API Std 527

This standard describes methods of determining the seat tightness of metal- and soft-seated pressure relief valves, including those of conventional, bellows, and pilot-operated designs.The maximum acceptable leakage rates are defined for pressure relief valves with set pressures from 103 kPa gauge (15 psig) to 41,379 kPa gauge (6000 psig). If greater seat tightness is required, the purchaser shall specify it in the purchase order.The test medium for determining the seat tightness—air, steam, or water—shall be the same as that used for determining the set pressure of the valve.For dual-service valves, the test medium—air, steam, or water—shall be the same as the primary relieving medium.To ensure safety, the procedures outlined in this standard shall be performed by persons experienced in the use and functions of pressure relief valves.