. Courtesy: FCT.

There is a step on the body and bonnet bolt holes for better connection to the bonnet. The seat retraction flange (Fig. 11.57) is machined from bosses integrated to the body during the casting as shown in Fig. 11.58. The flange for a seat retraction tool is not a pressure-containing part, so the seat retraction flanges are thinner than the body cavity drain flanges. Fig. 11.59 shows the holes on the bonnet, stem, and ball, which can be used for lifting these components. Fig. 11.60 shows removal of the ball from the valve body after operating the seat retraction tools.

544

11. Pipeline valves

FIG. 11.57

Seat retraction flanges.

FIG. 11.58

Body of a top entry ball valve.

545

Valve maintenance

THREADED HOLE FOR JACK SCREW TO LIFT THE BONNET AT STARTING OF DESASSEMBLING

THREADED HOLE TO LIFT THE BALL THREADED HOLE ON THE SHAFT

THREADED HOLE TO LIFT THE BONNET WITH EYEBOLTS (used for assembling of shaft extension)

FLANGE THICKNESS

CENTRING PIN

FIG. 11.59 Holes/pins on the ball, stem, and bonnet for lifting. Courtesy: FCT.

removing/installation of the ball seats retracted

Carefully verify that the ball is perfectly centred while installation to avoid a damage of the lower trunnion bushing

FIG. 11.60 Ball removal from the valve body after seat retraction operation. Courtesy: FCT.

546

FIG. 11.61

11. Pipeline valves

Special tools for lifting the ball from a top entry ball valve installed vertically. Courtesy: FCT.

A different approach in removing the ball from the top entry ball valve installed on the vertical line is illustrated in Fig. 11.61.

Valve internals protection In order to avoid any damage to the valve internals (particularly trim) during the construction, commissioning, and shutting down of the plant, the top entry ball valves, installed on the pipeline, can be designed with internal sleeves. The internal sleeves can be in PTFE (Teflon) material, for example (see Fig. 11.62). The sleeve is installed inside the valve instead of trim after the pressure test. The valve with the internal sleeve is connected to the line during construction. The valve internals are removed from the valve after pressure test and will be sent to the construction yard separately. The sleeves should be removed after the construction, pressure test, and commissioning, and the trim is replaced inside the valve. One approach is to operate one valve that is closest to the pig launcher so the two other top entry ball valves are filled with the sleeve. In this case, the ball, seat, and lip seal of the first valve after the pig launcher are subject to damage during the commissioning. Therefore, an additional ball, seat, and lip seal can be ordered as spares for the internals of the valves close to the launcher. The first valve internals after the launcher should be sent back to the valve supplier in case of damage and the spare valve internals can be used instead. There is much grinding during welding that could damage the valve internals, so it may be better to install the sleeves to protect the internals from the weld grindings. The valves need to be tested after returning the trims back to the valves. The sleeve is not installed inside the valves in some cases due to extra activities and the cost for returning the trim parts inside the valve, as well

Valve support

547

FIG. 11.62 PTFE sleeve on the top entry ball valve internals.

FIG. 11.63 Valve body cast with a circular area at the bottom for supporting the valve. Courtesy: FCT.

as retest. Therefore, the other option is to simply avoid sleeves for all of the valves since removing the valve internals and returning them back to the valve is very challenging in terms of lifting tons of valve internals and opening the tested valves. In addition, placing the valve internals into the valve increases the project time.

Valve support The valve is self-supported through a circular area at the bottom of the valve. Fig. 11.63 shows the circular area at the bottom of the cast valve body. The valve can sit on this circular area without any support requirement, but a support is usually designed on the downstream of the ESD valve (last valve) on the pipeline.

548

11. Pipeline valves

Valve coating Coating is usually applied for valves in the offshore industry. The type of coating could be thermal spray aluminum or zinc epoxy. Thermal spray aluminum is a more expensive coating than zinc epoxy. However, there are two layers of coating for thermal spray aluminum compared to three layers for zinc epoxy type. Therefore, coating with thermal spray aluminum is less time-consuming than coating with zinc epoxy. But repairing the thermal spray aluminum is more difficult than repairing the other coating type. The coating is not applied on the pup piece due to welding at the construction site. The pup piece is coated after welding to the line at the construction site. Fig. 11.64 shows the valve after coating with zinc epoxy in white color.

Valve preservation All valves including top entry riser valves require preservation during and after delivery in order to be protected against harmful environmental conditions. Wind, dust, humidity and salt, sand blasting and painting, high or low environment temperatures, and external forces are examples of harmful environmental conditions. Protection of the valves should cover all stages of transportation, storage, lifting, handling, installation, and testing in the construction yard. Preservation duration depends on the storage and fabrication period, which could be as short as 6 months or as long as 2–5 years. Corrosion inhibitors such as Tectyl, lube oil, wax, grease, or equivalents are recommended for using inside of the valves and body flange faces. The valves used in drinking water services should not be preserved with internal corrosion inhibitors since preservative chemicals can jeopardize the health of personnel. In addition, oil, wax, and grease are not allowed for internal protection of valves used in oxygen services. The inhibitor should be removed from the flange face before installation to avoid disturbing the valve and mating flange sealing. The corrosion inhibitor should be thin (not thick) enough to be removed easily from the valve flange faces. The valve body ending should be protected with rubbers (e.g., Nitrile rubber 1.5 mm thickness) and plywood (e.g., 6 or 10 mm thickness). Fig. 11.65 shows a top entry ball valve ending preservation with plywood and nitrile rubber.

Valve packing and lifting The riser valves are large, so they are not carried in a wooden box. A pallet (base) made of wood or metal that is seaworthy is used under the valve as a support against the valve weight and/or lifting.

Valve packing and lifting

FIG. 11.64 Top entry ball valve after painting. Courtesy: FCT.

549

550

FIG. 11.65

11. Pipeline valves

Top entry ball valve flange preservation.

A metallic option of the base frame with extra cost is also available upon project request (shown in Fig. 11.66). Fig. 11.67 shows the wooden frame that is placed under top entry ball valves for transportation. There are four lifting lugs on the body of the valve (Fig. 11.68) which are used for lifting. There is also a lifting point on the valve skid (the pallet installed under the valve) that should not be used for lifting if it is not certified. The valve lifting lugs are usually certified by the valve supplier and not the skid lifting points. There are chains for lifting of the valve that should be opened in opposite directions, as shown in Fig. 11.68, to avoid any clash with the valve actuator. Using the cross or H device (Fig. 11.69) provides four lifting points from the top of the valve. Two lifting points on the top of the valve can make the chain clash with the actuator in some cases, especially if the actuator is large (such as pneumatic). Dismantling the actuator

Valve packing and lifting

551

FIG. 11.66 Top entry ball valve with a metallic frame. Courtesy: FCT.

from the valve during transportation is not a preferred choice, since this requires reassembling the actuator on the valve in the construction yard and retesting the valve and actuator together. Fig. 11.70 shows the process of lifting the valve through the H device. The lifting lugs can be welded or integrally casted to the body. The body of the valve during the fabrication is lifted upside down because it is more stable in that position, as shown in Fig. 11.71. When it comes to ball transportation, there is a lifting point on the ball used for lifting with a fork. Lifting the valve with the fork is not suitable for a long distance on the deck. A trolley or cradle is used for transporting the ball on the deck. Fig. 11.72 shows a cradle that is used for transportation of the whole valve assembly on the deck.

552

FIG. 11.67

11. Pipeline valves

Wooden frame for top entry ball valves. Courtesy: FCT.

