Valve Selection EPT 09-T-02 August 1998
Scope This Mobil Engineering Practice Tutorial (EPT) supplements the valve requirements contained in the MP 16-P-30A (M&R) and MP 16-P-31A (E&P) series by providing tutorial information on valve selection selection and applic ation for onshore and offshore production production and processing facilities.
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Valve Selection
August Aug ust 1998
Table of Contents Scop Sc ope e................................ ............................................................. ................................ ............................... ..................................................................... ....................................................... .............. 1 Table Tab le of Figure Fig ures s ................................................................................................................................ 5 Table of Tables Table s ............ .................. ............ ............ ............ ............ ............ ............ ............ ............ ............ ............ ............ ............ ............ ............ ............ ............ ............ ............ ......... ...6 6 1.
Refer Ref erenc ences es.................................................................................................................................. .................................................................................................................................. 7 1.1.
MEP–Mobil ME P–Mobil Engineering Engine ering Practices......... Practi ces............... ............ ............ ............ ............ ............ ............ ............ ............ ............ ........... .......... .....7 7
1.2. 1.2 .
Mobil Tutorials Tutor ials ................................................................................................................. 7
1.3.
API AP I–American P etroleum Institute ............ .................. ............ ............ ............ ............ ............ ............ ............ ............ ........... ........... ........ ..8 8
1.4.
ASME–Soc ASME –Society iety of Mechanical Mechan ical Engineers Engine ers ........... ................ ........... ........... ............... ............... .......... .......... ........... ........... ......... .... 8
1.5.
ASTM ASTM –American –Amer ican Society Societ y of Testing Testin g and Materials Materia ls .......... ............... ........... ........... ................. .................. .............8 .......8
1.6.
BSI BS I–British Standards Standar ds Institute Institu te ............ .................. ............ ............ ............ ........... ........... ............ ............ ............ ............ ........... .......... ......... ....9 9
1.7.
MSS–Manufacturers Standardization Society of the Valves and Fittings Industry, Inc......................................................................................................................................9
1.8.
NACE–Ass NACE –Associatio ociation n of Corrosion Corros ion Engineers Engineer s ............ .................. ............ ............ ............ ........... ........... ........... ........... .........10 ...10
2.
Defini Def initio tions ns ................................................................................................................................1 0
3.
Gener Gen eral al ......................................................................................................................................1 5
4.
Valve Val ve Types Ty pes and an d Use ............ .................. ............ ............ ............ ............ ............ ............ ............ ............ ............ ............ ............ ............ ............ ........... .......... ........1 ...16 6 4.1.
General...........................................................................................................................16
4.2. 4.2 .
Gate Valves Valv es ...................................................................................................................17
4.3. 4.3 .
Ball Bal l Valves Val ves .....................................................................................................................1 9
4.4. 4.4 .
Check Che ck Valves Val ves............................. ................................ ............................... ............................................................................... .....................................................2 ..20 0
4.5. 4.5 .
Globe Glob e Valves Val ves ................................ ............................................................ ............................................................................... .....................................................2 ..24 4
4.6. 4.6 .
Plug Plu g Valves Val ves ....................................................................................................................2 5
4.7.
Butterfly Butte rfly Valves Valve s ............ .................. ............ ............ ............ ............ ............ ............ ............ ............ ............ ............ ............ ............ ............ ........... .......... ........27 ...27
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4.8. 5.
6.
7.
8.
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August Aug ust 1998
Special Specia l Application Applic ation Valves .............. ..................... ............... ........... .......... .............. .............. .............. ........... ........... ............. ............ .............28 .......28
Valve Valv e Design Des ign Details Detai ls ............ .................. ............ ............ ............ ............ ............ ........... ........... ............ ............ ............ ............ ............ ............ ............ ........... .........34 ....34 5.1. 5.1 .
Valve Val ve Bodies Bod ies.................................................................................................................. .................................................................................................................. 34
5.2.
Bonnets Bonne ts and Body Joints Joint s ............ .................. ............ ............ ............ ............ ............ ............ ............ ............ ........... ........... ........... ........... ...........35 .....35
5.3.
Seats and Seat Pockets ............ .................. ............ ............ ........... ........... ............ ............ ............ ............ ............ ............ ........... ........... ............37 ......37
5.4.
Stems Ste ms and Stem Seals ............ .................. ............ ............ ............ ............ ............ ............ ............ ............ ............ ............ ............ ............ ............38 ......38
5.5. 5.5 .
Closure Closu re Elements Eleme nts .......................................................................................................... 40
5.6. 5.6 .
Valve Valv e Operato Oper ators rs ............................................................................................................4 0
Materials Mater ials ....................................................................................................................................4 1 6.1.
Body and Bonnet Materials Materia ls .......... ............... .......... .......... .......... ............... ............... .......... .......... .......... ................ ................. ............ ............41 ......41
6.2. 6.2 .
Trim Materials ................................................................................................................4 3
6.3.
Stem Materials ............ .................. ............ ............ ............ ............ ............ ........... ........... ............ ............ ............ ............ ............ ............ ............ ........... .........43 ....43
6.4. 6.4 .
Seat Materials Material s ................................................................................................................4 4
6.5. 6.5 .
Closure Clos ure Members Memb ers.......................................................................................................... .......................................................................................................... 44
6.6.
Seat Spring Materials ............ .................. ............ ............ ............ ............ ............ ............ ............ ............ ............ ............ ............ ............ ............ .........44 ...44
6.7.
Sealing Surfaces–Resilien Surfa ces–Resilientt Seated Valves ........... ................. ............ ............ ............ ............ ........... ........... ............ ..........45 ....45
6.8.
Sealing Surfaces–Meta Surfa ces–Metall Seated Seat ed Valves Valve s ............ .................. ............ ............ ............ ............ ............ ............ ........... ........... .........45 ...45
6.9.
Elastomeric Elastomeri c Materials ............ .................. ............ ............ ............ ............ ............ ............ ............ ............ ............ ............ ............ ............ ............ .........45 ...45
Inspe Ins pection ction and Tests ............ .................. ............ ............ ............ ............ ............ ............ ............ ............ ............ ............ ............ ............ ............ ........... .......... ........4 ...47 7 7.1.
General...........................................................................................................................47
7.2.
Non-Destructiv Non-Destr uctive e Examination Examin ation ............ .................. ............ ............ ............ ............ ............ ............ ............ ............ ........... ........... ............ ........4 ..47 7
7.3. 7.3 .
Pressure Pres sure Tests Test s ..............................................................................................................4 9
7.4. 7.4 .
Low Temperature Tempera ture Tests ...............................................................................................5 0
7.5. 7.5 .
Functional Functi onal Tests ............................................................................................................5 0
Valve Valv e Standa Sta ndards rds ............ .................. ............ ............ ............ ............ ............ ............ ........... ........... ............ ............ ............ ............ ............ ............ ........... ........... ............51 ......51
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8.1.
ASME B16.34 ................................................................................................................5 1
8.2.
ASME B16.33, ASME B16.38.....................................................................................51
8.3.
API SPEC 6A................................................................................................................. 51
8.4.
API SPEC 6D ................................................................................................................51
8.5.
API STD 594..................................................................................................................5 1
8.6.
API STD 600..................................................................................................................5 2
8.7.
API STD 602..................................................................................................................5 2
8.8.
API STD 609..................................................................................................................5 2
8.9.
Miscellaneous Valve Standards .................................................................................52
Reconditioned and Surplus Valves ...................................................................................53 9.1.
Reconditioned Valves ..................................................................................................53
9.2.
Surplus Valves ..............................................................................................................54
Appendix A: Selection of Valve Type ......................................................................................55 1.
Introduction ..............................................................................................................................5 5
2.
Valve Characteristic Rating Charts ....................................................................................56
3.
Valve Type Selection Charts ................................................................................................57 3.1.
Legend for Tables A–3 through A–10 .......................................................................57
Appendix B: Figures of Typical Valve Types ........................................................................66
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Table of Figures Figure B–1: Typical Gate Valve ................................................................................................. 66 Figure B–2: Typical Through-Conduit Gate Valve ...............................................................67 Figure B–3: Typical Floating Ball Valve ..................................................................................68 Figure B–4: Typical Trunnion Mounted Ball Valve ..............................................................68 Figure B–5: Typical Utility Butterfly Valve .............................................................................69 Figure B–6: Typical High-Performance Butterfly Valve ......................................................69 Figure B–7: Typical Plug Valve ................................................................................................. 70 Figure B–8: Typical Globe V alve ...............................................................................................71 Figure B–9: Typical Swing Check Valve.................................................................................71 Figure B–10: Typical Single Plate Wafer Check Valve ........................................................72 Figure B–11: Typical Dual Plate Wafer Check Valve ...........................................................72
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Table of Tables Table 1: Commonly Used Body/Bonnet Materials ...............................................................42 Table 2: Cast Valves–NDE Requirements and Sampling Frequency..............................49 Table A– 1: Isolation Valve Characteristic Ratings .............................................................56 Table A– 2: Check Valve Characteristic Ratings.................................................................. 56 Table A–3: Service: Sweet, Dry Process ...............................................................................58 Table A–4: Service: Sweet, Wet Process ...............................................................................59 Table A–5: Service: Sour, Dry Process..................................................................................60 Table A–6: Service: Sour, Wet Hydrocarbons .....................................................................61 Table A–7: Service: Sweet Injection Water ...........................................................................62 Table A–8: Service: Injection Water with H 2S 4 ..................................................................... 63 Table A–9: Service: Utilities ......................................................................................................64 Table A–10: Service: Lube and Seal Oil .................................................................................64 Figure B–1: Typical Gate Valve ................................................................................................. 66 Figure B–2: Typical Through-Conduit Gate Valve ...............................................................67 Figure B–3: Typical Floating Ball Valve ..................................................................................68 Figure B–4: Typical Trunnion Mounted Ball Valve ..............................................................68 Figure B–5: Typical Utility Butterfly Valve .............................................................................69 Figure B–6: Typical High-Performance Butterfly Valve ......................................................69 Figure B–7: Typical Plug Valve ................................................................................................. 70 Figure B–8: Typical Globe Valve ...............................................................................................71 Figure B–9: Typical Swing Check Valve.................................................................................71 Figure B–10: Typical Single Plate Wafer Check Valve ........................................................72 Figure B–11: Typical Dual Plate Wafer Check Valve ...........................................................72
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References The following publications form a part of this Tutorial. Unless otherwise specified herein, use the latest edition.
1.1.
MEP–Mobil Engineering Practices
MP 16-P-30A
Piping - Materials and Service Classifications (M&R)
MP 16-P-30B
Piping-Classifications-(M&R)-Line Class 125
MP 16-P-30C
Piping-Classifications-(M&R)-Line Class 150
MP 16-P-30D
Piping-Classifications -(M&R)-Line Class 300
MP 16-P-30E
Piping-Classifications-(M&R)-Line Class 600
MP 16-P-30F
Piping-Classifications -(M&R)-Line Class 900
MP 16-P-30G
Piping-Classifications -(M&R)-Line Class 1500
MP 16-P-30H
Piping-Classifications-(M&R)-Line Class Atmospheric
MP 16-P-30I
Piping-Classifications-(M&R)-Appendices
MP 16-P-31A
Piping-Classifications-(E&P, On/Offshore)
MP 16-P-31B
Piping-Classifications-(E&P, On/Offshore)-Line Class 125
MP 16-P-31C
Piping-Classifications-(E&P, On/Offshore)-Line Class 150
MP 16-P-31D
Piping-Classifications-(E&P, On/Offshore)-Line Class 300
MP 16-P-31E
Piping-Classifications-(E&P, On/Offshore)-Line Class 600
MP 16-P-31F
Piping-Classifications-(E&P, On/Offshore)-Line Class 900
MP 16-P-31G
Piping-Classifications-(E&P, On/Offshore)-Line Class 1500
MP 16-P-31H
Piping-Classifications-(E&P, On/Offshore)-Line Class 2500
MP 16-P-31I
Piping-Classifications-(E&P, On/Offshore)-Line Class Atmospheric
MP 16-P-31J
Piping-Classifications-(E&P, On/Offshore)-Appendices
1.2.
Mobil Tutorials
EPT 08-T-03
Materials for Sour Service
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August 1998
API–American Petroleum Institute
API SPEC 6A
Specification for Wellhead and Christmas Tree Equipment Seventeenth Edition
API SPEC 6D
Specification for Pipeline Valves (Gate, Plug, Ball, and Check Valves) Twenty-First Edition; Supplement 1 - 1996
API SPEC 6FA
Specification for Fire Test for Valves Second Edition
API STD 594
Wafer and Wafer-Lug Check Valves Fourth Edition
API STD 598
Valve Inspection and Testing Seventh Edition
API STD 599
Metal Plug Valves - Flanged and Welding Ends Fourth Edition
API STD 600
Steel Gate Valves - Flanged and Butt-Welding Ends, Bolted and Pressure Seal Bonnets Tenth Edition
API STD 602
Compact Steel Gate Valves - Flanged, Threaded, Welding, and ExtendedBody Ends Sixth Edition
API STD 607
Fire Test for Soft-Seated Quarter-Turn Valves Fourth Edition
API STD 609
Lug- and Wafer-Type Butterfly Valves
1.4.
ASME–American Society of Mechanical Engineers
ASME B16.33
Manually Operated Metallic Gas Valves for Use in Gas Piping Systems up to 125 psig (Sizes 1/2 Through 2)
ASME B16.34
Valves - Flanged, Threaded, and Welding End
ASME B16.38
Large Metallic Valves for Gas Distribution (Manually Operated, NPS 2 1/2 to 12, 125 psig Maximum) R(1994)
ASME B16.47
Large Diameter Steel Flanges NPS 26 Through NPS 60
ASME B31.3
Process Piping
ASME B31.4
Liquid Transportation Systems for Hydrocarbons, Liquid Petroleum Gas, Anhydrous Ammonia, and Alcohols
ASME B31.8
Gas Transmission and Distribution Piping Systems
1.5.
