API 6D

Covers — design, manufacturing, materials, welding, testing, marking, and documentation of axial, ball, check, gate, and plug valves for the natural gas and petroleum pipeline industry, including full-bore (piggable) and reduced-bore designs.

Does NOT cover (exclusions) — the following are governed elsewhere:

• Plant/process piping valves → API 600/602/603/608/609 to ASME B16.34.
• Pressure-relief valves → API 526/527; subsea wellhead/tree valves → API 6A.
• The pipeline systems themselves → ASME B31.4 / B31.8.

API 6D valves are selected for transmission/gathering pipeline duty and pigging, distinct from plant valve standards.

API 6D sets minimum requirements for pipeline valves:

• Materials & Welding — line-pipe-compatible materials with qualified welding and quality control for buried/remote duty.
• Design — full-opening (piggable) or reduced bore; double block-and-bleed and antistatic/fire-safe features as required.
• Examination & Testing — shell, seat, and drain/vent testing; supplementary NDE per specification; fire test per API 6FA where required.
• Documentation — traceability and process controls suited to pipeline integrity requirements.

API 6D (Spec 6D) is the transmission-pipeline valve standard, covering gate, ball, check, plug, and axial valves built for buried, remote, and piggable service. Full-opening designs let inspection and cleaning pigs pass without obstruction, and double block-and-bleed features support safe isolation.

It aligns with pipeline codes ASME B31.4/B31.8 and is incorporated into pipeline safety regulations, distinguishing it from the plant valve standards (API 600/608/609). Testing adds drain/vent checks beyond the plant API 598 regime.

Engineering Note: Specify full-bore (piggable) API 6D valves on any line that will be pigged — a reduced-bore valve will block the pig.