API and ASME rated ball, gate, globe, check and plug valves for upstream, midstream and downstream service

The principal API valve standards are API 600 (steel gate valves), API 602 (compact gate and globe valves), API 6D (pipeline valves, gate, plug, ball and check) and API 6A (wellhead and christmas tree equipment). Each defines dimensional, material, testing and documentation requirements that go beyond the equivalent EN standards.

Fire-safe valves conforming to API 607 or API 6FA have been independently tested to demonstrate that the valve retains acceptable shutoff capability after exposure to fire conditions. Fire-safe certification is mandatory on many process plant isolation duties and is routinely specified for ball valves in hydrocarbon service regardless of individual site requirements.

API and ASME pressure classes (Class 150, 300, 600, 900, 1500, 2500) define the pressure-temperature envelope of the valve based on the body material. Class 150 covers most ambient-temperature applications up to approximately 20 bar; Class 300 extends to around 51 bar; Class 600 to approximately 103 bar. Actual allowable working pressure depends on the material grade and operating temperature, confirm against the ASME B16.34 tables for the specific material.

Flanges conforming to ASME B16.5 are standard for all API-rated valves. EN 1092-1 flanges are not interchangeable with ASME flanges even at notionally equivalent pressure ratings, so confirm the flange standard at the time of specification.

Hydrogen sulphide (H2S) causes sulphide stress cracking (SSC) in susceptible steels. NACE MR0175 / ISO 15156 defines the material requirements for equipment in sour service: maximum hardness limits for body, bonnet, stem and fastener materials, and restrictions on certain alloys. Standard WCB carbon steel and 316 stainless steel may require additional hardness verification for sour service duty; duplex stainless steels require specific heat treatment and testing.

Where sour service compliance is required, specify it explicitly in the RFQ along with the H2S partial pressure and temperature envelope. Material test certificates (MTR) and hardness reports are standard documentation for sour-service valves.