ASTM–American Society of Testing and Materials
ASTM A36/A36M
Standard Specification for Carbon Structural Steel
ASTM A564/A564M
Standard Specification for Hot-Rolled and Cold-Finished Age-Hardening Stainless Steel Bars and Shapes
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Valve Selection
BSI–British Standards Institute
BS 6364
Specification for Valves for Cryogenic Service
BS 6755-2
Testing of Valves–Part 2: Specification for Fire-Type Testing Requirements
1.7.
August 1998
MSS–Manufacturers Standardization Society of the Valves and Fittings Industry, Inc.
MSS SP-25
Standard Marking System for Valves, Fittings, Flanges and Unions
MSS SP-42
Class 150 Corrosion Resistant Gate, Globe, Angle and Check Valves with Flanged and Butt Weld Ends R(1995)
MSS SP-44
Steel Pipeline Flanges; Errata - 1996
MSS SP-45
Bypass and Drain Connections
MSS SP-53
Quality Standard for Steel Castings and Forgings for Valves, Flanges and Fittings and Other Piping Comp onents Magnetic Particle Examination Method
MSS SP-54
Quality Standard for Steel Castings for Valves, Flanges and Fittings and Other Piping Components Radiographic Examination Method
MSS SP-55
Quality Standard for Steel Castings for Valves, Flanges and Fittings and Other Piping Components Visual Method for Evaluation of Surface Irregularities
MSS SP-61
Pressure Testing of Steel Valves
MSS SP-70
Cast Iron Gate Valves, Flanged and Threaded Ends
MSS SP-71
Cast Iron Swing Check Valves, Flanges and Threaded Ends
MSS SP-80
Bronze Gate, Globe, Angle and Check Valves
MSS SP-91
Guidelines for Manual Operation of Valves R(1996)
MSS SP-92
Valve User Guide R(1992)
MSS SP-93
Quality Standard for Steel Castings and Forgings for Valves, Flanges and Fittings and Other Piping Components Liquid Penetrant Examination Method R(1992)
MSS SP-94
Quality Standard for Ferritic and Martensitic Steel Castings for Valves, Flanges, and Fittings and Other Piping Components Ultrasonic Examination Method
MSS SP-96
Guidelines on Terminology for Valves and Fittings
MSS SP-99
Instrument Valves
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Valve Selection
NACE–National Association of Corrosion Engineers
NACE MR0175
2.
August 1998
Sulfide Stress Cracking Resistant Metallic Materials for Oilfield Equipment
Definitions Actuator
The mechanical, hydraulic, electric or pneumatic device or mechanism used to open, position or close a valve.
Angle Valve
A variation of the globe valve, in which the end connections are at right angles to each other, rather than being in line.
Backseat
A seat on the bonnet or bonnet bushing which contacts a corresponding seating surface on the stem of the valve when the stem is fully retracted.
Backface
The surface of a flange on a valve that is opposite the gasket face.
Ball
The closure member in a ball valve or the closure member in a ball check valve.
Ball Valve
A valve using a spherical closure element (ball) that is rotated through 90 degrees to open and close the valve.
Ball Check Valve
A check valve in which the check closure member is a ball.
Bellows Seal Valve
A valve with a stem seal using a bellows.
Bidirectional Valve
A valve with substantially equivalent flow and shut-off capability in both directions.
Block and Bleed Valve
A valve with two seating surfaces that provide simultaneous blockage of flow from both valve ends and a means for draining or venting the cavity between the seating surfaces. This feature may be useful for testing the integrity of seat seals and providing positive isolation.
Blowdown or Blowoff Valve
A valve used to release the pressurized contents of a pressure vessel or piping system.
Body
The principal pressure containing shell of a valve that has ends adapted for connecting into a piping system.
Body-Bonnet Joint
The connection of a valve body to the bonnet. This may be threaded, union, bolted, welded or pressure seal type or a combination thereof. A capability for seal welding may be included.
Bonnet
The top part of a valve that contains an opening for the stem. It guides the stem and adapts to extensions, operators, actuators, etc.
Bonnet Bushing
An insert in a bonnet that serves as a stem or plug guide and may also provide a back seat surface.
Bore (or Port)
The inside diameter of the smallest opening through a valve (for example,
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the inside diameter of the ball, plug, seat rings, flange, etc.). Boss
A raised area on the surface of a valve body or bonnet, used for making a connection into the valve cavity.
Butterfly Valve
A valve that uses a rotatable disc as a closure member and obstructs flow when the disc is rotated to block the flow. The valve is available with various end connections, such as wafer (no flanges), lugged (single flange) or double flanged.
Buttwelding
The ends of a valve that are adapted for welding to the pipe by abutting the ends and welding within the groove formed between the prepared ends.
Bypass
A piping loop provided to permit flow around a valve closure member in its closed position.
Casting
A part formed by pouring molten metal into a mold.
Chainwheel
A manual actuator that uses a chain-driven wheel to turn a valve stem, handwheel or gearing.
Check Valve
A one-direction (unidirectional) valve that is opened by the fluid flow in one direction and that closes automatically when the flow stops or reverses direction, thus preventing flow in the reverse direction.
Chevron Packing
A type of packing consisting of a nest of "V-shaped" cross-sectional rings.
Clapper/Flapper
The hinged closure element of a swing check valve.
Closure Member (Element)
The moveable internal component attached to the valve stem that provides variable flow restriction, including shutoff. In specific designs, it may also be called a disc, wedge, plug, ball or gate.
CRA
Corrosion-resistant alloy.
Cold Working Pressure (CWP)
The maximum pressure at which a valve is allowed to be used at ambient temperature.
Control Valve
A valve serving as a control element in a system providing means for varying the flow of the fluid passing through the valve.
Diaphragm Valve
A valve containing a diaphragm deformed to permit throttling of fluid flow by forcing it against a raised section or weir in the body flow passageway to close off line flow.
Disc
The closure member (element) of a gate, globe, check or butterfly valve.
Double Disc
A two-piece disc used in a gate valve.
Dual Sealing Valve
A valve that uses redundant seat sealing means.
End Entry Ball Valve
A design of ball valve in which the ball and seats are accessible by the removal of an end piece.
ENP
Electroless-nickel plating; a nickel plating process that requires no external electrical power and is the result of a chemical reaction between the part and the plating solution.
Expanding Gate
A gate valve with flat, finely finished, parallel faces (as opposed to a wedge
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gate) and a mechanism that forces each face into contact with its seat ring in the closed or open position. Fabricated Valve
A valve in which the body parts are not cast or forged but are formed from plate or pipe, then welded or bolted together.
Flexible Wedge Disc
A gate valve disc that has a solid center but is flexible at the sealing periphery.
Floating Ball Valve
A ball valve with the ball held in position only by the seat rings; the ball is free to "float" between the seat rings. This type of valve is significantly impacted by the pressure in the system.
Flow Coefficient (C v)
A measure of the flow capacity of a valve in fully turbulent flow. In U.S. Customary units, the valve flow coefficient, Cv, is the flow rate in U.S. gallons per minute of water at 60 °F, through the valve at a pressure drop of 1.0 psi.
Four-Way Valve
A valve with four ports, arranged to control the direction of fluid flow through the valve.
Full Bore (Full Port)
Describes a valve whose bore/port is nominally equal to the bore of the connecting pipe.
Gate
The closure member of a gate valve.
Gate Valve
A valve with a straight through pattern whose closure element is a gate, wedge, disc, double disc or parallel sided slab. The closure element is situated between two fixed seating surfaces, with means to move it in and out of the flowstream in a direction perpendicular to the pipe axis.
Gland
See Packing Gland.
Globe Valve
A valve whose closure member is a flat disc or conical plug, sealing on a seat, which is usually parallel to the flow axis. The winding flow path produces a relatively high-pressure loss.
Handwheel
A rimmed component designed to facilitate manual actuation of a valve.
Hardfacing
A surface preparation in which an alloy is deposited on a metal surface, usually by weld overlay, to increase abrasion and/or corrosion resistance.
High-Performance A butterfly valve of rugged construction (as opposed to rubber-lines butterfly valves), with the shaft and/or disc offset in one, two or three Butterfly Valve directions to enhance the valve's shut-off capabilities. Also referred to as Category B valves in API STD 609. Injection Lines
All piping from the pump or compressor final discharge block valve to the injection wellhead.
ISRS
A valve whose stem threads are inside the valve body and exposed to the line fluid.
Metal-Seated
The seal produced by metal-to-metal contact between the sealing faces of the seat ring and the closure element, without the benefit of a synthetic seal (e.g. PTFE, Viton, etc).
Mill Certificates (Mill Test
Certificates provided by the manufacturing steel mill that indicate the chemical composition and physical properties of a specific batch (pour) of
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Reports)
steel.
Needle Valve
A type of small valve used for metering flows, with a tapered needlepoint plug or closure element and a seat with a small orifice.
Non-Rising Stem
A gate valve having its stem threaded into the gate. As the stem turns, the gate moves, but the stem does not rise. Stem threads are exposed to the line fluid.
OS&Y (Outside Screw and Yoke)
A valve in which the line fluid does not come in contact with the stem threads. The stem sealing element is between the valve body and the stem threads.
Packing
The deformable sealing material inserted into a valve stem stuffing box, which when compressed by a gland, provides a tight seal around the stem.
Pipeline or Transmission Line
A pipe installed for the purpose of transmitting a fluid from a source or sources of supply to one or more distribution centers or a pipe installed to interconnect sources of valve whose closure element is usually a tapered plug having a rectangular port; the plug is rotated through 90 degrees to open or close the valve.
Plug Valve
A quarter-turn valve where the closure element is a slightly tapered or cylindrical plug, usually with a trapezoidal, rectangular or round port. Some plug valves use sealant distributed about the plug-body interface for sealing, others may use non-metallic liners.
Regular Port
A term usually applied to ball or plug valves. The "regular" port of such valves is smaller than the bore of the connecting pipe. In ball valves, this port is customarily reduced one line size from the connecting pipe. In plug valves, the port can vary from 40 to 100 percent of the line size open area.
Regulating Valve
A term used to describe valves that throttle (regulate) flow, such as globe and needle valves.
Quarter Turn
A term used to describe a valve whose closure rotates 90 degrees to open and/or close, as opposed to a valve whose closure element moves perpendicular to the line.
Resilient Seat
A valve seat containing a soft seal, such as a nylon or PTFE insert or a non metallic O-ring.
Rising Stem
A valve stem that moves into and out of the valve when the valve is actuated.
Seat (or Seat Ring)
That part of a valve against which the closure element (gate, ball, plug, disc, etc) presses to effect a shut-off.
Slab Gate
A gate with flat, finely finished, parallel faces, as opposed to a wedge gate. Such a closure element slides across the seats and depends on line pressure rather than on stem force to achieve tight shut-off.
Sour Service
A fluid service containing water as a liquid and hydrogen sulfide exceeding the limits defined in NACE MR0175. This type of fluid service may cause stress corrosion cracking (SCC) of susceptible materials.
Stop Check Valve
A check valve in which the closure member can be mechanically closed.
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Stuffing Box
The annular chamber provided around a valve stem; the part of a sealing system into which deformable packing is introduced.
Swing Check Valve
A check valve in which the closure member is mounted so that it swings away from the seat.
Three-Way Valve
A valve with three ports, arranged to control the direction of fluid flow through the valve and connected piping system.
Throttling
The changing of valve position (flow resistance) for process control, for example to achieve a desired flow rate, pressured, pressure drop or liquid level.
Through-Conduit
An expression characterizing valves where, in the open position, the bore presents a smooth, uninterrupted interior surface across the seat rings and through the valve bore, thus affording minimal pressure drop. There are no areas that can accumulate debris that might impede pipeline cleaning equipment or restrict the valve's motion.
Tilting Disc Check Valve
A check valve in which the closure member pivots, but not entirely, out of the flow passage.
Trim
The components of a valve that are not integral with the body and that are in contact with the process fluid. Usually refers to the stem, closure member and seating surfaces.
Trunnion
The part of a ball valve that holds the ball on a fixed vertical axis and about which the ball turns.
Trunnion Ball Valve
A ball valve with the ball supported by two bearings (trunnions) in the valve body.
Unidirectional Valve
A valve designed for sealing in one direction only.
Wafer Valve
A valve designed to be installed between flanges, with a short face-to-face dimension in relation to the pipe diameter.
Waterhammer
The pressure surge resulting from a rapid change in liquid flow velocity, as when a pipeline valve is closed. Severe vibration and a hammering noise are associated with this phenomenon; damage to the piping system (including supports) can result.
Wedge
A gate valve closure member with inclined surfaces that mechanic ally forces sealing contact between the gate or disc(s) and seats.
Wedge Gate
A gate whose seating surfaces are inclined to the direction of closing thrust, so that mechanical force on the stem produces tight contact with the inclined seat rings. The gate may be solid or have a groove designed in for flexibility (to account for thermal expansion and/or pressure thrust).
Y-Type Valve
A modified globe valve in which the seat and bonnet are at an angle other than 90 degrees to the flow passage.
Yoke
The part of a gate valve that serves as a spacer between the bonnet and the handwheel/operator.
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3.
Valve Selection
August 1998
General Valve selection and application for onshore and offshore production and processing facilities shall be in accordance with requirements of this EPT, unless superceded by more stringent local regulations. All valves have pressure-temperature (P-T) ratings. This means that for any given temperature, the valve has a maximum pressure to which it can be exposed. Pressure ratings are expressed in PN (SI metric) or Class (U.S. customary units). •
•
•
Commonly used ratings are: −
PN 20 (Class 150)
−
PN 50 (Class 300)
−
PN 110 (Class 600)
−
PN 130 (Class 800)
−
PN 150 (Class 900)
−
PN 260 (Class 1500)
−
PN 420 (Class 2500)
API SPEC 6A also has ratings as follows: −
API 1000
−
API 2000
−
API 3000
−
API 5000
−
API 10000
−
API 15000
−
API 20000
−
API 30000
ASME B16.34 is the recommended source for obtaining the P-T ratings of valves. The rating for Class 800 valves are listed in API STD 602.
