Hydrotest Pressure Calculator

Units

Inputs

Applicable Code

Design Pressure

Allowable Stress at Test Temperature (ST)

From ASME Table A-1 at 38°C (100°F) ambient test temp.

Allowable Stress at Design Temperature (S)

From ASME Table A-1 at design temperature.

Class Location (B31.8)

Per B31.8 Table 841.3.2-1.

Result

Minimum hydrotest pressure

—barg

Stress ratio applied (ST/S)

—

Formula used

—

Formula & Code Reference

B31.3 (para. 345.4.2): P_test = 1.5 × P_design × min(ST/S, 6.5) B31.1 (para. 137.4.5): P_test = 1.5 × P_design × ST/S B31.4 (para. 437.4.1): P_test = 1.25 × P_design B31.8 (Table 841.3.2-1): P_test = (1.25 to 1.50) × P_design, class-dependent

ST / S values: from the applicable ASME B31.3 Table A-1 (or equivalent) for the pipe material. ST is evaluated at the test fluid temperature (usually 38°C / 100°F ambient). S is evaluated at the design temperature.

B31.3 cap on ST/S: if the ratio exceeds 6.5 (extreme case, very high design temperature), the code caps the ratio at 6.5 to prevent over-pressurizing the system at ambient.

Practical note: this is the MINIMUM hydrotest pressure. Actual field test pressure is usually set slightly above (typically +5%) to account for gauge accuracy and to ensure the minimum is achieved throughout the hold period. Never below the code minimum.

Brownfield caution: on existing systems, the hydrotest must not exceed the yield strength of the weakest component (valves, flanges, fittings). Always check the test pressure against the component ratings before pressurizing.

⚠ For preliminary sizing only Results are based on nominal ASME dimensions and typical material densities. They do not account for manufacturing tolerances, coatings, supports, flanges, fittings, corrosion allowance, or actual site conditions. All final designs must be verified by a qualified engineer and validated against the applicable code edition. Piping Passion accepts no liability for decisions made using this tool.