ASME B16.47

Applies to: Large-diameter steel flanges NPS 26 through NPS 60; Series A (derived from MSS SP-44, smaller bolt circle) and Series B (derived from API 605, larger bolt circle); pressure Classes 75–900.

Does NOT cover: NPS 24 and smaller (ASME B16.5 applies); non-metallic flanges; flanges above Class 900; specialty alloy flanges without specific material supplement.

• Series designation (A or B) must match across all mating flanges — Series A and B are physically incompatible at the same NPS
• Pressure-temperature ratings per material group (same framework as B16.5)
• Ring gasket and raised face dimensions per series
• Bolt pattern, bolt hole diameter, and bolt length
• Inspection and testing equivalent to ASME B16.5 practice

ASME B16.47 consolidates two historically separate large-flange dimensional systems. Series A flanges (from MSS SP-44) have smaller bolt circles and are physically incompatible with Series B flanges (from API 605) of the same NPS — mixing Series within a joint is a classic field assembly error that causes bolt-hole misalignment and gasket seating problems.

Engineering note: Always specify the Series explicitly in the piping material specification and verify it on procurement documents and mill test reports. For pipeline interconnections with existing flanges, measure and confirm the Series before specifying replacement or mating flanges. A Series mismatch discovered during construction requires flange replacement — an expensive error on large-diameter, high-pressure equipment.