It is recommended to transport the ball stands on the trunnion (Fig. 11.73), but since the ball is not stable on the trunnion, it is proposed to be fastened to the frame or wall by a bolting system. On the other hand, transporting the ball in the other direction increases the risk of the ball damage, especially during the turning of the ball. But the ball is more stable when it sits on the hole of the ball and not on the trunnion (Fig. 11.74). Fig. 11.75 shows the ball that sits on the hole and not on the trunnion on the shop floor of the company.

Valve packing and lifting

FIG. 11.68 Lifting with two lifting points without a cross and clash with an electrical actuator.

FIG. 11.69 Cross or H device for providing the chain angle.

553

554

FIG. 11.70

11. Pipeline valves

Lifting of the valve with a Cross/H device. Courtesy: FCT.

Valve experience after FAT

555

FIG. 11.71 Lifting of a valve body upside down. Courtesy: FCT.

FIG. 11.72 Cradle for transportation of a pipeline valve.

Valve experience after FAT It is important to dry the valve after a hydrostatic test to avoid rust and corrosion. Fig. 11.76 shows a 3800 Class 1500 body of a pipeline ball valve in low-temperature carbon steel including

556

11. Pipeline valves

FIG. 11.73

Ball of a ball valve on the trunnion.

FIG. 11.74

Ball of a ball valve sitting on the hole.

the cavity drain flange. The water was not drained after the pressure test and there is some rust on the flange face (Fig. 11.77). There is more than just corrosive products and rust on the cavity drain flange. Additionally, the darker color may contain chemicals used for preservation, such as Tectyle or Socopac. Some corrosion inhibitor products can be used for removing rust.

Valve experience after FAT

FIG. 11.75 Ball of a ball valve sitting on the hole. Courtesy: FCT.

FIG. 11.76 Opening the valve cavity drain.

557

558

FIG. 11.77

11. Pipeline valves

Rust on the body cavity flange.

C H A P T E R

12

Valve technology and selection Valve definition What is a valve? A valve is a mechanical device used to control the flow of fluid. Valves start, stop, and regulate the flow; prevent backflow; and provide double isolation to prevent leakage and for safety reasons. Valve selection tips in this chapter do not cover valves for drilling, Christmas tree valves, or the following valves: • Pressure safety valve (PSV): This type of valve is designed to open and relieve the excess pressure from equipment such as vessel to flare systems. Fig. 12.1 shows a PSV. The overpressurized fluid coming from the bottom overcomes the spring torque and pushes the disk upward. The fluid has 90° rotation to the outlet line and toward the flare. • Chock valves: These valves can be used to control and reduce the pressure from the drilling well and reservoir to the topside. Thus, they can stop the pressure from the reservoir and regulate the downstream pressure in the flow line. Fig. 12.2 shows an angle chock valve. As with PSVs, the fluid enters the valve through the inlet line and the fluid pressure is reduced through the valve internal plug. The fluid will have a 90° rotation to the outlet line.

Valve selection tips There are no bad valves; just poor valve selection. The following sections introduce and discuss some important considerations and parameters that affect valve selection.

Valve applications The most important parameter that affects valve selection is the application. Table 12.1 presents the valve choices suitable for different applications.

A Practical Guide to Piping and Valves for the Oil and Gas Industry https://doi.org/10.1016/B978-0-12-823796-0.00021-0

559

# 2021 Elsevier Inc. All rights reserved.

560

FIG. 12.1

12. Valve technology and selection

Pressure safety valve.

The ball valve (Fig. 12.3) is the first choice of valve for many end users (operator companies) for the start/stop of fluid, especially in process services such as hydrocarbon (oil and gas). The valve is more robust in comparison to butterfly and wedge-type gate valves. This valve is a “quarter turn valve,” which means that opening and closing the valve is done through a

FIG. 12.2

Angle chock valve.

Valve selection tips

TABLE 12.1

561

Valve choices suitable for different applications.

Application

Valve choices

Start/stop fluid

Ball valve, butterfly valve, wedge gate valve, through conduit gate valve, plug valve

Regulate fluid

Straight pattern globe valve, Y-type globe valve, axial on-off valve, axial control valve

Nonreturn fluid

Swing check valve, tilting check valve, dual plate check valve, nonslam axial flow check valve, piston and ball lift check valve

Double isolation

Modular valves, double wedge gate valve

90° rotation of the ball (closure member). Another choice for starting or stopping fluid is the butterfly valve, which is more compact, lighter, and cheaper than the ball valve. Fig. 12.4 shows a Class 150 wafer-type butterfly valve in titanium material for seawater (firewater) application in the offshore industry. The wafer design is a flangeless design when the valve is placed between the flanges. One disadvantage of the butterfly valve is the flow capacity which is less than that of the ball valve. A third option for stopping or starting fluid is the wedge gate valve (Fig. 12.5), which is generally cheaper than a ball valve in the same size and pressure class. However, the wedge gate valve is not popular except for small sizes for the line drain and vent applications in the Norwegian offshore industry. Through conduit gate (TCG) (Fig. 12.6) and plug valves (Fig. 12.7) are two other valve options for starting or stopping the flow of fluid in very unclean (dirty) services where even a metal seat ball valve is not a suitable choice. TCG valves are produced in two design types: slab and expanding. A plug valve is more compact than a TCG valve. Straight pattern globe valves (Fig. 12.8), Y-pattern globe valves (Fig. 12.9), and axial valves (Fig. 12.10) are three more alternatives for flow control or regulation. In a straight pattern globe valve (Fig. 12.8), the flow reaches the center of the valve where the trim (seat and plug) are located. There is a narrow area (vena contracta) in the center of the

FIG. 12.3 Ball valve (open position).

FIG. 12.4

Wafer-type butterfly valve.

FIG. 12.5

Wedge gate valve.

FIG. 12.6

TCG valve.

FIG. 12.7 Plug valve.

FIG. 12.8 Straight pattern globe valve.

FIG. 12.9 Y-pattern globe valve.

564

FIG. 12.10

12. Valve technology and selection

Axial valve.

valve where the pressure is minimal and the velocity is maximal. After the flow reaches the vena contracta, it makes a 90° turn toward the seat, followed by another 90° turn to the outlet port. These three alterations to the flow create a substantial pressure drop in the globe valve. The pressure in the narrow area below the plug can drop below the vapor pressure of the liquid in a globe valve in liquid services. This results in the bubbles of the gas being vaporized from the liquid, which is called flashing. The bubbles will recover the pressure and collapse firmly in a way such that they create pressure waves. Consequently, the pressure waves cause damage to the seat, plug, and body of the globe valves. This phenomenon, called cavitation, is known as the most common operation problem of straight pattern globe valves. Thus, straight pattern globe valves operated for throttling or flow control are at the high risk of wearing, erosion, and cavitation mainly due to high-pressure drop. API 623 specifies the requirements for heavy duty bolted bonnet straight pattern globe valves to minimize the risk of wearing and cavitation. These requirements include heavier wall sections, larger stem diameters, hard facing on the seat and disk for high-pressure classes, etc. In addition, a globe valve is a heavy valve that is not generally selected for large sizes above 1400 . Y-pattern globe valves have less pressure drop compared to straight pattern globe valves, with less cavitation risk. Axial valves are lighter than globe valves, with high flow capacity and low-pressure drop. The smooth flow path through an axial flow valve avoids turbulence and prevents erosion, cavitation, and vibration. However, an axial flow valve is more expensive than both straight and Y-pattern globe valves. Check valves, including swing type (Fig. 12.11), dual plate (Fig. 12.12), piston (Fig. 12.13), and ball lift, as well as axial flow nozzle check valves (Fig. 12.14), are commonly used in both offshore and onshore platforms. A swing check valve is cheaper than a dual plate and suitable for particle-containing services. However, the disk of this valve is closed by gravity forces. If the disk is closed too quickly, gravity can cause the disk to slam against the body of the valve. The other most common operation problem of a swing check valve is water hammering, which is the result of high-pressure shock waves that occur in a relatively noncompressible fluid. When the liquid is forced to stop suddenly as a result of fast valve closing, a shock wave is produced with a slamming effect.

