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

By Karan Sotoodeh

A Practical Guide to Piping and Valves for the Oil and Gas Industry covers how to select, test and maintain the right oil and gas valve. Each chapter focuses on a specific type of valve with a built-in structured table on valve selection. Covering both onshore and offshore projects, the book also gives an introduction to the most common types of corrosion in the oil and gas industry, including CO2, H2S, pitting, crevice, and more. A model to evaluate CO2 corrosion rate on carbon steel piping is introduced, along with discussions on bulk piping components, including fittings, gaskets, piping and flanges.

Rounding out with chapters devoted to valve preservation to protect against harmful environments and factory acceptance testing, this book gives engineers and managers a much-needed tool to better understand today’s valve technology.

• Presents oil and gas examples and challenges relating to valves, including many illustrations from valves in different stages of projects
• Helps readers understand valve materials, testing, actuation, packing and preservation, also including a new model to evaluate CO2 corrosion rates on carbon steel piping
• Presents structured valve selection tables in each chapter to help readers pick the right valve for the right project

• Language: English
• Publisher: Elsevier Science
• Release date: Jan 12, 2021
• ISBN: 9780128241875

Karan Sotoodeh

Karan Sotoodeh recently earned his PhD in Safety and Reliability in Mechanical Engineering from the University of Stavanger. Previously, Karan was the Senior / Lead Engineer in valves and actuators for Baker Hughes, one of the world’s largest oil field services company. He was responsible for engineering and delivering valves and actuators in subsea manifolds, working with valve suppliers, R&D activities, and maintaining the company’s valve database. He has also worked for AkerSolutions, NLI Engineering, and Nargan Engineers as a senior specialist in piping and valves, assisting with many projects around the world. He is the author of Prevention of Valve Fugitive Emissions in the Oil and Gas Industry and Subsea Valves and Actuators for the Oil and Gas Industry, both published by Elsevier. Karan earned a Master of Research in Mechanical Engineering and a Masters in Oil and Gas Engineering, both from Robert Gordon University of Aberdeen, and a Bachelors in Industrial Engineering from the Iran University of Science and Technology

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Chapter 1: Ball-valve applications and design

Abstract

This chapter is dedicated to ball valves as a very robust valve choice used for stopping and starting the flow. This chapter provides a relatively in-depth and detailed review of different critical metallic and soft components in this type of valve. Double isolation and bleed characteristic of the ball valves as per the API 6D standard for pipeline valves have been explained in detail. Different aspects of ball valve design such as bore, flow capacity, end connections to the piping system, torque requirement, and interlocking are included. A separate section is dedicated to material selection for different components of the ball valves such as body, bonnet, seat, stem, etc. This chapter is very well illustrated with pictures of ball valves during assembly, test, packing, and preservation. This chapter addresses different requirements of this valve more than design, such as lifting, tagging and marking, testing as well as packing and preservation.

Keywords

Ball valves; Design; Testing; Packing and preservation; Oil and gas industry

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).

Fig. 1.1 Ball valve.

Injection lines that inject seawater into the reservoirs for enhanced oil recovery in high-pressure 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 12″, 14″, and 16″, 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 12″ 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 2″, 1″, 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.

•1″ or ¾″ 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.

Fig. 1.2 Wedge gate valve.

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).

Fig. 1.3 Blowdown valve.

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 30″ and 38″ 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 24″-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.

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.

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).

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

Fig. 1.6 shows the male end of a tubing connection in the Swagelok brand.

Fig. 1.6 Tubing connector (male end) (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.

Fig. 1.7 Tubing connector (female end).

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).

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.

Fig. 1.10 Three-way ball valves.

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.

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

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.

Fig. 1.12 Full-bore ball-valve upstream and downstream of the PSV.

API 6D, the standard for pipeline valves, gives a minimum bore diameter for rating 150–600 equally up to 60″ 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 20″ bore in CL2500 and 36″ 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 24″ and pressure classes 150–600 has a bore much closer to the pipe. For example, a 24″ ball valve in duplex material and class 300 has about 2 mm less bore than the pipe. However, a 20″ class 150 ball valve as per API 6D standard could have a bore that is approximately 8 mm smaller than the pipe.

Table 1.1

According to the API 6D standard, an RB ball valve has one size reduction up to and including 12″ (e.g., 12″ × 10″) and two size reductions for sizes above 12″–24″ (e.g., 24″ × 20″), and customer and manufacturer agreement for sizes above 24″. This could result in three size reductions for above 24″ (e.g., 36″ × 30″). 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).

