February 1st, 2018 by Amanda Schumann

Main Valve Test Standards

API 598 Valve Inspection and Test

The most widely used test specification in the world. The standard covers all types of valves (soft & metal seated) in sizes up to 600NB (NPS 24). It also includes leakage rates and testing criteria for metal-seated and resilient seated valves.

API6D Pipeline Valves Test Standard

Used for API6D ball valves, plug valves and API6D design pipeline check/gate valves (also now adopted as part of ISO 5208).

ISO 5208 Valve Test Standard

Incorporates an adoption of API6D test standard. Leakage rate A is specified for soft seated valves and plug valves (zero leakage*). Also includes standards for gate, globe and check valves (EN 122661-).

BS 6755 Valve Test Standard

Previously used by some European Manufacturers, now superseded by ISO 5208 (EN 12266-1) standard. It includes leakage rates and testing criteria for metal and resilient seated valves.

ASME B16.34 Valves – Flanged, Threaded and Welding End

The primary valve design standard, it also contains pressure/temperature charts for determining the working pressures of valves to be used in conjunction with other test standards, such as API 598.

ASME PTC 25 Pressure Relief Devices

The main reference document for the testing of pressure relief valves, PTC 25 contains detailed procedures for testing relief valves with air or steam.

API 527 Seat Tightness of Pressure Relief Valves

This covers the seat tightness of pressure relief valves. It also includes allowable leakage rates for testing with steam, water and air.

FCI 70-2* Control Valve Seat Leakage

This document contains detailed test procedures and leakage rate classes for control valves. The leakage classes are also occasionally referenced by other documents and used as acceptance criteria. Supersedes ANSI B16.104. Class VI is the highest shut off class*.

ISA S75 Hydrostatic Testing of Control Valves

This standard provides a procedure for the hydrostatic shell testing of control valves. Seat testing and acceptance criteria are out of the scope of this document and usually are covered by referencing FCI 70-2.

ISO 5208 Industrial Valves, Pressure Testing of Valves

ISO’s primary testing standard, this document covers all types of valves and has four levels of allowable closure test leakage rates.

MSS SP70 Cast Iron Gate Valves, Flanged and Threaded Ends

The primary design standard for cast iron gate valves, it also contains testing procedures and acceptance criteria.

MSS SP71 Iron Swing Check Valves, Flanged and Threaded Ends

The primary design standard for cast iron check valves also contains testing procedures and acceptance criteria.

MSS SP61* Hydrostatic Testing of Steel Valves

Similar to API 598 (in the case of soft seated valves) this document has some minor variations in test holding times and leakage rates. Metal seated valves the leakage can be a little higher than API598.

MSS SP78 Cast Iron Plug Valves, Flanged and Threaded Ends

The primary design standard for cast iron plug valves also contains testing procedures and acceptance criteria.

MSS SP80, Bronze Gate, Globe, Angle and Check Valves

The primary design standard for commodity bronze valves also contains testing procedures and acceptance criteria.

MSS SP85, Cast Iron Globe & Angle Valves

The primary design standard for cast iron globe valves also contains testing procedures and acceptance criteria.


In general, specification such as API598 or MSS SP-61 that govern leakage for soft seated valves call for ‘0’ bubbles of air or ‘0’ drops of water under the specified test conditions over the minimum test time period. These valves are therefore sometimes referred to as ‘zero leakage’ valves. In reality, there really is no such thing as ‘zero leakage’, since microscopic amounts of material may indeed cross the seat or packing boundaries, especially if helium or hydrogen or other small molecule gases are used. Another common term for soft seated valves is ‘bubble tight’.

Less frequently, the leakage performance for soft seated valves is referred to as Class VI, which is the tightest leakage under FCI 70-2, and generally applies to resilient seated control valves (as opposed to metal seated control valves or soft seated shut off valves). In fact, FCI 70-2 Class VI (formerly ANSI B16.104) allows a small number of bubbles per minute, increasing with valve size, during the test, whereas API598 and MSS SP-61 do not (for soft seat, but does for metal seat). FCI 70-2 Class VI is for soft seated control valves but is frequently used as a leakage acceptance test criteria for metal seated isolation valves such as ball and butterfly valves. FCI 70-2 only requires a low pressure test, consequently closure and seat tests should also be done per API 598 or MSS SP-61.

In actual fact even for metal seat valves the API 598 leak acceptance criteria for metal seated valves allows less leakage than FCI 70-2 Class VI above 150NB (6”) and 50NB (2”) and under. For zero leakage metal seated valves API 6D or API 598 soft seated zero leakage criteria can be specified (such as triple offset metal seated butterfly valves and some metal seated ball valves). Special provisions for zero leakage gate valves can also be specified to BS 6755 and ISO 5208 under special zero leakage classes. Metal seated valves, on the other hand, usually (not always, triple offset butterfly and ball valves for instance are available bubble tight) have some level of acceptable leakage when tested, defined first as some acceptable amount of liquid, under test conditions and over the time period of the test.

ISO 5208 (EN 12266-1) supersedes BS 6755-1 and specifies acceptable leakage rates such as ‘Rate A’ and ‘Rate B’. Rate A allows ‘no visible leakage’, similar to API 598 for resilient seated valves. Rate B is used for gate valves.


For cross reference tables and charts of ASTM/ANSI specifications covering equivalent materials used for valves, flanges & fittings click here.

For other ANSI, ASME, ISO, API, valve related technical cross references relating to pressure, temperature, application, suitability, equivalents, valve body & trim materials, valve manufacturing & test standards, etc., go to the technical section of our website.

If we don’t have the valve in stock we can source it from our overseas network of stockists and very short lead time specialty manufacturers. We can even supply exotic grades like Nickel, Super Duplex F55 and Monel (ASTM A494-M35-1) Cd4M-Cu, Hastealloy C (ASTM A494 CW12MW), 317 (C8G8M) in short lead-time.

For technical references and cross reference information on stainless, duplex, chrome-moly and Alloy steel used in valves and piping systems in the petrochemical and refining industry go to the technical section of our website.

We stock valves in A105, LF2, 304, 304L, 316, 316L, F51, CF8, CF3, F82, WC5, WC6, WC9, F11, F5, Bronze, Iron, etc. Ball, Butterfly, Check, Control, Gate, Globe, Needle, Parallel slide, Plug, etc. Valves are manufactured to API 600, API 602, API 603, API 6D, BS1868 and numerous other standards.

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