Edge Weld Penetration Assessment via Electric Current Deflection Measurements

Because of the awkward and somewhat irregular shape of the weidment, conventional methods [I] could not be adapted to the nondestructive measurement of GT A W edge weid penetration on clamshell-style catalytic converters and a special inspection system based on the eiectric current deflection method was developed. DC or low-frequency AC electric resistance measurements, also known as the Potential Drop Method (PDM), are well-developed for plate thickness assessment and crack detection [26]. The operating principle ofthese methods is that, under certain arrangement ofthe electrodes, the defect or crack in a conducting specimen will cause a measurable increase in resistance between given points compared to the situation without the defect or crack. In recent years, this simple contact technique was largeiy obscured by more sophisticated noncontacting eddy-current techniques especially in industrial applications. In this article, we demonstrate the distinct advantages of the Potential Drop Method through the exampie ofGTAW edge welds where the awkward shape ofthe specimens and the required large penetration depth render the eddy-current method less feasible.