Pressure–Temperature Ratings Explained: Understanding ASME B16.34 Tables

Pressure–temperature ratings are the backbone of ASME B16.34. These tables define the maximum allowable working pressure (MAWP) for each valve class at different temperatures.

The ratings depend on:

1. Material group (carbon steel, stainless steel, alloy steel, etc.)
2. Pressure class (150 to 2500)
3. Temperature range
4. Allowable stress values

As temperature increases, the allowable pressure decreases due to material strength reduction. For example, a Class 300 carbon‑steel valve may handle 51 bar at 38°C, but only 20 bar at 400°C.

Understanding these tables helps engineers:

1. Select the correct valve class
2. Prevent over‑pressurization
3. Ensure compliance with ASME piping codes
4. Improve system safety and reliability

These ratings are essential for designing safe, efficient, and long‑lasting fluid‑handling systems.