Stress corrosion cracking under extreme near-neutral GCC conditions, parametric and comparative study using phase field modeling

Stress Corrosion Cracking (SCC) is a failure mechanism that occurs when certain materials are subjected to both external or residual stresses and corrosion. This combined effect leads to the development of cracks in the susceptible materials. Submerged steel pipelines in the petroleum sector are built of low-alloy steels having a ferrite-cementite composition, including API 5L X70. Such materials are sensitive to SCC damage in aqueous systems. The film rupture dissolution repassivation (FRDR) process is used in this study to evaluate the cracks and pits growth in oil and gas pipelines in the Gulf area under diverse SCC environmental conditions. The SCC crack propagation and pit growth under near-neutral environmental conditions were analyzed using phase field modelling. X70 steel under NS4 the solution was used for the analysis to represent the anodic dissolution film rupture mechanism. A parametric study was done to study the impact of different electrochemistry and phase field parameters on crack growth behaviour. The study assess the susceptibility to SCC caused by an pit by employing diverse settings to evaluate the impact of corrosion parameters and the interaction among the FRDR mechanism. The corrosion rates are influenced by the interface kinetics coefficient (L), which exhibits an accelerated effect as L increases. This transition from fracture-controlled to dissolution-controlled SCC growth occurs until the system reaches the diffusion limit, beyond which further increases in L do not significantly impact corrosion rates. Moreover, higher values of the kinetic coefficient (k) advance the creation of SCC cracks at the crack front, resulting from corrosion originating from pitting at the crack mouth. This process leads to the refinement of the pit and its transformation into a crack. A comparison analysis was utilized to validate our simulation under a near-neutral NS4 solution for X70 steel by correlating the findings with other numerical methods for crack growth utilizing the same material and environmental parameters. The results show decent agreement with the comparative study.