All valve body and trim components shall be suitable for the full range of operating temperatures expected in service. This is of particular importance where the valve incorporates non-metallic resilient materials for seating or sealing (e.g. packing). Care shall be taken to ensure that short-term excursions are included in the specifications for a valve.
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August 1998
Provided pressure drop considerations are not critical, the use of reduced port valves shall be maximized wherever possible, especially offshore, to reduce weight and cost. Valves for use in lines subject to pigging shall be full bore. All valves shall be marked in accordance with the requirements of the applicable specification. Markings shall not be less than those specified in MSS SP-25.
4.
Valve Types and Use 4.1.
General Valves control fluids in piping in three ways: •
Shutoff (flow on or off)
•
Modulation (regulation of flow rate or pressure)
• Non-return (prevention of reverse flow)
The focus in this EPT is on shutoff valves operated by hand (including with gear operators) and non-return (check) valves. Although most of the shutoff valves can be fitted with actuators for on/off operation, they are usually different from valves intended to continuously modulate fluid flow or pressure.
4.1.1.
Commonly Used Valves The types of valves commonly used in the oil industry are:
4.1.2.
•
Gate
•
Ball
•
Plug
•
Butterfly
•
Globe
•
Check
Common Characteristics Each of these types of valves comes in a variety of different designs, materials, seat designs, etc. However, they all have the following characteristics in common: •
Fluid-flow passageway
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4.2.
Valve Selection
August 1998
•
Stem or shaft for opening/closing the passageway
•
Lever/wrench for operating the valve
•
Packing gland for sealing the opening(s) through which operating parts pass through the pressure boundary wall
•
Seats and seating surfaces for sealing the passageway
•
Bonnet, cap or tailpiece for assembling and disassembling the valve
Gate Valves Gate valves are the most generally used valves for isolation service in onshore facilities (ball valves are more generally used offshore, because of their more compact size). Gate valves offer high reliability and favorable economics. However, other factors, such as actuator torque requirements, space limitations, etc., may drive the selection to other valve types, such as ball, plug and butterfly valves. All NPS 3/4 and larger gate valves shall be the OS&Y type.
4.2.1.
Wedge Type Of the various types of gate valves available, those of the wedge style are the most compact. This type shall be used where the service is essentially clean and the exposed valve cavity is not likely to fill with solid matter, blocking valve closure. •
All wedge style gate valves are normally supplied as metal seated, with various metallurgies available for different services. Metal seating is essential in dirty services, where the seat sealing surfaces, as well as the gate, may be hardfaced.
•
Wedge type gate valves shall be selected based on one of the following design standards: API STD 600, API STD 602, ASME B16.34 or API SPEC 6D. If valves only conform to ASME B16.34, they shall be tested in accordance with one of the API standards, because ASME B16.34 has no leakage criteria.
4.2.1.1.
Advantages of Wedge Type Valves
The advantages of wedge type gate valves are: •
Low pressure drop
•
General purpose valve used in many types of service
•
Generally the lowest priced flanged valve
•
Suitable for hig h temperature service because it has no elastomers
•
Generally provides a tight shutoff
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•
August 1998
Can be supplied in a wide variety of body and trim materials
4.2.1.2.
Disadvantages of Wedge Type Valves
The disadvantages of wedge type gate valves are:
4.2.2.
•
Unsuitable for throttling service
•
Has a body cavity that traps solids
•
Is not suitable for slurry applications, because the seats are exposed to the flowing medium
•
Is not easy to automate
•
Inline repair to the valve/seats is difficult
Through-Conduit Style Through-conduit style valves have been used successfully in E&P applications for isolation in dirty liquid and high pressure gas services. •
Of these, the slab type is normally used, with the expanding type selected for critical shutoff applications and for double block and bleed isolation. If the expanding-type valve is used in liquid service, it shall be provided with an external means of cavity pressure relief. Slab type valves do not normally need external cavity pressure relief, provided the valve seats are pressure energized and not fixed.
•
Through-conduit style gate valves may be supplied with resilient seats or metal seats. Resilient seated gate valves are often used in double block and bleed applications where tight shutoff is required. Resilient seats are less likely to be damaged in through-conduit type valves, as opposed to wedge gates, because they are protected in both the open and closed positions.
•
Through-conduit gate valves shall be in accordance with API SPEC 6D or API SPEC 6A for wellhead valves.
4.2.2.1.
Advantages of Conduit Gate Valves
Through-conduit gate valves overcome some of the disadvantages of the wedge gate. Since the seats are protected in both the open and closed positions, it is suitable for services containing solids and slurries. Also, the design prevents solids from accumulating in the body cavity. It can also be used as a double-block and bleed.
4.2.2.2.
Disadvantages of Conduit Gate Valves
The disadvantages of this type of valve are its large size/weight and that it is usually more expensive than many other types of valves.
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4.3.
Valve Selection
August 1998
Ball Valves The ball valve is a quarter-turn valve, similar to the plug valve, except the opening in the ball is round. The opening in the ball may be full line size (full port) or smaller than line size (reduced port). Generally a reduced port valve is used, because of its smaller size/weight and lower cost. A full port is required if the line shall be pigged. Ball valves are suited to both liquid and gas services and provide a compact means of isolation. They are also used where relative quick shut-off is required. However, their reliability in dirty liquid service is generally inferior to that of metal seated valves, such as gate and plug valves. Therefore, resilient seated ball valves are not recommended for dirty services. All ball valves for use in liquid hydrocarbon service shall be designed so that liquid trapped in the valve cavity will not overpressure the valve as the liquid heats up. This is usually accomplished by having self-relieving seats or by providing some means for relieving the cavity pressure, such as a hole behind the seat, hole in ball, etc. All ball valves in hydrocarbon service shall be of a fire safe design. Fire safe designs have been tested with liquid in the valve cavity, which provides a good test of the valve's cavity relief feature.
4.3.1.
Types of Ball Valves •
4.3.2.
The two basic types of ball valves are: −
Seat-supported ball
−
Trunnion supported ball
•
The seat supported type is generally referred to as a "floating ball" valve, since the ball is suspended between the two seats. Line pressure assists in sealing by pushing the ball into the downstream seat. Floating ball valves are used for smaller size valves and lower pressure classes.
•
All valves NPS 6 and larger shall be trunnion type for Class 150 and 300.
•
For Class 600 and higher, all ball valves shall be trunnion type.
Use of Resilient and Metal Seats Ball valves are usually supplied as resilient seated, which is essential for bubble tight shut-off in most ball valve designs. The use of resilient seats affects the pressure-temperature rating of the valve; the rating can vary between manufacturers. A large variety of resilient seat materials are available; each material may have a different P-T rating. Generally PTFE (Teflon) is commonly used in the chemical and refining industries and nylon is more generally used in E&P applications. Metal seated ball valves are gaining in popularity, but are still relatively expensive, compared to resilient seated ball valves. Some specialty metal
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August 1998
seated designs are available that can provide "bubble tight" shut-off at high pressures.
4.3.3.
4.3.4.
4.4.
Advantages of Ball Valves •
Provide a smooth flow path, resulting in a low pressure drop, especially for full bore valves
•
Quarter-turn operation, which makes it a quick opening/closing valve
•
Easy to automate for on/off service
•
Use of resilient seats provides tight shutoff
•
Many designs and manufacturers from which to chose
•
Relatively low in cost
Disadvantages of Ball Valves •
Unsuitable for throttling service.
•
Except for expensive metal-seated designs, they are temperature limited because of the resilient seats.
•
The resilient seats can be easily damaged by construction debris, solids in fluid, etc.
•
Proper selection of resilient seats, body seals and stem seal requires experience and good engineering judgement.
•
Fire-safe design is required for hydrocarbon service.
Check Valves There are a wide variety of check valves, but all operate in essentially the same manner. As long as fluid is flowing through the valve, it stays open. When the fluid velocity drops to zero or actually reverses, the valve closes. Their success relies principally on proper selection of type and internal trim. Because an operating mechanism is usually not required, the valve is normally smaller and less expensive than other type of shutoff valves. The various types fall into two main groups, based on flow pattern through the valve. •
The normal choice of dual plate check or swing check provide straight-through flow with minimal pressure drop.
•
Alternatively, ball and piston check valves are usually offered in a globe type body, which introduces a higher pressure drop.
Check valves shall not be used in lines where the normal flow is vertically downward. Valves for use where "non-slam" characteristics are required shall be given special
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Valve Selection
August 1998
consideration (see axial flow type and dual-plated type). Check valves in lines that will be pigged also require special checks.
4.4.1.
Swing Check Valves This is the oldest type of check valve. It consists of a disc, hinged at the top by means of an arm, that is swung open by fluid force and that falls closed when flow stops or slows. Swing checks have traditionally been used in onshore and offshore applications, but offer little advantage over the dual plate check, except in lines that require pigging. Ordinary flanged and buttweld swing checks are considerably more bulky than dual-plate wafer checks. Except for lines requiring pigging, use of swing checks shall be limited.
4.4.1.1.
Design of Swing Checks
•
Swing checks shall be designed in accordance with API STD 600 or API STD 602 wall thickness.
•
For E&P applications, swing checks in accordance with API SPEC 6D and API SPEC 6A are also used.
•
When API SPEC 6D check valves are used, body wall thickness shall be in accordance with ASME B16.34 as a minimum.
4.4.1.2.
Sizes 1
Forged swing check valves are available in sizes NPS /2 –2. These valves are generally more reliable than piston and ball checks in these sizes, although piston checks are more commonly used in these sizes because of their slightly lower costs.
4.4.1.3.
Advantages of Swing Check Valves
•
Piggable designs are available.
•
They are suitable for high pressure/temperature services.
•
They operate equally well whether installed horizontally or vertically.
•
They can be designed with mechanical closure assistance.
4.4.1.4. •
Disadvantages of Swing Check Valves
Valve is large and heavy, compared to dual-plate checks.
• Not suitable for pulsating flow. •
The fluid force required to lift the disc can be considerable, especially in large valves.
•
It is not suitable in services where a non-slam valve is required.
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•
4.4.2.
August 1998
The disc may flutter or slam shut frequently at low flow rates.
Dual-Plate Check Valves The spring actuated dual-plate check valve has become the most widely used style of check valve being used today. It has been successfully used in either gas service or clean/dirty liquid service. •
Valves in dirty service shall be provided with hardfaced metal-to-metal seats.
•
In clean service, a soft seat insert can be provided to improve reverse leakage performance or enhance "non-slam" behavior.
The recommended body style for hydrocarbon service and firewater service is either lugged (with through-drilled holes) or flanged. Wafer style valves may be used in utility services.
4.4.2.1.
Design Considerations
•
Use of the "pin retainerless" design is recommended for hydrocarbon service. The threaded body plugs used for valve assembly are eliminated in this design and it is now standard design for at least one major check valve manufacturer. This design also eliminates the gasket seating surface interruption (at the fasteners for the retaining ring) that occurred in the older design.
•
For gas applications that will subject the dual-plate check to rapid openings, special designs with extended bodies are recommend. These designs are more rugged and have a plate configuration that allows each plate to strike the stop pin in its center of percussion. The stop pin is oversized and the hinge lugs of the plates are enlarged to absorb high impacts.
•
Dual-plate check valves shall be in accordance with API STD 594. Note that the overall length of the "retainerless" design and the double -flanged valves may be greater than given in API STD 594.
4.4.2.2.
Advantages of Dual-Plate Check Valves
•
Compact design
•
Light weight
•
Low pressure drop
•
Lower in cost than swing checks, especially in alloys and stainless steel
4.4.2.3.
Disadvantages of Dual-Plate Check Valves
• Not suitable for pulsating flow.
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Valve Selection
•
August Aug ust 1998
Wafer-type Wafer -type designs are subject to external leakage due to exposed bolting bolting durin during g a fire. fire.
• Not Not a non-slam non-slam valve, valve, but but it is better better at reducin reducing g water-ha water-hamme mmerr than than a swing check. •
4.4. 4.4. 3.
If the t he valve fails, pieces of the springs or discs can travel down the line and end up in equipment.
Ball Check Valves Ball check valves are available in either straight or angle body patterns. Their use shall be limited to utilities and non-fouling non-fouling process services in sizes 1 NPS / –2. 2
4.4. 4.4. 4.
•
In general, the straight through pattern shall be used in vertical lines, (with upward flow only) and the angle pattern in horizontal lines.
•
All ball check valves shall be fitted with springs to assist closure.
•
Ball checks shall not be used in applications where scale or other solid particles particles are are present present or anticipa anticipated. ted.
•
They are also unsuitable for lines subject to pigging.
•
Both piston and swing checks checks are preferable over the ball check.
•
Ball checks shall not be used in pressure classes higher than Class 800.
Piston Check Valves These valves are similar to and can be interchanged with ball check valves in the smaller sizes (NPS 2 and smaller). The same limitations on application apply; however, however, piston checks are more more commonly used used than ball checks.
4.4. 4.4. 5.
•
All piston check valves shall have a spring load piston so it can be used in both the vertical (upward flow) and horizontal lines. Unless specified, some manufacturers will supply piston checks without springs.
•
Spring loaded piston check valves are the preferred type for reciprocating 1 pump and compr compressor essor servi service ce for lines NPS NPS / –2. 2
•
Y-pattern piston checks provide a smoother flow pattern and lower pressure pressure drop. drop.
•
Both piston and ball checks shall not be used in applications where scale, rust and other solid particles particles are present. Swing check valves are more tolerant for applications of this nature.
Axial Flow Check Valves Axial flow check valves are only used in special applications where a nonslam check valve is required. Axial flow describes describes the in-line symmetrical
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August Aug ust 1998
flowpath between the valve inner-body and outer-body. The valve shall be carefully designed and sized for the expected flow conditions. This type of valve is generally only used where a non-slam check valve is required, such as pipelines, discharge lines for large pumps, liquid loading lines, etc.
4.4.5.1. 4.4.5.1.
Advantages of Axial Flow Check Valves
•
A true non-slam check valve.
•
Very low pressure drop.
•
Tight Tight shut-off seats are ar e available.
