Optimum frequency variations with coil geometry and defects in tone burst eddy current thermography (TBET)

This paper focuses on the non-destructive evaluation of components using the transient induction heating thermography technique through modelling and experiments. The method consists of heating the component inductively, monitoring the surface temperature profle and analysing the transient data for defect detection and material property evaluation. The coupled equations of electromagnetic induction and heat transfer were solved using a 2D axisymmetrical fnite element model. Optimisation studies were carried out to determine the infuence of the frequency of excitation in order to maximise the surface temperature generated on a plate through induction. The effect of changing the coil geometry has also been studied. It was observed that the presence of a wall-thinning defect in the plate altered the optimum frequency and the variation was noticeable only when the defect diameter was more than the coil inner diameter.