Electric Field Analysis of Simultaneous Evaluation of Crack on an Inner Pipe Surface and Pipe Wall Thickness Using Direct-Current Potential Difference Method of Multiple-Probe Type

The direct-current potential difference method (DC-PDM) is a promising nondestructive technique for evaluating cracks in the conductors on the basis of change in current paths or the potential difference due to cracks. In a previous study, the authors proposed a method for the simultaneous evaluation of the location and size of a semi-elliptical crack on the back surface of a plate and the plate thickness. Its theoretical validity and practical utility were shown by numerical analyses and experiments. This study extends the method to the simultaneous evaluation of a crack on the inner surface of a pipe and the pipe wall thickness. The related electric field analyses are performed using the finite element method. The results show that the location, length, and depth of a semi-elliptical crack on the inner surface of the pipe and the pipe wall thickness can be evaluated based on the distribution of the potential difference measured on the outer surface of the pipe. This extension will prove useful for various practical cases, which are often seen in the piping of power-generating and petrochemical plants.