Simulation And Experimental Verification Of Small Diameter Pipe Internal Detection Based On Pulsed Eddy Current Technology

Oil-gas pipe is the artery of energy transmission,timely detection and disposal of pipe defects is of great significance for maintaining routine operation of pipe and reducing casualties and economic losses caused by pipe leakage.This thesis studies the detection of defects in the inner wall of small diameter oil-gas pipe based on pulsed eddy current technology,makes theoretical analysis,simulation and experimental research.Firstly,the method of quantitative detection of defects is explored based on the theory of pulsed eddy current detection.On this basis,the internal defects of pulsed eddy current detection model is established by using finite element method and the related regulation of pulsed eddy current detection is concluded by detailed simulation analysis on the factors affecting the precision of pulsed eddy current detection.At the same time,the design of pulsed eddy current detection system is carried out by using experimental method,including detection probe,data acquisition module and data display and storage module design.Establish the experimental system platform,on which the detection experiment of artificial defects in a pipe section is carried out.By collecting and analyzing experimental data,the quantitative detection of artificial defects is realized and thus verify the feasibility of the pulsed eddy current detection system.The following conclusions are obtained through finite element simulation and experiment.(1)Compared with the non-defective condition,the distribution of eddy current and magnetic field in the test piece are obviously changed.And the defect quantitative information can be obtained by collecting and analyzing the change of the magnetic field.(2)The quantitative information of the length and width of the artificial defect can be obtained by separating the three-dimensional magnetic field information and detecting the magnetic component along the length and width direction of the defect.This method has high detection accuracy and meets the precision requirement of defect length and width detection.(3)The depth of the defect can be qualitatively obtained by judging the decline of the displacement-detection signal curve along the defect length direction.The change of the defect width has an effect on the detection of defect depth,and the quantitative information of defect depth can be acquired based on the curve or surface fitting of the defect depth signal measured under different defect width.This method can meet the precision requirement of defect depth detection when the sample size is sufficient and the influence of defect width is fully considered.(4)Pulsed eddy current detection has a skin effect,and the sensitivity of the defect detection decreases with the increases of the defect depth.When the defect depth reaches or exceeds a certain threshold,the detection signal no longer changes.(5)Within a certain range,it is good for the detection to select excitation signal with higher amplitude and lower frequency,detection components with higher sensitivity and probe with smaller size.Conversely,increasing probe lift-off height,probe vibration and detection speed change is unfavorable for defect detection.These factors should be taken into consideration in pulsed eddy current detection system design.The research of this thesis provides a reference for improving the defect detection method of small diameter oil-gas pipe inner wall and improving the defect quantitative detection precision.And it has good theoretical significance and engineering application value.