Environmentally Assisted Cracking of Subsea Pipelines in Oil & Gas Production Environments-Effect of Static Loading

Fatigue crack growth rate of line pipe steels in sour environments typically exhibits a steady-state value at low frequencies. However, in highly inhibited sour environments, there is no evidence of a steady-state fatigue crack growth at low frequencies. This is likely a result of static crack growth rate at K-max. Stable static crack growth measured under constant stress intensity factor (K) conditions in inhibited sour environments was in the range of 10(-7) mm/s to 10(-8) mm/s. The crack growth rate in inhibited sour environments is likely associated with crack tip processes associated with metal dissolution/film formation and associated hydrogen evolution. The results obtained were modeled based on a crack tip strain rate based approach, where the rate limiting step was the metal dissolution/FeS formation and the corresponding hydrogen generation reaction.