Investigation by numerical modeling of the mechano-electrochemical interaction of circumferentially aligned corrosion defects on pipelines

In this work, a finite element based multi-physics field coupling model was developed to investigate the mechano-electrochemical (M-E) interaction between adjacent, circumferentially aligned corrosion defects on an X46 steel pipeline. The M-E effect existing between the defects results in a high local stress concentration, a negative corrosion potential and a large anodic current density at the defect adjacency, contributing to an increased corrosion of the pipeline steel in service environments. At increased internal pressures, local stress concentration and plasticity occur primarily at the corrosion defects, while the effect on the adjacent area between the defects is slight. With the increase of the defect spacing, the interaction between the defects disappear, and the defects can be treated separately. The increased internal pressure caused a shift of corrosion potential more negatively and a more rapid increase of the anodic current density at the corrosion defects than the adjacent area. The ratio of the anodic current density at the middle of the defect adjacency to that of the uncorroded region is used as to define the separation of adjacent corrosion defects which can be considered as non-interacting. The critical ratio depends on the defect geometry under a given internal pressure.