Precise Inner Radius and Inner Surface Shape Estimation in Finite Conductive Tubes Using Eddy Current Technique

Inner radius inspection is critical in the production of tubes, particularly those with small thicknesses, to ensure structural integrity and performance. Traditional ultrasonic methods often fall short in measuring thin-walled tubes, necessitating the use of eddy current method for its non-contact and highly sensitive capabilities. In this paper, we employ the finite element method (FEM) to calculate the output signal of a vertical surface probe in the vicinity of a finite conductive tube. We address the significant impact of edge effects, which can deteriorate the primary signal from material properties. The probe data are then used to determine the inner radius through a regression method, and an evaluation technique is proposed to inspect the ovality of the inner surface. Our results demonstrate the accuracy and efficiency of the FEM to predict coil impedance and regression methods to evaluate both the inner radius and the shape of the inner surface, even in the presence of noise. This research provides significant contributions to the field of tube inspection, particularly in industries where precision is paramount, such as oil and gas industries, automotive, and medical sectors.