The aim of this study is to investigate the feasibility of Pulsed Eddy Current Testing (PECT) for detection and evaluation of local wall thinning defect at the bottom side surface of a multilayer structure. To cope with the large thickness of the specimen, a high sensitive Flux Gate (FG) sensor is employed and a self-differential exciting mode is proposed to efficiently apply the FG sensor. Experimental results show that the FG sen- sor combined with the self-differential exciting mode can detect a small defect located in a thick specimen which can not be detected by using conventional Hall sensor. Moreover, through analyzing the simulation results of PECT signals calculated with an efficient numerical simulation solver, it was found that the distance between the positive peak and the negative peak of the Bz signal (magnetic flux density in z direction) is a suitable feature parameter to quantify the width of a local wall thinning defect, while the mini- mum time to peak of the differential Bx signal (magnetic flux density in x direction) is applicable to predict the defect depth.

Keywords: Defect size, Pulsed ECT, Quantitative NDE, Self-differential exciting mode, Wall thinning.