FIG. 12.11 Non-slam check valve.

FIG. 12.12 Dual plate check valve.

FIG. 12.13 Piston check valve during the face-to-face measurement. Courtesy: Bonney Forge.

566

FIG. 12.14

12. Valve technology and selection

Axial flow check valve (a type of non-slam check valve). Courtesy: Crain Stockham.

Non-slam check valves (Fig. 12.11) are designed specifically to avoid water hammering. As the name implies, non-slam valves close without slamming quickly, so no pressure spikes are created. A dual plate check valve (Fig. 12.12) has an internal spring opposing the opening fluid flow pressure. When the flow is strong enough, the spring compresses, the valve opens, and the spring smoothly pushes the disk back toward the seat as the flow slows down and stops, but before flow direction reverses. Dual plate check valves are not suitable for dirty services. Piston or ball lift check valves are common nonreturn valves on small sizes, such as 200 and below, for nitrogen purging applications. Axial flow check valves are a type of non-slam check valves mainly selected for use downstream of compressors and pumps. These robust valves can withstand the vibrations and loads produced by the upstream equipment. An axial flow check valve has a very light disk with a very short distance between the disk and the seat, which makes it a very quick-closing valve. These valves have a very low-pressure drop, which reduces energy consumption and loss of the upstream pump or compressor. However, axial flow check valves usually have longer face-to-face measurements than dual plate check valves with the same size and the same pressure class. In addition, axial flow check valves are more expensive than other types of check valves in terms of capital expenditure (CAPEX). Modular valves called double block and bleed valves are often used to provide double isolation in high-pressure classes and/or hazardous fluid services (toxic or flammable fluids and those that can damage human tissues). A double block and bleed valve, when closed, provides a seal against pressure from both ends of the valve with a means of vending/bleeding the cavity between the seating surfaces. The modular valve in Fig. 12.15 is made of two ball valves with a needle valve as a bleeder between. Modular valves provide double isolation in different applications. They isolate instrumentation such as pressure or level gauges from the connected piping or pressure vessels in case of instrument gauge maintenance. Orifice flanges are used for the purpose of measuring the

Valve selection tips

567

FIG. 12.15 Modular valve including two ball valves and a needle between. Courtesy: Bonney Forge.

flow rate. Pairs of pressure tapping are machined directly opposite each other on pairs of orifice flanges. The tapping holes are connected to pressure gauges, which are double isolated by modular valves in some cases.

Valve size One important consideration is how the valve size can affect the valve selection. Wafertype butterfly valves are good alternatives to ball valves in utility services such as water, air, etc. in on/off applications because they are lighter, more compact, and cheaper than ball valves. API 609, the design standard for butterfly valves, covers eccentric butterfly valves from 300 and above. In addition, the valve flow coefficient (Cvvalue) of a butterfly valve is less than that of even a reduced bore ball valve. The Cv value is a number that represents the capacity of a valve to allow fluid to flow. More accurately, a Cv value of 100 means that 100 gal of fluid per minute are passing through the valve at 60°F, with a differential pressure of 1 psi. Having the disk right in the middle of a flow stream can create a significant flow restriction, especially in smaller sizes. Therefore, butterfly valves for utility services are selected in sizes 400 and above in the Norwegian offshore industry due to flow capacity problems. By the same token, a ball valve is the choice for sizes smaller than 400 for on/off applications in utility services. The other example in which the valve size affects the valve selection is for nonreturn fluid applications. Piston or ball lift check valves are usually selected for the valves in small sizes less than and equal to 200 as an example.

Valve dimensions and weights Saving weight and space is more important in the offshore industry than in onshore applications since there are limited spaces on a platform or ship. The face-to-face dimension of a wafer-type butterfly valve is much less than that of a ball valve, as shown in Fig. 12.16. The figure shows a 2000 CL 150 butterfly valve for a firefighting water service

568

12. Valve technology and selection

FIG. 12.16

Comparison of a wafer-type butterfly valve (A) and a full-bore ball valve (B), soft seat. (A) 2000 CL150, titanium body; face to face: 127 mm; weight: 231 kg. (B) 2000 CL150, 22Cr duplex body; face to face: 914 mm; weight: 1569 kg. (A) Courtesy: Westad, (B) Courtesy: FCT.

and 2000 CL150 full-bore ball valve in process services, and compares the weight and face-toface dimensions of these two valve types. Additionally, a butterfly valve is lighter with less torque requirement for opening and closing compared to a ball valve, which could save the size and cost of the actuator or gear box. Torque is a measure of how much force is needed from a valve operator to rotate the valve closure member to be opened or closed. A butterfly valve disk is lighter compared to the closure member (ball) of a ball valve, and the disk does not have contact with the seat during its travel. The other comparison is between a ball valve and a through conduit gate valve regarding space requirements (see Fig. 12.17). Both of these valves are mainly used for process services such as hydrocarbon (oil and gas). When it comes to space requirements, TCG valves require more vertical space when they are installed on a horizontal line regarding the height of the valve, as well as vertically installed mounting actuators. On the other hand, ball valves require more space horizontally when they are installed on a horizontal line. Therefore, the lack of vertical space can make a TCG valve an unacceptable choice.

FIG. 12.17

Height comparison of an actuated ball valve (left) and a TCG valve (right). Courtesy: ATV.

Valve selection tips

569

FIG. 12.18 Jet water injection line to separator.

Fluid types Even metal seat ball valves are not recommended for very dirty fluid services due to possible seat damage during the opening and closing of the valve. Therefore, TCG or plug valves are the acceptable alternatives in very dirty services. One of the typical examples of dirty piping lines in an offshore unit is the jet water injection outlet lines from the separators (Fig. 12.18). The water jet is injected into the separators to wash out sand and particles that have accumulated at the bottom of the separators. The water jet outlet line valves should be selected for very dirty sand-containing water services. The produced water outlet line valves should be TCG valves or plug valves, since the produced water contains a high amount of sand. Fig. 12.19 shows a TCG valve 400 and pressure class 300 equal to 50 barg that was selected in a project for separator outlet lines.

Required flow capacity (Cv values) The flow capacity must be considered during valve selection. For example, butterfly valves are not selected for sizes 400 and below in the Norwegian offshore industry because they cannot provide the required flow capacity in small sizes. Another example is the comparison between axial and dual plate check valves. Axial flow check valves are a very good choice of valve selection downstream of pumps and compressors. The low-pressure loss and high fluid capacity of this valve minimizes pump and compressor energy loss and consumption.

Operating pressure and pressure drop Higher operating pressure and higher pressure drop increase the chance of cavitation in globe valves for flow regulation in liquid services. One solution is to select an axial on/off or Y-type globe valve instead of a straight pattern globe valve, as discussed earlier.

