Distinguishing Between Internal and External Defects Based on Stepped Array Sensor in Thick-Walled Ferromagnetic Components

Distinguishing between internal and external defects is extremely important for defect evaluation, but it is difficult for traditional methods to distinguish between internal and external defects in thick-walled ferromagnetic components effectively. In this article, a method based on a stepped array sensor is proposed for distinguishing internal and external defects in thick-walled ferromagnetic components. Theoretical modeling and simulation analysis show that the magnetic permeability perturbation testing (MPPT) signals of internal and external defects show different trends as the sensor size increases. Experiments show that the method can distinguish between $1 \times 1$ mm internal and external defects in a ferromagnetic plate with a thickness of 12 mm. In addition, this method has shown good performance when applied to ferromagnetic components of different thicknesses (including 8, 10, and 12 mm), and the magnetization state has no effect on the change trend. It is worth noting that it can distinguish defects with a depth of 8.3% of the total plate thickness, ensuring accurate and reliable detection. This method has no need for prior knowledge of the parameters of the ferromagnetic components and the optimum magnetization strength, which is of greater practical value.