<P> Variations in the electrical conductivity and magnetic permeability of the test object, and the presence of defects causes a change in eddy current and a corresponding change in phase and amplitude that can be detected by measuring the impedance changes in the coil, which is a telltale sign of the presence of defects . This is the basis of standard (pancake coil) ECT . </P> <P> ECT has a very wide range of applications . Because ECT is electrical in nature, it is limited to conductive material . There are also physical limits to generating eddy currents and depth of penetration (skin depth). </P> <P> The two major applications of eddy current testing are surface inspection and tubing inspections . Surface inspection is used extensively in the aerospace industry, but also in the petrochemical industry . The technique is very sensitive and can detect tight cracks . Surface inspection can be performed both on ferromagnetic and non-ferromagnetic materials . </P> <P> Tubing inspection is generally limited to non-ferromagnetic tubing and is known as conventional eddy current testing . Conventional ECT is used for inspecting steam generator tubing in nuclear plants and heat exchangers tubing in power and petrochemical industries . The technique is very sensitive to detect and size pits . Wall loss or corrosion can be detected but sizing is not accurate . </P>

What materials can be tested with an eddy current tester
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