Investigation by numerical modeling of the mechano-electrochemical interaction at a dent-corrosion defect on pipelines

Abstract

Dent-corrosion combination defect causes the curvature change and wall thickness thinning on the pipeline simultaneously, which poses a higher threat to pipeline integrity than a single type of defect. In this work, a finite element (FE) based multi-physical field coupling model was developed to investigate the mechano-electrochemical (M-E) interaction at the dent-corrosion defect on an operating X80 pipeline. Parameter effects, including internal pressure, the diameter-to-thickness ratio of the pipe, and the geometries of the defect, were determined. Results demonstrate that the local equivalent plastic strain and anodic current density are insensitive to practical operating pressure but highly dependent on the diameter-to-thickness ratio and the geometries. A critical dent depth of 4% of the pipe diameter existed, exceeding which the increase of dent depth hardly affects the maximum equivalent plastic strain of the pipeline. The size of the indenter is negatively correlated with the equivalent plastic strain and the anodic current density at the defect center. There is also a critical threshold of 10% pipe diameter, below which the distribution of equivalent plastic strain and anodic current density at the defect is significantly affected. The effect of the circumferential dent is significant, while that of the axial dent is marginal.