1、Valve Selection GuideAPI RECOMMENDED PRACTICE 615 SECOND EDITION, AUGUST 2016Special NotesAPI publications necessarily address problems of a general nature. With respect to particular circumstances, local, state, and federal laws and regulations should be reviewed.Neither API nor any of APIs employe
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18、PI Standards Department, telephone (202) 682-8000. A catalog of API publications and materials is published annually by API, 1220 L Street, NW, Washington, DC 20005.Suggested revisions are invited and should be submitted to the Standards Department, API, 1220 L Street, NW, Washington, DC 20005, stan
19、dardsapi.org.iiiv Contents 1 Scope 1 2 Terms and Definitions 1 3 Considerations for Valve Selection 3 3.1 Valve Functions . 3 3.2 Valve Types . 4 3.3 Other Considerations 4 4 Primary Valve Types . 4 4.1 Valves to Stop Flow or to Provide for Equipment Isolation (Block Valves) 4 4.2 Valves for Prevent
20、ing Flow Reversal (Check Valves) 8 4.3 Valves for Throttling (Controlling) FlowGlobe Valves . 10 5 Service Considerations . 10 5.1 General 10 5.2 Chlorine Service . 10 5.3 Cryogenic (Low-temperature) Service 11 5.4 Hydrofluoric Acid Service 11 5.5 Hydrogen Service . 11 5.6 Oxygen Service 11 5.7 Sour
21、 Service (Wet H2S Service) 11 5.8 Viscous or Solidifying Service 12 6 Valve Material Selection . 12 6.1 Body Material Selection . 12 6.2 Valve Trim Selection . 12 6.3 Seating SurfacesSoft Seats . 13 6.4 Stem SealingFugitive Emissions 13 6.5 Valve Bonnet Gaskets 14 7 Valve Specific Features and Optio
22、ns 14 7.1 Valve Operation 14 7.2 Position Indication . 14 7.3 Hot Tap Valves 14 7.4 Double Block Valves for Positive Isolation 14 7.5 Double Block-and-Bleed (DB the final responsibility is that of the user of this document. Valve Selection Guide 1 Scope This Recommended Practice (RP) provides genera
23、l guidance on valve selection for the hydrocarbon processing industry (HPI), which includes refineries and petrochemical, chemical, and liquefied natural gas (LNG) plants and their various associated processes. Selection guidance is provided for valve types covered by ASME B16.34 and API Valve Stand
24、ards for the Downstream Segment, which include gate, ball, plug, butterfly, check, and globe valves. Modulating control valves and pressure relief valves are outside the scope of this RP. 2 Terms and Definitions For the purposes of this document, the following terms and definitions apply. 2.1 abrasi
25、ve service Abrasive service is a term used to identify fluids containing particulates that are likely to damage a valves pressure boundary or internals through erosion. Fluids containing rust, scale, welding slag, sand, catalyst fines, grit, and hydrocarbon particles (coke) may fall in this category
26、. 2.2 bellows seal A flexible metal bellows used in place of or in addition to valve stem packing to provide a positive seal against leakage to atmosphere. 2.3 chlorine service Services containing liquid or vapor chlorine in concentrations higher than 1 ppm as defined in 29 CFR 1910. This does not i
27、nclude water services containing chlorine for pH balancing or as a biocide. 2.4 clean service Clean service is a term used to identify fluids free from solids or contaminants that could interfere with proper valve operation and/or closure. Clean fluids include most light hydrocarbons, instrument air
28、, nitrogen, water, steam, lube oil, diesel oil, methanol, etc. 2.5 closure member This refers to the component in the valve that serves to stop flow (internal disc, ball, and plug, for example). A closure member may also be referred to as the valve obturator. 2.6 cryogenic service The lower end of l
29、ow temperature service (such as liquefied gas) typically between 163 C to 196 C (261 F to 320 F).2.7 dirty service Dirty service is a general term used to identify fluids with suspended solids that may impair the proper performance of a valve. Detrimental effects of suspended solids on valve perform
30、ance can be mitigated by minimizing or purging dead zones where suspended solids may accumulate. Dirty service can also be an abrasive service. 12 API RECOMMENDED PRACTICE 615 2.8 double block and bleed (DB fluid service; materials of construction; valve trim selection; acceptable leakage rate; valv
31、e special features such as fire testing, cavity venting, purge connections, etc.; flow capacity and pressure loss; cycle frequency. 4 Primary Valve Types NOTE Some valve types are capable of performing multiple functions. If not used for their primary intended function, they may not perform well or
32、may experience a premature failure. 4.1 Valves to Stop Flow or to Provide for Equipment Isolation (Block Valves) 4.1.1 Gate Valves 4.1.1.1 General The gate valve is a common type of block valve for on-off service. The gate valves closure member (gate) moves out of the flow stream perpendicular to th
33、e flow path. Typical process gate valves use a wedge type gate. Upon closing the gate to effect shutoff, the two faces of the gate engage the matching angle of the valve body seats. Turning the handwheel forces the disc firmly into the seats, which, assisted by line pressure, provides for shutoff of
