A multi-frequency balanced electromagnetic field measurement for arbitrary angles of pipeline cracks with high sensitivity

Alternating current magnetic flux leakage (ACMFL) technology has been used for sizing pipeline cracks. However, traditional ACMFL methods are limited in sensitively identifying arbitrary angles of pipeline cracks due to the complexity of crack morphology. To solve the problem, a multi-frequency balanced electromagnetic field measurement (MF-BEFM) method is proposed. First, the distortion of the magnetic field and eddy current field caused by crack defects was studied. Then, the effects of the excitation frequency on balanced electromagnetic field measurement (BEFM) signals were considered to select optimal parameters. Next, the relationship between the BEFM signal and crack angle was studied. Finally, the MF-BEFM experiment was conducted to prove the superiority of the proposed method. The results show that the BEFM method cannot only overcome the deficiency of directional detection of ACMFL methods but it can also achieve high detection sensitivity for identifying arbitrary angles of cracks on the pipeline surface.