API Standard 598, from the American Petroleum Institute, provides industry standards for valve ratings and valve leakage. The standard is currently in the 9th edition, which was released in 2009.


API 598 covers the inspection, examination, and testing requirements for resilient-seated, nonmetallic-seated, and metal-to-metal-seated gate, glove, plug, ball, check, and butterfly valves. It is relevant to examination and testing by the valve manufacturer, supplementary examinations performed at the valve manufacturer’s plant, and pressure tests performed at either the plant or another mutually agreed-upon facility.


API 598 specifies the following tests and examinations:



Visual examination
Assure compliance with all applicable standards for all valve bodies, bonnets, covers, and closure elements
Shell tests
  • Shell test
  • High-pressure pneumatic shell test
Validate the soundness of the pressure containing structures within the valve
Backseat tests
  • Low-pressure backseat test
  • High-pressure backseat test
Verify leakage through the stem or shaft to the seal
Closure tests
  • Low-pressure closure test
  • High-pressure closure test
  • Double block and bleed high-pressure closure test
Verify leakage through the closure mechanism


Testing requirements

  • Shell tests are required for all gate, globe, plug, check, floating ball, and butterfly and trunnion mounted ball valves.
  • Backseat tests are required for all gate and globe valves.
  • Closure tests are required for all gate, globe, plug, check, floating ball, and butterfly and trunnion mounted ball valves, with the type (low- or high-pressure) depending on the valve size and class.

Test fluids


Test fluid

  • Shell
  • High-pressure backseat
  • High-pressure closure
Air, inert gas, kerosene, water, or a noncorrosive liquid with a viscosity less than or equal to that of water (5°C to 50°C [41°F to 122°F], unless otherwise specified by the purchaser)
  • Low-pressure backseat
  • Low-pressure closure
Air or inert gas


A full copy of API 598, with complete testing procedures and specifications, can be purchased from the American Petroleum Institute.

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