This calculator implements the wall thickness formula from ASME B31.3 Equation 304.1.2 (3a).
t = (P × D) / [2 × (S × E × W + P × Y)]
tm = t + c
tnom = tm / (1 − millTol%)
Verify allowable stress (S) against actual design temperature using the Material Analysis tab.
Design checks
- Design condition: use the pressure and material allowable stress for the same governing temperature case. Do not combine an unrelated maximum pressure with an ambient-temperature stress value.
- Allowances: the pressure thickness t excludes corrosion, erosion, threading, grooving, and other mechanical allowances. Combine the applicable additions in c.
- Mill tolerance: apply the negative manufacturing tolerance when converting minimum required wall into the nominal ordering thickness.
- E, W, and Y factors: select these from the applicable material, product form, seam, temperature, and code tables. The default values are not universal.
- Final schedule: choose a commercially available nominal wall at least as thick as the reported ordering thickness, then check external pressure, sustained loads, branches, and component-specific limits separately.
Recommended values
- Corrosion allowance: Carbon steel 1.5–3 mm typical; set from corrosion rate × design life.
- Mill tolerance: Seamless/ERW pipe is −12.5% on nominal wall — the tool adds this back.
- Joint factor E: Seamless 1.0, ERW 0.85, furnace-butt 0.60 (B31.3 Table A-1B).
- Coefficient Y: 0.4 for ferritic steel ≤ 480 °C; rises with temperature (Table 304.1.1).
Limitations
- Internal pressure: Barlow straight-pipe (B31.3 304.1) only — not external pressure, bending, or high-pressure Ch IX.
- Add allowances: Add threading/grooving depth and any specified extra before selecting a schedule.
About the standards
- ASME B31.3: Process Piping.