Research on weak magnetic detection of coating layer pipelines based on adjustable excitation

To explore an effective nondestructive testing method for coating layer pipelines, a weak magnetic detection method with adjustable excitation is proposed in this paper. Based on the Jiles-Atherton (J-A) magneto-mechanical coupling model, the optimal stress-sensitive excitation magnetic field is set at 600 A·m⁻¹. The electro-magnetic-mechanical multiphysics coupling simulations are conducted to investigate the variations of magnetic signal in excitation magnetic field. To achieve optimal excitation, the excitation current should be adjusted according to the coating thickness, following a quadratic relationship. Two characteristic parameters have been introduced to quantitatively analyze the effect of the excitation magnetic field on the weak magnetic signal. The characteristic parameter S_t under the excitation magnetic field is approximately 20 times higher than in the geomagnetic field. The influence of defect size, load magnitude, and coating layer thickness on the magnetic signals are respectively discussed. The experimental results of weak magnetic detection on 20# steel specimens align well with the simulation results. This indicates that the excitation magnetic field can effectively enhance the magnetic signal intensity and improve the sensitivity of defect detection. The results provide a theoretical foundation for the application of adjustable weak magnetic excitation methods in the inspection of coated pipelines.