This article provides some information relevant to piping engineers working on the engineering, procurement, construction or management of pipeline and piping systems for the petroleum and natural gas industries. The references section of this article contains some references that address valve basics.
API 6D provides a good description of ball, check, gate and plug valves commonly found in the Oil and Gas industry. BS 1873 provides a good description of globe valves commonly found in the Oil and Gas industry.
Ball Valve: The closure element or obturator is a ball with a cylindrical hole bored through the centre.
The ball rotates 90 degrees on its vertical axis to seal off the flow. Typical ball valves
for the Oil and Gas industry are shown in Figures B.4, B.5, B.6 of API 6D - 2015.
A typical ball valve from here, accessed 9-Feb-2017.
- A ball valve can be:
- Floating. The ball is attached to a stem at the top of the ball only
- Trunnion mounted. The ball is attached to ta stem at the top of the ball and also to a trunnion at the bottom of the ball
- A ball valve can also be:
- Top entry. The shell is typically made from a single piece with a top cover that is bolted to that piece. This enables the valve internals to be removed without having to remove the entire valve from the piping
- Three piece. The shell is made of 3 pieces, bolted together. 2 pieces contain the end connection with once piece between these. Entry of the ball is from the side
- Two piece. The shell is made of 2 pieces, bolted together. 1 piece contains only the end connection while the other contains both the end connection and also houses the ball. Entry of the ball is from the side
- Fully welded. The shell is made of 2 pieces welded together. Like the two piece, 1 piece contains only the end connection while the other contains both the end connection and also houses the ball. Entry of the ball is from the side
Ball valves have the following advantages:
- Quick quarter turn shut off. Ball valves are therefore often used as shutdown valves in oil or gas processing systems
- Usually smaller and more compact than other types of valves
- Low pressure drop compared to globe, plug and butterfly valves
Their disadvantages are:
- Poor throttling characteristics
- In fluids with particles, the particles can stick to valve internals causing abrasion damage
This reference contains general information on ball valves, including material selection.
Plug Valve: Similar to a ball valve, but the obturator is a cylinder or a tapered cylinder.
A typical plug valve is shown in API 6D - 2015, Figure B.3.
A typical plug valve from here, accessed 11-Feb-2017.
-A plug valve can be:
- Unlubricated. A soft body liner or sleeve is installed in the body cavity. The tapered plug acts as a wedge and pushes the liner against the body creating a seal. An unlubricated plug valve is used instead of a lubricated one where low maintenance is required. Since there is no gap between the obturator and the body at the body cavity, the valve can be used in applications where trapped fluid may freeze, expand and damage the valve. [This reference]
- Lubricated. A sealant, injected into the valve flows between the the obturator and the body of the valve creating a seal and providing lubrication. Is commonly used for upstream fluids with entrained particles, where some contamination of the fluid by the sealant is tolerable. [This reference]
Globe Valve: The closure element is a plug which moves downward onto the seat to cut off the flow.
A typical globe valve is shown in this version of BS 1873, Figure 1.
A typical globe valve from here, accessed 17-Feb-2017.
Since the entire pressure force acts directly on the closure element, the size of globe valves is commonly limited to DN300. Globe valves can be used for throttling applications, since they have good throttling characteristics. As a rule of thumb the pressure differential should be no more than 20% the upstream pressure of 200 psi (1380 kPa) whichever is less. [this reference]
Gate Valve: The closure element is a flat disc that moves downward to cut off the flow.
Typical gate valves commonly found in the Oil and Gas industry are shown in
this version of API 6D, Figure B.1, B.2.
A typical gate valve from here, accessed 17-Feb-2017.
This reference contains general information on gate valves.
There are a few types of check valves commonly used in the Oil and Gas industry. They are:
Reduced opening swing check valve. Shown in this version of API 6D, Figure B.7.
A typical reduced opening swing check valve from here, accessed 22-Feb-2017.
Full opening swing check valve. Shown in this version of API 6D, Figure B.8.
A typical full opening swing check valve from here, accessed 22-Feb-2017.
Single plate, wafer type, check valve, long pattern. Shown in this version of API 6D, Figure B.9.
A typical single plate, wafer type, check valve, long pattern from here, accessed 22-Feb-2017.
Dual plate, wafer type, check valve, long pattern. Shown in this version of API 6D, Figure B.10.
A typical dual plate, wafer type, check valve, long pattern from here, accessed 22-Feb-2017.
