Testing and Commissioning of PVC Pressure Pipes
Pre-Test Precautions
Pressure testing is a potentially dangerous operation and all hazards should be addressed, including the establishment of exclusion zones where necessary.
Solvent Cement Jointed pipelines shall not be pressure tested until at least 24 hours after the last joint has been made.
Pipelines should be bedded and backfilled, but with the joints left uncovered for inspection before and after testing if possible.
All thrust supports for fittings and valves must be finished and the concrete properly cured (the minimum time is seven days). Blank ends installed temporarily should be adequately supported to take the pressure thrust.
Pressure Testing
The pipeline may be tested as a whole or in sections, depending on the diameter and length of the pipe, the spacing between sectioning valves or blank ends and the availability of water.
Fill the pipeline with water, taking care to purge all free air from the pipeline or section being tested. Allow the temperature to stabilise. Pressurise the system. Selection of field test pressures is related to the system operating conditions. A maximum test pressure of 1.25 times the system design pressure, measured at the lowest point in the system, is specified although the test pressure should not exceed 1.25 times the PN of the lowest rated component in the system. Additional water will be required to bring the line up to pressure because the pipe expands slightly.
AS/NZS 2032 recommends that the pressurised pipe should be allowed to stand for a minimum period of 15 minutes without make up pressure. Where the joints are available for inspection, and there is no evidence of leaks after 15 minutes, the pipeline is deemed to have passed the test.
Where joints are not accessible, measure the amount of water required to re-pressurise the section. Where the make-up water does not exceed the allowance in the equation below, the pipeline is deemed to have passed the test. The make-up water is not a leakage allowance. It is normal for a pressure drop to occur as the remaining air goes into solution and some further expansion of the pipe occurs.
Q =0.14 LDH
where:
This simple test above should suffice if the pipe is well supported by soil. If, however, the allowable make up water level is exceeded, it does not necessarily mean that the pipeline has a leak. Viscoelastic creep of the pipe can give result in a drop in pressure even if there is no leak, particularly for higher strain pipes such as PVC-M and PVC-O if the soil compaction levels are not high. In this situation, further testing will be required to verify the leak tightness of the test section. This testing is based on the known relationship between creep strain and time.
Re-pressurise the pipe and maintain the pressure for 5 hours by successively pumping in sufficient water at the same temperature (±3°C) as the water in the pipeline. Measure and record the volume (V1) of water required between the second and third hour. Measure and record the volume (V2) of water required between the fourth and fifth hour. The pipeline is deemed to have passed the test if the following equation is satisfied:
V2 =0.55 V1 + Q
Where Q is the allowable make-up water calculated above
It should be borne in mind that static pressure testing does not necessarily simulate pressures developed under operating conditions, and in order to obtain adequate testing of all parts of the line it may be desirable to divide it into sections.
Flushing and Disinfection
Where Vinidex PVC pipes are used for potable water applications, standard flushing and disinfection procedures must be carried out. Local authority requirements should be followed.