P.E.S Technical Instruction

General Considerations

Hydraulic tests (internal pressure test) should be performed prior to operation to ensure sealing of the piping system. The internal pressure test was carried out according to DVGW W400-2. This procedure has replaced DIN 4279 standard. The internal pressure test should be performed by skilled staff. The experimenter should have comprehensive information on the piping system, measurement and safety issues.

 

Safety

Entry to the pipe trench under the test is prohibited. All pressure gages should be calibrated before the internal pressure test. The pressure gages should be connected under supervision of skilled staff according to relevant procedures. The pipeline under the test should be fully controlled during the

 

Preparation

Safety equipment coverage: the pipe surface should be covered to prevent temperature variations during the test if necessary. Although only connection points, for example welding points or fittings, are kept uncovered, they should be protected from direct sunlight.

 

Effect of temperature

The effect of temperature should be minimized using the above-mentioned procedure. The temperature of the pipe surface should not exceed 20 ̊C during the test. In particular, the temperatures of the pipe wall should be almost equal at the start and end of the final test.

 

Pipeline filling

The whole pipeline or some sections are placed under internal pressure test. The pipe sections should be properly divided to reach the test pressure at downstream. The minimum pressure at upstream should reach 1.1 times the pressure calculated for MDS system.

The length of pipeline under the test may reach up to 3 km considering pipe diameter and piping location. The water volume needed for the test and its discharge after the test should also be taken into account. The lack of any additional material inside the pipe should be ensured prior to the test.

The pipeline should be de-aerated prior to the test. To this end, the pipe is slowly filled with water by opening de-aerators from the lowest level to remove air from de-aerators.

Water velocity should not be too high. A filling velocity of 1 m/s is recommended.

The pipeline can be filled immediately or even one day before the test. No pressure is applied on the pipe at this stage. If the pipeline is filled before the test, it should be left intact for 1 h before starting the test.

 

Test method

The test is carried out in three stages:

• Initial test or saturation
• Pressure drop test
• Final step

 

Test equipment

A pressure gage with a precision of ≥0.1 bar should be used. For testing pressures up to 15 bar, a pressure gage with a measurement range of 0 to 20 bar should be employed. Thermometers and thermocouples with a precision of ≥0.1 K should be used to measure the surface temperature.

 

Initial test

Initial test can be started at least one hour before filling the pipeline. After filling, both ends under the test should be closed. The pressure should be increased to STP pressure limit within 10 min. STP pressure limit equals:

• STP = MDP x 1.5

or

• STP = MDP + 5 bar

 

where MDP is the pressure calculated for the pipeline. For selecting the test pressure, the smallest one from the above formulas should be chosen. After reaching STP, the pressure should be kept constant by a pressure pump in the case of pressure drop within next 30 min. The operator should wait for one another hour for balancing viscoelastic variations in the pipe. A maximum pressure drop of 20% is acceptable within 1 hr. A larger pressure drop indicates likelihood of water leakage or impermissible variations in water temperature.

Final test

Despite establishment of a constant pressure within 1 h, the pipe is still expanding. To reach equilibrium and prevent expansion, the pressure is reduced in less than 2 min. In this way, the pressure of 10 bar and 16 bar pipes is respectively reduced to 2 and 3 bar in less than 2 min.

This pressure reduction causes contraction. Sealing or pipe leakage can be tested within the next 30 min.

After pressure reduction and at onset of 30 min final step, the pressure is gradually increased in the pipeline or remains constant. In the case of unreliable results, the test can be continued for another 1.5 h after the first 0.5 h.

 

End of test

In the case of pressure drop in the pipeline, the leakage should be found and eliminated. The test should be repeated several times to ensure sealing of the pipeline. If a pipeline is tested at certain intervals and all test results are positive, it is exposed to a nominal pressure for 2 h after launching the whole pipeline.

This should be repeated after any maintenance on the pipeline.

 

Documentation

After the end of test, all test steps should be carefully written and recorded in the report form.