| ProjectSample Project — Demonstration Only | Job No.SAMPLE-001 | Client— |
| CalculationASME B31.1 Power Piping Wall Thickness Calculator | Calc byPiping Toolset (calc-core) | Checked byUNCHECKED — sample |
| Date2026-10-12 | Rev0 | BasisASME B31.1 ¶104.1.2 (also B31.5-2022 ¶504.1.2 Eq. (3a) with E = W = 1; used for B31.9 as ¶904.1.1 permits) |
NPS 8 (8.625 in OD) main steam-class line at 1,000 psi. SE = 15,000 psi, y = 0.4, allowance A = 0.065 in, 12.5% mill tolerance.
| Design pressure P | 1,000 | psi |
| Outside diameter Do | 8.625 | in |
| Allowable SE | 15,000 | psi |
| Coefficient y | 0.4 | — |
| Allowance A | 0.065 | in |
| Mill tolerance | 12.5 | % |
Pressure design of straight pipe under internal pressure, B31.1 ¶104.1.2 (Eq. 7 form):
t = P·Do / ( 2 (S·E·W + P·y) )
tm = t + A
torder = tm / (1 − mill tolerance)
The calculator applies the equation exactly as written. It first forms the denominator 2·(S·E·W + P·y): S·E is the maximum allowable stress including longitudinal joint efficiency, taken from the B31.1 Appendix A tables for the material at design temperature, W is the weld strength reduction factor of ¶102.4.7 (Table 102.4.7-1, defaulting to 1.0), and y is the temperature coefficient of Table 104.1.2-1, which credits stress redistribution through the wall as temperature rises. Dividing P·Do by that denominator gives the pressure design thickness t. The additional thickness allowance A — corrosion, erosion, threading or grooving, structural — is added to give the minimum required wall tm, and dividing by (1 − mill tolerance) grosses tm up to the nominal thickness to order, so pipe delivered at the bottom of the mill's under-tolerance still meets tm. Units are consistent-unit: psi with inches, or MPa with millimetres. If t reaches Do/6 the calculator flags the result as outside the thin-wall validity of the equation.
| t — pressure design thickness | 0.28003 | in |
| tm — minimum required | 0.34503 | in |
| Ordering thickness | 0.39432 | in |
The result values above are locked as fixture b311-wall-thickness.json, case
“NPS 8 @ 1000 psi, S=15000, E=1, W=1.0, y=0.4, A=0.065, 12.5% mill tol”, tolerance 0.00001, in the calc-core continuous
verification gate (see https://pipingtoolset.com/trust/validation.html). Allowable-stress and factor data are
user-supplied inputs; citations: ASME B31.1, Power Piping — ¶104.1.2, pressure design of straight pipe (Eq. 7 form, SEW + Py since the 2018 edition). · ASME B31.1-2024 — Mandatory Appendix A Tables A-1 / A-2 / A-3 (maximum allowable stress SE, the material lines listed on the source policy page), Table 102.4.3-1 (E, plus the Appendix A seamless line E = 1.00), Table 104.1.2-1 (y) — embedded and cited by table and line on the Pro pickers; typed from your governing edition otherwise. Table 102.4.7-1 (W, the ¶102.4.7 weld strength reduction factor; 1.0 below the tabulated temperatures, and carbon steel is exempt) is not embedded — W is a typed input that defaults to 1.0. · ASME B31.5-2022 ¶504.1.2 Eq. (3a) — t = P·D<sub>o</sub> / 2(S + P·y), the same form with S taken from Table 502.3.1-1 as the allowable hoop stress (for welded pipe that tabulated value is already S×E, so no separate joint factor is applied) and no weld strength reduction factor; the Building & HVAC line runs it with E = W = 1.0. ASME B31.9-2025 ¶904.1.1 — B31.9's own equation is t_m = P·D/(2·S·E) + A with no y or W term; the paragraph permits the B31.1 equations as an alternative, which is the form the Building & HVAC line runs.