Methodologies for CO2 Stress Corrosion Cracking Testing of Carbon Steel Armor Wires for Flexible Pipes

Abstract CO2 stress corrosion cracking (CO2-SCC) of carbon steel armor wires in flexible pipes poses significant concerns for offshore oil and gas operations. Small-scale and full-scale tests have been developed to better understand and mitigate CO2-SCC. However, reproducing this phenomenon in laboratories is challenging due to the highly confined environment of the flexible pipe annulus. CO2-SCC in flexible pipes results from the interplay of environmental factors, stresses, and material characteristics. In laboratory investigations, while material composition/microstructure remains constant, variables such as static, dynamic, or continuous loading, manufacturing induced plastic deformation, and environmental conditions are examined for their impact on CO2-SCC. This work focuses on static loading employing four-point bend configuration to introduce stress distributions in test samples. Furthermore, the effect of accumulated plastic strain is studied by pre-straining samples in both bending and uniaxial modes. Environmental parameters, including test solution Fe2+ saturation, oxygen contamination, confinement level, and exposure duration are systematically investigated. The study ultimately compares these test methodologies, evaluating both their effectiveness in qualifying materials for resistance to CO2-SCC and simulating flexible pipe annulus conditions. The results further elucidate how various mechanical and environmental factors contribute to CO2-SCC susceptibility, providing insights for improving material testing practices.