Alternating current field measurement detection probe design for oil tubing

Alternating Current Field Measurement (ACFM) has emerged as a promising non-destructive testing (NDT) technique. However, its application to the inspection of the inner walls of oil tubing with metal coatings has not yet been explored. This study aims to design a detection probe based on ACFM through numerical simulations, specifically for detecting cracks on the inner wall of coated oil tubing. To enhance the efficiency of crack detection on the inner surface, a numerical simulation model of the inspection device is developed, enabling evaluation of the magnetic field perturbations caused by cracks. The simulation results were compared with the experimental data to verify the accuracy and reliability of the proposed model. The model incorporates three key structural parameters, namely core diameter, number of magnetic cores, and number of magnetic sensors, to assess their influence on the magnetic-field perturbations above cracks. The results show that the model has a high degree of fit with the experimental results, based on the analysis of simulation and experiments. Based on the optimized probe parameters, an ACFM inspection system for coated oil tubing was developed and experimentally validated. The coefficient of determination (R 2 ) was 0.9803 for the simulated relationship between crack depth and the Ba peak-to-peak value, and 0.9866 for the experimental relationship between crack length and the Ba peak-to-peak value at a fixed crack depth of 1 mm. Background: Alternating Current Field Measurement (ACFM) has emerged as a promising non-destructive testing (NDT) technique for crack detection. However, its application to the inspection of the inner walls of oil tubing with metal coatings has not yet been explored. Objective: This study aims to develop and optimize an ACFM-based detection probe specifically designed for detecting cracks on the inner wall of metal-coated oil tubing. Methods: A numerical simulation model of the ACFM inspection device was established to investigate the magnetic-field perturbations induced by cracks. The effects of three key probe structural parameters, namely core diameter, number of magnetic cores, and number of magnetic sensors, on the magnetic-field perturbations above cracks were systematically analyzed. The simulation results were compared with experimental measurements to verify the accuracy and reliability of the numerical model. Based on the optimized probe parameters, an ACFM inspection system was developed and experimentally validated for crack detection in coated oil tubing. Results: The numerical simulation results showed good agreement with the experimental measurements, demonstrating the accuracy and reliability of the proposed model. The optimized probe parameters effectively enhanced the magnetic-field response to cracks on the inner wall of coated oil tubing. The coefficient of determination (R 2 ) was 0.9803 for the simulated relationship between crack depth and the peak-to-peak value of the axial magnetic-field component (Ba), and 0.9866 for the experimental relationship between crack length and the Ba peak-to-peak value at a fixed crack depth of 1 mm. Conclusion: The proposed ACFM-based inspection method and optimized probe provide an effective approach for detecting and quantitatively characterizing cracks on the inner walls of metal-coated oil tubing. The results demonstrate the potential of ACFM for NDT applications involving coated oil tubing and provide a foundation for the further development of practical inspection systems.