Valve Pressure-Temperature
Rating Reference Tables

What is ASME B16.34 pressure-temperature rating?

ASME B16.34 defines the maximum allowable working pressure for industrial valves at various temperatures, grouped by body material. The standard establishes seven pressure classes (150, 300, 600, 900, 1500, 2500, 4500) for flanged, threaded, and welding-end valves. The rated pressure for a given class decreases as operating temperature increases, because metal yield strength reduces at elevated temperatures. Engineers must select a pressure class that provides adequate rating at the maximum operating temperature, not just ambient.

What is the difference between ANSI and ASME pressure class — are they the same?

ANSI Class and ASME Class are numerically identical — Class 150, 300, 600 etc. In common industrial usage, 'ANSI 150' and 'Class 150' refer to the same pressure class defined in ASME B16.34. ANSI (American National Standards Institute) previously published flange and valve dimensional standards before transferring administration to ASME. The terms are used interchangeably on purchase orders and datasheets.

Which material has the highest pressure rating at elevated temperature?

ASTM A217 Grade WC9 (1.25Cr-0.5Mo alloy steel) maintains the highest pressure rating at temperatures above 450°C, making it the standard material for high-temperature steam valves in power generation and refinery applications. At ambient temperature, WCB carbon steel has comparable ratings to WC9, but WC9 retains significantly more strength above 450°C. For temperatures above 538°C, A217 WC11 (2.25Cr-1Mo) or A217 C12A (9Cr-1Mo-V) are specified.

Why does CF8M (316 stainless) have a lower pressure rating than WCB carbon steel?

ASTM A351 CF8M (cast 316 stainless steel) has a lower yield strength than ASTM A216 WCB carbon steel at ambient temperature — typically 170 MPa vs 250 MPa. ASME B16.34 pressure-temperature ratings are derived from the yield and ultimate tensile strength of each material, so a lower-strength material in the same wall thickness produces a lower allowable pressure. This is why Class 150 CF8M valves are rated at 15.1 bar vs 19.6 bar for WCB. The advantage of CF8M is corrosion resistance, not pressure capability.

Can I use a Class 150 valve on a 15 bar steam line?

It depends on the temperature. At ambient (38°C), Class 150 WCB is rated to 19.6 bar — which would accommodate 15 bar. However, at 200°C steam temperature, the Class 150 WCB rating drops to approximately 15.8 bar, leaving only 0.8 bar margin. At 250°C, the margin is minimal and Class 300 would be required. For any steam application, always verify the P-T rating at the maximum operating temperature, not ambient. Also confirm IBR (Indian Boiler Regulations) certification requirements for steam service in India.