Single plate, wafer type, check valve, short pattern. Shown in this version of API 6D, Figure B.11.
A typical single plate, wafer type, check valve, short pattern from here, accessed 22-Feb-2017.
Axial flow, check valve. Shown in this version of API 6D, Figure B.12.
A typical axial flow, check valve from here, accessed 22-Feb-2017.
Piston check valve. Shown in this version of API 6D, Figure B.13.
A typical piston check valve from here, accessed 22-Feb-2017.
ASME B16.34 specifies pressure temperature rating, dimension, material, non-destructive examination and testing requirements for
cast, forged and fabricated;
flanged, threaded, welding ends and wafer type/flangeless valves;
of steel, nickel based alloy and materials listed in Table 1. (Clause 1.1)
Pressure-temperature ratings defined in ASME B16.34 are Class 150, 300, 600, 900, 1500, 2500 and 4500 (Clause 1.5.1). Each pressure-temperature rating in turn can be identified as Standard, Special or Limited Class (Clause 2.1).
- Standard - Valves which conform to all the requirements of this standard, except for section 8 (additional NDE requirements) and Appendix V.
- Special - Threaded and welding end Valves which conform to all the requirements for Standard valves, and section 8 (additional NDE requirements). The pressures for Special valves are typically higher than for Standard valves at the same temperature.
- Limited Class - Threaded and welding end Valves with nominal pipe size (NPS) 2 1/2 and smaller which conform to all the requirements for Standard valves and Appendix V. The pressures for Limited Class valves are the same as those for Special valves at 480 degrees C and below but can be higher at elevated temperatures.
Flanged valves can only be Standard valves. Also linear interpolation between classes for flanged valves is not permitted
except for Class 400 (Clause 2.1.1).
The pressure-temperature ratings are only applicable to valves fabricated by welding provided the welding, heat treatment and NDE of the welds conform to ASME VIII Div 1 (Clause 2.1.6).
The valve body, bonnet/cover and bolting must be made of ASTM materials specified in Table 1 or the equivalent ASME materials
The valve pressure-temperature rating is based on the rating of the body (Clause 5.1.1).
Unless specified by the purchaser, the end dimensions for butt welding end valves must conform to ASME B16.25 (Clause 6.2.1).
The end dimensions for flanged end valves must conform to ASME B16.5 or ASME B16.47 Series A or B (Clause 6.2.2).
The end dimensions for socket welding end valves must conform to ASME B16.11 (Clause 6.2.3).
The end dimensions for threaded end valves must conform to ASME B16.11. The threads must conform to ASME B1.20.1 (Clause 6.2.4).
The end to end length of the valve is are per ASME B16.10 or as agreed between manufacturer and purchaser. (Clause 6.2.6)
The valve body must be pressure tested to 1.5 times the pressure rating at 38 °C with the closure element in the partially
Generally speaking, visible leakage through the pressure boundary is not permitted. (Clause 7.1)
Valves for shut off or isolation service and for limiting flow reversal must also be given a closure test. The test pressure must be not less than 1.1 times the pressure rating at 38 °C. This test can be substituted with a gas closure test at a pressure no less than 5.5 Bar (80 Psi), for certain nominal pipe sizes and pressure-temperature ratings. The leakage criteria is to be determined by agreement between manufacturer and purchaser. Standards such as API 598, ISO 5208 and MSS SP-61 provide example criteria. (Clause 7.2.1)
Double seating valves must have the closure test applied to both ends consecutively. During the test, the cavity between the seals must be filled with the test fluid (Clause 7.2.4).
Specifies requirements for the design (including pressure-temperature ratings, dimensions, design features such as vent, drain, sealant lines), material, welding, non destructive examination and testing of ball, plug, gate and check valves for pipeline and piping systems for the petroleum and natural gas industries. (Clause 1)
- Double Block and Bleed (DBB) - Valve with two seating surfaces, that in the closed position, can seal against pressure from both ends and has a means of bleeding off pressure in the valve cavity
- Double Isolation and Bleed (DIB) - Valve with two seating surfaces, that in the closed position, will form a seal against pressure from one end at both ends and has a means of bleeding off pressure in the valve cavity. This function can be provided in one or both directions
- Full Opening - The valve internal diameter is approximately the same as that of the piping. The minimum required diameters are specified in Table 1
- Reduced Opening - The valve internal diameter is smaller by 1 or more sizes than that of the piping
Reduced opening valves have a minimum bore:
- For sizes up to and including DN 300, the minimum bore for a valve 1 size smaller as per Table 1
- For sizes between DN 350 and DN 600 inclusive, the minimum bore for a valve 2 sizes smaller as per Table 1
- For sizes greater than DN 600, by agreement
- The design of the valve must conform to an internationally recognized standard such as ASME VIII Division 1 or EN 13445
- The pressure rating is as per ASME B16.34 and is applied at the ends
Unless agreement upon, valve lengths are as per Tables C.1 - C.5 and where not stated they are as per ASME B16.10.
