This standard describes a method of determining seat tightness of safety relief valves as covered in API Standard 526: Flanged Steel Safety Relief Valves for Use in Petroleum Refineries. The maximum acceptable leakage rates are defined for commercial safety relief valves with metal-to-metal seats for set pressures up to 1@000 psig. If greater tightness is required@ it can be supplied but must be specified on the purchase order or inquiry.