•
Valve can be buried or installed in locations where spa ce is a premium.
4.4.5.2. 4.4.5.2.
4.4. 4.4. 6.
Disadvantages of Axial Flow Check Valves
•
High costs
•
Long deliveries because each valve is specially designed for the flow conditions conditions
Proprietary Check Valves Hoerbiger makes a proprietary check valve with spring loaded valves plates, similar to reciprocating compressor discharge valves. This design is available in either wafer or flanged type. This type of valve is non-slamm non-slamming ing and is recommended when check valves are required for discharge lines on reciprocating pumps and reciprocating compressors.
4.5.
Globe Valves The most common typ typee of throttling valve is the globe valve. valve. Other types, such as the angle, needle and Y-pattern valves, represent little more than variations on the same operating principle. •
This valve differs from a gate valve in that the disc moves directly away from, not across, the seat when it is opened. This requires that the seat be concentric with the stem, which places it at right angles to the flowpath. Thus, the flowstream shall make two right-angles turns, which generates a pressure drop much higher than that produced produced by a gate gate valve. valve. Because Because the the flow flow area changes changes linear linearly ly with with the stem movement, this valve is ideal for control applications.
•
Different shaped discs can produce different control characteristics. −
The most common disc is the plug type with a conical seating surface.
−
The ball type disc with a spherical seating surface is used for handling viscous fluids; it is slightly less likely to bind in the seat.
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−
The V-port disc gives very fine fine control at low flow rates. Smaller seat diameters diameters provide provide fine fine throttl throttling ing at at low flow rates. rates.
•
The globe valve can seat tighter under average operating conditions than can a gate valve. This is possible because the force applied to the stem is transmitted directly as a seating force, rather than as the wedging action in a gate valve.
•
Using manual type control valves as bypasses around conventional control valves is a typical application. application. Use of globe valves valves is generally restricted to sizes NPS 6 and smaller. For larger sizes, a gate valve is recommended recommended because of price and availability availability..
4.5. 4.5. 1.
4.5. 4.5. 2.
4.6.
August Aug ust 1998
Advantages of Globe Valves •
Can be used to modulate flow or to stay partially open to impose a certain cer tain pressure pressure drop.
•
The disc is usually free to rotate, so erosion and wear on it is usually distributed evenly.
•
Seating surface is more easily accessible through the bonnet than that of a gate valve, so inline regrinding or repair is easier.
•
A variety of different types of disc are available to accommodate different throttling applications.
•
Globe valves can provide tight shutoff, particularly when the disc is equipped with a resilient-seat.
Disadvantages Disadvantages of Globe Valves •
The pressure drop through the valve is several times that of an equivalent gate valve.
•
The globe valve performs poorly in dirty or erosive service and is larger and heavier than most other types of valves.
•
The stem force required to close it can be very high, because the disc is pushing pushing directl directly y against against the the oncomin oncoming g fluid. fluid.
•
Gear operators are usually required in the larger sizes.
•
The globe valve passes flow in only one direction, the flow coming from under the disc; reversing the flow can cause erosion or mechanical damage.
Plug Valves The plug valve is the simplest form of valve, composed of a body with a tapered seating surface, into which a tapered plug fits. A less frequently used design has parallel seating surfaces.
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August 1998
Plug valves are available in either a lubricated or nonlubricated design, a variety of port openings and several plug designs. When used, plug valves shall comply with ASME B16.34, API STD 599, API SPEC 6D or API SPEC 6A.
4.6.1.
Lubricated Plug Valves The use of lubricated plug valves declined in the 1970's and 1980's because of frequent maintenance (lubrication) requirements. However, recent innovations in lubricated plug valve design have reversed their declining usage. They are being successfully used in applications where a tight shutoff is required. Some examples of such applic ations are wellhead manifolds, pipelines and meter proving applications. The correct choice of lubricant is important for successful performance. Lubricants are available in stick form, tubes and bulk; stick or tube lubricant is usually used when a small number of valves shall be serviced or they are scattered throughout a plant.
4.6.2.
Advantages of Plug Valves •
Minimum installation space
•
Simple operation
•
Quarter-turn quick action
•
Relatively little turbulence within the valve
Another important characteristic of the plug valve is its adaptation to multiport construction. For diverting flow, multiport valves simplify piping and provide more convenient operation than multiple gate valves.
4.6.3.
4.6.4.
Disadvantages of Plug Valves •
Regular lubrication of the valve is required.
•
Lubricant can be washed from the plug's face and contaminate the process stream.
•
Pressure drop is higher than gate & ball valves.
•
Tapered plug is prone to "sticking" when the valve is not cycled regularly.
Non-Lubricated Plug Valves • Non-lubricated sleeve-lined plug valves never require lubrication. These valves are available in a variety of body/sleeve materials and are primarily used in chemical services. They are available in a wide variety of body/plug materials, as well as sleeve materials. Mobil has used this type extensively for services such as HF acid.
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•
4.7.
August 1998
Wedge type plug valves do not require lubrication and use O-rings for sealing both the upstream and downstream seats. This type of valve is designed for double block and bleed service, thus eliminating the need for two valves with a bleed valve between them. In liquid service, the valve shall be provided with a means to relieve cavity pressure in the closed position, since the seats seal the body cavity in both the open and closed position.
Butterfly Valves There are two totally different types of butterfly valves. •
The "rubber lined" type has been used in water services for more than 50 years. It is this type that has given butterfly valves a bad name with many users. This type is cheap and readily available, but usually provides a tight shutoff for only a short period of time. In API STD 609, the rubber-lined butterfly valve is called Category A type.
•
The second type of butterfly valve became popular in the early 1970's and it was referred to as a "high-performance" butterfly valve. This type of valve is referred to as Category B type in API STD 609. However, users had leakage problems with most early types of this valve, so they found out that many "high performance" butterfly valves were not truly high performance.
In recent years, butterfly valves with a triple offset disc and a laminated seat consisting of graphoil "sandwiched" between stainless steel rings have proved to be the first truly "high performance" butterfly valves. The seat is referred to as a "flexible metal" seat and zero leakage rates are possible with this type of seat design. •
Mobil has successfully used this type of valve in a wide range of applications, such as −
General hydrocarbon service
−
Steam service
−
Cryogenic service
−
Steam jacketed valves in liquid sulfur service
•
Since the valve has no elastomers, it has been used at temperatures as high as 430°C, (800°F) and as low as -196°C (-320°F). Several companies manufacturer this type of valve, such Adams, Vanessa and Orbit.
•
This type of valve is available with end flanges, rather than the "wafer" type. Generally, the valve is available in two face-to-face dimensions. One is a short pattern, based on an ISO standard and the other is a long pattern, which has the same face-to-face as gate valves.
4.7.1.
Application Considerations •
For hydrocarbon and firewater services, valves shall either be the flanged type or have lugs with through-drilled holes. Also, the valve design shall
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August 1998
have been proved fire safe to one of the following fire test standards; API STD 607, API SPEC 6FA or BS 6755-2.
4.8.
•
For applications where a positive shutoff in required, the triple offset disc type, with a laminated seat design, is recommended. With proper material selection, this type will provide tight shutoff, with minimum maintenance.
•
The rubber-lined butterfly valves shall only be used where tight shutoff is not required and where frequent maintenance of valves is acceptable.
Special Application Valves 4.8.1.
Wellhead Manifold Block Valves The proper selection of wellhead manifold block valves is very important because these valves cannot be depressurized for repairs without a shutdown of the manifold. This can result in production losses in the hundreds of thousands of dollars in some cases. Listed below is a discussion of the different type of wellhead manifold valves. Refer to Appendix A for information on selection of the appropriate valve type. Mobil's Approved Manufacturers List (AML) gives names of companies that manufacture the various types of valves mentioned below.
4.8.1.1.
Through-Conduit Expanding Wedge Gate Valves
Through-conduit expanding wedge gate valves offer excellent resistance to sand and scale. However, in sizes NPS 6 and larger, the top works can get quite large and require several dozen of turns to open and close. This type of valve has double block and bleed capability, which is achieved by mechanical means via the wedge gate design. The disadvantage to using this type of valve is cost and the large amount of space required for the manifold skid.
4.8.1.2.
Plug Valves
Plug valves offer excellent resistance to sand and scale. Operating torque is typically high for plug valves, but this can be overcome with gear operators and/or actuators. These valves typically have face-to-face dimensions about the same as ball or gate valves, but are lighter and more compact than gates. •
Use of hub (grayloc type) connectors will greatly reduce the weight and space of plug valves, especially for higher pressure classes and larger sizes.
•
Plug valves do require periodic lubrication, but this can be a plus, because valves that have developed leaks can usually be made leak tight again by lubricating them.
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•
August 1998
At least two plug valve manufacturers have developed a double block and bleed valve that incorporates two plugs in one body. This ty pe of valve has been used successfully in the North Sea and Gulf of Mexico. Its use has primarily been to replace existing valves that are experiencing seat leakage problems.
4.8.1.3.
Through-Conduit Slab Gate Valves
Through-conduit slab gate valves offer excellent resistance to sand and scale. It has the same characteristics as the expanding wedge gate mentioned above, except it seals on the downstream seat only, since it's sealing depends on the slab being "pushed" into the downsteam seat by line pressure. Double block and bleed (DBB) capability can be achieved by specifying that the upstream seat by pressure-energized. However, if DBB is required, a wedge type is recommended.
4.8.1.4.
Compact Floating Ball Valves
Compact floating ball valves have become popular because of their compact size and lower costs, compared to other types listed above. This valve has a floating ball with extra wide resilient seats. It has preformed very well in sizes through NPS 4. Starting at size NPS 6, Mobil has experienced high torque problems with this type of valve from one manufacturer. Higher torques occur with valves in gas service because of the lack of sufficient liquid hydrocarbon to lubricate the seats. Also, certain seat materials may "swell" in hydrocarbon services, causing the valve torque to increase.
4.8.1.5.
Trunnion-Mounted Ball Valves
Trunnion-mounted ball valves perform very well in solids -free gas or liquid service. However, if sand and/or scale is introduced in anything other than nominal amounts the risk of cutting the seats increases greatly. This can be overcome at great expense by going to a metal-seated design. If the solids are fine enough, the operation of the seat rings will be affected. This can manifest itself by leakage across the seat(s), even with a metal-seate d design or by extremely high operating torques. Double block and bleed can be achieved by specifying the seats as double-acting. In this mode of operation, the downstream seat will be reverse-acting in the event that the upstream seat develops a leak that causes the body cavity to pressurize.
4.8.2.
Double Block and Bleed Double block and bleed valves are generally available in at least five different designs: 1. Through-conduit valve with expanding gate 2. Non-lubricated expanding plug valve 3. Trunnion ball valve 4. Double plugs in one body
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Valve Selection
August 1998
5. Wedge gate with resilient seat inserts (used less often) Mobil's Approved Manufacturers List (AML) gives names of companies that manufacture the various types of valves mentioned below.
4.8.2.1.
Through-Conduit Gate with a Parallel Expanding Gate
•
The through-conduit gate with a parallel expanding gate has proved to be a very reliable double block and bleed for E&P applications. This type provides a tight mechanical seal, both upstream and downstream, and is available with a full-bore. Since the seating surfaces are protected in both open and closed positions, this type has excellent resistance to sand and scale.
•
The two main disadvantages of this type of valve are its large size/weight and relatively high costs. Liquid is trapped in the body cavity in the closed position, so a cavity relief valve is required in liquid service, but not gas service.
•
Manufacturers of this type of valve that are used most often include BEL and WKM.
4.8.2.2.
Non-Lubricated Wedge Plug Valves
• Non-lubricated wedge plug valves, with "slips" containing O-rings for sealing, have been a very popular valve for double block and bleed applications. •
The wedging action of the tapered plug and slip assembly against the sealing surface of the valve body helps minimize abrasion of the resil ient seal. Selection of the appropriate material for the resilient O-ring seals is very important.
•
Since the valve provides metal-to-metal secondary sealing, this type of valve can be used where fire safe valves are required. Liquid is trapped inside the body cavity in the closed position and a cavity relief valve is required in liquid service, but not gas service.
•
Manufacturers of this type of valve that are used most often include General's Twinseal valve and Orbit's TruSeal valve.
4.8.2.3.
Trunnion-Mounted Ball Valve
•
A trunnion-mounted ball valve can serve as double block and bleed if the seats are specified as "double -acting." In this mode of operation, the downstream seat will be reverse -acting in the event the upstream seat develops a leak that causes the body cavity to become pressurized.
•
Many ball valves are advertised as being double block and bleed, but they only work when the valve is pressurized from both sides simultaneously. This does not offer the same protection as that provided by the two valve types listed previously.
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•
Additionally, since the valve has resilient seats, it does not perform well if there is any sand/scale other solids in the fluid. In solids-free gas and liquid service, it has performed well, unless the seats are damaged during start-up by debris left in the piping system.
•
Manufacturers of this type of valve that are used most often include Grove, Pibivisse and PBV-USA.
4.8.2.4.
Double Plugs in One Body
•
A lubricated plug valve containing two plugs in one valve body has become increasing popular in recent years. So far, Mobil has used this type of valve primarily to replace existing valves that are leaking or causing problems. It has been used primarily in the North Sea and the feedback so far has been very favorable.
•
It does have the typical disadvantages of plug valves, namely a high pressure drop and the need for periodic lubrication.
•
Manufacturers of this type of valve that are used most often include Christensens and Serck-Audco.
4.8.2.5.
Wedge Gate with Resilient Seals
•
Wedge gate valves with elastomeric seals inserted in both sides of the disc have been used as double block and bleed valves.
•
This type of valve has the disadvantages listed in Section 4.2 of this Tutorial for gate valves, plus the added disadvantage of damage to the elastomer renders the valve ineffective as a double block and bleed.
•
Pacific has manufactured this type of valve for Mobil applications.
4.8.2.6.
Orbit Valve Design Limitations
Orbit can make their ball valve with double block and bleed capability, but it shall only be used in very clean service. Their design has two seating surfaces on one seat ring, with a bleed hole between the seating surfaces. Since the bleed hole is very small, it can become plugged easily by any solids in the fluid.
