API Standard 527, from the American Petroleum Institute, describes seat tightness testing and the maximum acceptable leakage rates for pressure relief valves. The current version of the standard was reaffirmed in 2007.
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 |
|
| Saturated steam | Same as above |
|
| Water near ambient temperature | Same as above |
|
* An alternative air or nitrogen testing procedure is specified for valves with open bonnets. For metal-seated valves the maximum allowable leakage rate is half that of the standard procedure, while for soft-seated valves it remains the same (i.e., no leakage for 1 minute).
A full copy of API 527, with complete testing procedures and specifications, can be purchased from the American Petroleum Institute.