Can ACFM detect transverse cracks?
Summary Yes, ACFM can detect transverse cracks. Detail The directional nature of the induced current in ACFM means that it will not flow across a crack that runs transverse to the scan direction. In practice an upward going butterfly is often obtained from a transverse defect (due to flux leakage effects), however because this cannot be relied on, and only occurs in ferritic steel, the procedure contains an instruction to make a scan with the probe rotated 90 degrees, in order to detect transverse defects. Once detected, such cracks are sized by scanning the probe along the crack. Detection and sizing of transverse defects is made quicker and simpler with use of an array probe which contains two energising fields at right angles to each other, so that defects in any orientation are detected in one pass.
