In order to ensure the safety of the West-East Gas Pipeline during the pressure test, a pressure test scheme using water as the medium is adopted throughout the line. However, there are problems such as large pipe diameter, complicated terrain along the route, large fluctuations, lack of pressure test water source, and limited equipment capacity. Fill the tested pressure pipe section with water through the water injection equipment and reach the condition of pressure increase. During the water injection process, the water injection pressure, water injection volume, ambient temperature, surface temperature, pipe wall temperature and inlet water temperature should be accurately recorded.
At the same time of pressure test and water supply, preparation should be made for drainage, that is, when water is supplied, two pigs are sent at the first end pressure test head to push the end to the end pressure test head for water drainage. First inject the flushing water into the 300m pipe in front of the first water injection pig, and then turn to inject water behind the first water injection pig, when the first water injection pig is pushed out of the test head by water, and at 300m After injecting water into the pipeline, continue to inject water immediately after the second water injection pig, and push the two pigs to the end until the injection of the pressure test pipe section is completed. During the pressure test of the pipeline, no air should enter. Once air enters the pipeline, cavitation will be formed, which will bring great danger to the pressure test and increase the difficulty of sweeping water after the pressure test.
After reaching the highest test pressure and stabilizing, the strength of the pressure test tube section begins to stabilize for 4 hours. If the pressure loss from the beginning of the test exceeds 2% of the minimum test pressure specified in the test pipe section, the test section will add water back to the original test pressure. After stabilizing for 4h, there must be a pressure stabilization period of 1h, otherwise the pressure test period should be extended until the 1h stabilization period occurs. When determining the change in test pressure, the relationship between temperature and pressure changes must be considered. If the strength test is maintained at the specified minimum test pressure for 4 hours without cracking, significant pressure drop, or increased water volume due to temperature loss, the strength test can be accepted. After the strength test is passed, the pressure at the highest elevation point of the pressure test pipe section is reduced to the tightness test pressure of 10.5MPa (the lowest).
When the tightness test is over, the pressure test section can be discharged to the state before the pressure increase. Special care should be taken during the entire pressure relief process. The drain valve should be opened and closed slowly to relieve pressure at a certain rate to prevent vibration and damage to the assembled pipeline caused by water hammer loads.
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