4.8.3.
Cryogenic Valves •
The temperature range where valves shall be designed for "cold" service, or "cryogenic" service is -50 °C to -196°C (-60°F to -320°F). Valves used in the temperature range of -18°C to -49°C (0°F to -59°F) need to be evaluated to determine if any of the features of cryogenic valves listed below are needed for the valves to be used.
•
Valve types that are available for cryogenic services include the following: −
Gate
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−
Globe
−
Ball
−
Butterfly
−
Check
August 1998
In sizes larger than NPS 24, butterfly valves are the most commonly used type for block valve service. Type 304 or 316 stainless steel is the most commonly used material. •
Special features of cryogenic valves may include the following: −
Extended bonnet
−
Body cavity relief
− NDE of castings −
Drip rings
−
Live loaded packing
−
Special testing, including cryogenic testing
−
Special marking/tagging
−
Special attention to piping layout
Valve design shall be in accordance with BS 6364, except union bonnets are not permitted. Additional requirements and recommendations are listed below. •
Packing gland (stem) extensions shall be in accordance with BS 6364, Table 1, as a minimum. An additional length of extension will generally be needed if the valve is not installed with the stem in the vertical position.
•
All gate valves and ball valves to be used in liquid service shall be designed to relieve pressures above normal working pressures that may build up in trapped body cavities due to thermal expansion or evaporation of liquid. −
For trunnion ball valves, this is accomplished through the use of spring-loaded self-relieving seats.
−
For floating ball valves and gate valves, a pressure relief hole is generally drilled in the disc/ball to relieve pressure in the bonnet/body cavity to the upstream side of the valve. This makes the valves unidirectional in operation, and the valve end with the vent hole shall be clearly tagged (see tagging below).
−
Valves that contain no body cavity, such as butterfly and check valves, require no cavity relief feature.
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August 1998
• NDE recommendations for cold service valves are listed in Section 7.2 of this Tutorial. •
A drip ring is recommended for all insulated valves NPS 2 and larger. For valves that are unidirectional, attach a metal tag marked "Vent Hole Side" to the drip ring so that it will be visible after the valve is insulated. The drip ring shall be attached to the shaft extension tubing by a continuous weld, and shall be located outside of the insulation.
•
Use of live loaded (Belleville spring washers) packing is recommended for gate valves NPS 3 and larger. Use of bellows seal valves is not recommended. Packing shall be flexible graphite and shall be in accordance with Section 5.4 of this Tutorial.
•
Pressure tests and low temperature tests shall be in accordance with Sections 7.3 and 7.4 of this Tutorial. Pressure test procedures shall ensure that no moisture remains in the valve. Packing/shipping procedures shall protect the valve from ingress of moisture. End covers shall have rubber gaskets and shall be secured with a minimum of four bolts. Covers shall remain in the valve until installation.
•
All unidirectional valves shall be tagged with a permanently attached stainless steel metal tag. The tag shall be marked "Vent Hole Side" to inform construction personnel of the correct valve orientation. NPS 3 and larger valves shall have the tag attache d to the drip ring. Check valves shall have a flow arrow cast into the body, in addition to a marked, permanently attached metal tag.
•
Valves with extended bonnets in liquid service shall be installed with the stems in a vertical position. The extension is intended to provide a vapor area that will protect the packing area from freezing temperatures. Valves in liquid service may be provided with the valve stem at or above 45 degrees above the horizontal position, if the valve manufacturer is so notified, and the extension length is sized for the intended position.
•
Special attention to piping layout is required for valves in cold service. For example, valves with extended bonnets cannot be installed in vertical lines because that would require the valve stem to be horizontal. Flanged joints shall not have excessive bending loads that may cause the joints to leak. Supports shall be designed so that support points will not have excessive loads, and so piping will not lift off the support in cold conditions. A computer stress analysis is recommended for cryogenic lines.
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5.
Valve Selection
August 1998
Valve Design Details 5.1.
Valve Bodies Valve bodies may be made as single or multipiece construction, using castings, forgings or fabricated plate. Use of fabricated valves may be considered in certain applications (for example, pipelines), but forgings or castings are preferred. Weld end valves may require "pup piece" extensions welded onto the valve by the manufacturer to reduce the possibility of damage to the valve resilient seats during fie ld welding or PWHT. Flanged valves shall be made with integrally forged or cast flanges. •
Welded-on flanges are not recommended for anything other than fabricated valves. When they are used, weld neck type flanges are required.
•
Flange dimensions shall be in accordance with the appropriate design standard.
•
The finish on the gasket surface shall be in accordance with the applicable ASME flange standard, which is in the range of 125–250 microinches Root Mean Square (RMS).
Valves that are unidirectional, such as check valves, or those with a preferred sealing direction, such as Orbit valves, shall have a directional arrow integral with the body.
5.1.1.
Wafer Type Valves Wafer type valves, such as check and butterfly valves, shall be provided with through drilled lugs or flanges to protect the long exposed bolting from a fire and also to facilitate installation.
5.1.2.
•
With Mobil approval, flangeless wafer valves may be used in hydrocarbon service if the bolt exposure between adjacent pipe flanges is 75 mm (3 in) or less.
•
All valves in locations where the downstream piping will be disconnected or for end-of-line usage shall have flanged bodies.
•
For valves with more than 75 mm (3 in) of exposed bolting, a less suitable alternative is to shield the bolting with 0.25 mm (0.10 in) thick stainless steel sheet. This shall be wrapped around the valve and banded to the outside of the mating flanges by means of stainless steel banding.
Corrosive Services In corrosive services, carbon and low alloy steel valve bodies fitted with seats that require non-metallic O-rings/seals behind them (to prevent by passing between the seat and the body) shall have the body seat pockets and
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body stem sealing area overlayed with a corrosion resistance material. In most cases, Type 316 stainless steel is adequate, but for some corrosive services the overlay material shall be subject to the approval of a Mobil materials/corrosion engineer.
5.1.3.
Auxiliary Body Connections The number of auxiliary body connections that are not needed for normal valve operation shall be minimized to reduce the risk of leakage or failure. This is especially true for plugged threaded connections, which shall be eliminated wherever possible.
5.1.4.
•
Original (and replacement) auxiliary piping/connections shall have corrosion resistance properties equal to or greater than the valve body (to minimize the potential for corrosion, including galvanic corrosion).
•
If a body connection is essential to assist with the valve testing, a studded flanged connection is preferable on hydrocarbon valves NPS 4 a nd larger.
•
Seal-welding of threaded plugs is not recommended and may not be possible on certain body materials.
•
Body connections required on low alloy valves (1 /4 Cr, 5 Cr, etc.) shall be welded in and post weld heat treated (PWHT) by the manufacturer. In addition, care shall be taken to protect these connections from damage during shipment.
1
Cavity Relief Valves that have a body/bonnet cavity that can be completely isolated from the piping system (for example, double seated ball and gate valves), shall be provided with a means to limit the excessive buildup of pressure in the cavity when in liquid service. Generally, ball valves are provided with self-relieving seats, which releases the cavity pressure into the valve bore. However, on valves with fixed seats (for example, expanding gate valves and seat supported ball valves), an alternative method, such as a relief valve, is necessary. If valves are in gas service only, then cavity relief is not required.
5.2.
Bonnets and Body Joints Bonnets shall be bolted, except gate and globe valves in sizes NPS 2 and smaller in noncorrosive service may be welded. •
Stud bolts shall be used for bonnet bolting for sizes NPS 2 and larger.
•
Hex-headed bolts (not cap screws) may be used on smaller sizes.
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August 1998
•
A minimum of 4 bonnet bolts are required, irrespective of valve size.
•
In sizes NPS 3 and larger, use of welded or pressure sealed bonnets may be considered, subject to Mobil approval.
5.2.1.
Bonnet and Body Joint Gaskets Bonnet and body joint gaskets are usually provided according to the valve design standard, such as API STD 600, API STD 602, API SPEC 6D, etc.
5.2.2.
•
Gasket materials shall be checked for compatibility with the body material, design temperature and process fluid. For example, Teflon is acceptable for use with most fluids, but shall not be used at temperatures above 260 °C (400°F).
•
A wide variety of bonnet gaskets are available and manufacturers are permitted to choose their own, as long as it is permitted by the valve design standard.
•
The two most widely used materials are graphit e and metal (with or without graphite). For example, spiral wound with flexible graphite filler material or corrugated metal with graphite bonded to the metal have proven to be very reliable and can be used at high temperatures.
•
Gate and globe valves shall be the OS&Y type, with an adjustable packing gland.
•
Two- or three-piece bodies shall be designed so that body joint gaskets and bolting can safely withstand piping loads generated by internal pressure and expected bending moments, without leakage or affecting valve sealing performance. The retention system of end entry designs shall not rely on adjacent piping for safe operation.
•
When valves are provided with low strength bolting, such as most of the stainless steel bolting, the bonnet and body joint design shall be checked to ensure there is sufficient bolt loading available to adequately seat the gasket. The required loading for gasket seating will vary according to type of gasket used. For example, spiral wound gaskets require larger loads than corrugated metal gaskets.
Subsea Valve Bonnets For subsea valve bonnets, a double seal is recommended: an outer seal to keep out the seawater and an inner seal to prevent fluid leakage. Note: Mobil has experienced a bonnet seal collapsing due to external sea pressure before the application of hydrostatic pressure test. Leakage occurred when hydrostatic internal pressure was applied.
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5.3.
Valve Selection
August 1998
Seats and Seat Pockets In corrosive services, carbon and low alloy steel valve bodies fitted with seats that require non-metallic O-rings/seals behind them (to prevent bypassing between the seat and body) shall have the body seat pockets overlayed with a corrosion resistant material. In most cases, Type 316 stainless steel is adequate, but for some corrosive services the overlay material shall be subject to review and approval by a Mobil materials/corrosion engineer. Certain valves, using a single seat, can provide double block and bleed (DBB) capability. Some of these, such as the Orbit valve, are susceptible to block in service because of the small bleed hole(s). Only valves whose DBB design accommodates the potential for blockage shall be used in dirty services.
5.3.1.
Hardfaced Seats Carbon steel and low alloy steel gate and globe valves shall have hardfaced seats. The seat rings can be welded or threaded into the body for Class 150 and 300 applications, but shall be welded into the body for Class 600 and higher. In sour service, all welding, including welds on seat rings, shall meet the requirements of NACE MR0175. In valves NPS 2 and smaller, the seats may be shrink fitted or hydraulically pressed into the body, provided the manufacturer has demonstrated this method does not allow leakage or corrosion between the seat and body. Use of metal seated ball valves shall be limited to dirty services or to critical applications where a long service life is required.
5.3.2.
•
For large valves or high pressure classes, the choice of ball material is critical if ball distortion is to be minimized.
•
Generally, balls made from lower strength materials, i.e. 316 stainless steel, may not have adequate strength when used in large valves or high pressures.
•
Care shall also be taken in high temperature applications to consider the effects of differential thermal expansion and potential distortion and/or binding.
Wiper Rings Wiper rings shall be used on expanding through-conduit gate valves to ensure that the sealing surfaces are kept clean during valve operation in dirty service. Their presence shall not be necessary to achieve seat leakage performance or affect the fire safe aspects of the valve design. Care shall be taken to ensure that the wiper ring is securely fixed into the seat so that it cannot be extruded or loosened during valve operation.
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5.3.3.
August 1998
Use of Resilient Seats The provision for injecting seat sealant in resilient seated valves is not recommended in services where fouling or blockage of downstream equipment or instrumentation may result. If used, the sealant material shall be compatible with the process fluid. Resilient seated valves used in hydrocarbon services shall satisfy the requirements of API SPEC 6FA or API STD 607. Use of any type of resilient (or soft non-metallic) seat shall be limited to clean service.
5.3.4.
•
The seat material shall be compatible with the intended service medium and temperature.
•
Seat design shall ensure that extrusion or pullout of resilient seat inserts is not possible.
•
On large ball valves, resilient seat width shall be the minimum necessary to give adequate shear strength, in order to minimize valve operating torque.
•
Fire safe valves shall have a backup metal-to-metal seating capability in the event the resilient seat is destroyed.
Spring-Assisted, Pressure Energized Seats Spring-assisted, pressure-energized seats are recommended for use on slab type, through-conduit gate and trunnion mounted ball valves. When used in self-relieving seats, the spring shall be so that the body cavity pressure never exceeds 120 percent of the valve design pressure. The design shall incorporate features to prevent or minimize the intrusion of fouling material into the spring or seat pocket area. Pipeline and other E&P valves fitted with pressure-energized seats that need to have additional sealing performance in one direction, can be fitted with a reverse- or double-acting seat in place on one of the normal seats. A reverseacting seat shall only be specified where a unidirectional valve is acceptable. Double-acting seats on ball valves are frequently used in E&P applications.
5.4.
Stems and Stem Seals •
All valve stems shall be provided with a means to prevent "blowout" of the stem if it fails. Packing glands shall not be used to provide this protection.
•
Inside screw gate and globe valves shall not be used, except in clean utility services.
•
For valves using packing rings (e.g. gate, globe and butterfly), the finish of the bonnet packing area (stuffing box) shall be approximately 125 microinches RMS, to obtain an effective stem seal. Also, it shall not be overly deep; in typical gate and globe valves,
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it shall be able to accommodate five rings of packing. Any excess depth shall be taken up using a spacer of appropriate material. In some applications, the stuffing box may require a lantern ring or other feature so sealant material can be injected in the event of stem leakage. •
Valves requiring seat pocket overlay (Section 5.3 of this Tutorial) shall also have the stem sealing area of the body overlaid with the same corrosion resistant alloy.
•
The surface finish on stems through the packing area shall be 32 microinches RMS or smoother. Also the stem runout/taper in the area contacting the packing shall not exceed 0.08 mm (0.003 in) through the full travel distance.
5.4.1.
5.4.2.
Seals •
O-rings seals shall not be used on rising stem valves.
•
All stem seals on rising stem valves, except those on valves fitted with backseats, shall be provided with a grease/sealant injection capability.
