Sizing of cracks using the alternating current field measurement technique

Recently a new technique for the detection and sizing of cracks and defects has been introduced in Australia. The alternating current field measurement (ACFM) technique is an electromagnetic inspection method that uses hand-held probes, and computerised control, data acquisition and computational models. ACFM is more efficient than conventional inspection methods (e.g. UT, MT, RT) due to a reduced need for surface preparation and an ability to work through surface coatings. ACFM also has an added benefit that it is not only capable of detecting flaws, it can also size defects for length and depth. This paper presents three case studies where ACFM has been used to size defects. In each case cracking has been detected in routine inspection, but to enable recommendations whether to run, repair or replace the component, better data on defect size was required. Results from the work suggest that ACFM can be an extremely useful method to determine flaw size, but that a knowledge of the limitations of the technique must also be well understood