Inspection of the Delamination of Magnetic and Non-Magnetic Conducting Layers Using NDT

The partial delamination of two metallic parts, one ferromagnetic and one non-magnetic, is inspected using nondestructive magnetic measurements. Defects of this type occur among others in the reactor of nuclear power plants, and are usually hidden. In the real-life inspection, low frequency AC current is injected into the metals, and the perturbation of the surrounding magnetic field is measured. However, numerical simulation of the defect-probe interaction is necessary too for the proper reconstruction of the parameters of hidden defects. In this paper an efficient finite element formulation is derived including both volumetric and surface type models of the delamination, and the numerical models are compared on a test problem.