ASME B31.3 Pipe Wall Thickness Calculator — Sample Report

ProjectSample Project — Demonstration Only	Job No.SAMPLE-001	Client—
CalculationASME B31.3 Pipe Wall Thickness Calculator	Calc byPiping Toolset (calc-core)	Checked byUNCHECKED — sample
Date2026-10-12	Rev0	BasisASME B31.3 ¶304.1.2 Eq. (3a)

1 · Design inputs

NPS 6 (6.625 in OD) carbon-steel line at 2,000 psi design pressure. Allowable stress 20,000 psi, seamless (E = 1.0, W = 1.0), Y = 0.4, corrosion allowance 1/16 in, mill tolerance 12.5%.

Design pressure P	2,000	psi
Outside diameter D	6.625	in
Allowable stress S	20,000	psi
Quality factor E	1.0	—
Weld factor W	1.0	—
Coefficient Y	0.4	—
Allowance c	0.0625	in
Mill tolerance	12.5	%

2 · Method

B31.3 Eq. (3a) for straight pipe under internal pressure, thin-wall form:

t = P·D / ( 2 (S·E·W + P·Y) )

t_m = t + c

t_order = t_m / (1 − mill tolerance)

where P is the internal design gauge pressure, D the outside diameter, S the allowable stress at design temperature from Table A-1C, E the quality factor from Table A-3 (longitudinal weld joints; 1.00 for seamless) or Table A-2 (castings) — Tables A-1, A-1B and A-1A in editions through 2022 — W the weld joint strength reduction factor of ¶302.3.5(e) and Table 302.3.5-1, Y the wall-thickness coefficient from Table 304.1.1-1, and c the sum of the corrosion/erosion allowance and any mechanical allowances (threading, grooving). The calculator evaluates the three quantities in sequence. Eq. (3a) returns the metal required to resist pressure alone; adding c gives the minimum wall that must remain at the end of the corrosion life; dividing by (1 − mill tolerance) grosses that up to the nominal wall to purchase, because seamless pipe may be delivered up to 12.5% under nominal and the delivered minimum still has to cover t_m. It then checks the thin-wall validity condition t < D/6 and warns when a result leaves the range where Eq. (3a) applies.

3 · Calculation

Denominator: 2·(S·E·W + P·Y) = 2·(20,000·1.0·1.0 + 2,000·0.4) = 2·20,800 = 41,600 psi.
Pressure design thickness: t = P·D / 41,600 = 2,000·6.625 / 41,600 = 13,250 / 41,600 = 0.31851 in.
Minimum required: t_m = 0.31851 + 0.0625 = 0.38101 in.
Ordering thickness: 0.38101 / (1 − 0.125) = 0.38101 / 0.875 = 0.43544 in → Sch 80 (0.432 in nominal) FAILS: at the stated 12.5% mill under-tolerance its guaranteed minimum is only 0.432 × 0.875 = 0.378 in, short of t_m = 0.38101 in (¶304.1.1(a) requires the delivered minimum T ≥ t_m). Order the next heavier standard wall: NPS 6 Sch 120 (0.562 in nominal).

4 · Results COMPUTED

t — pressure design thickness	0.31851	in
tm — minimum required	0.38101	in
Ordering thickness	0.43544	in

5 · Verification statement

The result values above are locked as fixture b313-wall-thickness.json, case “NPS 6 @ 2000 psi, S=20000, Y=0.4, c=1/16, 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 B31.3, Process Piping — ¶304.1.2 Eq. (3a), pressure design of straight pipe. · ASME B31.3-2024 — Table A-1C (allowable stress S, the material lines listed on the source policy page), Table A-3 seamless pipe/tube row (Ej = 1.00), Tables 302.3.4-1 (Ej) and 302.3.3-1 (Ec), Table 302.3.5-1 (W), Table 304.1.1-1 (Y) — embedded and cited by table and line on the Pro pickers; typed from your governing edition otherwise. (Tables A-1 / A-1A / A-1B in editions through 2022.)

SAMPLE REPORT — auto-generated from a verification fixture to show the report format. Not a project calculation. ⚠ Engineering-aid tool. Public code equations; allowable-stress and factor data are user-supplied. Results MUST be independently verified and reviewed by a qualified/licensed engineer before any design, fabrication, or operation decision.