•
Use of bellows seal valves is generally not recommended, because of their higher costs and higher torque requirements. The graphitic packing described below has been found to adequately address stem leakage. Bellows seal valves may be considered as alternatives for rising stem valves in services where absolutely no stem leakage is allowed.
Packing •
For valves using packing rings, the preferred stem packing material for most services is flexible graphite. This packing shall meet the following specifications: −
The material shall be a minimum of 95 percent pure carbon.
− No binders, lubricants or similar additives are allowed. −
The packing shall incorporate an approved corrosion inhibitor.
−
Die formed rings to a density of 1120–1280 kg/m (70–80 lb/ft ) shall be used.
3
3
•
In most applications, a stack of five packing rings is sufficient, consisting of three inner rings of die-formed flexible graphite and end rings of braided graphite to serve as anti-extrusion rings.
•
Teflon packing may be used in low temperature utility services (air, water, nitrogen, steam), but it is not recommended for hydrocarbon services, due to its deterioration at higher temperatures, particularly in fire situations. Note that Teflon packing is often supplied as the standard packing in stainless and other high alloy valves. Teflon packing shall never be used in high temperature (greater that 205 °C [400 °F]) services.
•
Pipeline valves typically use chevron, "T" or "U" type pressure ac tivated packing. The preferred material for these is Viton, provided the
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temperature limitations are met. In addition, provisions are normally provided for injecting sealant into the packing area shall leakage occur. •
5.5.
The use of a spring-assisted packing gland design (e.g. Belleville spring washers) is not normally required. However, this design could be considered for use in certain applications (e.g. toxic services, severe cycling, etc.) to maintain an adequate load on the packing material.
Closure Elements Depending on the type of valve, closure elements may be called a gate, disc, ball, plug or flapper. The design of closure elements made from low strength materials, such as 316 stainless steel, in high-pressure valves shall be reviewed to ensure the elements are adequately sized to prevent excessive distortion and leakage, especially in gate and ball valves. Alternatively, higher strength materials may be used for the closure elements. •
•
5.6.
On rising stem valves, the stem-to-gate/disc connection shall be designed so that no permanent deformation occurs when opening the valve against full design differential pressure. −
Additionally, the connection shall be designed so that if failure does occur, the first point of failure is outside the valve body.
−
Further, the load for the second point of failure shall be significantly higher that the load for the first failure.
−
For actuated shut-off valves, the stem connection shall be designed to safely withstand the maximum available actuator load.
The stem-to-ball/plug/disc connection on quarter-turn valves shall be designed so that no permanent deformation occurs during opening of the valve against full design differential pressure. −
For actuated shut-off valves, the stem connection shall be designed to safely withstand the maximum available actuator load.
−
For pipeline and other ball valves subject to pigging, the stem-to-ball connection shall be designed to ensure that the ball is sufficiently fixed to the stem to prevent any offset when the valve is in the open position.
Valve Operators A gear operator shall be provided for all valves in the sizes listed below. Sizes smaller than those shown may be handwheel/lever operated, provided the torque to break open or close the valve at maximum differential pressure does not exceed 205 N-m (150 ft-lb). The handwheel/lever shall be sized so that a force of no more than 35 kg (75 lbs) on the end of lever or handwheel will open/close the valve.
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All manually operated valves shall be provided complete with handle/handwheel. The maximum lever length shall be 500 mm (20 in) for hand operated valves. For valves with handwheel, the handwheel diameter shall not exceed the valve face-to-face dimensions. Gear operators shall be heavy-duty type and shall be completely housed in a weatherproof enclosure. Provide gear operators for the following NPS and larger size valves:
6.
Class
Gate
Globe
Ball (Floating)
Ball (Trunnion)
Plug
Butterfly
150
14
10
8
8
8
8
300
12
8
6
8
8
8
600
8
4
–
6
–
6
900
6
3
–
4
–
–
1500
4
3
–
3
–
–
2500
4
3
–
2
–
–
Materials This Section addresses some of the more fundamental factors affecting valve material selection for body, trim and seats. Wherever possible, material selection shall be confirmed by a Mobil Materials/Corrosion Engineer. Valves for sour service shall comply with NACE MR0175 and the recommendations in EPT 08-T-03.
6.1.
Body and Bonnet Materials Valve body material selection follows the materials selected for the other piping components in the same line class. Normally, the same material type and grade as used for pipe and flanges shall be used. However, in some cases, selection of a superior material for the valve construction can offer distinct cost and delivery advantages. An example of this is the use of 316 stainless steel valves in a 304 stainless steel piping system (because of availability and pricing). Some of the commonly used body/bonnet materials are listed in the table below.
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Table 1: Commonly Used Body/Bonnet Materials Valve Materials Nominal Material
Minimum Temperature
ASTM Specification for Product Form Forging
Casting
Plate (Note 1)
Carbon steel
-29°C (-20°F)
A105
A216 WCB
A515, A516 Gr. 70
L.T. carbon steel
-46°C (-50°F)
A350 LF2
A352 LCB
A515, A516 Gr. 65
-29°C (-20°F)
A182 F11
A217 WC6
A387 Gr. 11, Cl. 2
2 /4 Cr–1 Mo.
-29°C (-20°F)
A182 F22
A217 WC9
A387 Gr. 22, Cl. 2
5 Cr– 1/2 Mo.
-29°C (-20°F)
A182 F5a
A217 C5
A387 Gr. 5, Cl. 1or 2
9 Cr–1 Mo.
-29°C (-20°F)
A182 F9
A217 C12
13 Cr (410 SS)
-29°C (-20°F)
A182 F6a
A217 CA15
-255°C (-425°F)
A182 F304
A351 CF8
A240 304
-255°C (-425°F)
A182 F304L
A351 CF3
A240 304L
16 Cr–2 Ni–2 Mo (316 SS)
-198°C (-325°F)
A182 F316
A351 CF8M
A240 316
16 Cr–2 Ni–2 Mo (316L SS)
-255°C (-425°F)
A182 F316L
A351 CF3M
A240 316L
18 Cr–10 Ni–Ti (321 SS)
-198°C (-325°F)
A182 F321
18 Cr–10 Ni–Cb (347 SS)
-255°C(-425°F)
A182 F347
1
1
1 /4 Cr– /2 Mo. 1
18 Cr–8 Ni (304 SS)
2
18 Cr–8 Ni (304L SS)
2
A240 321 A351 CF8C
A240 347
B381
B 265
22 Cr Duplex SS 25 Cr Duplex SS Incoloy 825 (UNS N08825)
B 425
Inconel 625 (UNS N06625)
B 564
Titanium
B 367
Alloy 20
A351 CN-7M
Monel
A494 M35-1
Ni-Al-Brz
B148 C95800
-29°C (-20°F)
NOTES:
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1. The minimum temperatures shown are for valves with cast or forged bodies. For minimum temperature of valves fabricated from plate, refer to Appendix A in ASME B31.3. 2. 316 stainless steel valves are commonly used in 304 stainless steel piping system, because they are generally more readily available and cost no more than 304 SS valves.
6.2.
•
In the case of expensive material, such as Incoloy 825, consideration shall be given to using internally clad carbon steel valves, especially in sizes NPS 6 and larger. Clad carbon steel valves might also be considered as alternatives to other alloys.
•
For fabricated valves and other valves requiring weld repair, the need for PWHT shall be confirmed with a materials/corrosion engineer. In addition, all welds on valves in sour service shall meet the requirements of NACE MR0175.
Trim Materials Valve trim includes all internal valve components that are not an integral part of the body but are in contact with the process fluid. The selection of trim material is governed by body material, service fluid and availability.
6.3.
•
For wedge style gate and globe valves in sweet hydrocarbon service or utility service, 13 Cr trim is preferred. For example, use Trim No. 1 or 8 for API STD 600 and API STD 602 valves. When 13 Cr trim is required, the "free-machining" grades (e.g. type 416 SS) shall not be used, due to their susceptibility to cracking in H 2 S environments.
•
For subsea valve applications, when long delays are expected between hydrotest and commissioning, consideration shall be given to the potential for galvanic corrosion induced by seawater in contact with dissimilar metals.
Stem Materials •
Stems shall be made from forged materials of high strength. Upset forged T-head stems shall be used in gate and globe valves; welded stems are prohibited.
•
The use of 316 stainless steel for stems shall be minimized because of its low strength and the resultant increase in required stem size. Except for 13 Cr trim valves, the conventional stem material is 17-4 PH. It shall be specified as ASTM A564/A564M, Type 630, Condition H1150M. However, in valves requiring the corrosion resistance of duplex stainless or better, the stem material shall normally be Inconel 718. In valves for operation at low temperatures, 17-4 PH and duplex stainless trim materials shall not be used below -46°C (-50°F).
•
17-4 PH steel is not resistant to pitting type corrosion in water service. Mobil has experienced a number of failures in water flood service with this alloy and it's use in components that may come into contact with water (balls, stems, seat rings, etc.) is not recommended.
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6.4.
Valve Selection
Seat Materials •
Metal seats that are not integral with the body shall be made from solid alloy material. Coated or plated carbon steel seat rings are not recommended except in pipeline applications in conjunction with resilient seats.
•
For API STD 600 valves with metal seat rings that are seal welded into the body, manufacturers typically use carbon steel seat rings with a hardfacing (weld applied) applied to the sealing surface of the seat ring. This is permissible and is in compliance with API STD 600.
•
When required, the minimum finished thickness of hard-faced weld overlay shall be 1 1.5 mm ( /16 in).
6.4.1.
6.5.
August 1998
Seating Materials •
The preferred resilient seating materials are nylon and reinforced Teflon (PTFE), but Viton has also been used successfully in a number of pipeline applications. Nylon is more typically used in E&P applications and PTFE in chemical and refinery applications. These materials are subject to maximum temperature limits; nylon to 121 °C (250° F), Viton to 175°C (350°F) and reinforced Teflon to 205°C (400°F). (See Section 6.9 of this Tutorial).
•
For valves required to operate at low temperatures [-29 °C (<-20°F)], Kel-F and unreinforced Teflon are usually required to overcome the tendency to harden with decreasing temperatures.
•
Resilient seating materials are not recommended in services where solids and/or abrasives are present in the process medium.
Closure Members The base material of the valve closure member (gate, disc, ball or plug) shall be selected to suit the service fluid. Solid corrosion resistant alloy material is preferred for hydrocarbon and chemical service, but plated or coated carbon steel closures may be considered.
6.6.
Seat Spring Materials For the majority of applications, Inconel X-750 or X-718 are the preferred spring materials. Suitable materials for bronze and titanium valves shall be recommended by the valve manufacturer and approved by Mobil.
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6.7.
Valve Selection
August 1998
Sealing Surfaces–Resilient Seated Valves All closure members and seats shall be made of a corrosion resistant material (CRA). In sizes NPS 6 and larger, it may be more cost effective to use non-corrosion resistant closure members and coat the surface of the members with a weld deposited CRA material or with electroless-nickel plating (ENP). Electroless-nickel plating shall have a minimum thickness of 75 µ (3 mil). Chrome plating is not recommended, except when a layer of ENP is first applied. The entire closure member shall be coated to avoid undermining the coating edges. Valves such as Orbit ball valves, which have the sealing area coated with a layer of weld applies CRA material, are an exception. All coatings shall be sufficient to account for expected wear during the life of the valve.
6.8.
Sealing Surfaces–Metal Seated Valves For services containing solids or for erosive services, all sealing surfaces on the closure member and seats shall be coated with a wear-resistant material. Preferred materials are Stellite 6 (weld deposit) or tungsten carbide (spray deposit by Praxair 'D-Gun' process or equal). All hard facing deposition procedures, together with any heat treatments, shall be subject to Mobil approval.
6.9.
Elastomeric Materials The use of non-metallic materials in a valve can often lead to premature valve deterioration or failure due to incorrect selection or use. In addition, their presence in valves designated as fire sa fe requires the valve to undergo a fire test to demonstrate that the valve integrity is not dependent on such fire degradable materials. It is essential that the use of any non-metallic materials, especially elastomers, has been confirmed either by previous performance in the particular service or by relevant testing. Elastomers are commonly used as O-ring seals at stems and/or behind floating seats or as body seals in end entry valves. The secondary components in a hydrocarbon stream are usually the things that complicate material selection. These are components like H2 S, CO 2, chlorides in water, amine (as used in corrosion inhibitors), methanol or glycol (as used in hydrate inhibitors), etc. Sulfide compounds associated with H2 S can cause elastomer embrittlement. CO2 can cause explosive decompression in high pressure gas service. Amines can cause excessive swelling and methanol can act as a solvent.
6.9.1.
Nylon Nylon is a commonly used seating material for E&P applications. It is a harder material than Teflon and is more resistant to solids in the hydrocarbon stream. Nylon shall be limited to a maximum temperature of 121°C (250°F).
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6.9.2.
August 1998
Viton F and Viton GFLT Viton F and Viton GFLT are generally acceptable materials. The individual temperature limitations and their compatibility with the process fluids shall be checked when specifying them for a particular service. Generally, they can be used up to a temperature of 175 °C (350°F). Viton has good resistance to hydrocarbons and chemicals and has been used successfully in pipelines and other E&P applications.
6.9.3.
Reinforced Teflon Reinforced Teflon is a common seat material for ball valves used in chemical plants and refineries. It has outstanding resistance to most chemicals as well as hydrocarbons. It also has a low coefficient of friction, so valve torques are usually lower than for many other types of seat materials. It can be used up to a temperature of 205 °C (400 °F). However, it does "cold flow", so a valve's pressure-temperature rating drops off sharply as the temperature approaches 205°C (400°F). PTFE is normally only used in Class 300 and lower valves.
6.9.4.
PEEK PEEK is a high temperature material that can be used up to 230 °C (450°F). It has a high coefficient of friction, so the operating torques will be high for PEEK seats.
6.9.5.
Buna-N Buna-N (Peroxide cured) is a commonly used elastomer. The curing process enhances its high-temperature properties and resistance to explosive decompression. The Shore Hardness of Buna-N shall be 70 or harder.
