Modeling of mechano-electrochemical interaction between circumferentially aligned corrosion defects on pipeline under axial tensile stresses

Abstract

Defect assessment on oil/gas pipelines has been used for fitness-for-service determination. However, the mechano-electrochemical (M-E) interaction of adjacent corrosion defects is usually ignored. In this work, a finite element-based model was developed to determine the M-E interaction between adjacent, circumferentially aligned corrosion defects on an X46 steel pipe, which has been widely servicing in West Canada, under axial tensile stresses, simulating the stressing condition induced by pipe-soil interaction. Distributions of von Mises stress, corrosion potential and anodic current density at the corrosion defects were determined. A new criterion is proposed to define the threshold condition that a mutual M-E interaction exists between adjacent circumferential corrosion defects, i.e., the ratio of the anodic current density at the middle of two defects to the anodic current density of uncorroded area on the pipe. For corrosion defects with a width of 0.025πD, 0.05πD and 0.1πD (where D is the pipe outer diameter), the critical circumferential spacing between them is 0.08πD, 0.09πD and 0.09πD, respectively, exceeding which a mutual interaction between the defects is negligible.