Introduction:
The current method, which is approved by different polymer research institutes and standards, is suggested to the consumers of polyethylene pipes to ensure the health of the piping system.
The general purpose of this test:
Ensuring the correctness of the work, the appropriateness of the pipe, valves, accessories and the size of the equipment used, and as a result, all the parts of the line bear the necessary pressure, against the design pressure, and no water leakage in excess of its allowed amount.
Points to consider before starting work:
1- Pipes and fittings and line equipment should be checked before installation and if any visible defects are observed, their installation should be prevented.
2- All welds must be completely cold before starting the test. Also, all mechanical connections must be fully mounted and all their accessories, including washers, must be installed and tightly closed.
3- If concrete restraints are used, it should be allowed to complete the curing of the concrete and obtain the necessary strength to withstand the axial forces.
4- The best fluid used for hydrostatic test is water. The use of gas or air is allowed only in situations where liquid fluids such as water cannot be used due to the special conditions of the pipe design. During the hydrostatic test of the pipeline, gas or air condenses and stores energy. In such a situation, if the pipe bursts, both the tension energy of the pipeline and the compression energy of the gas will be released, which is very dangerous (there is a possibility of serious damage to the test equipment and operators). For this reason, the pipe must be completely vented when using water. Also, if there is no proper ventilation of the pipe, due to condensation of the air, the pressure inside the pipe will increase and pressure stabilization will be a problem. In some cases, it has been observed that during the test, despite the system being water-tight and applying the appropriate time to achieve isothermal and initial expansion of the pipe, the test pressure had a large drop due to air leakage.
5- The device used to provide water pressure (pump or any other device) should be provided with a suitable capacity so that it can provide pressure again at the right time when the system is under pressure.
6- In order to estimate the amount of water needed, first of all, the internal volume of the pipeline under test should be calculated:
V=πri2
where ri is the inner radius of the pipe and l is the length of the pipeline under test. Then about 40% should be added to this amount (due to pipe expansion, possible leakage or retesting).
7- All expandable connections must be completely restrained or temporarily removed from the system during the test.
8- Clean water must be used to fill the system for the test. This water must be clear, odorless and free of any suspended matter visible to the naked eye
9- Pipeline test pressure in standard conditions (Cº 20) for pipelines or working pressure up to 10 atmospheres, 1 to 1/5 times the working pressure (depending on the opinion of the consulting engineer and the pipeline designer) and for pipelines with a working pressure of more than From 10 atmospheres, the working pressure is +5 atmospheres.
10- The length of the pipe under test in small diameter pipes is about 800 meters (according to the publication 303 of the Vice President of Strategic Planning and Supervision) and in pipes with a higher diameter, it is recommended to be less than the above value. The length of parts and accessories should be such that the minimum pressure at the highest point of the pipeline is 1/1 times the working pressure.
11- Before conducting the hydrostatic test, a preliminary earthing of at least 30 cm must be done on the crown of the pipe. The connection of the pipes to each other and the location of the accessories should be open and visible.
12- Filling the pipeline should start slowly and from the downstream point.
13- After filling the line and ensuring that the pipes are saturated and all the air in the production line is evacuated, the test begins.
14- A calibrated pressure gauge with an accuracy of 0.1 bar (one meter of water column) should be installed on the cover of the beginning of the pipe at the lowest point. The test pressure is always a combination of the pump pressure and the pressure resulting from the water height difference (head) inside the pipe (for every 10 meters the pressure height difference increases by about 1 bar). For this reason, the pressure gauge should be installed at the beginning of the pipe at the lowest point that has the highest pressure.
15 – No executive operation is allowed in the trench during the test period.
16- Whenever, during the hydraulic pressure test, defects appear and are observed in the line and accessories, the operation must be stopped and the water must be drained and restarted until working conditions are provided in the desired location or locations. Testing is allowed after fixing the fault.
17- If the temperature of polyethylene pipe is more than 30 degrees, it should not be subjected to hydrostatic test.
18- The following figure shows an example of the different components of the hydrostatic test of the pipeline:
