RESEARCH ON LEAK TEST FOR LONG DISTANCE GAS PIPELINE

The main purpose of pre-service leak test is to prove the tightness of the pipeline system. It plays an important role to guarantee the safety operating of pipeline. However, the duration of leak test is different in different countries. If the duration of tightness test is longer, the tightness level can be sufficiently detected, which is benefit for pipeline safe operating, but the cost and the time of project must be extended; if the duration of tightness test is shorter, the defect of pipeline can not be fully exposed, which may be left hidden trouble for pipeline safe operating. Meanwhile, the tightness test may be influenced by many factors, for example the test medium, pipeline capacity, pressure, ambient temperature variation, leak detection methods, and so on. Therefore, it is unreasonable to leak test with same duration for different kinds of gas pipeline, which regulated in some standards, for example GSA Z662-11, BS EN1594:2000, ISO 13623:2008, GB 50251-2003, and so on. At the same time, those standards all regulated that the duration of tightness test should be properly extended while the pipeline capacity and ambient temperature variation obviously affect the accuracy of leak test, but the definite value is not regulated. In addition, they also regulated that the pressure increases or decreases during leak test shall be acceptable provided that it can be demonstrated through calculations that the pressure change is caused by ambient temperature variations, but there is no explicit calculation method. Now, the specified duration of leak test in different standards are all based on the engineering experience. Because there is no rational theory way, it makes the identification and modification of the duration for different kinds of pipeline become blind. Based on the theory of fluid mechanics, material mechanics, elastic mechanics, a mathematical model about the duration of leak test for long distance gas pipeline is developed for the first time. The influences of the test medium, pipeline capacity, pressure, ambient temperature variation and other factors which may impact the duration of leak test are synthetically considered in the model. The experimental verification shows that the result calculated by the model is accurate. It can provide reliable theoretical guidance for determining reasonable leak test duration for long distance gas pipeline.