Enter the design pressure and the allowable stress at both the design and test temperatures, then press Calculate. At an ambient hydrotest the S_T/S ratio ≈ 1, giving the familiar 1.5 × design pressure.
Hydrostatic: P_T = 1.5·P·(Sₜ/S)
Pneumatic: P_T = 1.1·P
σ_test = P_T·D/(2t)
Engineering tips
- Temperature correction: S_T/S > 1 when the design temperature is high (lower S); the code caps the ratio at 6.5.
- Pneumatic risk: stored energy is far higher than hydrostatic — para 345.5 requires extra precautions; prefer water.
- Yield check: the optional Barlow hoop-stress check flags a test pressure above 90% of SMYS.
Recommended values
- Hydrostatic: P_T = 1.5 × design × (S_T/S); the usual first choice.
- Pneumatic: 1.1 × design — use only where hydro is impractical (stored energy is hazardous).
- Hold time: ≥ 10 min at pressure, then reduce and examine at the design (or lower) pressure.
- Gauge full-scale: 1.5–4 × test pressure so the reading sits mid-dial.
- Test temperature: Keep metal ≥ MDMT + margin to avoid brittle fracture during the test.
Limitations
- Screening only: Does not check flange/valve rating limits, support capacity for water weight, or high-point venting of trapped air.
- Pneumatic risk: Stored energy demands a formal risk assessment and exclusion zone — the radius shown is indicative only.
About the standards
- ASME B31.3: Process Piping.