Eddy Current Testing
An electrical technique detecting surface breaking defects in all electrically conducting materials through paint and surface coatings. All electrical methods are indirect; a material property is measured as an electrical property variation. A coil carrying an AC current is placed on the specimen surface.
This generates circulating eddy currents in the specimen close to the surface and these in turn affect the current in the coil by mutual induction. Flaws and material variations affect the strength of the eddy currents. The presence of flaws is therefore measured by electrical changes in the excitation coil. Applications range from crack detection including weld inspections.
The benefits of eddy current inspection over MPI is that it can detect through surface coatings. It's able to detect defects through non-conductive surface coatings in excess of 5mm thickness.
Also there's little pre-cleaning required. Only major soils and loose or uneven surface coatings need to be removed, reducing preparation time.
Combined with rope access techniques eddy current has proven itself to be a very efficient inspection method.