What is the basis for ASME flange pressure Class 150 rating?

• A. Flange Weight
• B. Sealing Groove Depth
• C. Bolt Circle Diameter
• D. Pressure-Temperature Rating at Reference Material Group

Answer: (D)

The key idea is that flange class ratings come from the pressure–temperature capability of the flange material, as standardized for a reference material group in ASME B16.5. The class number (for example, 150) is the allowable pressure the flange can handle at a reference temperature, derived from tables that relate material strength (grouped materials) to pressure at different temperatures. Different materials are assigned to material groups so their strength is represented on a common basis, and any temperature derating is built into that rating.

Therefore, the class rating is not determined by flange weight, groove depth, or bolt circle diameter. Those geometric and physical attributes affect fit, sealing performance, and bolting requirements, but the rating itself is defined by the pressure–temperature capability of the material in its reference group.