Operation requirements Both TCG and plug valves are used for on/off applications in very dirty services. The TCG valve is the preferred choice of some end users simply because lubricated plug valves should

570

FIG. 12.19

12. Valve technology and selection

TCG valve 400 class 300 with electrical actuator for sandy water service. Courtesy: Valvitalia.

be lubricated by an operator as a part of the operation and maintenance program. A lubrication schedule requirement as a part of an operation and maintenance program may not a desirable solution for some end users. For this reason, TCG valves can be selected in the case of jet water injection to the separator in Fig. 12.18. The positive side of a plug valve when compared to a TCG valve is its compact design. Another example of an operation issue that affects valve selection is the risk of cavitation in straight pattern globe valves. Cavitation (explained earlier) can create irregular pits and erosion in the trim (seat and plug) and body of globe valves as well as downstream piping. Fig. 12.20 shows cavitation damage in the form of small pits, very similar to the corrosion damage, in the plugs of globe valves. Cavitation intensifies the effect of corrosion, which could then be called “cavitation corrosion.” Fig. 12.21 shows a major cavitation attack in the form of pits on the plug sealing areas in a globe valve. The valve loses its sealing capability when the plug sits on the seat due to the cavitation. Cavitation can produce excessive noise and vibration and create localized stresses (loads) on valve bodies in addition to pitting, corrosion, and erosion. Vibration and noise due to bursting of the bubbles reduce the globe valve efficiency. Alternative valve selections such as Y-pattern globe and axial valves should be selected instead of straight type globe valves to reduce or eliminate the risk of cavitation. Additional issues to consider when selecting an appropriate valve include tightness, cost, delivery time, and client (end user) preferences. Fig. 12.22 shows an export pipeline from the platform to the shore. The pipeline includes two parts, topside and subsea, with the different design codes of ASME and DNV. The export

Valve selection tips

571

FIG. 12.20 Cavitation damage to the plug of a globe valve.

FIG. 12.21 Cavitation damage to the sealing area of a globe valve plug.

FIG. 12.22 Export pipeline from the platform to the shore plus three valves.

line valves are installed on the pipeline on the platform upstream of (before) the subsea section and they are designed based on the ASME code. These pipeline valves are the most important valves in an offshore platform since they are the largest, heaviest, most expensive, and most complex valves with the longest delivery time in an offshore plant. The valves usually selected for an export pipeline are either top entry ball

572

FIG. 12.23

12. Valve technology and selection

Actuated ball valve 2800 and Class 1500.

valves or TCG valves for inline maintenance. Fig. 12.23 shows a 2800 CL900 actuated top entry ball valve. Top entry valves can be TCG, as an alternative. The selection of a ball valve or a TCG valve depends on parameters such as cost, delivery time, valve dimensions, space availability, weight, client preference, etc. A 3800 Class 1500 TCG gate valve was compared to a top entry ball valve with the same size and pressure class, considering the cost and delivery time, in an offshore project. Two different valve manufacturers were questioned about the cost and delivery time of these two types of valves. It was concluded that the 3800 CL1500 TCG valve was more expensive than the top entry ball valve, but it had a shorter delivery time. Some end users may prefer ball valves and some may rather use TCG valves, so both options have been selected and experienced in different projects.

Valve selection case studies Other parameters affect valve selection, such as fast opening. This section aims to describe a fast-opening valve selection experience in the flare system. When equipment in an oil and gas plant is over-pressurized, the pressure relief valves or the safety instrument system releases the over-pressured gas or liquid to the flare headers. The flare lines are usually connected to knockout (KO) drums, which are liquid-gas separators, to remove any liquid in the form of oil and water from the gas. The separated gas will be burned in the flare stack located downstream of the KO drum. Fig. 12.24 shows the basic flare system flow diagram. When increasing the KO drum pressure to the high-high (HH) limit, the pressure transmitter sends a signal to a control system and the fail open valve should be opened very quickly to release the extra pressure in the KO drum. In this example, the valve located downstream of the KO drum is 2800 and pressure class 150 in 6MO material. The process engineer asks for 2 s of opening time for the fail open emergency valve. Usually, the opening time for an actuated valve with a fail open function should be 1 s per size (in inches). Therefore, this 2800 emergency

Ball valve selection

573

Control System

FIG. 12.24 Basic flare system flow diagram.

fail open valve should be opened in 2 s instead of 28 s as a result of a fast opening (FO) application. In fact, the extra quick opening requirement of the valve imposes further attention on the valve selection considerations. Three types of valves—ball, butterfly, and axial control—were evaluated for application of the FO application downstream of the KO drum. After considering the three, an axial control valve was selected by the operator company.

Ball valve selection Ball valves are not recommended for FO applications. Generally, it is possible to reduce the opening time of the fail open actuated valve by installing a quick exhaust valve on the control panel to release the instrument air from the pneumatic actuator in the fail mode quickly. However, a ball valve’s seat and disk are in contact during the opening and closing, which can jeopardize FO. In addition, moving the relatively large and heavy ball requires a higher stem torque, a larger actuator, and perhaps a longer opening time. The ball valve manufacturer was asked about the possibility of using a soft seat ball valve for this application. The manufacturer believed that FO of the soft seat ball valve in 2 s could cause damage to the soft seat because of the very quick contact with the ball. On the other hand, the manufacturer stated that a 2-s opening time can be achieved with a metal seat ball valve. But a metal seat has the disadvantage of possible leakage, unlike a soft seat, and it is a more costly solution than butterfly and axial control valves due to the valve and the large mounted actuator. Unlike FO applications, a ball valve is a good choice as a blowdown valve with less opening time than an FO valve. Fig. 12.25 shows a blowdown ball valve to release the overpressured fluid from the equipment in an emergency mode. The blowdown ball valve is an 1800 Class 2500 in a 6MO body and a metallic Inconel 625 seat, which may need 18 s

574

FIG. 12.25

12. Valve technology and selection

1800 Blowdown ball valve 6MO material CL2500. Courtesy: FCT.

for opening. Blowdown or FO valves on flare lines usually see low operating temperatures because of the released gas pressure drop. Gas pressure drop reduces the operating temperature to 46°C or even lower, so the minimum design temperature is typically below 100°C. The low temperature application makes it impractical to use 22Cr duplex with a minimum design temperature of 46°C for the valve, so 6MO or Inconel 625 are the correct choices of materials. An extended bonnet is used for the valve to keep the packing away from the relatively cold service, similar to cryogenic valves.

Wafer butterfly valve selection It was a challenge for the butterfly valve manufacturer to design a wafer-type double offset butterfly valve in 2800 for FO applications since a large diameter stem was required in a very thin wafer body. Large size (2800 ), actuation, and a very quick opening put great amounts of force/torque on the valve and necessitated designing a larger stem diameter. Flanged-type butterfly valves (Fig. 12.26) with a thicker body, particularly triple offset, can be suitable for FO applications. Triple offset butterfly valves are currently used for process services in some plants instead of ball valves, and they have the advantage being less costly than ball and axial control valves. Another important consideration for butterfly valve selection is the Cv value of the valve. Butterfly valves are reduced bore, unlike full-bore ball valves, with lower Cv values. Full-bore ball valves are usually applicable for the flare and sub flare lines upstream and downstream of pressure relief valves. Therefore, it is recommended to check the required Cv value of the butterfly valve based on the process requirement with the actual Cv value provided by the valve manufacturer. In this case, the valve manufacturer confirmed that the 2800 CL150 double offset butterfly valve had a Cv value of 28,000 gal per minute, and a minimum 25,000 gal per minute flow was acceptable by the process department. It is noticeable that triple offset butterfly valves have an even less Cv than double offset valves because of a larger and heavier disk and stem on the flow path.

Axial control valve selection

575

FIG. 12.26 Flanged butterfly valve. Courtesy: Westad.

Axial control valve selection An axial valve (Fig. 12.27) can be used instead of a globe valve to eliminate the risk of cavitation for flow control application, and this type of valve is a good choice for FO purposes. Fig. 12.28 shows the internals for a typical axial valve. The disk in an axial flow valve is moved back and forth through the loads transmitted from the stem and adjusts the flow. Several characteristics of this valve make it suitable for FO. The distance between the disk and the seat is short and the disk mass is low, so the opening and closing time is short and the applied torque for valve operation is relatively low. In addition, there is no contact between the disk and seat during valve operation. Low-pressure drop and almost no cavitation risk reduce the risk of the seat and disk material failing due to erosion

FIG. 12.27 2800 CL1500 axial control valve ASTM A352LCC body valve. Courtesy: Petrol Valve.

