MSS SP-44

Applies to: Large-diameter steel pipeline flanges NPS 12–60 for oil and gas transmission systems; pressure Classes 150–2500; commonly paired with API 5L high-strength pipe; dimensions form the basis of ASME B16.47 Series A.

Does NOT cover: Process plant flanges (ASME B16.5/B16.47 Series B); refinery in-plant flanges; non-metallic flanges.

• Pressure-temperature ratings per material group
• Weld neck design optimized for high-pressure pipeline service
• Hydrostatic shell test at 1.5× rated pressure
• Dimensional tolerances on bolt circle, bore, and face
• Marking: size, pressure class, material grade, heat number, manufacturer

MSS SP-44 flanges originated from pipeline industry practice and form the dimensional basis of ASME B16.47 Series A. They are routinely specified alongside API 5L high-strength pipe in cross-country and offshore gas and liquid transmission systems. The pressure ratings in MSS SP-44 and ASME B16.47 Series A are equivalent but minor marking and tolerancing differences may exist between editions.

Engineering note: For most pipeline projects, specifying ASME B16.47 Series A is preferred over MSS SP-44, as ASME documents are more universally available and accepted. However, some legacy operating company standards explicitly reference MSS SP-44. Verify the client's standard before specifying — using "ASME B16.47 Series A or MSS SP-44" in the material specification avoids disputes over dimensional equivalency.