Conductivity measurement of metal tube based on high-frequency eddy current method

Metal materials, particularly metal tubes, are essential in industries, such as aerospace, nuclear power, and oil and gas. Ensuring their safety and integrity is critical, with conductivity being a key parameter related to hardness and material defect detection. Eddy current testing (ECT) is widely used for this purpose due to its high speed and non-contact nature. In this paper, high-precision measurement of metal tube conductivity is achieved using high-frequency single-frequency signals. Starting from the classical Dodd-Deeds solution, Bessel functions and the skin effect in eddy currents are leveraged for the approximation, leading to a simplified conductivity calculation formula. At high frequencies (on the order of MHz), the real part of the coil impedance is inversely proportional to the square root of the tube conductivity. Additionally, the influence of both metallic tube and coil parameters on the proposed method is also investigated. Experimental validations are carried out to confirm the accuracy of the simplified formula and conductivity measurement. Results indicate the proposed conductivity measurement method significantly improves measurement speed while maintaining accuracy, with less than 1.75% relative error.