576

12. Valve technology and selection

Stem Disk Seat

FIG. 12.28

Axial valve internals.

and cavitation, and minimize the cost of operation and maintenance. Although this valve is more expensive than the butterfly valve, it was finally selected for FO application in the project. The most significant consideration was that the Cv value of the axial control valve is much less than that of the butterfly valve. The manufacturer of this valve confirmed that the Cv value of the 2800 axial valve is 12,000 gal per minute, which was less than half the Cv value required by the process department. It was decided to have a special bore of 3000 with a 2800 flange axial valve for this application to increase the Cv value to 25,000 gal per minute. Another situation involves an 1800 wafer-type actuated butterfly valve with an emergency shutdown (ESD) function that should be closed quickly in case of failure, as shown in Fig. 12.29. It is important to decide whether a butterfly valve with ESD function is sufficient, or if the valve should be changed to a ball valve. The butterfly valve should be fine for a quick closing action, especially considering the fact that the disk is light and would not touch the seat during closing and opening. However, an ESD function can increase the load on the valve stem,

FIG. 12.29

1800 Class 150 wafer-type butterfly valve.

Axial control valve selection

577

especially when closing the valve. Therefore, the stem of the valve may need to be thicker to withstand the loads. It should be noted that a wafer-type butterfly valve has a compact faceto-face design, according to the API 609 standard. Therefore, it could be challenging for a butterfly valve supplier to accommodate manufacturing a thick stem into a thin wafer body. Another case study is related to the valve selection for dirty services. According to API RP 615, “Dirty service is a general term used to identify fluids with suspended solids that may seriously impair the performance of the valve unless the correct valve type and trim are selected.” Trim refers to valve internals in contact with the service, such as the valve closure member, the seat, etc. Hard materials such as martensitic stainless steels (13Cr or 13Crd4Ni) and 22Cr duplex stainless steel, as well as applying hard materials such as Stellite, are recommended for the valves used in dirty services. Dirty service can be divided into two categories on production platforms: 1. Limited amount of abrasive particles that do not create significant erosion on the pipe wall thickness and valve parts. 2. Large-scale amount of abrasive services such as sands and scales that can cause a small amount (such as 1 or 2 mm) of erosion on the pipe wall and valve parts. This case study covers valve selection for category 2 dirty fluid services for offshore production platforms. The selected valves should be robust with minimum maintenance requirements, and durable enough to be operated during the long design life of the plant (e.g., 30 years). Dirty service category 2 usually exists in two main areas of an offshore production platform. First, the mixture of oil, water, and gas produced at the wellhead, which is transported to the first stage separator through the flow lines, contains a large amount of sand coming out from the reservoir. Therefore, valves on the flow lines downstream from the wellhead and upstream of the first stage separator should be selected for very dirty services. Second, the sand that is produced is accumulated under the separators, so jet water is injected into the separators to wash them. The outlet lines from the separators contain large amounts of sand, so selected valves for those lines should be robust enough to handle very dirty services. Fig. 12.30 shows a typical very dirty line (in red color, light gray in print version) in an offshore plant including the flow line and the produced water outlet line of the separator, as well as associated valves (in blue color, dark gray in print version). It is remarkable that there is more than one flow line and also several produced water outlet lines in a typical offshore platform. All valves are for on/off applications and not flow control. Different types of valves are typically selected for dirty services such as pinch valves, diaphragm valves, knife gate valves, plug valves, and TCG valves. A metal seat ball valve is not a good choice for very dirty services, because particles can get stuck between the ball and the seat while opening or closing the valve and damage the seat. A pinch valve (Fig. 12.31) is not recommended since a rubber tube closure member is pushed by stem movement and two pinch bars, which causes a high risk of damage due to frequent operation (opening and closing). In addition, the valve is not fire safe so it is not suitable for high-temperature services. A pinch valve can be operated by hydraulic or pneumatic forces rather than a handwheel, as illustrated in Fig. 12.32.

578

FIG. 12.30

12. Valve technology and selection

A schematic showing very dirty service lines including the flow line and separator-produced water

outlet line.

Rubber tube closure member is pressed to close the pinch valve through stem movement and two pinch bars before and after the rubber

FIG. 12.31

Pinch valve.

PINCH VALVE

Hydraulic - “Calper Type”

Hand Wheel Type PNEUMATIC

FIG. 12.32

Pinch valve operation types.

Axial control valve selection

579

FIG. 12.33 Diaphragm valve.

Due to the flow line design pressure that is usually class 1500 (pressure nominal of 250 barg) and the possibility of having high temperature, both pinch and diaphragm valves are not suitable. Both of these valves have nonmetallic internals with limited resistance against pressure and temperature. Although it is not common to use a diaphragm valve (Fig. 12.33) for very dirty process lines in the Norwegian offshore industry, it might be a good idea to consider the diaphragm valve as an option and evaluate the suitability of this type of valve for separator-produced water outlet line valves. Separator-produced water outlet line valves are usually of small size and low pressure (e.g., 400 and CL300) and not high temperature. A diaphragm valve does not have any complete tube inside the valve, unlike a pinchtype valve, and just a layer of rubber isolates the top of the valve that is pushed down by the stem to the metallic body as illustrated in Fig. 12.34. In case of actuation, both pinch and diaphragm valves have the actuator vertically installed on the top of the valve.

FIG. 12.34 Straight through diaphragm valve.

580

FIG. 12.35

12. Valve technology and selection

Knife gate valve.

The pinch valve rubber tube can be replaced easily and quickly with inline maintenance. The tube can have a sensor to keep the operator informed of the required maintenance. The pinch valve should be leak-free due to rubber-to-rubber contact during closing, and it is bidirectional. The face-to-face dimension should be adjusted based on ASME end-to end in order to be replaceable with a plug, gate, or ball valve. A pinch valve is not robust due to using just a rubber tube as the closure member that is forced by the stem. It is not a fire-safe design and not for higher temperature ranges. A knife gate valve (Fig. 12.35), as per the MSS SP 81 standard, is bonnet-less and not suitable for high-pressure classes above 150-psi cold working pressure. Thus, this valve should also not be considered for the previously mentioned applications. TCG valves (slab, double, or single expanding) are very common choices for dirty services in both flow lines and separator-produced water outlet lines. A significant advantage of the TCG valve is to provide double isolation, which cannot be achieved through pinch, diaphragm, and typical knife gate valves based on the MSS SP 81 standard. Fig. 12.19 shows a slab gate valve 400 CL300 with two self-relieving seats in 22Cr duplex material with an electrical actuator for a separator-produced water outlet line before pressure testing at the manufacturer’s factory. In some cases, a TCG valve occupies a large space, considering the fact that this type of valve is relatively high compared to other types of valves such as ball and plug valves. In this situation, lubricated plug valves can be selected. The important point is that a lubricated plug valve is not a desired valve for some end users because regular lubrication must be performed by the operators to provide effective sealing between the plug and the body. Fig. 12.36 shows a 2400 Class 2500 slab gate valve in 22Cr duplex material coated with phenolic epoxy located on a very dirty line connected to the first stage separator. The actuator is hydraulic and spring return. The challenge is to make sure that there is enough space available for both the valve and the vertically installed actuator.

Axial control valve selection

581

FIG. 12.36 2400 CL1500 22Cr duplex body slab gate with a hydraulic spring return actuator. Courtesy: Valvitalia.

