Wall Thickness Calculator

Estimate the required wall thickness of straight pipe under internal pressure using ASME B31.3 Equation (3a), then see the thinnest ASME B36.10M schedule that meets it.

Design pressure P (barg)

Pipe size (NPS)

Allowable stress S (MPa) From B31.3 Table A-1 at design temperature. 137.9 MPa (20 ksi) is A106 Gr. B at moderate temperature: check your temperature.

Quality factor E 1.0 seamless; 0.85 typical for ERW (Table A-1B).

Weld strength reduction W 1.0 below the creep range.

Coefficient Y 0.4 for ferritic and austenitic steels below 482 °C (Table 304.1.1).

Corrosion allowance c (mm) Plus thread or groove depth where relevant.

Mill under-tolerance (%) 12.5% is usual for seamless pipe to A106 / A53.

How it works

Pressure design thickness: t = P·D / [2(S·E·W + P·Y)], where D is the outside diameter.
Minimum required thickness: tm = t + c, where c is the corrosion allowance plus any thread or groove depth.
Nominal thickness: tm / (1 − mill tolerance), then rounded up to a standard schedule.

Limits

Valid when t is less than D/6. Thicker pipe, or P/(S·E) above 0.385, needs special design consideration under B31.3.
Use the allowable stress S for your material at the design temperature from B31.3 Table A-1.
Doesn’t cover external pressure, bends, branches or other loads such as weight, thermal and occasional loads.