MEC/Mechanical/TBT-MEC-003

Pressure Testing Safety

MEICA Works › Mechanical › Pressure Testing Safety

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Pressure testing verifies the integrity of pipework, vessels, and systems by applying pressures above normal operating conditions.
Hydrostatic testing uses water as the test medium — it is preferred because water is nearly incompressible and stores less energy.
Pneumatic testing uses air or nitrogen and is far more dangerous because compressed gas stores enormous explosive energy.
A joint, fitting, or component failing under test pressure releases the medium with potentially lethal force.
Exclusion zones must be established around all equipment under test — no person may enter the zone during pressurisation.
The test pressure, hold duration, and acceptance criteria must follow the approved test specification exactly.
All test equipment including pumps, gauges, hoses, and safety valves must be rated for the test pressure being applied.
End caps, blank flanges, and thrust blocks must be designed to resist the test pressure without displacement or failure.
Pressure must be raised gradually in stages, with hold points to check for leaks before proceeding to the next increment.
A competent person must supervise every pressure test, controlling the process and making all pass/fail decisions.

Explosive failure	A fitting failing under pneumatic test pressure releases energy equivalent to an explosion — exclusion zones are non-negotiable.
Hydrostatic preferred	Water stores far less energy than gas at the same pressure — hydrostatic testing is always safer when the system allows it.
Gradual pressurisation	Applying full pressure in one step can cause sudden catastrophic failure — staged pressure build-up catches leaks early.

Don't

Use hydrostatic testing in preference to pneumatic testing wherever the system allows.
Establish exclusion zones around all equipment before applying any test pressure.
Follow the approved test specification for pressure, duration, and acceptance criteria.
Ensure all test equipment is rated for the maximum test pressure being applied.
Verify end caps, flanges, and thrust blocks are designed for the test pressure load.
Raise pressure gradually in stages with hold points to check for leaks at each step.
Ensure a competent person supervises the test and controls the pressurisation process.
Record all test data including pressures, times, temperatures, and pass/fail results.
Vent pressure safely through designated relief points after the test is complete.
Brief all nearby workers on the exclusion zones and the test schedule before starting.

DON'T use pneumatic testing when hydrostatic testing is feasible and permitted.
DON'T allow anyone within the exclusion zone while the system is under test pressure.
DON'T deviate from the approved test specification for pressure or duration.
DON'T use hoses, gauges, or pumps rated below the maximum test pressure.
DON'T rely on temporary end caps that are not designed for the test pressure load.
DON'T apply full test pressure in a single step — increase gradually with leak checks.
DON'T carry out a pressure test without a competent person supervising the process.
DON'T accept a test result without documented records of all parameters.
DON'T release test pressure suddenly — vent gradually through controlled relief points.
DON'T enter the exclusion zone until pressure is fully released and the system is depressurised.

See also: Pipe Fitting and Flange Safety | Hydrostatic Pressure Testing

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