Study On Leak Detection For Gas-liquid Pipeline On Basis Of Pressure Signal

In management of two-phase pipelines,it is guarantee of safely operation to timely detect the occurrence and location of leakage on the pipe.But by now there is not yet a mature technology of leak detection especially for multiphase pipes,so there is a pressing need for a real-time and effective detection method to ensure the security operation of multiphase pipelines.Therefore,it is of great significance to analyze the leak characteristic and determine a detection method suitable for multiphase pipes.In this paper,theoretical research,numerical simulation,experimental research and programming process are all used to study the characteristic and detection method of leaking on multiphase pipelines.And the main research contents and results are as follows:(1)Analyze the difficulties of detecting the leak for gas-liquid pipelines,and the main difficulties are unstable flowing state,influence of leakage parameters on leaking rules,large pressure fluctuation and poor accuracy of multiphase flow meter.(2)To analyze the transient process of leakage,establish a mathematical model of leakage system for gas-liquid pipelines and analyze the leak characteristics and solve the model by implicit difference method.The leakage numerical solution of gas-liquid two-phase flow is calculated by C++ programming.The solution shows that pressure,liquid,velocity of gas and liquid down the pipe all drop as the leakage occurs.And the numerical results are in good agreement with the experimental data.(3)Take use of multiphase software to analyze the influence of leaking size,location and gas-liquid ratio on leakage;pressure,which changes regularly and is easy to be monitored,is put forwarded as the indicating parameter for leak detection.And then get the fitting formula of leakage parameter according to the simulation results.(4)Calculation method of pressure velocity and identification method of singular points of pressure signals are key points for location principle on basis of pressure.The formulas for calculating the velocity of stratified flow are derived and analyzed.Based on the formulas of pressure wave velocity,location formula and hydraulic characteristic equation,a cyclic iteration method for leak location is proposed.Recognize the dropping point of pressure with the use of Modulus Maxima method in Wavelet Transform technology.Take SYM4 as the wavelet basis and the leak point will be clearly identified at the seventh floor of decomposition.(5)Multiple experiments are carried out on water-gas circuit to collect data of flow rate and pressure.Pipe diameter,flow rate,circumferential position is changed to obtain various experimental conditions on pipes with diameter of DN50 and DN80 and the main flow pattern is stratified flow.Results show that transient operation such as changing flow rate,starting or stopping the pump and compressor will not result to the same changing regulation as leak does,so that there will be little misinformation caused by these transient actions.(6)Combine SPRT and pressure-based technology to process the experimental results and to recognize the weak leak under a strong background pressure noise.Use Labview to filter the pressure signal and judge the occurrence of leak by programming,and use the program to figure out the influence of background noise and leakage parameters on detection judgment.