Research On Simulation And Measurement Method Of Pipeline Defects Based On Far-field Eddy Current Theory

Oil casing is a steel pipe used to support oil well,which is the basis of normal transportation of oil and plays an indispensable role in oil production.Under the influence of various complex environments,oil casings are prone to corrosion damage,which affects oil production and transportation,resulting in economic losses.Therefore,it is of great significance to detect and evaluate the oil casing in time for the safety of oil production.Based on the theory of eddy current testing,in this thesis a multi frequency and far-field eddy current testing method is introduced by combining the multi frequency and far-field eddy current testing technology.According to the characteristics of the detection signal,several phase difference detection methods are compared and analyzed,and digital phase sensitive detection method is selected to detect phase difference.At the same time,the detection model is designed according to the detection principle,and the detection model is simulated by the simulation software COMSOL to simulate the pipeline detection environment.According to the characteristics of eddy current testing,the eddy current testing and measuring method is designed.According to the characteristics of the testing signal,the problem of signal data correction is analyzed,and the air correction processing flow of the testing signal is proposed.Through the analysis of the actual measurement environment,the noise signal is mixed with the simulation signal,the median filter,wavelet de-noising,morphological filtering and other methods are selected for simulation,and the filtering effect is analyzed to restore the simulation signal.According to the requirements of the detection process,the problem of the main and pseudo signals in the detection signal is proposed,and a blind source separation model based on the detection signal is established.A non negative matrix decomposition method is used to solve the problem of the separation of the main peak signal from the pseudo one.The detection signals are separated by selecting reasonable constraints and verified by simulation experiments.In order to verify the accuracy of the measurement method and simulation design,the signal excitation circuit and the signal receiving circuit are designed as the experimental circuit,and the DSP + FPGA structure is selected as the signal acquisition and calculation module.At the end of the thesis,the experimental conditions of the experimental device in the laboratory conditions have been measured,which verify the reliability and accuracy of the experimental device.And according to the detection signal measurement method proposed in the thesis,the detection data is processed to get the situation of the measurement pipeline.By comparing with the standard information,the accuracy of the measurement method is verified.