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Morphology and stress evolution during the initial stages of intergranular Morphology and stress evolution during the initial stages of intergranular corrosion of X70 steel corrosion of X70 steel

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. KeywordsIntergranular corrosion, Dissolution-induced degradation, Stress corrosion cracking, Grain boundary softening, Nanoindentation Disciplines Aerodynamics and Fluid Mechanics | Aerospace Engineering | Nanoscience and Nanotechnology | Structures and Materials CommentsThis is a manuscript of an article published as Yavas, Denizhan, Pratyush Mishra, Abdullah Alshehri, Pranav Shrotriya, Kurt R. Hebert, and Ashraf F. Bastawros. "Nanoindentation study of corrosion-induced grain boundary degradation in a pipeline steel." Electrochemistry Communications 88 (2018) This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. A C C E P T E D MA N U S C R I P T AbstractHigh-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 mechanicallydegraded 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.

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