Section 5 of their Pressure Testing of Steel Valves, relates to seat closure tests, and defines the following leakage rates:ġ0 cc/hr per inch of nominal pipe diameter. Refer to standard ANSI/FCI 70-2 for Control Valves. It is not intended for use with control valves. It was developed for the purpose of providing a uniform means of testing valves commonly used in the "full open" and "full closed" type of service. The MSS standard MSS-SP-61: Pressure Testing of Valves was originally adopted in 1961. ¶ Manufacturer's Standardisation Society ( MSS) The maximum permissible leakage rates shall be 1.5 standard cubic feet (0.042 cubic meter) of gas per hour per inch of nominal pipe size.The maximum permissible leakage rate shall be 0.18 cubic inch (3 cubic centimeters) per minute per inch of nominal pipe size.For gas test, 0 bubble means less then 1 bubble per minimum specified test duration. For liquid test, 0 drop means no visible leakage per minimum specified test duration. There shall be no leakage for the minimum specified test duration.Shall be per agreement between purchaser and manufacturer. For check valves larger than NPS 24, the allowable leakage rate.1 milliliter is considered equivalent to 16 drops.The allowable rate for leakage of test fluid past the seats, for the duration of the tests, is listed in the following table: Valve Size For both the low-pressure closure test and the high-pressure closure test, visual evidence of leakage through the disk, behind the seat rings, or past the shaft seals (of valves that have this feature) is not permitted (Plastic deformation of resilient seats and seals is not considered structural damage). If the test fluid is air or gas, no leakage shall be revealed by the established detection method. If the fluid is a liquid, there shall be no visible evidence of drops or wetting of the external surfaces (no visible leakage through the body, body liner, if any, and body-to-bonnet joint and no structural damage).
All valves built to the various API standards are required to meet API-598 leakage criteria prior to shipment from the manufacturer or supplier.ĪPI 598 states for shell and BACK SEAT tests, no visible leakage is permitted.
It has acceptable leakage rates for liquid as well as gas testing. The API standard 598: Valve Inspection and Testing, covers the testing and inspection requirements for gate, globe, check, ball, plug and butterfly valves.
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