Characterization of cracks using eddy current tomography

Abstract

Nuclear reactor coolant tubes are routinely inspected using eddy current methods. Classical methods rely on either human or automatic interpretation of impedance plane trajectories generated by differential eddy current probes to determine the condition of the tube. An alternative approach is to use a modified version of the Electrical Impedance Tomography (D.C. Barber and J. Sikora, 1995) (in this case called the Eddy Current Tomography) for the material coefficient imaging in a certain sub-region of the tubing. The problem can be defined as the inverse problem involving the estimation of the material coefficients (conductivity \gamma ) (S.-y. Hahn et al., 1995). In order to solve the inverse problem it is necessary to carry out the sensitivity analysis that provides the gradient of the objective function F . The main goal of this paper is to present the adjoint variable method, an efficient tool for gradient calculation.