The following conclusions can be made regarding valve selection for very dirty services: 1. Very dirty services refer to fluids with large amounts of sand that cause erosion on piping and valves. 2. Metal-seated ball valves are not suitable for very dirty services, but could be acceptable valves for dirty services with limited amounts of sand. 3. Flow lines and separator-produced water outlet lines are typical piping systems with very dirty services on a production offshore platform. 4. Pinch, diaphragm, and knife gate valves are not recommended for offshore applications. 5. TCG valves are the best choice for very dirty applications. It is recommended to select the full-bore TCG valves with guiding plates (gate guides), as shown in blue (dark gray in print version) in Fig. 12.37. 6. A plug valve may be selected for a separator-produced water outlet line if there is not enough space available for a TCG valve. This discussion is an example of valve selection in a typical oil and gas preliminary processing (treatment) plant based on the fluid category, size, and application. Table 12.2 provides different valve choices based on different applications. Fluids belong to one of four categories: Category 1: Process clean (e.g., clean gas). Category 2: Process dirty (e.g., sandy oil).

582

12. Valve technology and selection

FIG. 12.37

Double expanding gate wedge including two half disks and gate guides. Courtesy: Orion.

TABLE 12.2 Valve selection options based on each application. Valve type

On/off flow

Flow regulation

Nonreturn

Double isolation

1

Ball valve

Standard globe valve

Piston check valve

Double ball valve with a needle between (modular valve)

2

Wedge gate valve

Y-type globe valve

Ball lift check valve

Double gate valve with a needle between

3

TCG valve

Axial valves

Swing check valve

4

Butterfly valve

5

Dual plate check valve Axial flow check valve

Category 3: Utility (e.g., air, fresh water). Category 4: Seawater. The next step is to define the type of fluid category in each process and utility unit (Table 12.3). The next step is to select the suitable valve for each fluid category based on each application. The proposed valves are given with two codes in Table 12.4. Table 12.5 gives detailed definitions of each code and the reasons for valve selection.

TABLE 12.3

Process and Utility unit’s fluid category determination.

Process and utility units

Fluid name

Fluid category

1. Separation unit

Multiphase hydrocarbon including sand

2

2. Crude handling and metering system

Clean crude oil

1

3. Gas compression system

Clean gas

1

4. Gas treatment system

Mainly clean gas

1

5. Oil export system

Clean oil

1

6. Gas export and metering system

Clean gas

1

7. Water injection system

Mixture of seawater with oil

1

1. Cooling medium system

TEG with water

3

2. Heating medium system

TEG with hot water

3

3. Chemical injection

Chemicals

1

4. Flare system

Hydrocarbon or nonhydrocarbon

1 or 3

5. Oily water system

Oil plus water

1

6. Fuel gas system

Fuel gas

1

7. Chlorination system

Sodium hydrochloride

1

8. Seawater system

Seawater

4

9. Freshwater system

Drinking water

3

10. Open drain system

Mainly utility and nonhazardous services

3

11. Closed drain system

Hazardous hydrocarbons probably with particles

2

12. Diesel oil system

Diesel oil

1

13. Compressed air system

Air for instrumentation

3

14. Inert gas system

Inert gases

3

15. TEG storage system

TEG

3

16. Hydraulic system

Hydraulic oil

1

A. Process units

B. Utility units

TABLE 12.4 Final valve selection. Double isolation

On/off

Flow regulation

Nonreturn

Cat. 1: Process clean

BL

Low-pressure class: LY < 400 and LS > 300 ; high-pressure classes: LY < 400 and AO > 300

CP < 3, CD > 2, CN for after pumps and compressors

DB

Cat 2: Process dirty

TC / PL

Low-pressure class: LY < 400 and LS > 300 ; high-pressure classes: LY < 400 and AO > 300

CS

DB

Cat 3: Utility

BL < 400 FH > 300

LY < 400 and FH > 400

CP < 3, CD > 2, CN for after pumps and compressors

DG

Cat 4: Seawater

BL < 400 FH > 300

LY < 400 and FH > 400

CP < 3, CD > 2, CN for after pumps and compressors

DG

TABLE 12.5 Valve definition and analysis. On/off values BL

Ball valve. Selected for process services because it is robust with zero leakage risk in case of a soft seat. In addition, a ball valve is selected for categories 3 and 4 (utility and seawater) services for small sizes less than 400 since a butterfly valve cannot provide enough Cv value

TC

TCG valve. A TCG valve performs properly in a dirty service, unlike a ball valve. (Refer to note 4)

PL

Plug valve. Plug valves perform properly in a dirty service, unlike ball valves. (Refer to note 4)

FH

Butterfly valve. Selected for utility and seawater in sizes 400 and above to save space and weight compared to ball valves. (Refer to note 3)

Flow regulation valves LY

Y-pattern globe valve. Selected for small sizes up to and including 300 to avoid high-pressure drop and erosion and wearing problems. (Refer to note 6)

LS

Straight pattern globe valve. Proposed in some cases and better to be based on the API 623 standard.

AO

Axial valve. Good valves for flow regulation, with a low-pressure drop and minimum wearing and erosion.

FH

Butterfly valve. Proposed for flow regulation in utility and seawater services instead of straight globe valves, to minimize wearing and cavitation. In addition, a butterfly valve is more compact and lighter than a globe valve.

Nonreturn valves CP

Piston check valve. Very common for small sizes up to and including 200 .

CD

Dual plate check valve. The proposed choice for sizes up to and including 300 if the fluid is not dirty and if the valve is not located after pumps and compressors. The valve is not robust enough for installation after pumps and compressors.

CN

Non-slam axial flow check valve. The best choice of check valve to locate after pumps and compressors (refer to note 8). It provides less pressure drop and better resistance to the vibration coming from the pump and compressor. However, this valve is not proposed for dirty services.

CS

Swing check valve. The only option for a check valve in dirty services. This valve is not proposed for other applications since it has a high-pressure drop and causes a slamming effect.

Double isolation valves DB

Double ball valve and a needle valve as a bleed. This is a very common choice of double isolation.

DG

Double gate valve and a needle between for utility and seawater (nonhazardous) services to reduce cost and save space in terms of the face-to-face dimension compared to DB selection.

C H A P T E R

13

Piping and valve corrosion study Corrosion is defined as the deterioration or destruction of a material or its properties because of its reaction with the environment. It is nearly impossible to avoid corrosion in the oil and gas industry. However, it is possible to control corrosion by addressing fundamentals in a safe and economical manner. Therefore, corrosion control is very essential to reduce corrosion risks and reduce costs. Corrosion in oil and gas is a very costly and dangerous phenomenon. Like natural disasters such as earthquakes, corrosion can cause serious damages to human health, ecosystems, and facilities in oil and gas plants. Corrosion can cost 3% of the gross national product (GNP) or even more in a developed country such as the United States. The impact of corrosion in the oil and gas industry has had a significant impact on three aspects of the US economy: capital expenditures (CAPEX), operation expenditures (OPEX), and health, safety, and environment (HSE). It has been mentioned that 25% of all failures in the petroleum industry are associated with corrosion failures. Engineers and scientists face significant challenges in controlling the impact of corrosion on safety and economy in the oil and gas industry. The National Association of Corrosion Engineers (NACE) conducted a survey in 1972 to estimate the cost of mitigating corrosion in the United States. NACE announced that the cost of corrosion in the United States at that time was approximately $10 billion per year. A subsequent survey in 2001 revealed that the cost of corrosion had risen to more than $600 billion, which was 4%–6% of the country’s GNP. In 2014, the International Tanker Owners Pollution Federation Limited (ITOPF) published a technical report that detailed the economic effect of oil spillage due to corrosion or any other reason. Firstly, corrosion leads to oil spillage and losing a precious product (asset). As a result of that loss, more barrels of oil are required to be transported from other countries. Secondly, oil spillage cleanup is an expensive process that requires government aid. Thirdly, tourist activities dramatically reduce in areas with oil spillage, which reduces the tourist industry revenue. Fourthly, companies that produce and distribute the oil can lose their reputations due to oil spillage disasters caused by corrosion failures. The cost of corrosion is not limited to these items. In 2013, Volkan Cicek added more items to the cost of corrosion, such as corrosion preventive measures, plant shutdown, and maintenance costs. In fact, corrosion prevention requires more expensive material selection or sometimes greater thickness of material, and design and installation of corrosion monitoring

