AC-MFL testing of orthogonal cracks detection of square billet based on the flexible-printed parallel cable magnetizer.

Longitudinal and transverse cracks that appear in the manufacturing and processing of square steel billets are a critical safety hazard. An integrated alternating current magnetic flux leakage (ACMFL) detection probe is composed of parallel cables (PC) magnetizer and pick-up coils manufactured by flexible printed circuit (FPC). Experiments verified the probe could detect longitudinal and transverse cracks in a unidirectional scan. It was proven that when the probe scans the cracks parallel to the direction of the magnetic flux line, the signal at the end of the crack mainly originates from the local magnetic flux leakage (LMFL) field. With an increase in the frequency, the LMFL characteristics become more obvious. Experiments show that the probe can effectively detect longitudinal cracks with a width of 0.4 mm or more when the depth is 0.4 mm, and cracks with a depth of more than 0.3 mm when the width is 1.0 mm in the axial scanning. [Display omitted] • The content discussed in the paper is inspiring for the AC-MFL probe design. • The probe offers a new solution for the inspection of both the transverse and longitudinal defects of square steel billet. • The mechanisms of the AC-MFL method and the ACFM method for detecting cracks in different directions have been analyzed. [ABSTRACT FROM AUTHOR]