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PRESSURE TESTING
On reaching test pressure, and satisfying the condition for minimal air entrapment, the pipeline should be isolated and the pressure allowed to decay. The pressure loading time (t¹) to achieve test pressure is used as a reference. The natural pressure decay readings at predetermined times (multiples of t¹) are recorded. A correction of t¹ is then used to calculate ratios (N), the values of which indicated either the soundness of the main or the presence of an unacceptable leak.
As the pressure decay is of exponential form the use of logarithms is necessary when comparing readings but the use of a pocket calculator is all that is required for 'on site' calculations.
PE pipes should be tested in reasonable lengths appropriate to the pipe diameter and the prevailing site conditions. Pipelines longer than 1000 metres may require testing in sections. The pipeline should not be subjected to any pressure, via filling from the mains supply or from standing heads, as this may affect the result. Polyethylene pipelines must not be pressure tested unless the wall temperature is kept below 30°C; this includes open trench situations. To enable a precise analysis of the pressure test data, pressure transducers with a logging process facility and display should be used.
The detailed procedure is found here PRESSURE TESTING PROCEDURE
Note: this represents a slight modification of the procedure detailed in the first printing of the WRc Manual for Polyethylene Pipe Systems for Water Supply - 1986.
PIPELINE COMMISSIONING
1. Clean and/or swab the pipeline
2. Fill and sterelise
3. Flush and/or neutralise
4. Refill
5. Take sample for bacteria
6. Receive certification - no bacteria!
7. Commission main
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