The alternating current field measurement (ACFM) technique has been developed to provide reliable crack detection and depth sizing without the need to remove paint and coatings. In addition because there is no need for paint removal and repainting, the need for expensive scaffolding can often be avoided and instead the technique can be deployed using much more cost effective rope access methods.

ACFM is an electromagnetic inspection technique originally developed for subsea inspection in the offshore industry where there was a requirement to improve the reliability of in-service inspection and reduce the reliance on the inspector’s interpretation. The technique is now widely used across a range of infrastructure applications where quantitative measurements are made in order to determine structural integrity. The capabilities of the technique have been independently assessed leading to its acceptance by major international classification and certification Societies.

This paper will describe how the ACFM method works and how it differs from other electromagnetic methods. Examples of its application to a range of inspection tasks including bridges, cranes, pressure vessels, pipelines and transportation systems will be given, together with discussions on how automation of the process has virtually removed the requirement for skilled inspectors for some specific applications.