ASME B16.34 Valve Specifications Explained
What ASME B16.34 covers — pressure-temperature ratings, pressure classes, material groups, minimum wall thickness, and testing — in plain language.
ASME B16.34, "Valves — Flanged, Threaded, and Welding End," is the cornerstone standard for industrial valve pressure-temperature ratings. It defines how a valve's maximum allowable working pressure falls as temperature rises, based on the body material group and pressure class. Understanding it is essential for correctly specifying valves for any pressure system.
Pressure Classes & What They Mean
Key Concepts
- Pressure-temperature ratings: the allowable working pressure decreases as temperature increases — always read the rating at the actual service temperature
- Material groups: ratings are tabulated by material group (e.g. Group 1.1 = A105/WCB, 2.1 = 304, 2.2 = 316) — different alloys give different curves
- Minimum wall thickness: B16.34 sets the minimum body wall for each size and class
- Standard, Special, and Limited classes: Special Class permits higher ratings with extra NDE
- Testing: references API 598 / B16.34 shell and seat pressure tests
Frequently Asked Questions
What is ASME B16.34?
ASME B16.34 is the standard that establishes pressure-temperature ratings, dimensions, materials, wall thickness, and testing requirements for flanged, threaded, and welding-end valves. It is the basis for almost all industrial metal valve ratings.
What does "Class 150" or "Class 300" mean?
The class is a pressure rating designation. A higher class means a higher allowable working pressure at a given temperature. For a WCB body, Class 150 allows about 19.6 bar at 38°C, Class 300 about 51 bar, and so on — and the allowable pressure drops as temperature rises.
Why does the allowable pressure drop with temperature?
Material strength decreases as temperature increases, so the maximum allowable working pressure in the B16.34 tables reduces accordingly. Always select the rating at your maximum service temperature, not at ambient.
What is the difference between Standard and Special Class?
Standard Class uses the default ratings; Special Class permits higher pressure-temperature ratings for the same body provided additional non-destructive examination (NDE) is performed to verify integrity.
Need Help Specifying ASME B16.34 Valves?
Request a technical datasheet, material certification details, or a project quotation from our engineering team. We export to Saudi Arabia, the UAE, and across the Gulf.