Finite Element Simulation and Failure Assessment of Corrosion Defect Growth in X65 Pipeline Steel under Mechano-electrochemical Coupling

The safety implications of corrosion defects in oil, gas, and hydrogen pipelines represent a current research focus. However, most studies typically consider coupled mechano-electrochemical (M-E) interactions solely under steady-state conditions. This research establishes a time-dependent finite element model based on coupled M-E theory, simulating the dynamic evolution of corrosion defects in X65 pipeline steel within weakly alkaline soil environments. It models defect growth changes over a 0 to 25-year period. Through parametric modelling, the effects of varying circumferential coefficient ( k₁ ) and radial coefficient ( k₂ ) on stress distribution around corrosion defects, anodic current density distribution, and pipeline defect geometry were investigated. Pipeline risk assessment was conducted by analysing corrosion rates and plastic strain variations during service life. Results indicate that a lower circumferential coefficient k₁ elevates von Mises stress at the defect base, induces a multi-peak distribution of local anodic current density, and triggers pronounced serrated corrosion morphology. The onset of this morphology occurs earlier as k₁ decreases. An increase in the radial coefficient k₂ intensifies the M-E interaction, markedly elevating the corrosion rate. Particularly when k₂ = 0.354, the von Mises stress at the defect reaches the material's tensile strength limit around the 18th year. Severe collapse occurs at the defect base, with the plastic deformation zone extending into the inner wall of the pipe, indicating that the failure risk has reached a critical level.