Mechanical Stress Identification Method in Anisotropic Ferromagnetic Materials Using Eddy Current Testing

This work presents an identification method for multi-axial stresses in steel pipelines. The proposed electromagnetic non-destructive technique evaluates the impedance variation of an eddy current (EC) sensor. The method applies to ferromagnetic materials, including anisotropic ones. It is a model-based approach using a finite-element model (FEM) that incorporates the magneto-elastic behavior of the material and simulates the variation of the EC sensor impedance with stress. Four parameters are needed to describe the material behavior. Although the magnetic parameters used in the numerical model are identified from anhysteretic measurements, the results of the identification method correlate with experiments performed on samples extracted along two orthogonal directions of a pipeline.