Alternating Current Field Measurement Probe for Coiled Tubing Inspection of Arbitrary Direction Defects

To reduce the serious accident caused by coiled tubing (CT) defects, the full axial defect detection of CT outer surface based on alternating current field measurement (ACFM) was studied. Combined with the advantages of traditional magnetic flux leakage (MFL) circumferential detection, the arbitrary direction defects detection problem of CT was realized. Currently, the study of the ACFM theoretical model only involves excitation in a single direction, and it is difficult for the probe to provide sufficient magnetic field information in an arbitrary direction for visual inversion of defects. In this work, the magnetic disturbance on the axial defects of CT is analyzed. The characteristic signals of defects recognition are extracted, and the excitation frequency, liftoff height, defects shape, defect depth, and defects cluster are analyzed. The optimal parameters of magnetic field characteristic signal distribution and defects detection on the CT surface are obtained. Finally, a new ACFM array probe is designed for CT 360° (full circumferential) axial defect detection. The results show that the method overcomes the limitation of the directional detection of the single detection technique. The designed ACFM probe can completely evaluate the 360° axial defects of CT.