Engineering Reference
ASME B16.5 Table 2 publishes the maximum allowable working pressure for each flange material group and class, at temperatures from −29°C (−20°F) up to the group's upper limit. The rating decreases with temperature because material strength decreases.
Find Max Pressure: select a material group, class, and design temperature — the calculator interpolates the rated pressure between the two nearest published temperature points.
Find Min Class: enter design pressure and temperature — the calculator checks every standard class (150 through 2500) for the selected material group and returns the lightest one that still meets the requirement at that temperature.
Gasket dimensions (when an NPS is selected) come from ASME B16.20 spiral-wound and flat non-metallic ring tables, matched to the chosen flange class and pipe size.
- Ratings are interpolated between published ASME B16.5 Table 2 temperature points; extrapolation beyond the table is not performed
- Class 75 (cast iron, low-pressure) is excluded from the minimum-class search
- Corrosion, bolt load, gasket seating stress, and flange flatness are not evaluated — this is a P-T rating lookup only
- Verify the final material group / spec match against your project material specification before issuing for design
The maximum allowable internal pressure a flange of a given material group and class can withstand at a specific temperature, per ASME B16.5 Table 2.
Find the lowest class whose rated pressure at your design temperature meets or exceeds your design pressure, for your flange's material group.
B16.5 groups materials with similar high-temperature strength and publishes one P-T table per group — the same class number rates differently in a different group.