A simulation study for locating defects in tubes using the weak MFL signal based on the multi-channel correlation technique

This paper proposes a method for the axial and circumferential locating of defects in coiled tubing during magnetic flux leakage (MFL) testing. Based on the correlation features of the MFL signals, this method firstly calculates the correlation operation value among signals of different channels and then uses the correlation coefficient waveform characteristics to identify the axial and circumferential information of defects. An analysis of the FEM simulation data shows that the proposed method can reduce the minimum threshold value for detecting defects, improve the signal-to-noise ratio of MFL testing and enhance the anti-interference ability of the detection system. It can serve as an auxiliary to a customary amplitude detection method. Helmholtz coils were used as magnetisation equipment in the research. The most appropriate magnetisation value and lift-off distance value were discussed with the aid of the finite element simulation method.