Thickness measurement for non-ferromagnetic metal under the large liftoff based on the last peak point of differential pulsed eddy current signals

Pulsed Eddy Current Testing (PECT) has been used to measure the wall thickness of ferromagnetic metallic component with thick insulation. However, for the non-ferromagnetic metallic component, there is still the problem to be solved. The main purpose of this study is to find an effective feature, to measure wall thinning of the non-ferromagnetic metallic component under the large liftoff, and further expand application of the PECT technology. Hence, the time to the last peak point (TLPP) is proposed based on the analytical predicted signals. Furthermore, the influence of the variable liftoff is studied, and the error caused by the liftoff is within the acceptable range. Two sets of experiments are conducted to test the performance of the TLPP under various liftoffs. The results show that when the wall thickness is reduced by more than 40%, the measurement error based on the TLPP is within 11%.