Research On Pipeline Defect Detection Method Based On Coded Ultrasonic And Source Identification Technology

Traditional ultrasonic detection methods for pipeline defects generally use pulse excitation to generate ultrasonic waves.This ultrasonic wave generation method has the characteristics of simple excitation circuit and easy implement,but there are also limitations on the average emission sound power,and it is necessary to ensure the emission by increasing the excitation voltage,which is not conducive to signal source excitation in multi-sensor applications.At the same time,the ultrasonic frequency band generated by this method is single,which is not conducive to the advantages of ultrasonic frequency variation in the study of the sensitivity of different types of defects.In the case of an ultrasonic array detection where there is a large number of incidents,the lack of information on the source of the transmitted sensor results in insufficient utilization of the echo information,which restricts the acquisition of more abundant defect echo information.Therefore,this thesis uses binary coded FM signal to excite ultrasonic sensors to realize the detection of pipeline defects,and realizes the source identification of the sensor by pulse frequency discrimination of the echo signal,so that the echo signal has the identity identification characteristics.Based on the analysis of the principle,characteristics and applications of the existing coded ultrasonic signals,the thesis adopts a binary coded ultrasonic excitation scheme.The characteristics of the time-frequency distribution of binary coded ultrasonic is analyzed,and the mathematical model of the response of binary coded ultrasonic is established.First,the response characteristics of the coded ultrasonic,the requirements of the sensor performance parameters,and the factors affecting the response performance were studied through simulation.The FPGA-based hardware code generation circuit and the coded excitation boost circuit were designed to realize the generation of coded signals,power amplification and excitation of ultrasonic transducers,which further validated the simulation results.Finally,the pipeline defect internal detection method and the test system builded were used to test the artificial standard defects.The detection characteristics of coded ultrasonic for defects were analyzed.According to the principle of pulse frequency identification,the main parameters affecting the effect of source identification are analyzed.A binary coded ultrasonic response identification circuit is designed.The circuit is applied to pipeline defect detection and the source identification is realized.The actual inspection of the defect in the pipeline sample shows that under the premise of increasing the average emission sound power of the excitation signal,the method enriches the defect echo information,expands the detection band diversity,and identifies the signal source of the reflected echo.It has certain reference value for the follow-up development and application of coded ultrasonic detection technology in pipeline defect arrays.The main research contents of the dissertation are as follows:(1)On the basis of analyzing the advantages and disadvantages of the existing coded ultrasonic excitation methods and their applicable occasions,a binary code generation and excitation method suitable for pipeline defect detection is proposed.(2)The time-frequency characteristics of binary coded ultrasonic are studied,and the mathematical model of binary coded ultrasonic response is established.The response characteristics and influencing factors are studied.(3)Based on the analysis of the characteristics and applicable occasions of the existing ultrasonic signal source identification method,a pulse identification frequency identification method of ultrasonic echo signal suitable for binary coded excitation scheme was adopted,and the main effect factors of echo signal identification was analyzed.(4)The FPGA binary coded ultrasonic pipe defect detection system based on EP4CE6F17C8 is designed,which mainly includes EP4CE6F17C8 code generation circuit,HV7350K6 and MAX4940 excitation boost circuit,LM7171 amplification filter circuit and SN74LS123 identification circuit.(5)A binary coded ultrasonic pipeline flaw detection system was designed and tested.By comparison with a conventional pulse excitation method on the experimental platform constructed,following defects were detected: a flat bottom inner hole with a diameter of 2mm and a depth of 3.6mm;a flat bottom inner hole with a diameter of 4mm and a depth of 3.6mm;a horizontal inner crack of 10 mm,width 1mm,depth 1.8mm;a longitudinal inner crack of 10 mm,width 1mm,depth 1.8mm.The detection rate of 2 to 4 bit code with a statistical sample number of 128 in angle incidence,at an average noise level of 9.2 dB,was 87.5%,93.8%,and 96.9%,respectively.(6)The feasibility and influencing factors of the signal source identification method are analyzed through simulation experiments.The self-made source echo identification circuit is used to identify the pipeline echo signal,and the sources identification rate of 2 to 4 bit code with a statistical sample number of 96 in angle incident was 95.8%,94.8%,and 93.8%,respectively.