Research On Key Techniques Of Urban Underground Gas Pipeline Leak Mornitoring

As a kind of clean and efficient energy, Natural gas get more and more attention of the world. Flammable and explosive make the security of gas pipeline, which is the mainly transportation method, become much more important. With the adjustment of the energy source structure in China, urban underground gas pipeline is being developed. Campared to long-distance pipeline, the leak of urban gas pipeline is more dangerous. What's more, due to the low pressure, multi-branch and layed in complex urban noise and so on, the detection and location of the pipeline leak are very difficult.Generalized Acoustic Emission is a developing theory which is used to explain the stress wave caused by leak of the pipeline. In this theory, the leak signal is considered as continuous signal. Unlike negative pressure wave theory, continuity of the leak signal will not fail to detect the leakage signal just for not capturing negative wave in time. Higher-order statistics, as a new signal processing method, has much more superiority to the general method based on two-order statistic. This thesis integrated generalized acoustic emission with higher-order statistics, and applied them to the leak detection of urban underground gas pipeline. The main works of this thesis are:1)According to the National Criterion, thirty-six-meter-long pipeline was layed. Thirty-meter-long pipeline was straight.2) Generalized acoustic emission theory was used to illuminate the stress wave phenomenon caused by the leakage. After studied the intermediate and low pressure of the urban gas pipeline, the audio frequency leakage signal was choosed as the detection target.3)Base on the third- and forth- cumulant and bispectrum, which can distinguish Gaussian and Nongaussian , stationery and non-stationery of the signal, the urban surrounding noise properties were studied. Bispectrum was applied to analyse the Stationarity of some peculiarly circumstance noise in urban, including vehicle noise, construction noise and so on.4)Leakage signal, flow noise and instrument noise were sorted in Gaussian and non-gaussian signal. Three statistics based on HOS (higher-order-statistics) were involved in the thesis to implement detection and location the leak.5)On the hypothesis of statistical independency among the two leakage signal and noise, two-leak-point modal was presented. Forth order cumulant was used to estimate source number between the two leakage detection systems. Experimental results show that the correctness ratio attained 95%.6) From the two-leak-point model, equation group composed by auto and cross bispectrum were used to location the two leakage event. Bispectrum on the two lines of the ( ) plane were involved. Experimental results show that method was available.Abuntant experimental results show that bispectrum applied to the urban middle or low pressure pipeline lied in complex surrounding is available. At 0.005～0.2Mpa, this method can detect and locate leak in 30m. The absolute location errors are less than 1.5m.