Hydrotest & Pressure Testing

Q: Which standards or codes apply?

ASME B31.3 Chapter VI (leak testing), ASME PCC-2 (pressure testing), ASME VIII (vessels), and project pneumatic-test safety procedures.

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Quick pick (TL;DR)

Default to a hydrostatic test at 1.5 × design pressure (ASME B31.3), adjusted by the St/S temperature ratio.
Use clean water; for stainless keep chlorides < ~50 ppm.
Hold ≥ 30 min and accept on no leakage / no permanent deformation.
Pneumatic testing (1.1 × design) only where water is impractical — it stores huge energy, so it needs a stored-energy calc and an exclusion zone.
Isolate PSVs, instruments and rotating equipment, and protect the system with a calibrated relief during the test.

Step 1 — Hydrostatic vs pneumatic

	Hydrostatic	Pneumatic
Test pressure	1.5 × design	1.1 × design
Stored energy	Low	Very high
Use when	Default	Water impractical

Step 2 — Worked test pressure

CS line, design 20 barg

ASME B31.3 hydrostatic Pt = 1.5 × P_design × (St / S) Given P_design = 20 barg St / S ≈ 1.0 (test at ambient) Step 1 — Test pressure Pt = 1.5 × 20 × 1.0 = 30 barg Step 2 — Hold & accept hold ≥ 30 min at 30 barg accept: no leakage, no permanent deformation Answer → hydrostatic 30 barg, 30 min, water

1.5× proves margin; St/S corrects for temperature; verify the lowest-rated component can take it.

Step 3 — Safety & precautions

Isolate PSVs, instruments, rotating equipment.
Calibrated relief & gauge.
Pneumatic: stored-energy calc & exclusion zone.
Vent/drain; low-chloride water for SS.

Test pressure calculator (B31.3)

Hydrostatic / pneumatic test pressure

Hydrostatic Pt = 1.5 × design × (St/S); pneumatic = 1.1 × design.

Design pressure (barg)

Test medium

St/S ratio

St/S ≈ 1 at ambient. Verify flanges & lowest-rated component take Pt.

Common mistakes

Leaving low-rated items in line.
High-chloride water on stainless.
Pneumatic without energy assessment.

Requisition & datasheet

System, design P/T, medium.
Test pressure, hold, acceptance, relief.

Frequently asked questions

What should I know about Hydrotest & Pressure Testing?

Default to a hydrostatic test at 1.5 × design pressure (ASME B31.3), adjusted by the St/S temperature ratio. Use clean water; for stainless keep chlorides < ~50 ppm. Hold ≥ 30 min and accept on no leakage / no permanent deformation. Pneumatic testing (1.1 × design) only where water is impractical — it stores huge energy, so it needs a stored-energy calc and an exclusion zone. Isolate PSVs, instruments and rotating equipment, and protect the system with a calibrated relief during the test.

Which standards or codes apply?