Study On Micro-leakage Acoustic Emission Detection Of Launch Vehicle Pipe Connections

Carrier rocket assembly pipeline system connection(including pipe joints and flange connection interface)for air tightness detection is a very important part in the rocket assembly process,and there are often leakages at the pipeline connection due to assembly problems.At present,the method used in the inspection of the airtightness of the final assembly pipeline is the "soap bubble method",and this method has a long time and is prone to misjudgment and missed judgment due to environmental and human visual effects during the manual brushing of soapy water.In order to solve the problem of the traditional "soap bubble method",the research aims to improve the efficiency of the new equipment for testing the airtightness at the joint of the launch vehicle assembly pipeline and provide a new testing process.Based on the above-mentioned problems,this article,with the support of the National Defense Basic Scientific Research Program and the sub-project(XXX pipeline gas tightness detection technology and equipment development)project,takes the launch vehicle pipeline connection(pipe joint and flange connection)as the research object.The construction of the experimental platform,the selection and design of various parts of the equipment hardware,the laboratory experimental analysis and research,and the rocket assembly on-site experimental analysis and research carried out research in several aspects:(1)Experimental design and research of pipeline micro-leakage acoustic emission detection system.In order to complete the identification of the on-site rocket pipeline for leaks,the leak diagnosis mechanism of the pipe joint/flange connection pipeline should be explored first.Carry out experimental research on the pipeline micro-leakage experimental platform(calibration and leak detection platform)built in the laboratory,determine the unit and calibration method of the leak,compare and analyze the time domain and frequency domain phenomena of the pipeline micro-leakage acoustic emission signal under different leak rates,and extract The pipeline can be used as an indicator for micro-leakage diagnosis of pipelines at different leak rates,which in turn lays a theoretical foundation for the next field experiment of rocket assembly.(2)Research on hardware testing and implementation of pipeline micro-leakageacoustic emission detection system.In the early stage,the laboratory used commercial PAC equipment to detect the simulated leak conditions of the rocket pipeline,and determined the relationship between its different leak rates and leak signals.It was determined that the frequency domain of the fitted characteristic can be used as the core algorithm to determine the leak level.The larger the area of the fitted frequency domain is,the larger it is.On this basis,then select and design and manufacture sensors,amplifiers,single-chip and other components,such as selecting the sensor sensitive to the characteristic frequency band according to the measured characteristic signal,selecting the suitable single-chip module according to the sampling frequency domain,etc.,and performing hardware debugging To meet the performance requirements.(3)Laboratory phenomena and analysis of micro-leakage acoustic emission detection system.Firstly,an experimental analysis is made on the connecting pipeline of the launch vehicle tube joint.It is found that if the time-domain signal is characterized by the maximum amplitude or variance of the signal amplitude,different leakage levels can be distinguished,but it is easy to cause misjudgment due to the influence of environmental noise.Then,the signal is further subjected to fast Fourier transform,and after removing unnecessary spectrum,it is found through experiments that the area envelope of the frequency band of 50 KHz to 70 KHz has a high degree of anti-interference,feasibility and reliability for judging the leakage level.Finally,a simple analysis of the launch vehicle flange connection pipeline is carried out,which is consistent with the conclusion obtained by the pipe joint,but the frequency band is slightly shifted to 60 KHz to 70 KHz.Preliminary conclusions were obtained in the laboratory experiment,which laid the foundation for the laboratory research for the subsequent experimental research of the rocket assembly site.(4)On-site experimental phenomena and analysis of carrier rocket pipeline assembly.Using broadband sensors to study environmental noise detection,it is found that the complex environment in the factory has a great influence on the detection time domain of the special micro-leakage acoustic emission detection equipment,and there is only a peak of 5KHz at the beginning of the spectrum,and the subsequent frequency band It is a smooth curve.When there is leakage,it is found that there are two "wave packets" between 60 and 85 KHz.Although the environmental noise will affect the detection of the development board and cause the overall amplitude to increase,there is no "wave packet" in the frequency domain,and there is an obvious "wave packet" phenomenon in the characteristic frequency domain when the leak is detected..Therefore,if the "wave packet" is found based on 50 ~ 125 KHz,it can be well judged whether there is leakage.The research shows that this article aims to solve the actual problem of misjudgment and missed judgment of the "soap bubble method",which has practical significance for meeting the needs of the factory,and has reference significance for the inspection of the airtight performance of the total docking pipeline system of the launch vehicle of domestic aerospace enterprises.