What Is API 6D? Pipeline Valve Standard

Quick Answer

API 6D is the specification for pipeline valves (gate, ball, plug, check) used in petroleum and natural gas transportation systems. It covers sizes 1/2” to 60”+, pressure classes 150 to 2500, and mandates individual factory testing of every valve. API 6D applies to cross-country pipelines; for plant piping, use API 600 (gate), API 623 (globe), API 608 (ball), or API 594 (check).

Scope and Applicability

API 6D applies to valves installed in pipeline systems that transport crude oil, natural gas, petroleum products, and other fluids between facilities (wellheads, processing plants, terminals, refineries). It does not apply to valves within plant piping, which are covered by separate API standards.

The distinction matters: API 6D has stricter testing requirements and additional design provisions for buried, remote, and unmanned pipeline service.

Specifications

Parameter	Details
Full title	Specification for Pipeline and Piping Valves
Scope	Gate, ball, plug, check valves for pipeline service
Size range	1/2” to 60”+
Pressure classes	150, 300, 600, 900, 1500, 2500 per ASME B16.34
End connections	Flanged (B16.5, B16.47), butt-weld (B16.25)
Body materials	ASTM A216 WCB, A352 LCB/LCC, A351 CF8M, and others
Face-to-face	ASME B16.10
Testing	Shell test, backseat test, low-pressure closure, high-pressure closure
Marking	Size, class, material, manufacturer, trim, API 6D monogram

Valve Types Under API 6D

Valve Type	API 6D Design	Typical Pipeline Application
Gate	Slab gate, expanding gate, wedge gate	Mainline block valves
Ball	Floating, trunnion (most common)	Mainline block, pig launcher/receiver
Plug	Lubricated, non-lubricated	Manifold block valves, crude oil
Check	Swing, piston, dual plate	Pump station discharge

Trunnion mounted ball valves are the dominant valve type for modern pipeline applications due to their tight shut-off, low maintenance, and suitability for pigging operations (full bore design).

Testing Requirements

API 6D mandates more rigorous testing than API 600 or API 608:

Test	Medium	Duration	Acceptance
Shell (body) test	Water	Per size (min. 2 min for valves up to 4”)	No visible leakage
High-pressure closure	Water	Per size (min. 2 min)	Zero leakage (for metal-seated: limited drip rate per API 598)
Low-pressure closure	Air or gas	Per size (min. 2 min)	Zero bubble leakage (soft seat)
Backseat test	Water	Per size	No visible leakage past backseat

Each valve is tested individually at the factory. No sampling or batch testing is permitted for API 6D valves.

Common Mistake

Specifying API 608 (general-purpose ball valve) for a cross-country pipeline application. API 608 does not include the additional testing, design, and marking requirements of API 6D. Pipeline valves must carry the API 6D monogram to comply with pipeline regulations and operator specifications.

For valve types used in plant piping (inside battery limits), see the complete valve types guide.

Read the full guide to valve types