Effect of dissolved oxygen on stress corrosion cracking of X70 pipeline steel in near-neutral pH solution

To clarify the role of dissolved oxygen in near-neutral pH stress corrosion cracking (SCC), slow strain rate test (SSRT), dynamic polarization technique, and electrochemical impedance spectroscopy (EIS) were used to investigate the relationship comprehensively between SCC susceptibility and the electrochemical corrosion reactions occurring at the steel/solution interface in diluted, varying N₂-purged, near-neutral pH solutions. Results showed that SCC susceptibility is inversely proportional to dissolved oxygen (DO) concentration. At open-circuit potential, concentrated dissolved oxygen reacts with H and forms oxide film to reduce hydrogen embrittlement, resulting in the reduction of SCC susceptibility in NS4 solution. In NS4 deoxygenated solution, the SCC of X70 pipeline steel is controlled by a combined electrochemical process in which anodic reactions and hydrogen penetration occur at the same time.