6.9.6.
EPDM EPDM is an ethylene-propylene compound that has good resistance to hydrocarbon fluids. It is susceptible to explosive decompression and has a tendency to swell in liquid hydrocarbon streams.
6.9.7.
TFE/P TFE/P is the generic name of Aflas and is sometimes referred to as "TeflonPropylene." This material has been used successfully as an O-ring material, but it has the same limitations as EPDM listed above.
6.9.8.
Chemraz Chemraz has been used as an O-ring material. It's temperature limitations and compatibility with the process fluids shall be checked when specifying this material for a particular service.
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6.9.9.
August 1998
Kalrez Kalrez is a very expensive proprietary material manufactured by Dont. It is an excellent material, but Mobil has little experience with it because other materials have been found to be more cost effective.
7.
Inspection and Tests 7.1.
General Valves shall be inspected and tested in accordance with their referenced design specification and any additional requirements listed in the project specifications and MP 16-P-30A (M&R) or MP 16-P -31A (E&P) series. When valves are purchased from Mobil approved manufacturers, additional inspection and/or testing is usually not required, unless Mobil has experienced problems with the particular manufacturer. However, in severe services and/or critical applications, additional steps shall be taken to ensure integrity and quality of the valves to be used. Some examples of where additional inspection is recommended are:
7.2.
•
Pressure Classes 1500 and higher
•
Sour or toxic services
•
HF acid service
•
Cryogenic service
Non-Destructive Examination • Non-destructive examination of valves and valve components generally consists of one or more of the following examinations:
•
−
Radiographic Examination (RT)
−
Magnetic Examination (MT)
−
Liquid Penetrant Examination (PT)
−
Ultrasonic Examination (UT)
−
Positive Material Identification (PMI)
Most valve specifications do not require any non-destructive examination of valves. Generally, this is a supplementary requirement that shall be specified by the user.
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7.2.1.
August 1998
Required Samples The following requirements apply to cast valves purchased from approved manufacturers. The manufacturer shall have available, for Mobil's review, the results of the radiography examination (RT) of a "sample casting" from each foundry source. A "sample" is required for: • New patterns
7.2.2.
•
Revised patterns
•
Re-rigged patterns
•
Changes in processing, such as core making, sand control and melt practice
•
Pattern is sent to another foundry
•
Rejection of a sample
Examination Requirements per Lot The quantity of valves to be examined shall be the required percentage of each lot, but a minimum of one per lot. The lot is defined as all the items of a single type, class, size and heat/batch.
7.2.3.
•
When sample inspection is carried out, the lot shall only be accepted if all items of the sample meet the acceptance criteria.
•
If any of the inspected items is found unacceptable, an additional sample shall be inspected. If the additionally inspected items are acceptable, the total lot shall be accepted with the exception of the rejected item(s) found in the initial sample.
•
However, if any of the additionally inspected items fail to meet the requirements, a 100 percent inspection of the total lot shall be carried out.
Examination Specifics •
The radiography (RT) procedure and acceptance standards shall be in accordance with ASME B16.34, Annex B. Critical areas for RT shall be as defined in ASME B16.34.
•
Castings of magnetic materials shall be examined by magnetic particle (MT) in accordance with ASME B16.34, Annex C. All accessible exterior and interior surfaces of the casting shall be examined.
•
Castings of non-magnetic materials shall be examined by liquid penetrant (PT) in accordance with ASME B16.34, Annex D. All accessible exterior and interior surfaces of the casting shall be examined.
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August 1998
Table 2: Cast Valves–NDE Requirements and Sampling Frequency Type of Service
Pressure Class
Visual
Radiography (MT) or (RT)* (PT)
General process, hydrocarbons
600 & lower
100%
0%
0%
Non-sour service, steam
900, 1500
100%
0%
100%
Condensate, chemicals
Class 2500
100%
10%
100%
API 5000
100%
10%
100%
API 10000
100%
100%
100%
Sour hydrocarbon service
900 & lower
100%
10%
100%
Hydrogen
1500 & higher
100%
100%
100%
Hydrofluoric (HF) acid service
All Classes
100%
100%
100%
Cryogenic (cold) service
All Classes
100%
10%
100%
Air, water, nitrogen
All Classes
100%
0%
*Critical areas, as specified in ASME B16.34.
7.3.
•
Forged valves generally do not require any NDE, unless it is specified in the valve standard or in the valve specifications. For special applications or for alloy valves, random examination of all accessible surfaces of the body and bonnet may need to be performed.
•
It is recommended that all welds in valves fabricated from plate be examined if the valve will be in hydrocarbon or chemical service. The examination shall include radiographic examination (RT) of welds. All plate used for pressure containing parts shall be inspected for laminations using MP or PT, as applicable. The mill certificates (certs) for the pipe and plate used in the fabrication of valves shall be reviewed for compliance with specifications.
•
The welding ends of buttweld valves shall be inspected for laminations using MP or PT, as applicable.
Pressure Tests Shell, seat and backseat tests (where applicable) shall be performed on all valves in accordance with the applicable standard to which the valve is purchased. As a minimum, the tests shall include a body/shell test, a closure/seat test and a stem backseat test where applicable. The test medium, test pressure and duration of the tests is dependent on the valve standard. All tests shall be carried out prior to any painting of the valve.
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August 1998
Valves conforming to ASME B16.34 shall have seat leakage tests performed in accordance with either API STD 598 or API SPEC 6D. (ASME B16.34 does not list any seat leakage criteria.)
7.4.
Low Temperature Tests •
For valves required to operate at a process temperature below -18 °C (0°F), a design proof test, incorporating closure and torque tests at the minimum design temperature, shall be carried out. In lieu of repeating this test, a manufacturer may submit a test report performed on previously tested valves of the same design for Mobil's approval.
•
Valves intended for cryogenic service shall be tested at cryogenic temperature in ac cordance with a test procedure approved by Mobil. A minimum of one valve for each size and pressure class shall be tested. Leakage rate shall be approved by Mobil. The recommended maximum allowable seat leakage during cold tests are: Ball and butterfly valves with metal seats: Class 150
15 ml/min/NPS
Class 300
30 ml/min/NPS
Class 600
40 ml/min/NPS
Ball and butterfly valves with resilient seats: Class 150
10 ml/min/NPS
Class 300
20 ml/min/NPS
Class 600
25 ml/min/NPS
Gate and globe valves with metal to metal seats:
7.5.
Class 150
30 ml/min/NPS
Class 300
40 ml/min/NPS
Class 600
50 ml/min/NPS
Functional Tests All actuated valves shall be subjected to a functional test with the actuator mounted on the valve. This test shall use the intended actuator control system and shall demonstrate the adequacy of the actuator sizing, along with the time required to stroke the valve against its full rated design pressure differential.
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8.
Valve Selection
August 1998
Valve Standards 8.1.
ASME B16.34 Use of valves fabricated from plate/pipe is not recommended. Use of "Special Class" and "Limited Class" valves is not recommended. Pressure Classes 400 and 4500 shall not be used unless approved by Mobil. Seat leakage rates for valves built to this standard shall not exceed the rates listed in API STD 598 or API SPEC 6D.
8.2.
ASME B16.33, ASME B16.38 Valves to standards ASME B16.33 and ASME B16.38, which address manually operated metallic valves in low pressure gas service, shall not be used.
8.3.
API SPEC 6A Gate, ball and check valves to API SPEC 6A may be used downstream of production choke valves or in injection systems when pressures greater than 5000 psig are required. They may also be used in lower pressure downstream applications, but valves to other design standards are usually more economical. Wherever they are used, the upper temperature limit and required quality level shall be approved by Mobil.
8.4.
API SPEC 6D Valves to API SPEC 6D may be used, subject to the following limitations: •
Structural grades of steel (e.g., ASTM A36/A36M) shall not be used for any pressure containing parts.
• No flanges shall be made from plate.
8.5.
•
O-ring stem seals shall not be used on rising stem valves.
•
Body wall thickness shall be in accordance with ASME B16.34, as a minimum.
API STD 594 NPS 24 and larger dual plate check valves shall have independently suspended plates. For sizes NPS 26 and larger, the valve purchase order shall specify the type of flanges that will be used. ASME B16.47, Series A flanges have the same dimensions as MSS SP-44 flanges. ASME B16.47, Series B flanges were previously known as API 605 flanges. For hydrocarbon service, use of the double -flanged check valve is recommended for the sizes
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Valve Selection
August 1998
where it is available (generally NPS 12 and larger). For smaller sizes, wafer valves with through-drilled lugs shall be specified. Body and plate material may be the same, unless serious corrosion or erosion problems are expected, in which case reference to Table 4 in API STD 594 shall be made. Use of the retainerless design is recommended for hydrocarbon and chemical services.
8.6.
API STD 600 Pressed or stamped steel handwheels shall not be used. For hydrocarbon services, use of valves from Mobil approved manufacturers will help ensure that fugitive emissions are kept within acceptable limits.
8.7.
API STD 602 Valves to this standard are generally used for vents and drains and sometimes as the root valve for instrument takeoffs and orifice taps. The extended body type is recommended if a more rugged takeoff connection is needed. Inside Screw Rising Stem (ISRS) and union bonnet valves are not recommended. Screwed packing glands shall not be used. Hex head bolts, not cap screws, shall be used for bonnet bolting.
8.8.
API STD 609 For valves with seat retainer rings, the width of the heads of the seat retainer screws shall not occupy more than 50 percent of the sealing width of gaskets for mating flanges. Where available, use of retainless designs shall be used.
8.9.
Miscellaneous Valve Standards •
The following API standards have been discontinued by API and shall no longer be used: −
API STD 593
−
API STD 595
−
API STD 597
−
API STD 604
−
API STD 606
•
Use of valves to AWWA shall be limited to valves for onshore water services.
•
MSS SP-80 bronze valves may only be used in air and fresh water service. The following additional MSS standards are very good sources of information on valving, valve inspection and examination:
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9.
Valve Selection
−
MSS SP-42
−
MSS SP-45
−
MSS SP-53
−
MSS SP-54
−
MSS SP-55
−
MSS SP-61
−
MSS SP-70
−
MSS SP-71
−
MSS SP-91
−
MSS SP-92
−
MSS SP-93
−
MSS SP-94
−
MSS SP-96
−
MSS SP-99
August 1998
Reconditioned and Surplus Valves 9.1.
Reconditioned Valves •
Valves removed from service at Mobil facilities may be reconditioned and reused, provided the reconditioning is done by Mobil-approved valve repair facilities in accordance with Mobil's "Specification for Valve Reconditioning." This document was prepared in 1996 as part of a program to reduce valving costs. At that time, Mobil evaluated various valve repair facilities and selected certain quality facilities near various Mobil facilities. Valves reconditioned as part of that program may be used as if they are new valves.
•
Valves that have been reconditioned following service at a non-Mobil facility are not recommended for use in Mobil facilities. These valves are normally unacceptable due to the uncertainty over the previous service conditions of the valve. If Mobil personnel can verify the previous service conditions and repairs are made by Mobil approved repair shops, these valves may be considered for usage.
•
Valves removed from Mobil facilities and reconditioned by the original manufacture r or at a repair facility authorized by the original manufacturer are suitable for reuse in Mobil facilities.
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Valve Selection
•
9.2.
August 1998
All reconditioned valves shall be pressure tested as if new, in accordance with Mobil's reconditioning specification mentioned above. A copy of this specification can be obtained by contacting one of Mobil piping specialists.
Surplus Valves Some new valves are delivered to a project, stored onsite and not used. These valves are sometimes restocked by the local supplier/agent and later resold as "new" valves or "new surplus" valves. Such valves shall not be used by Mobil unless: •
The valves are retested in accordance with the API STD 598 or API SPEC 6D.
•
The original documentation for the valves is available.
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Appendix A: Selection of Valve T ype
1.
Introduction The selection of an appropriate valve type for a particular service or application depends on a multitude of different parameters, such as flow characteristics, weight, operability, etc. The following charts are provided to assist the specifying engineer in evaluating the various types of valves. No chart is provided for regulating valves; these can be selected based on the size that is required. The charts rate the various valve types according to the different characteristics that are applicable to the category. For example, plug valves are rated excellent in providing tight closure, but are rated "Poor" with respect to pressure drop. However, there are exceptions if one considers special designs, since some plug valves are now available with full circular bores. Not every characteristic is considered; only those usually required in a category and which allow a common basis for comparison. To use the charts, the specifying engineer shall first identify the basis valve category (i.e. isolation or check) and then go to the appropriate chart. Using the characteristics that are important for the service/application in question, the engineer can develop an overall rating for a particular valve type. •
Note that engineering judgement will often be required to weight the relative importance of the individual characteristics.
•
The overall rating shall allow the engineer to choose the optimum valve type. In many instances, the overall ratings of several types will be close, making the optimum choice difficult to determine. In these cases, the choice may be based on considerations outside the charts (e.g., past experience, price, availability, etc.).
•
Information on price and availability can be obtained generating purchase descriptions from this document or the MP 16-P-30A or MP 16-P-31A series and obtaining quotations from the manufacturers of each type of valve. Whatever the case, engineering judgement will be required.
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Valve Selection
August 1998
Valve Characteristic Rating Charts Table A– 1: Isolation Valve Characteristic Ratings
Characteristic
Gate Valves
Ball Valves
Plug Valves
Butterfly Valves
Butterfly Valves**
EX
S
W
Piggability
E
E
P*
E
P
P
P
Quick Shut- off
P
P
P
G
G
E
E
Low Pressure Drop
E
E
E
E/G
P*
G
G
Size (Compactness)
P
P
G
E
G
E
E
Weight
P
P
G
G
G/P
E
E
In-line Maintenance E
E
G
P*
E
P
P
Tight Closure
E
G
G
G
E
G/P
E
Resistance to Solids
E
E
G/P
P
G
P*
G
Ease of Automating
G/P
G/P
G/P
E
E/G
E
E
Comparable Cost
P
G/P
G/P
P/G
P
E
G
EX = Expanding Gate
E = Excellent Rating
S = Slab Gate
G = Good Rating
W = Wedge Gate
P = Poor Rating
* Some designs are available that exceed the general rating. ** Triple offset, flexible metal seat type, such as Vanessa and Adams.
