Modelling of mechano-electrochemical interaction of multiple longitudinally aligned corrosion defects on oil/gas pipelines

Abstract

Assessment of corrosion defects and their effect on integrity of oil/gas pipelines are critical to the burst strength capability and safe operation of pipeline systems. In this work, a 3-dimensional finite element-based model was developed to investigate the mechano-electrochemical (M-E) interaction of multiple, longitudinally aligned corrosion defects on an X46 steel pipeline in a soil solution. A multi-physics field coupling technique was employed to derive the distributions of stress, strain, corrosion potential and anodic current density at the defects. For multiple corrosion defects, a critical spacing exists, below which there is an interaction between them to enhance the local corrosion. From this work, this value is between 100 mm and 150 mm. The maximum interacting spacing increases as the defect length increases. As the defect spacing reduces, there is a strong interaction between them, resulting in a high plastic stress at the defects. Under the identical defect spacing, the hoop stress condition causes an enhanced E-C interaction between adjacent corrosion defects, while the effect due to the uniaxial stress is ignorable. The interaction between multiple corrosion defects exists not only in the mechanical stress field, but also in the electrochemical corrosion field. An increase of the defect length, while keeping its depth fixed, enhances the local stress at the defects, shifts the corrosion potential negatively, and increases the anodic current density at both the defect and the adjacent area.