API 594 Check Valves
What API 594 requires for check valves — applicability, key and testing requirements, the alternative standards, and compliant supply with full certification.
What does API 594 require for check valves?
API 594 (Check Valves: Flanged, Lug, Wafer, and Butt-Welding, American Petroleum Institute (API)) sets the design, material and testing requirements for check valves in its scope. API 594 is the design and testing standard for flanged, lug, wafer, and butt-welding check valves including swing check, dual plate (double door), and tilting disc check valves. It defines face-to-face dimensions, pressure-temperature ratings, material requirements, and testing procedures. API 594 is mandatory for most process plant and refinery check valve procurement.
Applicable Pressure Classes
Key Requirements
- Face-to-face and end-to-end dimensions per API 594 tables (Type A wafer; Type B lug; Type C flanged)
- Minimum plate/disc thickness and spring material specification
- Body and disc material requirements per ASTM A216 WCB, CF8M, and duplex grades
- Anti-blowout hinge pin design for wafer-type valves
- Bi-directional pressure capability for Type B lug (dead-end service)
- Shell and seat hydrostatic tests per API 598 required before shipment
Testing Requirements
- Shell test: 1.5× rated pressure
- Seat leakage test: 1.1× rated pressure per API 598
- Low-pressure seat test: 6 bar air
Alternative Standards for Check Valves
Other standards that also govern check valves — useful for spec cross-acceptance.
Related Standards
Connected Engineering
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