Which standard governs flange pressure classes?

• A. National Board Inspection Code (NBIC)
• B. B16.25
• C. ASME Boiler and Pressure Vessel Code
• D. B16.5

Answer: (D)

Flange pressure classes are defined by the standard that specifically addresses pipe flanges and their rated pressures. ASME B16.5, Pipe Flanges and Flanged Fittings, sets the standard pressure–temperature ratings (Class 150, 300, 600, etc.) and the corresponding dimensions for flanges and flange fittings. This makes it the go-to reference for selecting a flange whose pressure rating matches the system’s service conditions. The broader ASME BPVC covers the overall design and construction requirements for boilers and pressure vessels but relies on B16.5 for the flange rating aspect. The National Board Inspection Code focuses on inspection and repair practices, not the rating system, and B16.25 covers welded flanges and fittings dimensions rather than the general flange pressure class framework.