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13. Piping and valve corrosion study

and management systems, which increase the cost of engineering work as well as procurement and construction in projects. Usually, at least part of a plant must be shut down when there is a corrosion failure. Plant shutdown is a costly action because production stops, which means losing money because the plant cannot sell oil. In addition, the corroded valve or pipe adds maintenance cost in terms of replacement or repair, which means loss of assets and the expense of buying new facilities. One of the most negative consequences of corrosion is hydrocarbon or oil spillage into the environment (e.g., sea). There is no question that an oil spill can seriously damage the environment and human life. The ITOPF report about oil spillage discussed the ways in which ecosystems and nature are affected negatively by marine oil spillage. As an example, oil spills in the sea make it difficult for animals (dolphins, fishes, birds, and mammals) as well as plants to survive in the water or even in the areas close to the sea. It is noticeable that shorelines are more vulnerable to the effects of oil spillage than areas in the sea. The impact of corrosion on HSE is as damaging as the cost consequences of the corrosion. If corrosion is not checked or is poorly controlled, it can damage plants and humans seriously as a result of leakage. It is noticeable that oil and gas are flammable fluids with a high risk of causing fire and explosions, and they can be extremely toxic due to hydrogen sulfide (H2S) content. It should be noted that although chemical, corrosion, and scale inhibitors are widely used to mitigate corrosion risk, they are not environmentally friendly compounds in case of entry into the environment. When North Sea offshore oil and gas drilling and production activities started in the mid1970s, concerns arose about the risk of oil pollution and spillage in the sea. As an example, in 2011, oil spillage in North Sea due to pipeline leakage released more than 200 tons of oil from the Gannet Alpha Oil platform located 180 km away from Aberdeen. This spillage, from a platform operated by Shell, The Dutch Operator Company, has been the largest oil spill since 2000. Much has been written about the long-term environmental impacts of oil spillage. It has been believed that oil spillage can have a negative impact in seawater for decades and create swamps and salt marshes. However, in most cases, the environment can recover itself in less than a decade. The recovery can be sped up through oil removal and cleanup operations but recovery is not an easy task. A model has been created to measure the estimate of oil spill costs including the cost of damage to the environment. This model takes oil spill factors into accounts such as spillage amount, type of oil or hydrocarbon, oil removal method and its effectiveness, and vulnerability of the water and wildlife to calculate and estimate the cost of the damage from each gallon of oil spillage. The model determined two types of cost of oil spillage per gallon (economical and environmental) based on different oil categories and different spillage rates per gallon. As an example, for fewer than 500 gal of heavy oil spillage, the damage was evaluated at $95 per gallon environmental cost and $150 per gallon economic cost. Corrosion of materials including piping and valves is divided into two categories— internal and external. The offshore environment, the external source of material corrosion, is highly corrosive due to the splashing of seawater containing chloride, as discussed earlier in the material selection literature review. Moreover, untreated produced hydrocarbon from a well contains many undesirable impurities and by-products such as carbon dioxide (CO2), H2S, chloride, etc. The most common internal types of corrosion include crevices, pitting,

External corrosion

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chloride stress cracking, CO2 (sweet), and H2S (sour). External chloride stress cracking corrosion (SCC) as a result of seawater splash is the main type of external corrosion. Galvanic corrosion can be either internal or external.

External corrosion External corrosion occurs as the result of mechanical induced stresses combined with the impact of pitting corrosion. The synergic effect of chloride coming from the environment, such as seawater spray, and the loads on the pressure-containing parts of valves such as bolts and stems, can cause brittle phase and crack failure in vulnerable materials such as stainlesssteel 316. Fig. 13.1 shows the three main elements in stress cracking corrosion including chloride stress cracking corrosion (CLSCC). Dr. Frank Cheng, an internationally recognized authority in corrosion science and engineering of pipelines, claims that the stress to make CLSCC should be tensile and not compressive. Compressive stress reduces the effect of CLSCC. The stress level required to make CLSCC can be lower than the yield strength of the material. Although Dr. Cheng has stated that the CLSCC for austenitic stainless steel in the offshore environment occurs at temperatures above 70°C, NORSOK M-001, the “Material Selection” discussion in the Norwegian standard, states 60°C as the maximum temperature with which austenitic stainless steel can be used. It has been stated that the welding of metals creates residual stresses because of high heat input. The residual stress concentration in welded areas makes the material very vulnerable to chloride attacks. One solution for avoiding residual stress in welded areas is to apply postweld heat treatment as per AME B31.3, “Process Piping Code.” Therefore, the source of stress for CLSCC could be externally applied stress (force) and/or residual stress. Residual stress can be introduced in ways other than welding such as forming, heat treatment, or cold work such as bending in pipeline and piping and grinding.

FIG. 13.1 Essential factors in CLSCC occurrence.

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13. Piping and valve corrosion study

Temperature effect is very important on CLSCC and a higher temperature means a higher risk of CLSCC. The NORSOK M-001 “Material selection” standard specifies higher temperature limits for some materials in the offshore environment to avoid CLSCC. Uncoated austenitic stainless-steel SS316, duplex, super duplex, and 6MO have maximum operating temperature limits of 60°C, 100°C, 110°C, and 120°C, respectively, in the offshore environment. It is possible to use these materials at higher than recommended operating temperature limits if they are coated. Coating and upgrading the material are two important CLSCC mitigation approaches. Figs. 13.2 and 13.3 show SCC on the bolt and pipe wall.

FIG. 13.2

Stress cracking corrosion of a bolt.

FIG. 13.3

Stress cracking corrosion of a pipe wall.

Internal corrosion

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Internal corrosion CO2 and H2S corrosion As hydrocarbons emerge from subsurface geological formations, they carry water and acid gases that need to be separated from the main product prior to transportation to the refineries. Two undesirable by-products of oil and gas, CO2 and H2S, are called “acid gases” simply because of their acidic chemical properties in the presence of water. The internal corrosion attack on pipelines and equipment due to wet corrosive media activating CO2, H2S, and other sulfur compounds is a long-term and commonplace adverse issue in the oil and gas industry. This in turn leads to serious costly hazards such as the loss of production and revenue, damage to assets and properties, human injuries, loss of life, and environmental pollution. The high degree of corrosion due to the acid-producing reaction of these two gases in the presence of water is a major risk for mild carbon steels,1 stainless steels, and many other ferrous materials. It is the reason why acid gas removal or gas sweetening process by amine solutions is applied for natural gas processing units, refineries, and petrochemical plants.

H2S physical properties H2S is a colorless, toxic, flammable, and fatal gas with an odor of rotten eggs. Regarding the gas density, H2S is heavier than air, which makes it extremely dangerous because of the risk of leakage due to filling hollows and pits and falling to low points. The lower and upper explosive limits are 4% and 44% and its autoignition temperature is 260°C. Exposure to even a low concentration of H2S at 10–500 mol parts per million (ppm) for only 1 h can result in losing the sense of smell, and exposure to more than 500 ppm H2S is fatal. Hydrogen sulfide is a poisonous and corrosive gas that can produce sulfuric acid in an aqueous solution and decrease the pH of the medium significantly. Therefore, it is preferred to reduce the toxic and corrosive H2S content to a maximum of approximately 4 ppm in natural gas.

