Fast Estimation of Metallic Pipe Properties Using Simplified Analytical Solution in Eddy-Current Testing

The eddy-current testing technique has been extensively explored for the measurement of metallic pipes in various industrial processes. In this study, a simplified analytical model of metallic pipes encircled by a coaxial sensor is derived according to the asymptotic forms of modified Bessel functions. The original Dodd and Deeds (DD) model is thus approximated by an elementary function describing the relationship between the measured inductance spectrum and the pipe properties. Due to the simple nature of the elementary function, the Jacobian matrix can be evaluated much more efficiently. Accordingly, a fast Newton–Raphson method-based optimization approach is developed. The proposed method has been evaluated by comparing it with the numerical simulation of the finite-element method (FEM) and experimental measurements which indicate its effectiveness for the measurement of metallic pipe properties.