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    Piping / Flanges

    Flange Rating (ASME B16.5)

    A flange class is not a pressure rating on its own: the allowable pressure falls with temperature. This looks up the ASME B16.5 table for carbon steel or stainless steel, interpolates between the published temperatures, and compares it with the design pressure.

    StandardB16.5Class150ResultPass
    Allowable pressure
    13.8 bar
    At 200 °C
    Design pressure
    10.0 bar
    Class 150
    Margin
    3.8 bar
    Within the rating
    Utilisation
    72%
    Of the allowable
    Class 150 rating against temperature
    Bar, gauge. Values between published temperatures are interpolated.
    Class 150 rating against temperature
    °CRating (bar)Utilisation (%)
    -2919.651
    3819.651
    5019.252
    10017.756
    15015.863
    20013.872
    25012.183
    30010.298
    3259.3100
    3508.4100
    3757.4100
    4006.5100
    4255.5100
    4504.6100
    4753.7100
    5002.8100
    5381.4100

    Below −29 °C use the −29 °C rating. Above 538 °C the table does not apply.

    Inspect the model
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    Allowable pressure against temperature
    The derating is steep above 400 °C for carbon steel.
    Allowable pressure against temperature0.0004.398.7813.1717.5621.95-29-2938385050100100150150200200250250300300325325350350375375400400425425450450475475500500538538bar
    Canonical equations
    The exact relationships implemented by this engine.

    Pallow = table(class, material, T) · ASME B16.5 Table 2.

    linear between published temperatures · Between classes is not permitted.

    Pdesign ≤ Pallow · Plus the code’s other loads.

    engineering methodology

    A clear path from inputs to results.

    A flange class is not a pressure rating on its own: the allowable pressure falls with temperature. This looks up the ASME B16.5 table for carbon steel or stainless steel, interpolates between the published temperatures, and compares it with the design pressure.

    Step-by-step methodWorked exampleAssumptions explained

    How to use

    1. Set material group.
    2. Set class.
    3. Set design temperature (°c).
    4. Set design pressure (bar).
    5. Read the headline metrics, then check the table for the detail.

    The formula

    Pallow=f(class,material,T)P_{allow} = f(\text{class},\text{material},T)

    Reference: ASME B16.5 Table 2, carbon steel and austenitic stainless groups.

    Worked example

    At the default inputs

    Inputs
    • Material group: carbon; Class: 150; Design temperature (°C): 200; Design pressure (bar): 10
    Calculation path
    1. 1

      Look up the class → 13.8 Compare → 72%

    Result

    Allowable pressure: 13.8 bar · Design pressure: 10.0 bar · Margin: 3.8 bar

    Interpreting the result

    A Class 150 carbon-steel flange is rated 13.8 bar at 200 °C, so a 10.0 bar design is within the rating by 3.8 bar.

    Assumptions & limitations

    • Pressure rating only; external loads are not included.
    • Linear interpolation between published temperatures.
    • Gasket and bolting are per B16.5.

    Frequently asked questions

    Why does the rating fall with temperature?

    The material allowable stress falls; the class is a cold rating.

    Can I interpolate between classes?

    No. B16.5 permits interpolation between temperatures, not classes.

    Methodology last reviewed 2026-10-23. Results are informational and not financial or engineering advice — see our disclaimer.