Numerical analysis of evaluation of local wall thinning on the inner surface of pipe by the direct-current potential difference method

Local wall thinning is one of serious problems in aged power generating and chemical plants. As the thinning grows inside the pipes, it is difficult to detect and evaluate it from the outer surface of pipe. In this study, an evaluation method of semi-ellipsoidal local wall thinning on the inner surface of pipe by the direct-current potential difference method (DCPDM) was proposed, and the related numerical analyses were carried out. At first, very fast electric field analysis method, i.e., defect-current modification method (DCMM), was extended to the local wall thinning with semi-ellipsoid shape on the inner surface of pipe, and the solution was validated by comparing with that obtained by the finite element method (FEM). Then, the geometry of the local wall thinning was evaluated by the proposed method based on the distribution of potential difference on the outer surface of pipe obtained by FEM. The evaluated results agreed well with the actual geometry. It was found that the DC-PDM is applicable to the evaluation of local wall thinning.