Potential drop detection of creep damage in the vicinity of welds

Abstract

Recent research indicated that directional Alternating Current Potential Drop (ACPD) measurements could be exploited for nondestructive evaluation of creep damage. Unfortunately, creep damage is often concentrated in welded sections where the inspection is less straightforward. In this work, a directional square-electrode ACPD probe with spring-loaded contact pins was used to evaluate different levels of creep damage in the vicinity of welds. The electric transfer resistance was measured in two orthogonal directions to detect creep-induced material damage. This is particularly difficult close to weld/base metal interfaces because the electric conductivity usually changes significantly from one side of the interface to the other and therefore exhibits an apparent anisotropy caused by the influence of the boundary. The feasibility of directional ACPD evaluation of creep damage in the vicinity of such transition regions was studied by experimental, analytical and numerical means. Finite element simulations validated the analytical and experimental results and offered an opportunity to further investigate secondary effects, such as the inclination angle of the interface relative to the surface and the influence of an extended transition zone.