Research On Acoustic Detection Method Of Liquid-filled Pipeline Damage

There are lots of underground pipelines in heating system of northern China.Alone with the flow inside pipe which rises both temperature and pressure,the corrosive effect of melt snow and snow-melting agent make pipes easier to damage.Once a leak occurs,it will cause economic loss and affect daily life of residents at the same time.Therefore,a reliable measure method in detecting liquid filled pipeline damage is needed urgently.The thesis draws on the acoustic detection methods of gas-filled pipelines(such as natural gas pipelines),and uses sound reflection method and acoustic impedance method to carry out simulation and experimental research on damage detection methods of liquid-filled pipelines.Among them,the acoustic impedance method includes two detection methods of continuous standing wave and pulse traveling wave,in the experimental test of the acoustic impedance method,a measurement method using a combined vector hydrophone is proposed,and the sound pressure and mass point of a point in the pipeline are measured Vibration velocity value,and then calculate the acoustic impedance value.Aiming at the acoustic reflection detection method of liquid-filled pipeline damage,the paper first studied the characteristics of the reflected echo under two different damage conditions of the pipeline with holes and blockages,and compared it with the research results of the inflatable pipeline.The results show that: The characteristics of the reflected echo caused by the holes and plugging damage of the liquid-filled pipeline are basically consistent with the research results of the gas-filled pipeline,which proves the feasibility of using the acoustic reflection method to detect the damage of the liquid-filled pipeline;at the same time,the COMSOL acoustic simulation software is used for the pipeline structure(sealing cover plate and round hole damage)may cause the detection of distortion in the liquid-filled pipeline.The simulation results provide reliable reference data for frequency band selection for experimental research.in air,the measured frequency band is 1.25 k Hz to 3.15 k Hz;In water,the frequency band suitable for reflection method measurement is 2k Hz to 5k Hz.Aiming at the method of detecting the acoustic impedance of liquid-filled pipeline damage,based on the study of underwater acoustic standing wave tube and underwater acoustic traveling wave management theory,the COMSOL acoustic simulation software is used to simulate the sound field distribution characteristics in the water-filled pipeline.The method of measuring the acoustic impedance in the pipeline by the vector hydrophone is analyzed.The experimental results show that: First,both the standing wave tube method and the pulse traveling wave method can identify and locate the hole damage and plugging damage in the liquid-filled pipeline according to the change in the acoustic impedance value,and the change rule of the impedance in the two detection results is consistent;The vector hydrophone can obtain the acoustic impedance value at a certain point in the pipeline very well;finally,the best detection frequency for the experiment of the acoustic impedance method for the damage of the liquid-filled pipeline used in the experiment is 3.15 k Hz and 4k Hz.