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The development of computer-based defect charact e r i z a t i o n schemes for automated electromagnetic methods o f n o n d e s t r u c t i v e t e s t i n g is demonstrated by comparing predicted results with experim e n t a l v a l u e s f o r p r a c t i c a l e x a m p l e s o f a c t i v e , r e s i d u a l and eddy c u r r e n t NDT s i t u a t i o n s .

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Eddy-current methods of nondestructive testing rely for their operation on the interaction of induced alternating currents and fields with defects to produce noticeable changes in search coil impedance. To date, analytical techniques have been largely ineffective in providing a model suitable for the basis of a general defect characterization scheme because of the inherent complexity of the field equations describing the phenomena. After an overview of the available analytical models, this paper describes the development of a numerical model that shows promise of providing a solution to the inverse eddy-current problem. Impedance plane trajectories are predicted for a differential probe passing through a tube with axisymmetric inside-diameter and outside-diameter slots to illustrate the use of the numerical approach.

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