CO₂-SCC in Flexible Pipe Carbon Steel Armor Wires

Carbon dioxide-induced stress corrosion cracking (CO₂-SCC) is an environmentally assisted corrosion cracking phenomenon that has recently been identified as a new failure mode in flexible pipe armor wires. The phenomenon has been observed to take place notably in severe CO₂ environments and is a cause of great concern to the flexible pipe industry. As its detection, a diverse and extensive testing program has been established to develop an understanding of the phenomenon and define safe application limits for carbon steel wires to prevent the initiation of CO₂-SCC. Several different testing methodologies have been explored and small-scale laboratory testing has played an instrumental role in this overall effort. This paper focuses on the results from three different small-scale testing methodologies and the impact of different parameters such as CO₂ fugacity, temperature, and confinement that play a crucial role in the initiation of CO₂-SCC. Furthermore, careful prominence has been given to the test setup and methodology that has been rigorously developed over the last few years. With this developed protocol in place, CO₂-SCC has been effectively reproduced on all wire grades in a small-scale testing environment. Results have also shown that for a CO₂ fugacity greater than 15 bar and applied stress at 100% of the actual yield strength, all existing wire grades are susceptible to CO₂-SCC thus creating significant limitations to flexible pipe design with respect to this new failure phenomenon.