Pipeline pressure test is the last process of pipeline construction engineering. It is not only a comprehensive inspection of pipeline construction quality, material performance and pipeline integrity, but also an inspection and guarantee of whether the pipeline system can operate safely without fault under the design operating pressure. Therefore, great attention should be paid to the pressure test.
The purpose of the pressure test of the main pipeline is to eliminate the hidden dangers and defects of the pipeline, obtain a greater degree of safety and ensure the safety of the pipeline in operation. There are generally two types of pressure test methods for long-distance pipeline: air pressure and water pressure. Water pressure can be divided into fresh water pressure test and sea water pressure test due to different pressure test media.
Using water as pressure test medium has the following advantages: low cost; Although water is compressible in theory, the effect of compression on hydrostatic test can be ignored; Water is not toxic; Water is not flammable; The emission problem is also small; The pressure of water on the pipe wall is uniform; When the pipeline breaks, the water pressure will be released quickly, which can reduce the damage to the environment; For most areas, water intake is also more convenient, and has been increasingly used as a main means of pressure test of long-distance pipeline.
Pressure test process of pipeline
The pipeline pressure test process mainly includes: water injection in the pipe, strength pressure test, tightness pressure test, pressure relief and drainage. The above processes are introduced below.
Pressure test steps: fill water and check whether the air in the exhaust pipe is drained; Conduct strength test after boosting; Conduct tightness test for pressure stabilization; Pressure relief for a period of time; Drain water after passing the hydrostatic test; If the natural gas pipeline is subject to hydrostatic test, it shall be dried after drainage.
Before water supply for pipeline hydrostatic test, the water quality of water source shall be tested and analyzed to confirm that the water for pressure test is clean and the PH value is neutral, which has no harmful impact on the pipeline. The cleanliness of the pipeline has a great impact on the pre commissioning, construction and operation of the pipeline. If there is a large amount of sediment deposition after the pressure test of the pipeline, it will increase the water pushing pressure, and seriously cause the phenomenon of ball passing and pipe blocking. It is very difficult and dangerous to deal with, especially if there are a large number of dust particles during the operation of the gas pipeline, it will cause damage to pipe fittings and valves, And different substances in the water will affect the corrosion of the pipeline:
After the pipeline is filled with water, start the pressure test pump to boost the pressure and conduct the strength pressure test of the pipeline. As long as the pressure at one end of the pipe section reaches the predetermined pressure, the pressure rise will be stopped. The strength test pressure in China is 1.25 times of the operating pressure, and the operating pressure shall be implemented in accordance with the relevant provisions in China’s specifications. If the strength is stabilized for 4 hours and the pressure drop is not greater than 1%, it is qualified.
The tightness pressure test shall be conducted after the strength stabilization is qualified. During the tightness test, slowly open the relief valve to reduce the pressure to the test pressure value. The same as the strength pressure test, the pressure relief shall be stopped as long as the pressure at one end of the pipe section reaches the predetermined pressure. The tightness test is qualified if the pressure is stabilized for 24 hours and the pressure drop is less than 1%.
After the pressure test is completed, the pressure of the pipeline shall be removed through the pressure relief valve, and the water in the pipeline shall be discharged by using the original water feeding pig in the pipeline and the air compressor. During drainage, the water can be discharged outside the pipeline, or the water can be discharged to the next pipeline as the water supply source of the next pipeline. This not only saves time and labor, but also saves limited water resources.
Source: China Chemical Pipelines Manufacturer – Yaang Pipe Industry Co., Limited (www.yaang.com)