API 6D and API 608 are standards specifications for ball valves; their scope, application, and inspection are different.

Standard Specifications

API 6D - Specification for Valves

API 6D defines the requirements for the design, manufacturing, materials, welding, quality control, assembly, testing, marking, documentation, and process controls of axial valve, ball valve, check valve, gate valve, and plug valves for application in the petroleum and natural gas industries.

API 608 -Metal Ball Valves—Flanged, Threaded, and Welding Ends

API 608 specifies the requirements for metal ball valves suitable for petroleum, petrochemical, and industrial applications that have:

  • Flanged ends in sizes DN 15 through DN 600 (NPS 1/2 through NPS 24);
  • Butt-welding ends in sizes DN 15 through DN 600 (NPS 1/2 through NPS 24);
  • Socket-welding ends in sizes DN 8 through DN 50 (NPS 1/4 through NPS 2);
  • Threaded ends in sizes DN 8 through DN 50 (NPS 1/4 through NPS 2).

API 608 applies to metal ball valves with pressure classes as follows:

  •  Flanged ends in Classes 150, 300, and 600;
  •  Butt-welding ends in Classes 150, 300, and 600;
  •  Socket-welding ends in Classes 150, 300, 600, and 800;
  • Threaded ends in Classes 150, 300, 600, and 800.

API 608 establishes requirements for bore sizes described as:

  • Full bore;
  • Single reduced bore;
  • Double reduced bore.

API 608 applies to floating (seat-supported) ball (Figure B.1) and trunnion ball valve designs (Figure B.2).These figures are to be used only for the purpose of establishing standard nomenclature for valve components—other floating and trunnion designs also exist.

API 608 establishes additional requirements for ball valves that are otherwise in full conformance to the requirements of ASME B1 6.34, Standard Class.

Applications and Scope

API 608 ball valves are applied in petroleum, petrochemical, and industrial applications for opening or cutting off flow. They are in applications such as high temperature and high pressure, inflammable and explosive, corrosive, and continuous operation, which require more requirements on valve sealing, material, and corrosion.

API 6D is the specification for piping and pipeline valves. API 6D ball valves are specially used for long-distance pipeline transportation. In addition to switching on or cutting off the medium, the ball valve under this standard also has functions such as blow-down, emptying, over-pressure relief, grease injection, and on-line leak detection.

API 608 covers ball valves in sizes 1/2" to 24", Class 150 to 800, while API 6D covers a larger size range, from 2" to 60", and Class 150–2500. API 6D also specifies axial valves, gate valves, swing check valves, dual plate check valves, axial flow check valves, and plug valves.


Inspection and Testing

API 608 provides for the inspection and pressure testing of ball valves in accordance with API 598. As a supplement to ASME B16.34, API 608 ball valves shall also fully meet ASME B16.34.

API 6D provides more detailed requirements for the inspection and testing of pipeline valves. They are more demanding than ASME B16.34 and API 598 in terms of longer pressure duration, more test items, and more complex operating procedures. API 608 ball valves usually test the seal by pressurizing one end and observing the seat at the other end during the seal test, while API 6D ball valves test the seal from the middle chamber by pressurizing one end.

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Valve type (ball, gate, globe, check etc.), valve size, pressure class, valve material, and end connection (flanged, butt welding etc.)