Research on the influence of composite defects on quantitative pattern in MFL detection of tubing

Abstract

This paper decomposes the sorts of tubing defects into three types of single defect, namely pit-like, through-hole and strip-like defect, as well as compound defects formed by the superposition of the above three types of single defect. Then the 2D finite element method was used to model the tubing with different defect types, and the variation of MFL caused by the change of width, depth and other parameters of a single defect is simulated and analyzed, and the corresponding quantitative relationship curve and fitting formula are obtained. Then the superimposed defects and the compound defects of the same side and the opposite side were simulated to obtain the quantitative relationship curve between the magnetic flux leakage of the compound defects and the width, depth or distance between adjacent defects. Finally, Based on the comparative analysis of the influence pattern of compound defects and single defect, the quantitative pattern of MFL detection is summarized. Simulation results show that the variation of magnetic flux leakage between single defect and compound defects with different defect parameters is similar. The MFL detection signal of compound defects is also affected by the location relationship of adjacent defects and changes regularly. Based on this rule, and further combined with the study of transient field, more comprehensive and accurate defect parameters and the density of compound defects can be obtained, so as to better meet the high requirements of non-destructive evaluation.