DN-15d - MP/LP Mains (Pneumatic pressure) testing

Title Page

Tools and equipment

Calibrated, certificated test standpipes
Electronic test equipment
Pressure testing warning signs (MP mains)
Pipe anchorage systems. (Refer to SGN/WI/DIS/4.2.2 - Anchorage systems operating up to 7bar – operatives)
Air compressor 80cfm-100cfm, foot pumps

Installation of standpipes &pressure gauges

Standpipes and gauges must be connected in accordance with Figure 95 in (SGN/WI/ML/2) and the following
must be carried out:
Standpipes must be located at all extremities of the new main and incorporate a relief valve set to lift at a pressure 10% above the specified test pressure
Pressure test instruments must be installed so that they can be read and operated without entering the trench or standing in line with the end of the main
Pipe systems under test must be restrained against movement. For all fused systems, it is sufficient to backfill the pipe under test
Test standpipes must all be of welded construction, have a current test certificate and be tested for soundness immediately prior to testing the pipeline or main
Warning notices must be prominently displayed to warn that pressure testing being carried out

Suitable test instruments are bourdon test gauges for LP mains or electronic testers for both LP and MP mains. The following must be checked before pressurising the main:
As determined by the Operation Manager an NRO/RO procedure must be authorised and all safety precautions carried out prior to the test commencing
- Yes
- No
- N/A
To minimise the effect of temperature variation; the main under test should be backfilled as much as possible and If the effects of temperature are to be taken into account this will be detailed in the NRO/RO procedure
Both LP and MP mains must be maintained at 350mbar air pressure, post testing, if purging and commissioning is delayed
All fittings must be approved for use
Test the pressure relief values on the standpipes to ensure that they are set to operate at 10% above the test pressure
All values must be tested in the open position and sealed with a blank flange
As applicable the Operation Manager or Operative must brief all team members on the test process prior to and during the test period
Use approved electronic test instruments that provide absolute pressure readings

The Operation Manager will specify the pressure test requirements that will be required and will provide a NRO/RO procedure. The following factors must be taken into account:
Noise levels whilst pressure testing is to be kept to a minimum
- Yes
- No
- N/A
If a hydrostatic test is deemed necessary, then this must be undertaken in accordance with Section G3, (SGN/WI/ML/2)
Creep occurring in PE pipe must be accurately accounted for
Where creep allowances are to be applied to PE mains tests, it is important that the exact conditioning time is established by recording the time of commencing pressurisation and the time at which the first test reading is taken. Conditioning time includes the effects of the 2-hour stabilisation period. The Operational Manager will determine the conditioning time

A Competent Operative must be in attendance at the pressurising point during the pressurisation period to ensure that the necessary safety requirements are met
No person must enter the designated test area or interfere with the pipe work whilst the pressure is being raised
A single or twin tool compressor (80 cfm to 100 cfm) with an inline fitter or foot pump is adequate for pressurising the majority of pipe systems
- Yes
- No
- N/A
Examine flexible pipes, hoses and their connections prior to use to ensure they are fit for their intended purpose. They must be secured and anchored by a secondary restraining device, (whip check) to prevent movement as a precaution in the event of failure
Air must be introduced under controlled conditions into the main until the appropriate test pressure is reached
The time of commencing pressurisation must be recorded on the test certificate
Do not over pressurise the main

Before the start of the test period, the temperature of the air in the main must be allowed to stabilise before the test period commenced
For metallic mains and low-pressure PE mains, this will normally occur within 2 hours, and will be indicated by a stable pressure reading
For Medium Pressure PE mains, the effects of creep must be taken into account and the conditioning time allowed as specified by the Operation Manager
All exposed mechanical joints must be tested for leakage upon initial pressurisation with an approved leak detection fluid
Following the period of the temperature stabilisation, the initial pressure reading must be taken. For PE mains at MP (where the effect of creep is being taken into account) the first test readings must be taken at the end of the conditioning time period
A further pressure reading must be taken at the end of the test period
Where a long duration pressure test period (i.e. over 24 hours) is to be undertaken, the Operational Manager may specify intermediate pressure readings; so, that the test may be assessed and aborted at an early stage if there is an indication that the test will ultimately fail
The Operative or Operational Manager responsible for the pressure test must completer the test certificate
The Operative responsible for the pressure test must be in attendance at the end of the test to witness de-pressurisation and this must be recorded on the test certificate

The test pressure should be reduced before carrying out an examination of the pipe work
All exposed connections plugs and external fittings must be re-examined for possible leakages by leak detection fluid
Care must be taken to undertake any repairs with the appropriate tools without applying excessive force
Where no obvious cause can be attributed to a pressure test failure and the test conditions have not altered, the Operation Manager can decide to extend the test, using the final or an intermediate test reading as the main starting point for the new period. However, if the mains pressure has been reduced then the main must be re-pressurised to the test pressure and test procedure carried out as above. In the case of pressure tests on MP PE mains, the revised creep allowance must be established following calculation of the new conditioning time.
Where an MP PE main is to be retested following de-pressurisation, it must remain at atmospheric pressure for a minimum of three hours before re-pressurisation, to allow creep from the original test to relax. The creep allowance for the retest can then be obtained from the appropriate table
Where a test failed, further investigations using tracing techniques or sectioning of the main as detailed by the Operational Manager can be carried out

The air must be released by opening the vents on the pressure test standpipes or vent pipe situated on the extremities of the main until atmospheric pressure within the main is achieved. This ensures that the entire system under test has been included in the test
Due to the noise of the venting air, ear protection may be required
Measures must be taken to minimise noise generated during de-pressurising and its impact of the public
The Competent Operative must confirm, by checking the gauges installed at the extremities, that the pressure within the whole of the main has been reduced to atmospheric
The Competent Operative responsible for the pressure test must record this information on the test certificate before authorising further construction work to proceed