ACFM combines the advantages of the alternating current potential drop (ACPD) technique and Eddy Current Testing (ECT) in terms of defect sizing without calibration and ability to work without electrical contact respectively. It is an electromagnetic technique suitable for detection and sizing of surface-breaking defects.

One of the characteristics of the technique which adds value to the inspection is that there is minimal or no particular surface preparation. Coating can be left intact and does not need removal or surface grinding. Depending on the probe type used several different inspection cases in terms of geometry and material type can be examined.

Special welding probes allow scanning over a weld producing data along the length of the weld utilizing the included encoder. The technique can also be used underwater with special underwater probes handled by a professional diver and the inspector working on the surface.

Testing is performed according to ASTM E2261. Characteristics of ACFM testing unclude:

• Applicable for base material or welds, ferritic or non-ferritic conductive metals
• Can be used on hot surfaces, underwater or in irradiated environments
• Accurate sizing of defects up to 25mm in depth
• Requires minimal surface preparation and can be applied over paint and other coatings
• Inspection data can be stored and further analyzed offline
• The inspection results can be encoded