Hydrostatic / Pneumatic Leak Test Pressure Calculator (ASME B31.3) — Sample Report

1 · Design inputs

Design pressure 300 psi; allowable stress 20,000 psi at ambient test temperature and 17,500 psi at design temperature; B31.3 factors.

2 · Method

P_hydro = 1.5 · P · (S_T / S)   (S_T/S limited only if you enter a specification cap — Eq. (24) itself sets none)

P_pneumatic = 1.1 · P (not to exceed 1.33·P, nor 90% of the ¶345.2.1(a) pressure, per ¶345.5.4)

where S_T is the allowable stress at test (ambient) temperature and S the allowable stress at design temperature. The logic of Eq. (24) is that a test performed cold must demonstrate a stress condition at least proportionate to the design-temperature condition: when the design temperature is high enough to depress S, the ratio S_T/S exceeds 1.0 and the test pressure rises above the bare 1.5×P. The calculator computes the ratio and, only if you enter a cap, applies it — a ceiling some owner specifications impose on top of the Code (6.5 is a common figure); leave the field blank and the calculator reports the bare Eq. (24) minimum, since the current Code itself sets no ceiling on the ratio, its own limits being the ¶345.2.1(a) yield and component-rating ceilings. A cap that actually engages is flagged in the result, because the capped number under-tests against the Code minimum unless a real specification requires it. The pneumatic alternative is bounded the other way, by ¶345.5.4: not less than 1.1×P and not more than the lesser of 1.33×P or 90% of the ¶345.2.1(a) pressure — the calculator warns if the entered pneumatic factor exceeds 1.33× but cannot evaluate the second, component-rating-dependent limit. The 1.5 hydro factor, 1.1 pneumatic factor and the optional cap are all inputs rather than constants, so the same engine serves B31.3, B31.1 (¶137.4.5: a flat 1.5× multiple with no S_T/S term at all — B31.1's own card on the Power Piping page hides those fields rather than faking a ratio of 1.0 through them), and company standards with stricter factors. Both allowables come from you; the card does no table lookups. The worked example shows the mechanics at moderate scale — a ratio of 1.14286 lifts a 300 psi design to a 514.3 psi hydro target, uncapped — and the same arithmetic runs uncapped well past that, into the range the ¶345.2.1(a) ceiling exists for.

3 · Calculation

1. Stress ratio: S_T/S = 20,000 / 17,500 = 1.14286 (no cap entered — this example leaves the ratio uncapped, matching Eq. (24) as written).
2. Hydro test: 1.5 · 300 · 1.14286 = 514.3 psi.
3. Pneumatic alternative: 1.1 · 300 = 330 psi.

4 · Results COMPUTED

5 · Verification statement

The result values above are locked as fixture leak-test-pressure.json, case “P=300, ST/S=20000/17500, B31.3 factors, uncapped”, tolerance 0.001, 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 — ¶345.4.2 Eq. (24) hydrostatic test; ¶345.5.4 pneumatic test. · ASME B31.1, Power Piping — ¶137.4.5 (same card with factor 1.5 and ratio 1.0).