Governing equation
t = (P × D) / (2 × (S × E × W + P × Y)). Required thickness tm = t + c, where c covers corrosion, erosion and threading allowances. Selected nominal wall must satisfy tm after mill tolerance (typically 12.5%).
Inputs you need
- Design pressure P and design temperature T
- Pipe outside diameter D and material specification
- Allowable stress S at design temperature (Table A-1)
- Joint quality factor E and weld strength reduction factor W
- Coefficient Y from Table 304.1.1
- Corrosion / erosion allowance c and mechanical allowances
Typical workflow
- Pick material and look up S at T
- Compute t, add c to get tm
- Divide by (1 − mill tolerance) to get ordered wall
- Select the next standard schedule that meets the ordered wall
Limits of use
Equation applies to t < D/6 and P/(SE) ≤ 0.385. Outside that range use Para. 304.1.2(b) or thick-wall formulas. Always confirm with the project specification and current code edition.
Key references
- · ASME B31.3 Para. 304.1
- · ASME B31.3 Table A-1, Table 304.1.1
Use of this content
This page is a decision-support and training reference. It is not a substitute for the governing code, the project specification, or the judgement of a responsible engineer. Always validate against the current edition of the applicable standard before use on live engineering work.