34、 flow. The API standards covering gate valves are API 600, API 602, and API 603. Gate valves are typically not recommended for throttling service. 4.1.1.2 API 600 Gate Valves API 600 covers sizes from NPS 1 and larger in pressure classes from Class 150 to Class 2500 with flanged or butt-welding ends
35、. This standard was developed for refinery applications to provide a robust, heavy wall design VALVE SELECTION GUIDE 5 suitable for service up to 538 C (1000 F). Pressuretemperature ratings for these valves are given in ASME B16.34 (standard class) for the listed materials. Body and bonnet wall thic
36、kness specified in API 600 are greater than those in ASME B16.34 thereby providing for an additional corrosion allowance capability. Stem diameters are also specified. The standard gate in API 600 is a one-piece, wedge-shaped, either solid or flexible wedge. The “flexible” wedge design provides for
37、a small amount of angular deflection of the disc faces to provide for a better engagement with the body seats. This allows the wedge to accommodate some deviation from the ideal seat position caused by deflection of the valve body due to line stresses or thermal expansion, thereby resulting in impro
38、ved seat tightness and reduced potential for gate binding in the closed position. See Annex A, Figure A.1 for a typical API 600 gate valve. 4.1.1.3 API 602 Gate Valves API 602 covers the smaller gate valves in sizes up to NPS 4 for pressure classes from Class 150 to Class 1500 including Class 800. A
39、PI 602 gate valves are commonly used in process plants in sizes from NPS 1/2 to NPS 2 inClass 800 with threaded or socket-welding ends. The standard port size is smaller than the line size but full port is an available option. These small valves are usually made from forgings. Flanged-end and butt-w
40、eld end valves are available where use of socket weld or threaded ends may not be desired, for example, in compressor lube oil service. See Annex A, Figure A.2 and Figure A.3 for typical examples of API 602 gate valves. 4.1.1.4 API 603 Gate Valves API 603 was developed to provide a lower cost altern
41、ative to API 600 valves in corrosive, lower pressure services. They provide a lighter-weight, corrosion-resistant design made of a stainless or nickel alloy with a thinner body wall than API 600 valves. API 603 specifies wall thicknesses comparable to those in ASME B16.34. Like API 600, API 603 spec
42、ifies minimum stem diameters. These valves are available in flanged or butt-weld ends in pressure Classes 150, 300, and 600 and in sizes NPS 1/2 and larger. The wedge design is typically solid or flexible althoughsplit wedge and parallel-sided double disc gates are covered in the standard. Seat hard
43、facing may be desirable to reduce the galling tendency of stainless wedge seat faces to stainless body seat faces. See Annex A, Figure A.4 for an example of a gate valve from API 603. 4.1.1.5 Pressure Seal Bonnet Gate Valves Gate valves with a special “pressure seal” bonnet closure design that avoid
44、s bonnet flanges are available from several manufacturers for Class 600 and higher and may typically be used in hydrogen service. The pressure seal bonnet design uses a compact bodybonnet joint that is pressure-assisted so that with increasing pressure the bonnet seals more tightly. The use of this
45、design should be restricted to services that are not highly corrosive to avoid damage to the pressure seal element. Maintenance that involves reassembly of the pressure seal should be done with the help of a manufacturers representative or a qualified valve repair organization to ensure proper assem
46、bly, testing, and preloading of the seal ring. Replacement seal rings may be available only from the original manufacturer. These valves are often supplied with weld ends thereby eliminating heavy line flanges. This valve design is not covered in API 600; however, it is covered in MSS SP-144. 4.1.1.
47、6 Orientation Considerations Although somewhat depending on pressure class and size, larger gate valves oriented in a position other than with the stem vertical may result with the disc getting hung up against the inside body guides such that the valve may get stuck, thereby rendering the valve inop
48、erable. Special attention to guiding details including clearances, avoidance of sharp corners on the disc leading edge, and the use of machining/hardfacing on the guides is recommended. Even with the stem vertical, there may be an accumulation of dirt and other deposits between the seats such that t
49、he valve may not close fully. Installation of a bleed valve between the body seats to provide a purge connection can help remove such deposits. 4.1.1.7 Other Gate Valve Designs Other gate valve designs used in process plants that are less common include double-disc designs for double block and bleed applications; “knife gate” designs for water, sludge, and other services with a high concentration of 6 API RECOMMENDED PRACTICE 615 particulates; and “slide valve” designs typically used in high temperature, highly erosive fluid solids service such as in fl
