Depth Evaluation of Subsurface Defects in Lead Seal Based on Accumulated Value Feature from Pulsed Eddy Current Signals

The lead seal is one of the piezoelectric cable components that is prone to failure. In this paper, the accumulated value of pulsed eddy current signals was utilized to characterize the subsurface defect depth of the lead seal for the safety of the lead seal in service. The characterization method of the defect depth was analyzed by the finite element model. The simulation results showed that the accumulated value feature had a linear relationship with the subsurface defect depth in a semilogarithmic coordinate system, and the linear fitting coefficient was 0.9982. The experimental results showed that the accuracy of the accumulated value feature in characterizing the subsurface defect depth was better than that of the peak value feature. Specifically, the maximum relative errors of the measurements were 12.51% and 9.07%, while the average relative errors were 5.83% and 8.00%, respectively.