Short answer
A commercial gas tightness test proves that installation pipework holds pressure within a permitted leak rate. The sequence is: calculate installation volume, choose the standard (UP/1 or UP/1A), select a gauge, carry out a let-by test of the isolation valve, raise to tightness test pressure, allow stabilisation, then monitor for the calculated test duration and compare any drop against the permitted value.
1. Preparation
Identify every section, appliance and valve. Calculate the installation volume including the meter, pipework and fittings. Decide the maximum permitted leak rate based on whether pipework passes through inadequately ventilated or occupied spaces. Confirm the MOP and the tightness test pressure required.
2. Let-by test
Before pressurising, the ECV or upstream isolation valve is checked for let-by: the section is vented to a low pressure, the valve closed, and the gauge watched for a rise. A passing valve gives false confidence in the test and must be dealt with first.
3. Pressurise and stabilise
Raise the pressure to the tightness test pressure using gas or air as appropriate, then allow the stabilisation period so temperature effects settle. Large or exposed installations need longer stabilisation, and the test should not be run while the building's heating is swinging pipework temperatures.
4. Test period and result
Monitor for the calculated or tabulated test duration. If the pressure drop is within the permitted limit and there is no smell of gas, the installation passes. Any drop above the limit means a leak must be located with leak detection fluid or an electronic detector, repaired and the test repeated.
5. Record it
Record the volume, gauge, pressures, durations and result on a test certificate such as a CP16 before the installation is purged and put into service.
Figures are typical for UK natural gas. The current edition of the relevant IGEM standard and the manufacturer's instructions always take precedence on site.
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