API 6D: Specification for Pipeline and Piping Valves (Explained)

Reviewed by the Crestflo Engineering Team

API 6D is the American Petroleum Institute's Specification for Pipeline and Piping Valves. It sets the requirements for design, manufacture, testing, marking and documentation for ball, check, gate and plug valves used in petroleum and natural-gas pipeline and piping systems. The current edition is the 25th, and ISO 14313 stands as its technically aligned international equivalent. Note that this covers pipeline valves, not instrumentation valves.

Scope note: API 6D is the specification for pipeline and piping valves used in petroleum and natural-gas transportation. It's not the same thing as API 6A (wellhead and tree equipment), API 6DSS (subsea pipeline valves), or ASME B16.34 (general flanged, threaded and welding-end valves). Globe valves, control valves, safety/relief valves, and instrumentation isolation valves fall outside it too. Crestflo doesn't manufacture API 6D pipeline valves. What it builds are the instrumentation valves at the instrument hook-up that ties into an API 6D line, see the honest scope note below.

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Also known as: API 6D designations & related terms

Specs, tenders and datasheets don't agree on how to write this standard. Whatever the wording, the designations below all point to the same pipeline-valve specification.

API 6D standard at a glance: attributes

The standard's exact numeric requirements, test durations, class spans, and per-clause acceptance criteria, are copyrighted and locked in by the current edition. This page sticks to summarizing scope, valve types, requirements, and comparisons rather than reproducing the document itself. Values follow the applicable standard, and can be tailored to what's needed.

What is API 6D?

API 6D is the American Petroleum Institute's Specification for Pipeline and Piping Valves. The American Petroleum Institute (API) publishes it, and it lays out requirements and recommendations for the design, manufacture, testing, marking and documentation of valves used in pipeline and piping systems across the petroleum and natural-gas industries. "6D" doesn't stand for anything. It's just API's number for the specification.

Unlike an inspection-and-testing standard such as API 598, API 6D is a full product specification: it governs how the valve is engineered and built, not only how it is tested before shipment. It covers four valve families, ball, check, gate and plug, and adds pipeline-specific requirements those valves need in transmission service, such as full-bore piggable bores, antistatic devices, and double block and bleed configurations.

ISO 14313 is the technically aligned international equivalent. The two standards are harmonized, but wording, national adoption and certain requirements can still differ. A project should therefore specify the exact document it references.

Who publishes API 6D, and what is the latest edition?

The American Petroleum Institute (API) writes and maintains API 6D. API revises its standards on a periodic cycle, with errata and addenda issued between full editions. The 25th edition is the version most widely cited in current specifications. Cite the edition, and any addendum, named in your project specification. Confirm it against the current API catalog, since contract references vary by edition.

Where can I get the API 6D PDF?

API 6D's full text is a copyrighted, licensed document, sold by API and authorized resellers such as ANSI and Accuris. This page summarizes the standard's scope, valve types, requirements and comparisons for engineering reference. It doesn't reproduce or distribute the document itself. For compliance work, buy the current official edition. Don't rely on unofficial "free download" copies; they may be outdated.

What API 6D covers: and what it doesn't (ball, check, gate & plug valves)

API 6D applies to four valve families and explicitly leaves several others to other standards. People often ask: does API 6D cover globe valves? The answer is no, plain and simple. Globe, control, safety/relief and instrumentation isolation valves all sit outside its scope.

Ball, gate and plug valves in API 6D handle on/off isolation for the pipeline. Check valves stop reverse flow. The standard also covers trunnion ball designs, plus full-bore and full-opening (full-port) configurations that let a pipeline pig pass through. That pigging requirement, more than anything, is what separates a pipeline valve from an ordinary industrial one.

API 6D editions & the ISO 14313 equivalent

API 6D is maintained on a periodic revision cycle. The 25th edition is the version most current specifications cite, and errata and addenda get published between editions. Contract references vary quite a bit, so always specify the exact edition and addendum your project names.

The technically aligned international equivalent is ISO 14313, "Petroleum and natural gas industries, Pipeline transportation systems, Pipeline valves." API 6D and ISO 14313 are harmonized so that a valve can be specified against either, but the two documents don't always agree on adoption route, wording, and a handful of requirements. That's why "API 6D or ISO 14313" is a real choice a specification has to make. It isn't automatic equivalence.

Key API 6D requirements: testing, DBB/DIB, fire-safe, pigging & marking

Beyond dimensions and materials, API 6D sets pipeline-specific requirements that shape how the valve is built and proven out.

On the monogram. The API 6D monogram gets applied only by manufacturers licensed under the API Monogram Program (APIQR) for the specific products that license covers. You'll find it stamped on the valve nameplate, sitting right alongside the specification and rating data the standard demands. When someone says "API 6D certification" or calls something an "API 6D certified valve," they're talking about this monogram licensing. There's no separate credential behind it.

On double block and bleed. API 6D defines DBB and DIB (DIB-1 / DIB-2) configurations for isolating a section of line with a bleed between two seats. The same isolation logic recurs at the instrument connection, where Crestflo's double block and bleed and monoflange valves, built to ASME B16.34, provide the equivalent isolate-and-bleed function on a small-bore take-off.

API 6D pressure classes, sizes & materials

API 6D valves are rated in ASME/API pressure classes, commonly Class 150 through Class 2500, and they span a wide range of nominal sizes (NPS). The exact class span, size range, and pressure-temperature rating for a given valve come from the standard itself and the dimensional standards it references. Values follow the applicable standard, and can be customized to requirement.

