Galvanic effects induced by siderite and cementite surface layers on carbon steel in aqueous CO2 environments

• Published in: Corrosion science Vol. 209; no. 110762; p. 110762
• Main Authors: Owen, Joshua, Ropital, Francois, Joshi, Gaurav R., Kittel, Jean, Barker, Richard
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.12.2022; Elsevier
• Subjects: Carbon steel; Chemical Sciences; Electrochemistry; Galvanic corrosion; Iron carbide; Iron carbonate; Localised corrosion; or physical chemistry; Theoretical and; Galvanic corrosion; Localised corrosion; Electrochemistry; Carbon steel; Iron carbide; Iron carbonate
• ISSN: 0010-938X; 1879-0496
• DOI: 10.1016/j.corsci.2022.110762

Siderite (FeCO3) and cementite (Fe3C) layers develop naturally on carbon steel surfaces in aqueous carbon dioxide (CO2) environments. This study evaluates galvanic corrosion induced by such layers when coupled to bare carbon steel. In CO2-saturated, 50 °C, pH 5 conditions, the Fe3C-filmed carbon steel acted as the net cathode, significantly enhancing bare steel corrosion rates. Galvanic currents induced by the FeCO3-filmed steel were much lower, with FeCO3 removed from the surface as Fe3C was revealed concomitantly on bare steel. It is proposed that the presence of Fe3C amongst the FeCO3 layer is responsible for galvanic interaction, rather than FeCO3 itself. •FeCO3 and Fe3C surface layers formed naturally on carbon steel coupons.•Galvanic current magnitude coupled to bare steel: Fe3C-layered > > FeCO3-layered coupons.•Gradual revealing of Fe3C on bare steel subsequently damaged FeCO3 layer.•Presence of Fe3C on the FeCO3-layered coupon was the cause of galvanic interaction.•Galvanic current when FeCO3-layered coupon coupled to pure iron > > carbon steel.