Assessment by finite element modelling of the mechano-electrochemical interaction at double-ellipsoidal corrosion defect with varied inclinations on pipelines

In this work, a 3-dimensional finite element model was developed to assess the double-ellipsoidal corrosion defect on an X100 steel pipe exposed to a near-neutral pH solution, where the double-ellipsoidal defect is more representative than the usually used ellipsoid of the realistic defects generated on the pipelines. Results confirm that the axial lengths of the two ellipsoidal defects affect the local stress and anodic current density distributions, and the effect depends on the inclination of the defect on the pipeline. When the primary axis of the corrosion defect is perpendicular to the axial direction of the pipeline, the maximum stress and anodic current density happen at the defect's deepest site, which is not necessarily the defect center. The reduced ratio of the axial lengths of the two ellipsoids, i.e., the increased difference of the axial lengths, remarkably increases the local stress concentration and anodic current density at the deepest site of the defect, making it the location of the fastest corrosion growth. When the corrosion defect is parallel to the axial direction of the pipeline, the maximum stress and anodic current density is always located at the center of the defect. The reduction in the axial length ratio does not obviously affect the stress and anodic current density. (C) 2020 Elsevier Ltd. All rights reserved.