API 6D vs API 608: Ball Valve Standards

API 6D and API 608 are the two primary standards for ball valves in the oil and gas industry. API 6D covers pipeline valves; API 608 covers process (facility) valves. The distinction determines design requirements, testing protocols, and documentation for ball valve procurement.

Comparison Table

Feature	API 6D	API 608
Full title	Pipeline and Piping Valves	Metal Ball Valves; Flanged, Threaded, and Welding Ends
Scope	Pipeline transportation systems	Petroleum and natural gas process facilities
Valve types covered	Ball, gate, check, plug (pipeline)	Ball valves only (process)
Ball design	Trunnion (standard), floating (small sizes)	Floating and trunnion
Bore	Full bore mandatory	Full bore or reduced bore
Size range	2” to 60”+	1/2” to 36”
Pressure classes	150-2500	150-2500
End connections	Flanged, butt-weld	Flanged, threaded, butt-weld
Double block and bleed	Required (Appendix A)	Not required (optional)
Cavity relief	Required	Not required
Fire testing	API 607 fire test mandatory	API 607 optional (as specified)
Pressure testing	Shell + seat (high and low pressure)	Shell + seat per ASME B16.34
Extended body test	Required (simulates buried service)	Not required
Marking	API 6D monogram (licensed manufacturers)	API 608 compliance
ISO equivalent	ISO 14313	ISO 17292
Documentation	More extensive (MTR, RT, test reports)	Standard per B16.34

Key Differences

Scope. API 6D applies to valves in pipeline transportation systems; cross-country pipelines, gathering systems, and distribution networks. API 608 applies to valves in process facilities; refineries, chemical plants, gas processing plants, and offshore platforms. The line between “pipeline” and “process” is typically the first block valve at the facility boundary.

Design requirements. API 6D mandates full-bore design, double block and bleed capability (trunnion valves), cavity pressure relief, and fire testing per API 607. These requirements reflect the higher consequence of valve failure in pipeline service, where isolation may be the only barrier between high-pressure hydrocarbon and the environment.

API 608 allows reduced-bore (standard port) design, does not require DBB, and makes fire testing optional unless the purchaser specifies it. These relaxed requirements reflect the additional safety layers present in a process facility (control systems, safety relief devices, fire protection).

Testing. API 6D requires both high-pressure and low-pressure seat testing. The low-pressure test (typically 60-100 psig gas) is critical for detecting seat leakage that may not appear at high pressure, where the seat is more heavily loaded. API 608 follows ASME B16.34 testing, which requires a high-pressure hydrostatic shell and seat test.

Documentation. API 6D valves come with more extensive documentation: material test reports for all pressure-retaining parts, NDE reports, pressure test certificates with witnessed results, and often third-party inspection reports. API 608 valves have standard documentation per the manufacturer’s quality system.

Common Mistake

Specifying API 608 ball valves for pipeline service. API 608 does not require full-bore design, DBB capability, low-pressure seat testing, or fire testing; all of which are critical for pipeline isolation. Always specify API 6D for any valve in a pipeline transportation system.

Both standards reference ASME B16.34 for pressure-temperature ratings and ASME B16.10 for face-to-face dimensions.

Read the full guide to valve types