Crack Growth Behavior in High pH Carbonate/Bicarbonate Environments: Application of Crack Tip Strain Rate Modeling

Aging pipeline infrastructure is subject to various degradation modes, in particular, there is a growing concern about stress corrosion cracking (SCC) from external environments. The current program focused on developing data in high pH carbonate/bicarbonate environments as a function of temperature, applied potential, and loading modes in three different pipeline steels. Crack growth rate (CGR) measurements indicate that the susceptibility to SCC increases with increasing temperature and is higher under low-cycle fatigue compared to constant K conditions. The CGR behavior at each temperature was a strong function of the applied potential, coinciding with the potential range of the active-passive transition in the polarization scans. The potential at which a peak in crack growth rate was observed, coincided with the peak value of the ratio of the current density from the fast to slow scans. The CGR data were fitted to a crack tip strain rate-based model to account for both the cyclic as well as static CGR. The model developed was able to successfully predict prior data in the literature generated under various loading conditions.