What Is ASME B16.34?

ASME B16.34 is the standard that defines pressure-temperature ratings for flanged, threaded, and welding-end valves made from steel, nickel alloys, and other materials. It specifies the maximum allowable pressure a valve can handle at a given temperature, based on its pressure class and body material group.

When to Use ASME B16.34

Every valve purchased for oil and gas, petrochemical, or power generation piping must comply with ASME B16.34 (or an equivalent standard). It is referenced by API 600, API 602, API 608, API 6D, and virtually every other valve product standard. Without ASME B16.34, there is no way to determine if a valve is rated for the service pressure and temperature.

Pressure Classes and Material Groups

Pressure Class	Approx. Max Pressure at Ambient (psi) (Group 1.1	Approx. Max Pressure at Ambient (bar)) Group 1.1
150	285	19.6
300	740	51.0
600	1,480	102.0
900	2,220	153.1
1500	3,705	255.5
2500	6,170	425.4
4500	11,100	765.3

These values apply to Material Group 1.1 (carbon steel, e.g., ASTM A216 WCB / A105) at ambient temperature (-29 to 38 degC). As temperature increases, the allowable pressure decreases.

Material Groups

ASME B16.34 organizes materials into groups based on their mechanical properties at temperature:

Group	Typical Materials	Application
1.1	A216 WCB, A105, A350 LF2	General carbon steel service
1.2	A216 WCC	Higher-strength carbon steel
1.5	A217 WC6, A182 F11	Chrome-moly alloy (high temp)
1.7	A217 WC9, A182 F22	2-1/4Cr-1Mo alloy (high temp)
1.9	A217 C5, A182 F5	5Cr-0.5Mo (high temp, moderate corrosion)
1.10	A217 C12, A182 F9	9Cr-1Mo alloy
2.1	A351 CF8M, A182 F316	316 stainless steel
2.2	A351 CF8, A182 F304	304 stainless steel
2.5	A351 CF3M, A182 F316L	316L low-carbon stainless
3.1	Monel, Inconel, Hastelloy	Nickel alloys (severe corrosion)

How to Read P-T Tables

Each material group has a table showing the maximum allowable pressure (in psi or bar) at specific temperatures, for each pressure class. To use the table:

1. Identify the valve body material and find its material group.
2. Determine the maximum operating temperature.
3. Look up the pressure class in the table for that material group.
4. Read the allowable pressure at the design temperature.
5. Verify that the design pressure does not exceed the tabulated value.

Common Mistake

Using the ambient-temperature rating for a valve operating at 400 degC. At elevated temperatures, the allowable pressure may drop by 50% or more. Always check the P-T table at the actual operating temperature, not just the nameplate class.

Relationship with Other Standards

ASME B16.34 works alongside ASME B16.5 (flange ratings), ASME B16.10 (valve face-to-face dimensions), and ASME B16.47 (large-diameter flanges). The pressure classes in B16.34 align directly with B16.5 flange classes, ensuring that a Class 300 valve matches a Class 300 flange.

For the full pressure-temperature rating tables and material group details, see the complete ASME B16.34 guide.

Read the full guide to valve types