Compared with the one-axis HD MFL detection technology, the three-axis HD MFL detection technology has a significant improvement in the identification ability of complex corrosion defects, axial grooves and long and narrow crack like defects. Because the MFL components in three directions can be collected at the same time, the defect type identification and dimensional accuracy quantization are improved. However, the technique still shows obvious limitations in identifying and quantifying the long and narrow defects in axial direction. Therefore, the research on circumferential excitation magnetic flux leakage detection technology began in the 1990s. Commercial grade circumferential excitation magnetic flux leakage testing equipment can detect the axial direction of pipeline narrow corrosion, cracks, mechanical damage and other axial groove defects.