Nanoindentation study of corrosion-induced grain boundary degradation in a pipeline steel

• Published in: Electrochemistry communications 2018-03, Vol.88, p.88-92
• Main Authors: Yavas, Denizhan, Mishra, Pratyush, Alshehri, Abdullah, Shrotriya, Pranav, Hebert, Kurt R., Bastawros, Ashraf F.
• Format: Article
• Language: English
• Subjects: Dissolution-induced degradation; Grain boundary softening; Intergranular corrosion; Nanoindentation; Stress corrosion cracking
• ISSN: 1388-2481; 1873-1902
• DOI: 10.1016/j.elecom.2018.02.001

High-strength low-alloy steels used for oil and gas pipelines are vulnerable to intergranular stress corrosion cracking in moderately alkaline soils. The mechanism of corrosion-induced embrittlement under such conditions is not yet understood. Nanoindentation was used to detect localized degradation of mechanical properties near internal grain boundaries of X-70 steel undergoing intergranular corrosion at active dissolution potentials at pH 8.2. The measurements identified a one-micron thick mechanically-degraded layer with 25% reduced hardness near corroded grain boundaries. It is suggested that the corrosion process may introduce an active softening agent, possibly non-equilibrium lattice vacancies generated by oxidation. •Corrosion induces local degradation of hardness at grain boundaries of X70 steel.•Degradation is in pH and potential range of stress corrosion cracking susceptibility.•Observed degradation is a possible mechanism of grain boundary embrittlement.•Degradation is accompanied by oxide formation at grain boundaries.•First known observation of corrosion-induced grain boundary softening.