H2S sour corrosion The type of corrosion related to hydrogen sulfide and other sulfur compounds, called sour corrosion, usually causes cracks in steel as a result of H2S reaction with water, which reduces the pH and increases the corrosivity by forming the acid. In addition, depending on the steel type and tensile stress distribution, the hydrogen in the steel may lead to hydrogen embrittlement and cracking. The general mechanism of this type of corrosion is stated chemically as follows: H2S + Fe + H2O ! FeS + 2H The iron sulfide that is produced by this reaction generally adheres to the steel surface as a black powder or scale. This scale tends to cause local acceleration of corrosion due to the iron sulfide that is cathodic to the metal. Figs. 13.4 and 13.5 illustrate the sour corrosion of tubing in a relatively sour service containing hydrogen sulfide.

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FIG. 13.4

Pitting from sour service in the tube of a heat exchanger.

FIG. 13.5

Sour corrosion effect (Temperature ¼ 60°C, H2S Partial Pressure ¼ 0.5 bar) (NACE).

This form of corrosion can be found in different forms of sulfide stress cracking (SSC), stress corrosion cracking (SCC), stepwise cracking (SWC), or different types of hydrogen embrittlement such as hydrogen-induced cracking (HIC), which are described further in this chapter.

National association of corrosion engineers (NACE) Guidelines on material selection, application limits of different material classes and groups, and precaution measures against sour corrosion at the design phase of projects are described in detail in the NACE standard MR0175/ISO 15156, which will be practically discussed later in this chapter. The standard is applicable where metallic equipment and piping are exposed to SSC or HIC risks due to the presence of considerable amounts of H2S and liquid water. The NACE standard enhances the steel resistance against sour corrosion of H2S by modifying the chemical composition, heat treatment, and methods of fabrication. The resistance of carbon and alloy steels is largely dependent on the H2S partial pressure as well as the pH of the solution.

Internal corrosion

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Carbon dioxide (CO2) properties and sweet corrosion Carbon dioxide (CO2) is an odorless, nonflammable, and nontoxic substance, unlike hydrogen sulfide, and colorless, similar to H2S. Although CO2 is a nontoxic gas, a high concentration of CO2 in the air (at least 10%–20%) is dangerous to human life. CO2 corrosion of carbon and alloy steels is known as sweet corrosion, which is defined as the deterioration of metal components resulting from contact with gas or solutions including CO2 and water. Therefore, CO2 is noncorrosive in the absence of water. Like H2S, CO2 forms carbonic acid in dissolved water according to the following reaction, leads to pH depression, and increases the corrosivity: CO2 + H2O ! H2CO3 Sweet corrosion is a serious problem in the oil and gas industry due to metal loss and its severity in terms of localized corrosion. It leads to the loss of material and pitting in production, transportation, and processing facilities. This is an especially severe problem in cheap carbon steel. Accurate prediction and modeling of the CO2 corrosion rate for carbon and alloy steel pipes is a very important task at the basic design phase of oil, gas, and petrochemical projects to either consider additional wall thicknesses for pipes or change the base materials. Anticipated pipe thickness loss is a basis for decision-making when considering the corrosion allowance for carbon steel pipes to make up for the metal loss or change the base material to corrosion-resistant alloys (CRAs). The most famous CO2 corrosion modeling for carbon steel pipes is the de Waard and Milliams model (DWM) that will be fully described in the next chapter. DWM is known as an applicable model for predicting the corrosion rate prediction of carbon steel pipes and selecting the most appropriate material. Many famous corrosion prediction software programs such as Predict, Predict-Pipe, Electronic Corrosion Engineering (ECE), etc., which are used worldwide by reputable companies including Shell, Foster Wheeler, Technip, etc., have been designed according to this model. CO2 concentration is the most essential parameter determining the potential for corrosion of any pipe and the concomitant damages caused by such corrosion. A variety of CO2 corrosion rate prediction models have been produced by research organizations and oil companies. However, no model exists, which is completely true to the real world due to the complexity of the phenomenon. The following models of CO2 corrosion rate assessment have been developed and recommended to the market recently: • • • • • • • •

de Waard and Milliams model Predict Model (Intercorr) NORSOK (M-506) (Statoil, Saga Petroleum, Hydro) LIPUCOR (Total) Hydrocorr (Shell) Casandra (British Petroleum) CorPos (Corr Ocean) Cormed—ELF

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13. Piping and valve corrosion study

Generally, the principle process parameters that affect the CO2 corrosion rate are summarized as follows: • • • • • • • • • • • • • •

The effect of fluid service operating temperature The effect of fluid service operating pressure Concentration of CO2 in the fluid service The water salinity and chemistry The effect of in situ pH The effect of scaling and the passive protective layer The effect of flow dynamics and velocity The effect of water cut The effect of corrosion inhibitors (type of inhibitor and its efficiency) The effect of Glycol The effect of H2S partial pressure Hydrocarbon type and API Gas-to-oil ratio/water-to-gas ratio The presence of oxygen

As mentioned earlier, the DWM model is the most widely accepted sweet corrosion model for hydrocarbon production and processing systems, forming the basis of the majority of the corrosion prediction software. Based CO2 corrosion rate prediction The evaluation of the uniform reduction of material thickness per year (corrosion rate) due to the presence of wet CO2 as per DWM is implemented initially by taking a few parameters into accounts, such as CO2 partial pressure and the operating temperature. The calculated corrosion rate based on the abovementioned parameters, called base corrosion rate, will be adjusted by more influential process parameters in turn. The base corrosion rate of CO2 for mild carbon steel material as per DWM is calculated by considering some process parameters such as operating temperature and pressure using the formula 13.1 as follows: Log ðC:RÞBase ¼ 5:8 

1710 + 0:67Log ðPCO2 Þ T

(13.1)

where C. RBase: Base corrosion rate based on DWM (mm); T: Operating temperature (Kelvin); PCO2: Partial pressure of CO2 (bar); The above formula can be easily used in the form of the de Waard Milliams nomogram (Fig. 13.6). Temperature effect Operating temperature generally accelerates the corrosion mechanism significantly. Studies indicate that the corrosion rate increases up to 70°C and decreases above that limit. The

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Internal corrosion

Temperature Scale °C Factor 140 130 0.1 120 110 100 90 1 80 70 60 50 40 Example: 30 0.2 bar CO2 at 120 °C 20 gives 10 x 0.7 x 7 mm/y

CO2 pressure 10 bar

Corrosion Rate mm/y

20 10

1

1 0.1 0.1

10 0.02

0

0.01

FIG. 13.6 CO2 Corrosion rate nomogram. (DWM) mm/y 0.35 0.3 0.25 0.2 0.15 0.1 0.05 0 0

20

40

100 60 80 Temperature (C)

120

140

160

FIG. 13.7 Temperature effect on CO2 corrosion rate at high pH.

reduction of corrosion rate at higher temperatures (more than 70°C) is simply because of the formation of a protective layer (Fig. 13.7). Temperature effect The partial pressure of CO2 is calculated by the following formula: PCO2 ¼ POperation  xCO2 where PCO2: Partial pressure of CO2. POperation: Operation pressure. XCO2: Mole fraction of CO2.

(13.2)

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TABLE 13.1 Severity of CO2 corrosion. P (CO2) (bar)

P (CO2) (PSI)

Corrosion level

Remarks

>2.07

>30

Highly corrosive

High risk of corrosion attack

0.207 ≪ 2.07

7 ≪ 30

Medium corrosive

Corrosion probable/medium risk