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When a tender says "valves to API 600" or "API 6D tested", it is not paperwork – it is a specific set of design, wall-thickness, testing and traceability rules that decide whether a valve survives in a refinery or pipeline. The American Petroleum Institute (API) family is the de-facto passport to oil, gas and petrochemical projects worldwide. This guide maps each major API valve standard to the valve and service it actually governs, so you can specify – and verify – with confidence.
The most common confusion is API 6D vs API 600. 6D is the pipeline specification – it applies to ball, gate, check and plug valves in long-distance transmission, and adds DBB/DIB (double block & bleed / double isolation & bleed), cavity-relief and high-pressure gas seat testing. API 600 is narrower: it is the bolted-bonnet steel gate valve standard for refinery isolation, and it mandates a heavier wall and larger stem than a generic ASME B16.34 valve. Use 6D when the valve is a pipeline isolation point; use 600 when it is a refinery process gate valve. For butterfly valves the relevant spec is API 609 (double- and triple-offset, lug/wafer); for ball valves it is API 608 (floating and trunnion, soft or metal seated).
ASME B16.34 is the engineering "spine" – it defines pressure-temperature ratings, material groups, minimum wall thickness and marking, and is referenced by almost every other valve code. API standards sit on top of that spine and add field-driven criteria: fire-safe qualification (API 607/6FA), anti-blowout stem design, leakage classification for pipeline service, and cyclic pressure testing. So a valve can be "ASME B16.34" in its pressure rating yet still be required to meet an API product standard for the project. When a spec line reads "Valves shall conform to ASME B16.34, tested to API 598", that is the normal combination – B16.34 for design, API 598 for the test.
API 598 is the universal test standard referenced by 6D, 600, 602, 608 and 609. It defines the hydrostatic shell test (about 1.5× the rating), seat leakage tests (high-pressure and, for soft seats, low-pressure air), backseat tests and operational cycles. Acceptance is strict: soft seats must be bubble-tight (zero visible leakage); metal seats are allowed limited leakage per the standard. For pipeline valves, API 6D goes further with gas seat tests and torque verification.
Any valve in a fire-risk area (refineries, tank farms, offshore, LNG) should be fire-tested to API 607 (quarter-turn) or API 6FA (all types) – the valve is held at 750–1000 °C for ~30 minutes, then checked for seat leakage after cooling to prove it keeps a secondary metal seal when the soft seat has burned away. For sour (H₂S) service, the material must also comply with NACE MR0175 / ISO 15156 to avoid sulfide stress cracking. These are referenced alongside the product standard, not instead of it.
Remember the distinction: "API compliant" describes the design; "API certified / monogrammed" means the manufacturer is audited and licensed. For tender-critical work, insist on the monogram and verify it yourself.
API 6D is the specification for pipeline valves – ball, gate, check and plug valves used in transmission pipelines, with strict DBB/DIB, cavity-relief and gas-seat-test requirements. API 600 is specifically for bolted-bonnet steel gate valves in refinery and process service, and mandates thicker walls and heavier stems than a general ASME B16.34 valve. Use 6D for pipeline isolation; use 600 for refinery gate isolation.
For most oil & gas and refinery project specifications, yes. API 598 is the universal inspection-and-test standard referenced by 6D, 600, 602, 608 and 609. It defines the hydrostatic shell test (about 1.5x rating), seat leakage tests, backseat and operational checks. Soft seats must be bubble-tight; metal seats allow limited leakage per the standard.
Only a licensed manufacturer may apply the API Monogram. 'API compliant' means the valve design follows the standard, but the maker may not hold the license. 'API certified / monogrammed' means the manufacturer is audited by API and listed in the API Monogram Licensee Directory. For tender-critical projects, insist on the monogram and verify the license number online.
Yes. Many leading Chinese valve factories hold API Monogram licenses (API Q1 quality system plus the product monogram). Always verify the license status on the official API directory and request the Mill Test Report (EN 10204 3.1) and test records, rather than accepting a catalogue claim.