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Pipe Section Modulus Calculator

Calculate standard and corroded Section Modulus for pipes. Critical for integrity assessments.

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About

In piping integrity management, calculating the remaining strength of corroded pipes is a daily task. This calculator determines the Section Modulus (S) of hollow circular sections, with a specific feature to deduct "Corrosion Allowance" or measured wall loss.

By inputting a corrosion value, the tool virtually reduces the wall thickness (increasing the inner diameter while keeping the outer diameter constant) and computes the "Corroded Section Modulus". This value is required for ASME B31.3 compliance checks and determining maximum allowable working pressure (MAWP).

piping engineering ASME B31.3 corrosion allowance section modulus oil and gas

Formulas

The Section Modulus for a pipe with outer diameter D and inner diameter d is:

S = π(D4 − d4)32D

When corrosion c is applied, the new inner diameter becomes:

dnew = D − 2(tnom − c)

Reference Data

TermSymbolDefinition
Outer DiameterDNominal outside dimension (Constant).
Nominal ThicknesstnomManufacturing thickness.
Corrosion AllowancecThickness reserved for material loss.
Effective Thicknesstefftnom − c

Frequently Asked Questions

Corrosion reduces the wall thickness, which significantly lowers the Moment of Inertia and Section Modulus. Since "d" is raised to the 4th power in the formula, even small thickness losses can result in large reductions in strength.
No. By default, this tool calculates based on nominal or input dimensions. For strict code compliance (API/ASME), you should manually subtract the mill tolerance (usually 12.5%) from the nominal thickness before inputting, or add it to the corrosion allowance.