Body and trim materials follow the referenced material standards for the service. Where the line carries sour (H₂S) service, the metallurgy must additionally satisfy NACE MR0175 / ISO 15156. Material and test traceability is commonly documented with EN 10204 3.1 / 3.2 material test certificates and heat-number traceability. For the corrosion-resistant alloys used at the instrument hook-up on these lines, such as Duplex 2205 and Super Duplex 2507, see the materials library.

API 6D vs API 598, API 608, API 6A, ASME B16.34 & API 607

Specifiers routinely ask how API 6D differs from its neighbors. API 6D is a full product specification for pipeline valves; the others cover different valve populations or different failure modes.

API 608 covers metal ball valves for general industrial service, and it sits apart from API 6D vs API 608, since API 6D adds pipeline-specific features such as DBB/DIB, pigging and antistatic devices. API 598 is an inspection-and-testing acceptance standard applied across many valve types. API 6D is a full pipeline-valve specification, though, and it comes with its own design, material, testing, marking and documentation requirements, that's the heart of API 6D vs API 598. One more comparison worth making: 6A specifies upstream wellhead and tree equipment, while 6D specifies pipeline transportation valves.

API 6D applications in oil & gas pipelines

API 6D valves live along the midstream and downstream flow path: gathering lines, gas and liquids transmission pipelines, distribution systems, and the piping at terminals, tank farms and refineries. Their full-bore, piggable designs make them the isolation and block valves used for pipeline sectionalizing, launcher/receiver stations, and pigging operations. For the sectors where these lines run, see oil & gas midstream and oil & gas.

Where Crestflo fits: the instrument hook-up on an API 6D line

Crestflo doesn't make API 6D pipeline valves. Crestflo builds instrumentation valves, and API 6D is a pipeline-valve specification, a separate product family with a different scope entirely. That distinction matters. Crestflo's value sits at the instrument hook-up that connects into an API 6D line, not on the line valve itself.

At that connection, Crestflo supplies the isolation valves, double block and bleed, monoflange and manifold assemblies that instrument a pipeline built to API 6D. Small-bore instrumentation valves round out the picture, built to the standards that govern their own product type.

• Design and rating to ASME B16.34, Crestflo's DBB valves are designed per ASME B16.34.
• Inspection and testing to API 598 acceptance criteria on request, with 100% seat- and shell-leak testing in house on manifolds.
• Fire-safe type-testing referenced to API 607 / API 6FA where a project specifies it.
• Sour service to NACE MR0175 / ISO 15156 where H₂S is present.
• Traceability via EN 10204 3.1 (3.2 on request) with a heat/lot number on every part.

Instrumentation valves qualify to ASME B16.34 and the API valve test standards, not to compression-tube-fitting standards, so Crestflo states conformance to the approvals applicable to each product type. Materials run from 316/316L stainless through high-nickel alloys and duplex grades. Small MOQ, private label, both imperial and metric sizes are available, and ready stock covers standard items while specials are made to order, with delivery in 6–8 weeks. Origin is Indian; US and European melt can be arranged on request, and full material traceability comes as standard. Crestflo holds ISO 9001, 14001, and 45001 certification, plus PED.

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Request instrumentation valves for your API 6D pipeline hook-up

Send your requirement, valve type, material/grade, size and end connections, pressure rating, quantity, plus any test standard (ASME B16.34, API 598, API 607/6FA) or NACE sour-service target, and the Crestflo Engineering Team will confirm the instrumentation valve and documentation for your line. Need a standards or brand cross-reference? Request your part-number cross-reference, and the Engineering Team will return it.

RFQ, tell us what you need:

• Name
• Company name
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• Requirement description (valve type, material, size, rating, quantity, test/service conditions)

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Secondary paths: browse instrumentation valves · double block & bleed · monoflange valve · become a distributor · contact Crestflo.

US contact: sales@crestflousa.com · +1 346 594 9005 · Houston, TX.

Ready stock covers standard items; specials are made to order. Delivery runs 6–8 weeks. Origin is Indian, though US or European melt can be arranged on request, with full material traceability.

Why Crestflo for the instrumentation valves on an API 6D pipeline

Precision, not over-claiming. Crestflo doesn't make API 6D pipeline valves and does not pretend to. It makes the instrumentation isolation valves at the hook-up, built to the standards that actually govern them: ASME B16.34, API 598, API 607 / API 6FA and NACE MR0175.

A manufacturer, not a reseller. In-house CNC machining, hydraulic proof/burst/impulse and pneumatic testing, PMI and NDT; 100% seat- and shell-leak test on manifolds; destructive testing at ISO/IEC 17025-accredited labs; third-party inspection on request.

• Traceability on every part. EN 10204 3.1 MTC (3.2 on request) with a heat/lot number on every part.
• Lead time that moves projects. Ready stock for standard items, made-to-order for specials, 6–8 week delivery.
• Honest origin. Indian origin; US / European melt available on request, with full material traceability.
• Small MOQ and private label, both imperial and metric, customizable to requirement.
• Certified quality system: ISO 9001 / 14001 / 45001 & PED certified.

Crestflo is the instrumentation division of a four-decade-old export house recognized by the Government of India, with a long delivery record across the Middle East. That manufacturing pedigree sits behind a focused, US-serving instrumentation brand. We Engineer Confidence.

Frequently asked questions

Explore related standards, valves & documentation

Standards: Standards hub · API 598 · API 607 · API 6FA · API 602 · ASME B16.34 · NACE MR0175 · ISO 15156 · EN 10204 MTC

Valves: Instrumentation valves · Ball valve · Check valve / NRV · Plug valve · Double block & bleed · Monoflange valve · Gauge root valve

Materials & industries: Materials library · Duplex 2205 · Super Duplex 2507 · Oil & gas midstream · Oil & gas