What is the smallest defect detectable with ACFM?
Summary In general the smallest defect detectable with ACFM is in the range 2mm long by 0.3mm deep to 10mm long by 1mm deep. This depends on the material, the surface condition and the type of probe used. A better question to ask of all NDT techniques, though, is “What is the largest defect that can be missed?”. Detail ACFM was designed to reliably detect and size in-service defects with a low number of false calls. It was designed to work on rough or corroded surfaces, or through protective coatings. It was not designed to be an ultra-sensitive detection technique. All NDT techniques miss some defects. With an ideal technique, the probability of detection should increase with increasing defect depth. ACFM achieves this because unlike some techniques, the deeper a defect is, the larger the ACFM signal becomes. The results of extensive POD trials carried out over the years have demonstrated that ACFM can reliably detect surface-breaking cracks of 10mm long by 1mm deep at manual multi-pa
