Crack Propagation in Pipelines Under Extreme Conditions of Near-Neutral PH SCC

Stress Corrosion Cracking (SCC) process through which cracks occur in a variety of susceptible materials is a result of a combination of residual or applied stresses and corrosion. In oil and gas field, buried pipeline steels are made of low-alloy steels with a ferritic-pearlitic structure, such as X70. In dilute solutions, these materials are prone to SCC failure. The Near-neutral simulated soil solution (NS4) solution is established to imitate SCC conditions and subsequently became the industry requirement for crack growth experiments in the majority of laboratories. The strain-assisted active crack pathways are considered while modelling SCC growth as an oxide film rupture and anodic dissolution process. It’s been hypothesized that increasing the strain concentration can help with dissolution at the film-free crack tip. This research focuses on estimating the SCC crack growth rate under various environmental conditions in oil and gas pipelines using finite element modelling. The simulation is carried out using the J-integral theory in the COMSOL Multiphysics program. Simulations are performed to model the crack growth rate (CGR) using slip anodic dissolution (film rupture) mechanism. The plastic strain gradient is required to compute the SCC CGR (da/dt). Because the plastic strain located at crack tip increases proportionally to the crack length as it propagates, the CGR increases as the stress intensity factor (SIF) increases. The crack growth rates increase when constant loads are applied and as the temperature rises, and elevating the cathodic potential has a minimal influence on the propagation rate of cracks but raises the material yield strength and imparts brittle behavior to it.