Valve ASME B16.34: Pressure-Temperature Ratings and Material Groups

ASME B16.34 is the foundational standard for valve pressure-temperature ratings. This guide explains material groups, pressure-temperature tables, and how to select the correct valve class for your service.

ASME B16.34 covers flanged, threaded, and welding-end valves. Defines pressure-temperature ratings for materials grouped by composition and heat treatment.

Valve class: Class 150, 300, 600, 900, 1500, 2500. Each class has a specific pressure-temperature rating based on the material group.

Group 1.x: Carbon steel (A105, A216 WCB, A350 LF2). Most common for general service up to 425degC.

Group 2.x: Alloy steel (A182 F22, A217 WC9). Used for high-temperature service (up to 550degC).

Group 3.x: Stainless steel (A182 F304, F316, A351 CF8, CF8M). Used for corrosive service.

Group 4.x: Nickel alloys (Monel, Inconel). Used for severe corrosion and high-temperature service.

ASME B16.34 tables list the maximum allowable working pressure (MAWP) at each temperature for each material group and class.

Example: Class 150, Group 1.1 (carbon steel), at 38degC: 19.6 bar. At 300degC: 9.8 bar. The rating decreases with temperature because material strength decreases.

Step 1: Determine design pressure and design temperature from process conditions.

Step 2: Select material group based on fluid compatibility and temperature.

Step 3: Use ASME B16.34 tables to find the class that meets or exceeds the design pressure at design temperature.

Step 4: Verify the selected class also meets the cold working pressure (CWP) requirement if applicable.

For flammable or toxic service, some companies require one class higher than calculated (e.g., use Class 300 instead of Class 150). This is called 'rating up'.

For cyclic service, fatigue may govern. ASME B16.34 does not cover fatigue. Refer to ASME VIII or API 6A for cyclic design.

No. At 300degC, the allowable pressure for Class 150 carbon steel is only about 9.8 bar (142 psi). You need Class 300 for 150 psi at 300degC.

Class 150 is a nominal pressure rating. The actual pressure capability depends on temperature and material. At room temperature, Class 150 is rated for about 285 psi (19.6 bar), not 150 psi.

Ted Wang

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