Fig. 1.13 Full-bore/reduced bore ball-valve drawings.

Fig. 1.14 Full-bore ball valves.

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 18″ 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 18″ 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.

Fig. 1.15 Full-bore ball valve coupled with a dual-plate check 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. 1.16 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 = d1/d2 to determine whether the flow capacity (CV value) of the RB was sufficient. These two parameters are shown in Fig. 1.17.

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, 2″ 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 2″ class 1500 wedge gate valve cannot provide full bore as per the API 602 standard that covers gate, globe, and check valves for sizes 4″ 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.

Fig. 1.18 Drift test on a riser ball valve.

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-to-face 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., 20″ 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.

Fig. 1.19 Regular standards facing of flanges.

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 4″ in class 150 and 6″ in class 300. Therefore, short pattern and long pattern ball plus gate valves have the same face-to-face dimensions up to and including 4″ in class 150 and 6″ in class 300. Short-pattern ball valves have the same face-to-face dimensions as gate valves according to ASME B16.10 in sizes 6″, 8″, 10″, and 12″ and class 150. Long pattern ball valves have longer face-to-face dimensions than short-pattern ball and gate valves in sizes 6″, 8″, 10″, and 12″ and class 150.

Table 1.2

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.

Table 1.3

A tolerance of ± 2 mm shall be allowed on face-to-face and end-to-end dimensions of valves with sizes of 10″ and smaller, and a tolerance of ± 3 mm shall be allowed for valve sizes of 12″ 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.

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

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.

Fig. 1.21 Hub-ended ball valves.

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.

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

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.

Fig. 1.23 Special tool on the ball valve for maintenance.

However, Fig. 1.24 shows a torque tool for bolt tightening or opening that will not interfere with the body flange.

Fig. 1.24 Torque tool for ball-valve bolt tensioning. Courtesy: FCT.

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.

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 8″ class 900 DIB valve has a face-to-face dimension of 10″ class 900 in the same pressure class).

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.

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

The other point about body flange design is that the flange bodies of classes 900 and 1500 up to and including 2″, as well as flange bodies of classes 300 and 600 up to and including 2″, are identical and compatible with each other.

Side-entry ball valves can have two or three pieces. Three-piece ball valves usually start from 6″, 8″, or 10″ 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-to-face 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 split-body 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.

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 time-consuming 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.

Fig. 1.26 Top-entry actuated ball valve during the test. Courtesy: ATV.

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 12″ 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.

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 20″ instead of casting them.

Case studies

Lack of body flange thickness

In one case, a 12″ × 10″ 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 12″ 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.

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

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. 1.28 Clash during the installation of body-piece bolts of a 3″ 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 4″ 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 body-piece-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.

Fig. 1.30 2″ Class 1500 RB ball valve in forged carbon steel (LF2) material. Courtesy: BFE.

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.

Fig. 1.31 3″ 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).

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 4″ and smaller have the same face-to-face dimension in both long and short patterns as per the ASME B16.10 standard, face-to-face 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 face-to-face dimension for a 3/4″ 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.

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.

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 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 2″ 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. 1.34 Lack of engagement between body-closure bolt and nut to provide enough space for body flanges bolt and nut. Courtesy: LVF.

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.

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.

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.

Fig. 1.36 No space for the nuts and bolts of the connecting flange 3″ ball-valve CL150 (Evaluation of flange thickness reduction).

The minimum thickness for a 3″ class 300 flange as per ASME B16.5 is minimum 22. 3 mm, so when it comes to the body flange, any thickness above 22.3 mm can be machined to provide the 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 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.

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

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.

Fig. 1.38 Three-piece body valve with the long-length bolt.

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 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.

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

The washer standard for the bolt is ASME PCC-1 as per Fig. 1.40, and the thickness is 6.4 mm for 1″ size and above.

Fig. 1.40 Washer dimensions as per ASME PCC-1.

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.

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

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. 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.

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

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 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.

Body defect (case study)

Fig. 1.43 shows the body of a top-entry valve 14″ × 10″class 1500 butt welded to the line with a crack in the body.

Fig. 1.43 14″ × 10″ Class 1500 butt weld valve.

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.

Fig. 1.44 Cracks inside the body and bonnet bolt holes of a 14″ × 10″ class 1500 butt weld valve.

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 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.

Fig. 1.45 Sketches for radiography test on the body casting.

Fig. 1.46 Radiography test on the body casting.

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.

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

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 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