API 526 Safety & Relief Valves
What API 526 requires for safety & relief valves — applicability, key and testing requirements, the alternative standards, and compliant supply with full certification.
What does API 526 require for safety & relief valves?
API 526 (Flanged Steel Pressure-Relief Valves, American Petroleum Institute (API)) sets the design, material and testing requirements for safety & relief valves in its scope. API 526 is the standard for flanged steel pressure relief valves (PRVs / PSVs) used in petroleum, petrochemical, and natural gas processing. It defines orifice sizes and designations (D through T), face-to-face dimensions, inlet and outlet pressure ratings, and materials - enabling interchangeability between PRV manufacturers and simplifying spare parts sourcing. API 526 PRVs are mandatory on all ASME-coded pressure vessels per ASME Section VIII.
Applicable Pressure Classes
Key Requirements
- Orifice designation (D through T) determines flow capacity per API 520
- Face-to-face dimensions: standardised so any manufacturer's D through T fits the nozzle piping
- Materials: WCB, SS 316, alloy steel - body and bonnet matching ASME B16.34 pressure groups
- Spring adjustment range to allow set pressure variation of ±10%
- Lifting lever required for steam and air service (per code)
- Blowdown adjustable: typically 7–10% below set pressure for reseat
Testing Requirements
- Set pressure test: valve must open at ± tolerance of set pressure
- Blowdown test: valve must reseat within 7–10% of set pressure
- Seat leakage test: per API 527
- Cold-differential test pressure (CDTP) accounting for back pressure and temperature correction
Alternative Standards for Safety & Relief Valves
Other standards that also govern safety & relief valves — useful for spec cross-acceptance.
Related Standards
Connected Engineering
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