Verification of an eddy-current flaw inversion algorithm

An eddy-current flaw inversion algorithm was experimentally verified as having 72-percent accuracy in the prediction of the shape, length (axial extent), and depth (radial extent) of flaws in stainless-steel tube walls. For calibration the algorithm requires data from only one flaw of known type (inclusion, crack), shape, and dimensions. The algorithm is based on least-squares techniques and is implemented using a modified algebraic reconstruction technique. The electromagnetic model system is an integral equation which is then discretized by means of the method of moments. The algebraic reconstruction algorithm, which is iterative, is applied to the discretized system. The algorithm utilizes a parameter for smoothing and a relaxation parameter to accelerate convergence. A discussion of these matters and a description of the experimental procedure and results are given.