Edge weld penetration assessment using the potential drop technique

A special inspection technique was developed based on the Potential Drop Method (PDM) for assessing edge weld penetration on clamshell-style catalytic converters. The electric resistance through the edge welded flange of stainless steel catalytic converters sharply decreases with increasing weld penetration, which can be exploited to quantitatively measure the weld penetration in a nondestructive way. The current distribution in the weld was simulated using the Finite Element Method (FEM) in order to optimize the electrode arrangement, to estimate the adverse effects of spurious geometrical variations in the weld shape and to obtain approximate theoretical calibration curves. Experimental measurements using a high-sensitivity four-point AC resistance bridge were carried out on specimens of varying weld penetration between 0.020 and 0.080 inches to verify the FEM predictions and to obtain empirical calibration curves. The experimental results were found to be in good quantitative agreement with both FEM simulations and destructive results. The verified accuracy, reproducibility and speed of the developed technique are quite satisfactory in most industrial applications. (C) 1997 Elsevier Science Ltd.