Can ACFM work through metallic coatings, scale or rust?
Summary Yes, ACFM will work through metallic coatings, scale and rust. Detail ACFM generally has no problem working through rust, surface oxides or other low conductivity layers. The technique also works through thin uniform metal coatings such as zinc galvanising, even if the crack does not penetrate the coating. However, some problems can occur with non-uniform metal coatings such as manually applied flame-sprayed aluminium. Such coatings can produce strong background variations in the signals due to overlapping coats and differences in thickness which can mask signals from any defects present. In such cases, it is advisable to inspect coated areas away from any anticipated cracks to determine the nature of the background variations (if any). The background variations are typically fairly constant over a wide area, so localised signals from a defect can be picked out by comparing adjacent scans (recommend using an array probe for this).
