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Carbon steel corrosion scales protectiveness study in CO2 aqueous solution

Abstract : This study is concentrated on the protectiveness of the carbon steel corrosion product scales in CO2 aqueous conditions. At first, a bibliographic study is performed on the characteristics of a corrosion product layer both from the electrochemical perspective and a structural perspective dealing with its morphology and composition. A specific section is dedicated to pseudo-passivation of carbon steels, a particularly protective condition that forms spontaneously in certain environments. Finally, the effect of relevant impurities presents in industrial environments such as chlorides, calcium ions and oxygen, is analyzed in relation to the protectiveness of the scales and the corrosion processes. In order to investigate the scales protectiveness and the changes that some inputs have on them pseudo-passivation, a reference experimental condition is selected. Pseudo-passive scales are composed by siderite; magnetite is observed occasionally and never forming a continuous film between the siderite layer and the carbon steel substrate. The electrochemical reaction mechanism explaining pseudo-passivation is investigated by applying different overpotential and flow conditions on the pseudo-passivated scales. Using the observations obtained with those experiments, an electrochemical impedance model is proposed explaining the behavior of the reactions before and after pseudo-passivity. It is considered that before pseudo-passivation, a simple reduction of the active surface slows down the corrosion of the carbon steel. After the pseudo-passivation, a diffusion limitation attributed to the anodic reaction (going through an adsorbed step process) is proposed. Finally, the effect of oxygen contamination in CO2 aqueous conditions is investigated. Oxygen contamination is introduced in the hundreds of ppb range. O2 changes the corrosion morphology from a uniform corrosion type to a localized one. Inside the localized corrosion features, other phases than siderite such as chukanovite, precipitate. The propagation of the localized corrosion features depth is strongly correlated to the oxygen content of the solution. The propagation of the pits stops when O2 is not present anymore and for our experimental conditions, a protective pseudo-passive layer is rebuilt. Our results could be explained with an O2 contamination model already proposed in the literature.
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Submitted on : Friday, July 22, 2022 - 3:34:11 PM
Last modification on : Friday, July 22, 2022 - 4:23:34 PM
Long-term archiving on: : Sunday, October 23, 2022 - 6:49:11 PM

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  • HAL Id : tel-03736581, version 1

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Edoardo Basilico. Carbon steel corrosion scales protectiveness study in CO2 aqueous solution. Material chemistry. Université de Lyon, 2021. English. ⟨NNT : 2021LYSE1305⟩. ⟨tel-03736581⟩

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