Valve API 6D vs API 6A: Specifying the Correct Standard for Your Application

API 6D and API 6A are the two primary standards for oil and gas valves. This guide clarifies the differences and helps you select the correct standard for pipeline vs wellhead applications.

API 6D covers valves for pipeline and piping systems. Includes ball, check, gate, and plug valves. Pressure ratings: Class 150 through Class 2500. Size range: 2 inch through 60 inch (larger by agreement).

Key requirements: Fire-safe design (API 607 or API 6FA), DBB (double-block-and-bleed) capability for ball valves, and extended bonnet for buried service.

API 6A covers valves and fittings for wellhead and christmas tree service. Higher pressure ratings: 2000 psi through 20000 psi. Includes gate valves, check valves, and needle valves.

Key requirements: PR1 or PR2 performance rating. PR2 requires additional testing including temperature cycling and pressure cycling. Valves must be suitable for sour service (NACE MR0175) if specified.

API 6D uses ASME B16.34 pressure-temperature ratings. Class 150, 300, 600, 900, 1500, 2500.

API 6A uses working pressure ratings: 2000, 3000, 5000, 10000, 15000, 20000 psi. Temperature rating: K, L, P, R, S, T (ranging from -60degC to 180degC).

API 6D: Fire test per API 607 (quarter-turn) or API 6FA (gate valves). Valve must maintain seal during and after fire.

API 6A: Fire test per API 6FA. More stringent than API 6D because wellhead valves are in high-risk fire areas (e.g., blowout preventer systems).

API 6D: Valves must have traceable heat numbers on body and critical parts. Material test reports (MTRs) per EN 10204 3.1 or 3.2 are required.

API 6A: Full traceability required. Each valve must have a serial number and be traceable to original melt. 3.2 certification (witnessed by third party) is common for critical wells.

Not recommended. API 6D valves are not designed for the high-pressure, high-cyclic-loading environment of wellhead service. Use API 6A valves for wellhead and API 6D for pipeline.

PR (performance requirement) levels define additional qualification tests. PR1 is the basic level. PR2 requires temperature cycling, pressure cycling, and enhanced gland leakage tests. Most production wells require PR2 valves.

Ted Wang

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Email: sales@wofervalve.com

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