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General
API Standard 527, from the American Petroleum Institute, describes seat tightness testing and the maximum acceptable leakage rates for metal- and soft-seated pressure relief valves. The current version of the standard was reaffirmed in 2020.
Scope
API 527 covers seat tightness testing of metal- and soft-seated pressure relief valves, including conventional, bellows, and pilot-operated designs.
Tests
API 527 specifies procedures for testing with air or nitrogen, steam, and water.
TEST | PRESSURE | MAXIMUM ALLOWABLE LEAKAGE RATE |
Air (or nitrogen) near ambient temperature | 10% or 5 psig below than nameplate set pressure, whichever is greater | l Metal-seated valves: Varies depending on pressure and effective orifice size l Soft-seated valves: No leakage for 1 minute |
Saturated steam | 10% or 5 psig below than nameplate set pressure, whichever is greater | No audible or visible leakage for one minute(both metal- and soft-seated valves) |
Water near ambient temperature | 10% or 5 psig below than nameplate set pressure, whichever is greater | l Metal-seated valves: Inlet with nominal pipe size ≥ 1 inch: Leakage not to exceed 10 cm3/h/in. Inlet with nominal pipe size < 1 inch: Leakage not to exceed 10 cm3/h. l Soft-seated valves: No leakage for 1 minute. |
NOTES: An alternative air or nitrogen testing procedure is specified for valves with open bonnets. For metal-seated valves the maximum allowable leakage rate is 50% of the standard procedure, while for soft-seated valves is no leakage for one minute. | ||
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