Approximate methods for the calculation of the ECT signal of a crack in a plate coated by conducting deposit

Approximate methods for the calculation of the interaction of a pancake type exciting coil and a crack in a nonferromagnetic conducting plate covered by a thin layer of conducting deposit are presented. The perturbations caused by the presence of the crack and the deposit are represented by secondary sources that actual values are obtained by the solution of a set of integral equations. Using different approximations, the coupling between these integral equations can be reduced, as a result, fast and accurate calculation methods are obtained for the prediction of the signal of the investigated eddy current testing (ECT) arrangement.