Pulsed Eddy Current Testing Method for Corrosion Thinning Defects of Ferromagnetic Components Based on Parameter Inversion Algorithm

ABSTRACT Based on the time domain analytical expression of the pulsed eddy current field of a ferromagnetic flat plate, the least square parameter inversion problem between the measured value of the time-domain induced voltage and the theoretical value is established. Set the conductivity of the tested component as a fixed constant and then compare the inversion results of the wall thickness of the two test points to obtain the relative change of the wall thickness between the two test points. The rectangular groove defect is machined on the steel plate, and the experiment verifies that the relative wall thickness detection method in this paper can eliminate the influence of the set value of component conductivity. When the area of the corrosion area is larger than the area of the foot of the probe, the residual wall thickness of the corrosion area can be accurately scanned, and the edge of the corrosion area has good recognition ability. When the area of the thinning area is smaller than the area of the probe foot, the thinning degree of local corrosion defects will be underestimated. The pulsed eddy current method is used to detect the relative wall thickness of ferromagnetic components without contacting with the tested components. The detection results are intuitive and the repeatability is high. It can be used for nondestructive testing and evaluation of the corrosion thinning of the wall thickness of ferromagnetic components with coating in industry.