Quantitative Evaluation of Buried Defects in Ferromagnetic Steels Using DC Magnetization-Based Eddy Current Array Testing

Eddy current array testing (ECAT) is a useful tool in evaluating defect sizes. However, it is difficult for ECAT to evaluate the inner defects in ferromagnetic materials due to thin skin effect. In this article, direct current (dc) magnetization-based ECAT (DCMECAT) is proposed to quantify buried defects existing in the inner surface of steel plates. Relying on permeability disturbance in the defect vicinity, DCMECAT can build links between the testing signals and defect sizes. The results show that the performance of evaluating defect sizes is better under the saturated magnetization state. Further, three features, i.e., the signal width, the peak voltage, and the contour orientation, are proposed to evaluate the width, the depth, and the orientation of defects, respectively. Relationships between features and defect sizes are investigated by using least-squares regression. Further, a testing example is shown in this article, and the evaluation error is 14%.