Experimental Study On Leak Detection And Location For Gas Pipeline Based On Acoustic Method

With the development of economy, the natural gas is in great demand and as the main means for long distance transmission of natural gas, a lot of natural gas pipelines are being built in our country. However, it is hard to avoid pipeline leaking because of corrosion of pipeline, damages from nature or people, and self-default of pipeline. It can not only lead to huge economic losses, but also bring significant environmental pollution. Thus, as the pipeline leak detection and location is a main mean to ensure the safe operation of pipeline, it is important to study it. And acoustic method has been proven to be the most effective, true real-time, on-line leak detection method, providing the quick leak detection, high sensitivity, precise leak location accuracy, and low false alarm rate.A data acquisition system for acoustic method is designed in this paper. And with the help of the high-pressure leak detection test loop of gas pipeline, experiments under different leak location, leak apertures and operation pressure based on acoustic method have been done. The acoustic signals gathered by sensors are processed by a de-noising method using wavelet transform. And the method to choose wavelet functions, decomposition scales, threshold selection rules and threshold functions is made to determine the parameters of wavelet transform. This paper extracts the characteristics of acoustic signal by using analysis of time-domain and frequency-domain of signal. In addition, the location errors are studied by the formula of acoustic velocity and cross-correlation method, and then pipeline hydraulic parameters under different conditions and the characteristic of acoustic signals are analyzed.The study on the pipeline leak detection and location has showed that:①The acoustic signal is nonstationary stochastic signal, which can be processed by a de-noising approach using wavelet transform;②Parameters of de-nosing using wavelet transform are: wavelet is sym8, the decomposition scale is 5, threshold selection rule is rigrsure, threshold function is quadratic formula and noise is the white noise;③The energy of acoustic signals concentrate on the low frequency band and decrease with the frequency increasing;④The acoustic velocity increases regularly with the operation pressure or temperature of pipeline increases; ⑤The minimum leak flow rate detected in the tests can reach to 7.58L/min, 3% of the total gas flow rate, each characteristic of acoustic signal can be detected without false alarm. And the maximum location error can reach to 1.623m, 0.814% of the whole test pipeline;⑥When a leak occurs, the flow rates of upstream increase while the flow rates of downstream decrease, and the pressures of upstream and downstream decrease. At the same time, the acoustic signal will generate a big falling quickly with a leak, and then would go back to zero around quickly;⑦Pipeline hydraulic parameters and the characteristic of acoustic signals changed with the leak points, leak apertures and operation pressure.