Deposit characterization by eddy current nondestructive evaluation

Abstract

In this paper, the eddy current nondestructive evaluation method is used to determine the electrical conductivity, the thickness and the size of a deposit located on the reverse side of a tested specimen. The eddy current probe consists in a coil. The impedance of the coil is calculated by a boundary integral method. The inverse problem is solved by combining a neural network and an iterative resolution. 2. Problem description and solution of the forward problem The study is based on the geometry description of the Benchmark problem #5-1defined by the Japan Society of Applied Electromagnetics and Mechanics (1), targeting the detection of deposit on steam generator tubes. The geometry of the problem is shown in Fig. 1. A cylindrical exciting coil is placed above an infinite conductor plate. The coil parameters are inner and outer radius r1 and r2, number of turns N and height h (r1 =0.61 mm, r2 =1.59 mm, N = 140, h= 0.76 mm). The lift-off is denoted by lo and is equal to 0.5 mm. The deposit support is an INCONEL 600 plate. Its electric conductivityσ, relative permeability µr and thickness t are: σ =0.97 MS/m, µr = 1, t =1.25 mm. The coil impedance is measured at three excitation frequencies: f1 = 150 kHz, f2 = 300 kHz and f3 = 450 kHz. The coil and the deposit are on the opposite sides of the plate. The deposit constituted of a conductive nonmagnetic