Estimate thin-wall pipe pressure from outside diameter, minimum wall and allowable stress, then check when ASME B31.3 Eq. 3a and Table A-1 apply.
Estimate the internal pressure a round pipe wall can carry from outside diameter, minimum wall thickness and allowable stress, then see the wall required for a target pressure. The Barlow result is a thin-wall screen; ASME B31.3 Eq. 3a, Table A-1 and project allowances still control the design.
Change the inputs to match the project. The result updates immediately and is not stored.
Use the minimum wall after mill tolerance and corrosion allowance. The allowable stress must come from the applicable code table for the design temperature.
Example only; verify the code table and design temperature.
Barlow: P = 2 S t / D. This is a thin-wall screen, not ASME B31.3 Eq. 3a.
Thin-wall pressure estimate
14.5MPa
2108 psi
D/t is below 20. The thin-wall Barlow assumption becomes less reliable; use a thick-wall calculation or the full code method.
Calculate pipe mass and scheduleUse the estimate to identify a feasible wall range. Then complete the design with the current code, the correct allowable stress and the project allowances.
Start with the minimum wall after mill tolerance and corrosion allowance. For a schedule check, subtract the permitted tolerance from the nominal wall before entering it.
Enter the allowable stress for the design temperature from the governing code table. The value changes with grade, product form and temperature; do not use a room-temperature tensile value as a substitute.
Recalculate with ASME B31.3 Eq. 3a, the weld joint factor, Y coefficient, corrosion allowance and the sustained and occasional load cases. Check external pressure, support loads and fatigue separately.
Barlow assumes the hoop stress is uniform through the wall. That is a reasonable screening assumption for thin walls, but it becomes less accurate as the wall becomes thick relative to the diameter. When D/t is below about 20, use a thick-wall formula or the full code method and check the additional stress components.
No. Barlow is a simplified thin-wall relationship, P = 2St/D. ASME B31.3 Eq. 3a uses t = PD / (2(SE + PY)) and adds the code allowable stress, weld joint factor, Y coefficient, corrosion allowance and mill tolerance. Use this calculator for early sizing only, then complete the B31.3 calculation with the current code edition and the project design conditions.
Enter the minimum wall expected after mill tolerance and any corrosion allowance. Using nominal wall overstates capacity. For stainless pipe, confirm the permitted tolerance in the ordered ASTM or ASME specification and subtract the allowance required by the project. The result is only as reliable as the wall and allowable stress entered.
Not directly. The allowable stress changes with temperature and must come from the applicable code table, such as ASME B31.3 Table A-1. Creep, thermal expansion, sustained and occasional loads, fatigue and external pressure also need separate checks. At elevated temperature, use the code allowable stress and complete the full B31.3 assessment rather than scaling the room-temperature Barlow result.
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