API 641

Applies to: Quarter-turn valves (ball valves, butterfly valves, plug valves) in hydrocarbon and VOC service requiring fugitive emissions type qualification; ISO 15848-1 Class A/B equivalent for rotary valves.

Does NOT cover: Rising-stem valves (use API 624); production acceptance testing of individual valves (type test certificates only); on/off control valves with actuation forces differing from manual test protocol.

• 600-cycle mechanical endurance test at ambient temperature
• Thermal cycling between low and high temperature per applicable class
• Test medium: methane or helium per agreed protocol
• Stem seal and body joint leakage measurement
• Class-dependent leakage limits (A ≤ 50 ppm(v), B ≤ 100 ppm(v), C ≤ 500 ppm(v))
• Testing by accredited third-party laboratory; certification transferable if geometry unchanged

API 641 mirrors API 624 for quarter-turn valves, addressing the different wear and sealing mechanisms of rotary actuators versus reciprocating stems. Both standards require type testing by an accredited third-party laboratory, and both use the same three-class emission limit framework.

Engineering note: Quarter-turn valves have inherently lower fugitive emission leakage than rising-stem valves due to their stem rotation mechanism generating less packing wear per cycle. API 641 Class A certification is increasingly specified as a default procurement requirement in new refineries and petrochemical plants to meet voluntary LDAR excellence targets, even where regulation would accept higher emission classes.