Can ACFM detect cracks which extend the full width across a plate?
Summary Yes, ACFM can detect cracks which extend the full width across a plate. Detail The usual (and most reliable) method for confirming the presence of a defect is to obtain a complete loop in the butterfly plot, which requires scanning a probe along the complete defect, including passing over both ends. For cracks that run up to an edge, this procedure is modified, so that only half a loop is expected. Obviously, if the defect runs completely across a plate, or full circumference around a pipe, there will be no defect end signals in Bz, and, if the defect is of uniform depth, there will be little change in Bx signal. In order to detect such defects, the inspection procedure requires a scan across the expected line of the defect. If a defect is present, a sharp dip in the Bx signal will be seen. This transverse scan provides the Bx background and minimum values for sizing purposes. In practice, long fatigue defects, especially at weld toes, normally consist of several cracks which h
