The Composite Defect Quantitative Identification Based On Transient Response Characteristic Signal Of Pipeline Magnetic Flux Leakage Testing

Pipeline magnetic flux leakage testing technology is applied widely inindustrial field, however, common used technology based on magnetic leakagetesting cannot figure out the type of defect. They only focus on singleness defectusing quantitative reorganization, and also have low level accurate quantizationand poor regularity. So it is complicated to generate completed accurate testingconclusion，therefore it is faulty and inaccurate to consider it as the evaluateevidence of pipeline’s defect.This paper first introduces the research background of Magnetic FluxLeakage technique, expatiated the principle and features of Magnetic FluxLeakage technique and its advantages over other NDT techniques. This paperdemonstrated the feasibility of setting up a2-D Magnetic Flux Leakage detectingsystem, and builds up a2-D Magnetic Flux Leakage NDT system. Based onabove problems, this thesis discusses a recognition method of transient responsecharacteristic signal quantitative, which can accurately distinguish the defectivetype and degree. This article analysis the feature of defect firstly, then foundthree types of singleness defect which are: Pit Detect, Hole Detect, Line ChartDetect and complex detect mixed singleness detect. Transient finite elementmethod which simulates the single damage of varied types of inside and outsideof the tube wall, and based on the analysis of more than50kinds of situationsfound that the quantization of peak value of the magnetic flux leakage’s curvesand the time span can consider as the transient response characteristic signal toidentify the varied categories of injuries and sizes with highly accuracy;considering that most of the pipeline damage formation are composite defects,we simulate three common types of superimposed injuries which are axial superposition of pit type damage, the radial superposition of longitudinal crackand the hole shape damage, the radial superposition of hole shape damage andtheir combination groups in different position and size.The result shows that: the information of curves and the time span which weget from the magnetic flux leakage testing technology can consider as thetransient response characteristic signal, which have the direct correspondingorder with the defective type and degree; we can restore the actual situation ofcomplex damage according to the different features of signal curve, achieve theautomatic identification of defects; at the same time, it can calculate the distancebetween the superimposed damage and other information and evaluate theintensive degree of damage.