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WCB Class 300 vs Class 150 — When to Specify
Updated 2026-10-30 · Supreme Valves India Engineering
Quick rule
Use Class 150 when the pipe class and design temperature stay within ASME B16.34 Class 150 allowable stress for ASTM A216 WCB. Step to Class 300 when the line list, design pressure, or temperature chart exceeds Class 150 — never by mixing flanges.
Class 300 is not a marketing upgrade. Flange thickness, bolt circle, face-to-face (ASME B16.10) and hydrostatic test pressure all change.
What changes between Class 150 and Class 300
Flange OD, thickness and PCD per ASME B16.5 increase at Class 300 for the same NPS.
Valve face-to-face length usually increases — a Class 150 body will not drop into a Class 300 spool.
Shell hydro test pressure rises with class. Seat test follows API 598 practice for the rated class.
Unit cost and weight rise. Quote Class 300 only when the P&ID / pipe class requires it.
RFQ wording we see
Buyers write: GATE VALVE 6 INCH CLASS 300 RF ASTM A216 WCB API 600 — or BALL VALVE CL300 WCB FIRE SAFE. Mirror that language on the RFQ: size, class, ends, trim, fire-safe / gear as applicable.
FAQ
Can I mate Class 150 valves to Class 300 flanges?
No. Flange dimensions and ratings differ. Match valve class to the pipe class.
Is Class 300 always needed for steam?
No. Many steam utilities run Class 150 WCB within the P-T chart. Follow design pressure and temperature, not habit.
Where are Class 300 RFQs?
See our Class 300 RFQ pages for gate, globe and ball WCB constructions.