Analysis of MFL Model for Sucker Rod Defects and Its MFL Signal Processing

Abstract Magnetic flux leakage (MFL) testing is a nondestructive testing technique widely used in the petroleum industry and pipeline transportation. In this article, the double-coil magnetization method was used to analyze and solve the MFL model of a sucker rod defect, and the collected MFL signals were processed and analyzed. The model of the sucker rod defect was established using the magnetic dipole model, and the leakage magnetic field intensity in the tangential and normal directions above the defect was solved. Then, the influences of the defect width, defect depth, and lift-off value on the leakage magnetic field were obtained. The magnetic field gradients of the MFL signals were deduced and discussed, and the trend of the magnetic field gradients in different directions were obtained. The cubic spline interpolation method (CSIM) was introduced and was applied to the interpolation of MFL data. Finally, the MFL testing platform of the sucker rod defect was constructed, and the collected MFL data were denoised by the wavelet filtering (WF) method; subsequently, the magnetic gradients of the MFL signals were analyzed. The experimental result shows that the continuous MFL signals can be achieved by using the CSIM, and the WF not only maintains the characteristic information of the effective signals but also has a good denoising effect and makes the signals smooth. Simultaneously, the result also indicates that the magnetic field gradients are good tools for analyzing the MFL signals, which reflect the characteristic information of the defect.