| Pipeline transportation and road,railway,water transportation and shipping are also called the five major transportation industries.They are important transportation tools for energy and other materials.They are irreplaceable and widely used in the world.Pipes will be damaged during production,manufacturing,processing and installation.During service,under the combined effect of external conditions and internal defects,corrosion,aging and cracking will occur,causing the pipeline to fail,which will lead to explosions and cause personnel casualties,environmental pollution and huge economic losses.Cracks are the most serious type of pipe failure,and there are huge safety hazards,therefore,it is of great significance to use scientific and efficient detection methods to detect and detect defects in time to ensure the safety and stability of the pipeline during its service.Nowadays,the technologies commonly used for non-destructive testing of pipelines include ray,ultrasonic wave,magnetic powder,eddy current,etc.These technologies can realize the detection of pipelines to a certain extent,but the above detection technology has higher requirements on operators and detected objects.The inspection cycle is long and costly.It is difficult to apply to a wide range of inspections with complex working conditions and harsh long-distance pipelines.As a dynamic on-line monitoring method,acoustic emission has high sensitivity to defect activities,has few requirements for the object to be inspected,and is easy to operate.It can provide real-time and continuous defect information for the pipeline,which is favored in engineering practice.In this paper,the corrosion location of pipelines and the attenuation of acoustic emission signals were studied under outdoor experimental conditions.The main research work is:(1)The characteristics of common non-destructive testing technology and the advantages and disadvantages of acoustic emission detection technology are analyzed.The formation mechanism,type and propagation characteristics of acoustic emission signals are analyzed.Acoustic emission signal processing and analysis techniques are studied.Time difference positioning method is used for sound.The attenuation of the transmitted signal and the study of the cracking of the simulated pipeline were carried out.(2)The guided wave theory in the pipeline and the spectral characteristics of the crack acoustic emission signal are analyzed.Through the numerical analysis of the guided wave model of the hollow cylindrical shell structure,the group phase velocity dispersion curves of the modal guided waves in the experimental pipeline are obtained.The theoretical wave velocity as a positioning study.(3)According to the mechanism of acoustic emission signal attenuation,according to the different structures of the pipeline,the energy and amplitude attenuation changes of acoustic emission signals through different structures of the pipeline are studied,and the attenuation between different structural pipelines and acoustic emission signals is obtained.Relationship,the adjacent sensor amplitude of the broken lead point has 10 dB attenuation,and the attenuation is about 14 dB without 1200 mm distance of the pipeline structure;the acoustic emission signal has 30 dB attenuation through the flange structure amplitude,and the sound source signal distance from the flange is more Nearly,the attenuation is larger;the attenuation of structure 1 and 3 is 7dB,and structure 2 has almost no effect;after the acoustic emission signal passes through the complicated structure of the pipeline,the amplitude will rise slightly in the normal region.(4)The Nielsen-Hsu lead-cut method was used to simulate the generation of crack signals in the pipeline,and the location of the pipeline crack signal was studied experimentally.The actual wave velocity of the sound source signal is measured by the time difference method,and compared with the positioning result under the theoretical wave velocity condition.Combined with the waveform diagram,power spectrum and correlation analysis method,the acoustic emission under different wave velocity,threshold value and pipeline structure conditions The positioning accuracy is analyzed,the linear fitting correlation coefficient is extracted,the positioning situation is evaluated,and the causes of leakage positioning and pseudo-positioning are analyzed.The factors affecting the positioning accuracy are also proposed,The positioning study has achieved good results. |
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