Study On The Leakage Detection Theory And Experiment Research Of Gas Pipeline Network

Corrosion, aging, and damage from third-party may cause leaking accidents of gas pipelines, which will result in energy waste, environmental pollution and economic loss. Therefore, timely detecting the leakage accident, ascertaining the leakage location and estimating the leakage level are badly needed during gas pipelines are in operation. With the methodology combining experimental and theoretical research, toward straight and branch municipal gas pipelines, researches on detection and locating of leakage are done as following:Based on the fluid dynamics theory and the signal detection methods, a gas pipeline leakage detection test bench is built. On the bench, online monitoring and inspection can be achieved on the different leakage aperture of straight and branch gas pipelinesAccording to measurable parameters of straight pipelines, two kinds of boundary conditions, A and B, are induced, and method of leakage detection which are based on transient-flow mathematical model is given under the two boundary conditions. The different operating characteristics of straight pipeline leakage, valve adjustment and compressor adjustment is determined through the experiment. This makes the mathematical method more convenient in the application of practical leakage detection. For the problems of leakage in straight pipelines, improved stimulus-response locating method is proposed. The method is efficient for the condition that leakage aperture ratio is bigger than 4% of the pipe diameter. Furthermore, the problem that time of valve stimulus action is uncertain can be solved; as a result, locating precision is greatly improved. Precision is respectively improved by 0.75%, 1.9% and 3.15% on 4m, 7m and 10m leakage spot in pipeline. Level of wavelet entropy leakage of the leakage signal is analyzed on different aperture ratio, criteria of classifying the leakage level is put forward, and the leakage calculating method on different leakage level is determined.By establishing the mathematical model of branch pipeline flow and analyzing the operation characteristic, the solution is worked out that the complex branch pipeline can be decomposed into simple pipelines with inlet branches or distributary branches only. Through the simulation research of a branch pipeline with 2.5MPa operation pressure, conclusions are obtained as following: when the leakage aperture-diameter ratio is up to 3.3%,6.6% and 10% in the inlet branch, it will result in 285Pa,545Pa and 1014Pa pressure fluctuations respectively; when the leakage aperture-diameter ratio is up to 3.3%,6.6% and 10% in the distributary branch, it will result in 28.23Pa,112.94Pa and 254.11Pa pressure fluctuations respectively.Considering that the existence of branch node on branch-like pipeline will bring interference noise and white noise to the pressure signals, the signal mutation caused by the pressure jump of branch node is removed by the signal wavelet transform. The relationship between wavelet modulus maximum and leakage is analyzed, and the influence of the branch node on the wavelet modulus maximum is inspected. The minimum detectable aperture-diameter ratio is ascertained,which is equal to 6%. The wavelet function qualified to detection and locationg of branch-like pipeline leakage is put forth, and leakage detection and location on branch pipeline with inlet and distributary is determined according to the wavelet mutation position.Along with the development of municipal gas, the safe problem of pipeline operation becomes much more important. Research on the detection and location of municipal gas pipeline system not only ensures the security of gas supply system and reduces accident damage, but also enhances the security management of municipal gas supply system, prolongs the service time of the system, and improves its economic and social benefits.