Exploring the susceptibility of P110 pipeline steel to stress corrosion cracking in CO2-rich environments

The low carbon P110 steel has been recently considered as a potential pipeline material for shale gas sequestration using CO2-based fracturing technique. The significant problem in such natural gas production and transportation system is a CO2 corrosion, especially the stress corrosion cracking (SCC) of pipelines. Due to the possible operating conditions, the aim of the present work was to investigate the susceptibility of P110 pipeline steel to SCC in CO2-rich environments. It was determined based on the stress corrosion test of U-bended specimens in the technically pure CO2 and wet CO2 (CO2 + H2O), tensile tests of miniaturized samples cut from different regions of U-bended specimens as well as slow strain rate bending tests in the wet CO2 followed by SEM observations. No clearly visible long SCC cracks and microstructural changes after exposure in CO2 and CO2 + H2O were observed. Nevertheless, some corrosion pits with micro-cracks in their vicinity were formed in the stressed/deformed areas of U-bend SCC specimens. Moreover, the results of tensile and slow strain rate tests indicated that P110 pipeline steel is susceptible to SCC in CO2-rich environments. It was manifested by a significant reduction of ductility in the stressed regions of U-bended specimens exposed to CO2 and CO2 + H2O. Besides, small cracks with brittle fracture characteristics were observed for P110 steel bended in the wet CO2 at the strain rate of 2 x 10(-6) s(-1). All observed phenomena indicated that the susceptibility of P110 steel to SCC in CO2-rich environments is associated with activity of anodic dissolution process and hydrogen involvement.