A Novel Wall Thickness Measurement of Metallic Tube Using Stacked Array Eddy Current Sensor

Due to its high strength, corrosion resistance, good thermal conductivity, and processability, the metallic tube has a wide range of critical applications in the industrial field, such as petrochemical, power industry, manufacturing, and other fields. In fact, the thickness of metallic tubes is closely related to their structural information. Accurate measurements are necessary to prevent safety incidents, meet industry regulations and standards, and develop sound maintenance programs. This article presents a novel method for measuring the wall thickness of metallic tubes using a stacked array eddy current sensor. A stacked array eddy current sensor, consisting of three absolute coils, is first designed. According to the configuration of the eddy current sensor, the analytical solution for the interaction between the sensor and the tube has been developed. Utilizing the analytical solution, the crossover frequencies of self-inductance variation are extracted in the sweep frequency mode. The logarithm of the crossover frequency is linearly related to the liftoff distance, with the slope of this linearity being solely dependent on the wall thickness and independent of the conductivity of the material. The relationship allows for the estimation of wall thickness by the slope of the fitting line. To evaluate the accuracy of the method, a series of experiments using different materials are conducted, demonstrating that the proposed technique yields an average relative error of only 1.3%.