Some important required design features of the valve are:
- Valve Cavity Relief - If pressure can build up in the body cavity between seals, automatic pressure relief is required, unless otherwise agreed
- Stem Retention - The stem will not eject under any internal pressure condition and/or if the gland packing components or the valve operator components are removed
- Fire Type-Testing - Fire type-testing certification may be required
- Anti Static Device - Soft seated ball, plug and gate valves are required to have an anti static device installed
Metallic pressure containing and controlling parts of valves shall be according to those permitted by the pressure-temperature rating. (Clause 6.1)
For valves in rapid gas decompression service operating at class 600 and above pressures, anti explosive decompression (AED) elastomeric parts are required (Clause 6.3)
To conform to ASME IX or ISO 15607, 15609 and 15614. (Clause 7.2)
The qualification of welders must conform to ASME IX or ISO 9606-1/EN 287-1. (Clause 7.2)
For valves with design temperatures less than 29 °C, impact testing is required as part of the procedure qualification testing. (Clause 7.3)
NDE where required by the purchaser shall be selected from a list specified in Annex G. (Clause 8.1) The qualification of NDT personnel shall be as per the manufacturer's documented training program, based on ASNT SNT-TC-1A. (Clause 8.3.1)
The test fluid must be water with corrosion inhibitor. Where agreed upon, the fluid can be light oil, with a density no greater than water. (Clause 9.1)
Stem backseat test: The minimum test pressure is 1.1 times the pressure rating at 38 °C. The test duration must be as per Table 4. No visible leakage is permitted during the duration of the test. (Clause 9.2)
Hydrostatic shell test: The minimum test pressure is 1.5 times the pressure rating at 38 °C. The test duration must be as per Table 5. No visible leakage is permitted during the duration of the test. (Clause 9.3)
Hydrostatic seat test: The minimum test pressure is 1.1 times the pressure rating at 38 °C. The test duration must be as per Table 6. For soft seated valves and lubricated plug valves, no visible leakage is permitted during the duration of the test. For hard seated valves not including check valves, the leakage rate is ISO 5208 Rate D. (Clause 9.5)
Full Bore Vs Reduced Bore Valves
A full bore valve enables the line to be piggable. The pressure drop across the valve is less. It however weighs more.
- Control Valve Handbook 4th Edition; Emerson Process Management (Local, WWW, 29-Mar-2017)
- Valve Selection Handbook 5th Edition; Peter Smith, R. W. Zappe; Elsevier
- ASME B16.34-2004, Valves—Flanged, Threaded, and Welding End.
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- API 594, Check Valves: Wafer, Wafer-Lug and Double Flange Type.
Specified requirements for pressure-temperature ratings, dimensions, materials, NDE and testing for steel and alloy single and dual-plate check valves.
- BS 5352 : 1981, Steel Wedge Gate, Globe and Check Valves 50 mm and Smaller For The Petroleum, Petrochemical and Allied Industries.
- ANSI-FCI 70-2-2006, Control Valve Seat Leakage.
Defines 6 levels for control valve seal tightness, including tests for each level. The most common levels are Level IV and VI
- ASME B16.10 - 2000, Valve Dimensions.
- API Standard 598, Valve Inspection and Testing, Ninth Edition, Sep 2009.
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- American Petroleum Institute Std. 607, May, 1993, Fire Test for Soft-Seated Quarter-Turn Valves.
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- Establishes requirements for testing and evaluating the pressure containing performance of API 6A and 6F valves when exposed to fire.
It states acceptable leakage rates through the valve and external leakage after exposure to fire for 30 min.
- ISO 10497, Testing of Valves — Fire Type-Testing Requirements; 3rd Edition; 15-Feb-2010.
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Evaluation of Surface Irregularities.
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