Table A– 2: Check Valve Characteristic Ratings Characteristic
Wafer-Plate (Single/Dual)
ThroughConduit Swing
Ordinary Swing
Ball
Piston
Axial Flow
Piggable
P
E
G
P
P
P
Size/Compactness
E
P
P
--
P
P
Weight
E
P
P
--
P
P
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August 1998
Characteristic
Wafer-Plate (Single/Dual)
ThroughConduit Swing
Ordinary Swing
Ball
Piston
Axial Flow
Low Pressure Drop
P*/G
E
E
P
P
E
Quick Acting
G
G
G
E
E
E
Comparable Cost
E
G
G
--
P
P
Resistance to water hammer
G
P
P
G
G
E
Resistance to Solids
E/G
E
E
P
P
G
E = Excellent rating
G = Good Rating
P = Poor Rating
* Some single-plate wafer check valves have a relatively high pressure drop.
3.
Valve Type Selection Charts 3.1.
Legend for Tables A–3 through A–10
Code
Description of Material
C.S.
Carbon or low alloy steel
C.S. (IPC)
Carbon or low alloy steel, internally plastic coated
C.S. (ENP)
Carbon or low alloy steel, electroless nickel plated
13 Cr
AISI 410 stainless steel
4140
AISI 4140 low alloy steel, used in quenched and tempered condition
17-4 PH
17-4 PH stainless steel, age hardened
303
AISI 303 stainless steel (wrought)
304
AISI 304 stainless steel
316
AISI 316 stainless steel
IN-X-750
Inconel alloy X-750, age hardened
Duplex
A stainless steel with a duplex structure of austenite and ferrite, for example 2205
In 718
Inconel alloy 781, age hardened
K500
Monel alloy K-500, age hardenable nickel copper alloy
In 825
Incoloy alloy 825
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August 1998
Code
Description of Material
M400
Monel alloy 400, nickel copper alloy
NiAlBz
Nickel aluminum bronze
Buna
Rubber compound or butadiene polymer
Nylon
Elastomer or polyamide material
Viton
Fluoroelastomer
Ryton
Thermoplastic resin of polyphenylene sulfide
Teflon
Plastic polymer of polyphenylene (PTFE)
PEEK
Plastic polymer of polyetheretherketone
Table A–3: Service: Sweet, Dry Process Component
Liquid
Body and Bonnet
C.S.
C.S.
Closure Elements (ball, disc, gate, etc.)
C.S. (ENP) 2 316 17-4 PH
C.S. (ENP) 2 316 17-4 PH
Metallic Seats/Seat Rings
C.S. (ENP) 13 Cr
C.S. (ENP) C.S. (316 overlay) 13 Cr
Resilient Seats
Nylon Teflon Viton
Nylon Teflon Viton
Stem
4140 (ENP) 13 Cr 17-4 PH 316
4140 (ENP) 13 Cr 17-4 PH 316
Springs
303 In X-750
303 In X-750
Elastomers
Buna-N Viton
Buna-N Viton
Packing
Viton Graphite
Viton Graphite
3
1
Gas 1
NOTES TO TABLE A–3:
1. In corrosive services, consideration shall be given to overlaying critical areas in the valve, such as seat pockets and stem seal area.
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August 1998
2. Where the service is erosive (e.g. presence of solids), harder seating areas (i.e. seat rings and closure elements) and/or hardfacing overlay shall be used. 3. Where CO 2 is present, elastomer selection shall consider the possibility of explosive decompression for pressure Class 900 and higher. Additionally, in glycol/methanol services or where amine-based corrosion inhibitors are used, the compatibility of the elastometric material to the service (or inhibitor) shall be confirmed.
Table A–4: Service: Sweet, Wet Process Component
Liquid
Body and Bonnet
C.S. C.S. (IPC)
Closure Elements (ball, disc, gate, etc.)
316 17-4 PH Duplex
316 17-4 PH Duplex
Metallic Seats/Seat Rings
13 Cr 4 316
C.S. (316 overlay) 13 Cr 4 316
Resilient Seats
Nylon Teflon Viton
Nylon Teflon Viton
Stem
316 13 Cr 17-4 PH Duplex
4
316 13 Cr 17-4 PH Duplex
Springs
303 In X-750 In 718
4
303 In X-750 In 718
Elastomers
Buna-N Viton
Buna-N Viton
Packing
Viton Graphite
Viton Graphite
3
1
2, 4
Gas 1
C.S. C.S. (IPC) 2, 4
4
4
NOTES TO TABLE A–4:
1. In corrosive services, consideration shall be given to overlaying critical areas in the valve, such as seat pockets and stem seal area. 2. Where the service is erosive (e.g. presence of solids), harder seating areas (i.e. seat rings and closure elements) and/or hardfacing overlay shall be used. 3. Where CO 2 is present, elastomer selection shall consider the possibility of explosive decompression for pressure Class 900 and higher. Additionally, in glycol/methanol services or where amine-based corrosion inhibitors are used, the compatibility of the elastometric material to the service (or inhibitor) shall be confirmed.
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August 1998
4. The use of 300 series stainless steels at temperatures above 66 °C (150°F) shall be evaluated by a materials/corrosion engineer.
Table A–5: Service: Sour, Dry Process Component
Liquid
Gas
Body and Bonnet
C.S. 1
C.S.1
Closure Elements (ball, disc, gate, etc.)
C.S. (ENP) 4 316 17-4 PH
C.S. (ENP) 4 316 17-4 PH
Metallic Seats/Seat Rings
C.S. (ENP) 2 13 Cr 2, 4 316
C.S. (ENP) 2 13 Cr 2, 4 316
Resilient Seats
Nylon Teflon Viton Ryton Peek
Nylon Teflon Viton Ryton Peek
Stem
4140 (ENP) 13 Cr 17-4 PH 3164
4140 (ENP) 13 Cr 17-4 PH 3164
Springs
In X-750 K500
In X-750 K500
Elastomers
Viton
Viton
Packing
Viton Graphite
Viton Graphite
3
NOTES TO TABLE A–5:
1. In corrosive services, consideration shall be given to overlaying critical areas in the valve, such as seat pockets and stem seal area. 2. Where the service is erosive (e.g. presence of solids), harder seating areas (i.e. seat rings and closure elements) and/or hardfacing overlay shall be used. 3. Where CO 2 is present, elastomer selection shall consider the possibility of explosive decompression for pressure Class 900 and higher. Additionally, in glycol/methanol servic es or where amine-based corrosion inhibitors are used, the compatibility of the elastometric material to the service (or inhibitor) shall be confirmed. 4. The use of 300 series stainless steels at temperatures above 66 °C (150°F) shall be evaluated by a materials/corrosion engineer.
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August 1998
Table A–6: Service: Sour, Wet Hydrocarbons Component
Liquid
Body and Bonnet
C.S. C.S. (IPC)
C.S. C.S. (IPC)
Closure Elements (ball, disc, gate, etc.)
316 17-4 PH In 718 In 825
316 17-4 PH In 718 In 825
Metallic Seats/Seat Rings
13 Cr 2, 4 316 In 825
2
13 Cr 2, 4 316 In 825
Resilient Seats
Nylon Teflon Viton Ryton Peek
Nylon Teflon Viton Ryton Peek
Stem
17-4 PH 4 316 In 718
17-4 PH 4 316 In 718
Springs
In X-750 In 718
In X-750 In 718
Elastomers
Viton Peroxide cured Buna-N
Viton Peroxide cured Buna-N
Packing
Viton Graphite
Viton Graphite
3
1
Gas 1
2
NOTES TO TABLE A–6:
1. In corrosive services, consideration shall be given to overlaying critical areas in the valve, such as seat pockets and stem seal area. 2. Where the service is erosive (e.g. presence of solids), harder seating areas (i.e. seat rings and closure elements) and/or hardfacing overlay shall be used. 3. Where CO 2 is present, elastomer selection shall consider the possibility of explosive decompression for pressure Class 900 and higher. Additionally, in glycol/methanol services or where amine-based corrosion inhibitors are used, the compatibility of the elastometric material to the service (or inhibitor) shall be confirmed. 4. The use of 300 series stainless steels at temperatures above 66 °C (150°F) shall be evaluated by a materials/corrosion engineer.
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EPT 09-T-02
Valve Selection
August 1998
Table A–7: Service: Sweet Injection Water Component
Liquid
Body and Bonnet
C.S. (IPC) 4 C.S. (ENP) 316 NiAlBz Duplex
Closure Elements (ball, disc, gate, etc.)
C.S. (ENP) 3162 2 M400 NiAlBz Duplex
Metallic Seats/Seat Rings
316 M400
316 M400
Resilient Seats
Nylon Teflon Viton
Nylon Teflon Viton
Stem
316 K500 In 718
316 K500 In 718
Springs
K500 In X-750
K500 In X-750
Elastomers
Viton
Viton
Packing
Viton Teflon Graphite
Viton Teflon Graphite
3
Gas 1
4
2
1
C.S. (IPC) 4 C.S. (ENP) 316 NiAlBz Duplex 4
C.S. (ENP) 3162 2 M400 NiAlBz Duplex 2
NOTES TO TABLE A–7:
1. In corrosive services, consideration shall be given to overlaying critical areas in the valve, such as seat pockets and stem seal area. 2. Where the service is erosive (e.g. presence of solids), harder seating areas (i.e. seat rings and closure elements) and/or hardfacing overlay shall be used. 3. Where CO 2 is present, elastomer sele ction shall consider the possibility of explosive decompression for pressure Class 900 and higher. Additionally, in glycol/methanol services or where amine-based corrosion inhibitors are used, the compatibility of the elastometric material to the service (or inhibitor) shall be confirmed. 4. Electroless-nickel plated coatings often fail after continuous long immersion in salt water. Their uses shall be limited to the less severe services (neutral pH's and temperatures <93 °C [200°F]) or to locations/services where successful use has been documented.
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Valve Selection
August 1998
Table A–8: Service: Injection Water with H2S4 Component
Liquid
Body and Bonnet
C.S. (IPC) 316 NiAlBz Duplex
Closure Elements (ball, disc, gate, etc.)
3162 2 M400 NiAlBz Duplex
Metallic Seats/Seat Rings
316 M400
316 M400
Resilient Seats
Nylon Teflon Viton
Nylon Teflon Viton
Stem
316 K500 In 718
K500 In 718
Springs
K500 In X-750
K500 In X-750
Elastomers
Viton
Viton
Packing
Viton Teflon Graphite
Viton Teflon Graphite
3
Gas 1
2
1
C.S. (IPC) 316 NiAlBz Duplex 3162 2 M400 NiAlBz Duplex 2
NOTES TO TABLE A–8:
1. In corrosive services, consideration shall be given to overlaying critical areas in the valve, such as seat pockets and stem seal area. 2. Where the service is erosive (e.g. presence of solids), harder seating areas (i.e. seat rings and closure elements) and/or hardfacing overlay shall be used. 3. Where CO 2 is present, elastomer selection shall consider the possibility of explosive decompression for pressure Class 900 and higher. Additionally, in glycol/methanol services or where amine-based corrosion inhibitors are used, the compatibility of the elastometric material to the service (or inhibitor) shall be confirmed. 4. Produced brine shall be kept deaerated as a general rule. Aeration increases the corrosion rate of the water and impedes the performance of corrosion inhibitors. It will cause formation of elemental sulfur in a sour water, which in turn can cause pitting in a number of alloys on this list.
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EPT 09-T-02
Valve Selection
August 1998
Table A–9: Service: Utilities Component
Gas or Liquid
Body and Bonnet
C.S.
Closure Elements (ball, disc, gate, etc.)
C.S. (ENP) 13 Cr
Metallic Seats/Seat Rings
C.S. (ENP) 1 13 Cr
Resilient Seats
Nylon Teflon Viton
Stem
C.S. (ENP) 13 Cr 17-4 PH
Springs
303 2
Elastomers
Buna-N Viton
Packing
Viton Teflon Graphite
NOTES TO TABLE A–9:
1. Where the service is erosive (e.g. presence of solids), harder seating areas (i.e. seat rings and closure elements) and/or hardfacing overlay shall be used. 2. Where CO 2 is present, elastomer selection shall consider the possibility of explosive decompression. Additionally, in glycol/methanol services, or where amine-based corrosion inhibitors are used, the compatibility of the elastomeric material to the service (or inhibitor) shall be confirmed.
Table A–10: Service: Lube and Seal Oil Component
Liquid
Body and Bonnet
304 316
Closure Elements (ball, disc, gate, etc.)
304 316
Metallic Seats/Seat Rings
304 316
Resilient Seats
Teflon Nylon
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EPT 09-T-02
Valve Selection
Component
Liquid
Stem
304 316
Springs
303 3
Elastomers
Buna-N Viton
Packing
Teflon Graphite
© Mobil Oil,1998
August 1998
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Appendix B: Figures of Typical Valve Types Figures B–1 through B–11 depict the typical types of valves described in the text of this EPT. These figures are intended to provide the user with some of the design features generally associated with the various valve types. Numerous design alternatives/enhancements are available that could be applicable to the user's specific service conditions. The user is urged to contact a Mobil valve specialist for assistance in evaluating the valve alternatives for his particular application.
Figure B–1: Typical Gate Valve
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Valve Selection
August 1998
Figure B–2: Typical Through-Conduit Gate Valve
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EPT 09-T-02
Valve Selection
August 1998
Figure B–3: Typical Floating Ball Valve
Figure B–4: Typical Trunnion Mounted Ball Valve
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EPT 09-T-02
Valve Selection
August 1998
Figure B–5: Typical Utility Butterfly Valve
Figure B–6: Typical High-Performance Butterfly Valve
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EPT 09-T-02
Valve Selection
August 1998
Figure B–7: Typical Plug Valve
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Valve Selection
August 1998
Figure B–8: Typical Globe Valve
Figure B–9: Typical Swing Check Valve
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