PE Testing and Commissioning

PE Testing and Commissioning

Field pressure testing PE pipelines may require special consideration due to the creep response and stress relaxation of the material. When a PE pipe is sealed at test pressure, there may be a pressure decay, even in a leak free system due to the continued expansion of the pipe through the test period. See AS/NZS 2033 and AS/NZS 2566.2 for more information.

Pressure Installations

Pre-Test Precautions

Pressure testing is a potentially dangerous operation and all hazards should be addressed, including the establishment of exclusion zones where necessary.

Prior to testing, the entire PE pipeline should be checked to ensure all debris and construction materials are removed from contact with the pipes and fittings.

Where concrete anchor or thrust blocks are used no pressure testing should take place within 7 days of casting the blocks.

All mechanical ring seal joints must be restrained either by sand bags, or by partial backfilling of the line leaving the joints open for visual inspection. All valves must be placed in the open position, and a valve provided at the end of the line to allow air to be vented from the line during filling.

Where thermal fusion jointing has been used, no testing should take place until the joints have completely cooled to ambient temperature.

Local authority regulations may differ between each other in the pressure testing routines, and individual requirements must be followed at all times.

Pressure Testing

Test water should be slowly introduced into the PE pipeline until all air is purged from the line and water flows freely at the end of the line. The water should preferably be introduced into the pipeline at the lowest point to assist the removal of air.

It is essential that all air is removed from the line prior to commencing the test procedure. Entrapped air can result in erroneous pressure/time recordings.

Test sections may be either the complete line, or, in large installations, in sections such that the test section can be filled with water within 5 hours to allow pressure observations.

Pressure should be built up evenly in the line without pressure shock. Pressure should be monitored at the lowest point of the pipeline or at some other convenient point with the pressure adjusted to account for the elevation difference between the measurement point and the lowest point of the pipeline

Basic visual pressure test

A test pressure of 1.25 times the operating pressure (but not more than 1.25 times the MAOP of the lowest rated component of the system) should be applied to the pipeline or pipeline section. The test section should then be allowed to stand without make-up pressure.  It is preferable for all joints to be accessible for inspection. In this case, all joints should be visually inspected for evidence of weeping or leakage and if no leaks are detected after at least 15 minutes under pressure, the section is deemed to have passed the pressure test.

If the joints are not accessible, the apparent loss of water should be calculated from the following equation:

Q ≤ 0.14 LDH

where:

Q	= allowable volume of make-up water, L/h
D	= nominal diameter of the pipe, m
L	= length of the test section, km
H	= average test head over the section under test, m

The make-up water covers the effect of entrapped air being forced into solution and is not a leakage allowance. The make-up water required should reduce with time. Test should be conducted over a minimum of 2 hours. If the volume of make-up water is less than the allowable, the pipeline is deemed to have passed the test. If after 12 hours the make-up water exceeds the allowable limit, the test should be stopped, and the cause of the leak investigated.

General pressure test

The viscoelastic properties of PE are such that the introduction of test pressures will cause expansion in the line and require make up pressure to restore gauge readings. This method is based on a linear relationship between hoop strain and log time at constant pressure.

The maximum test pressure to be applied should be 1.25 times working pressure of the pipeline but not more than 1.25 times the MAOP of the lowest rated pipe or fitting in the system. Test pressure in excess of this value may strain the pipe material and damage control appliances connected to the pipeline.

The pipe section to be tested should be raised to the system test pressure, closed off and allowed to settle for at least 12 hours. The pressure will drop during this period as a result of pipe expansion.

At the conclusion of this rest period, the pressure should be restored and maintained at the system test pressure for 5 hours using water at the same temperature as that in the pipe under test.

Measure the volume of water required to keep the pressure constant between 2 hours and 3 hours after the test has started.

Measure the volume of water required to keep the pressure constant between 4 hours and 5 hours after the test has started.

After 5 hours the test should be concluded, and the following should be calculated:

• ΔV(3h-2h) – the volume of water added between the second and third hour
• ΔV(5h-4h) – the volume of water added between the fourth and fifth hour
• V_all = 0.14 LDH

where:

Vall	= allowable volume of make-up water, L/h
D	= nominal diameter of the pipe, m
L	= length of the test section, km
H	= average test head over the section under test, m

If ΔV(5h-4h) ≤ 0.55ΔV(3h-2h) + V_all , there is no visible leakage and no components have failed, the pipeline section is deemed to have passed the test.

Other test methods

Refer to AS/NZS 2566.2 for details of other acceptable methods for field testing PE pressure pipelines.

Non-Pressure Installations

Either water, air or vacuum testing may be performed on non-pressure PE pipelines, depending on the availability of test water, or the ability to drain the test water away from the pipeline alignment after the testing is completed.

Water Testing

All sections of the installation should be sealed off and water introduced through a stand pipe to provide a static head of 3 metres above the top point in the PE pipeline. All openings in the PE pipeline must be sealed, or plugged, before starting testing.

A riser pipe should be fitted at the top point in the pipeline to allow a minimum water head of 1 metre at this point and a maximum of 5 metres at the lowest point to be applied.

The test water should be introduced evenly into the pipeline and brought up to pressure after allowing all entrapped air to be purged out of the line.

The test pressure should be maintained for a minimum period of 15 minutes and all joints and connections should be inspected for leakage. Any defects detected should be repaired and the pipeline retested.

Air Testing

Where water is unavailable, or undesirable, for testing then air testing may be performed.

All openings must be sealed prior to testing, and air pumped slowly into the PE pipeline until a test pressure of 50KPa is reached.

This test pressure should be maintained for a minimum time of 3 minutes, and if no leaks are detected, or pressure loss observed on the gauge, the air supply control valve should be turned off and the test pressure held for a minimum time of 1 minute.

If the test gauge pressure reading has not fallen below 35KPa after this time, then the test should be discontinued.

Should the test pressure drop below 35KPa after 1 minute, then the pressure should be returned to 50KPa and maintained until a full inspection of the PE pipeline has been completed. All joints and connections need to be individually inspected for leakage using a solution of water and detergent poured over any suspect joint. If a leak is present, it will cause the detergent solution to bubble, and foam.

Vacuum testing

All openings must be sealed prior to testing.

An initial vacuum pressure of approximately 27 kPa should be applied and then the vacuum line closed off and the pipe allowed to stabilise for at least 3 minutes. The gauge pressure should be allowed to drop to 23.6kPa and then time recording should be started. The pipeline is deemed to have passed the test if the test vacuum loss is ≤ 7kPa over the period of time specified in the table below.