ABSTRACT
The eddy current method of nondestructive testing, as currently practised, was pioneered by Friedrich Förster in the 1940s, and there has since been rapid progress in its development. Eddy current tests can be made on all materials which are electrically conducting. They include the sizing of surface and sub-surface cracks, measurements of the thicknesses of metallic plates and of non-metallic coatings on metal substrates, assessment of corrosion and measurements of electrical conductivities and magnetic permeabilities. These latter properties may be related to structural features such as hardness, chemical composition, grain size and material strength. An important advantage of eddy current testing over some other methods, such as ultrasonic, magnetic particle and potential drop techniques, is that there is no need for physical contact with the surface of the object being tested. Thus, careful surface preparation (other than the removal of metallic adherents) is unnecessary.
