Valve Standard Reference
API 526
AmericanFlanged Steel Pressure-Relief Valves
API 526 is the standard for flanged steel pressure relief valves (PRVs / PSVs) used in petroleum, petrochemical, and natural gas processing.
Overview — API 526
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.
Scope
Covers spring-loaded and pilot-operated pressure relief valves in flanged steel construction, from orifice D (0.110 sq in) to T (16.0 sq in). Inlet pressure ratings: Class 150 to 2500. Outlet pressure ratings: Class 150 to 600. Temperatures −29°C to +540°C.
Applicable Valve Types
Safety Relief Valves — API 526 (flanged)
Pressure Safety Valves (PSVs)
Pilot-Operated Relief Valves (PORVs)
Applicable Pressure Classes
Key Requirements — API 526
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 — API 526
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
Documentation Required for API 526 Compliance
API 526 data sheet with orifice designation and set pressure
ASME Section I/VIII/PTC25 certification (for boiler and pressure vessel installations)
National Board Certification (for ASME-code vessels)
IBR Form III-E/III-C (for steam service in India)
Related Standards
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