A new approach to increase the subsurface flaw detection capability of pulsed eddy current technique

In this paper, the detection of subsurface flaws by pulsed eddy current (PEC) technique has been studied. Experiments have been carried out on an 8.0mm thick stainless steel plate with subsurface flaws located at different depths below the surface by varying the excitation rise time (E-r). The conventional PEC signal parameters like peak amplitude (V-p), time-to-peak (T-p) and rise time (t(r)) are influenced by noise and could not be effectively used to detect flaws located beyond 4.0mm below surface. In this context, a new approach based on fitting the PEC response pulse to a modified inductor current equation has been proposed. Based on this approach, two parameters viz. time constant (tau) and voltage parameter (V-1/V-0) have been derived and used for detection and separation of flaws. The study shows that the two parameters derived from the proposed approach can be used to detect flaws located 6.0mm below the surface with improved sensitivity. The advantage of the proposed approach is that, it does not require subtraction from reference signal to detect flaws. The derived parameters are also able to differentiate the subsurface and surface flaws.