Corrosion of Carbon Steel in Marine Environments: Role of the Corrosion Product Layer

Abstract

This article presents a synthesis of recent studies focused on the corrosion product layers forming on carbon steel in natural seawater and the link between the composition of these layers and the corrosion mechanisms. Additional new experimental results are also presented to enlighten some important points. First, the composition and stratification of the layers produced by uniform corrosion are described. A focus is made on the mechanism of formation of the sulfate green rust because this compound is the first solid phase to precipitate from the dissolved species produced by the corrosion of the steel surface. Secondly, localized corrosion processes are discussed. In any case, they involve galvanic couplings between anodic and cathodic zones of the metal surface and are often associated with heterogeneous corrosion product layers. The variations of the composition of these layers with the anodic/cathodic character of the underlying metal surface, and in particular the changes in magnetite content, are thoroughly described and analyzed to enlighten the self-sustaining ability of the process. Finally, corrosion product layers formed on permanently immersed steel surfaces were exposed to air. Their drying and oxidation induced the formation of akaganeite, a common product of marine atmospheric corrosion that was, however, not detected on the steel surface after the permanent immersion period.

Influence of Mg2+ Ions on the Formation of Green Rust Compounds in Simulated Marine Environments

“…Therefore, the smallest [Mg II ]/[Fe II ] ratio of 1/3 considered here would correspond to a Fe 2+ concentration of 0.16 mol/kg in the bulk seawater, which is rather high. However, GR(SO 4 2− ) is the main GR compound identified in the corrosion product layers formed on steel immersed in seawater [1,2,[5][6][7]. At the vicinity of the steel/seawater interface, where the Fe 2+ cations are produced, the [Mg II ]/[Fe II ] ratio is necessarily lower than in the bulk seawater and it can be forwarded that the formation of GR(SO 4 2− ) only takes place close to the steel surface.…”

“…Green rust compounds (GR) are common and important corrosion products of steel exposed to marine environments [1]. They are mixed valence Fe(II,III) hydroxysalts and a particular case of layered double hydroxide (LDH).…”

“…This precipitation reaction is assumed to mimic the process leading from the dissolved species produced by the corrosion of steel to the GR compound. It corresponds to the first step of the formation of the corrosion product layer that covers steel surfaces immersed in seawater [1,2]. The aim of the study was then to determine the effects of dissolved Mg(II) species on the precipitation reaction.…”

Plasticity of Bead-on-Plate Welds Made with the Use of Stored Flux-Cored Wires for Offshore Applications

“…The degradation of the surface of wires is one of the first signs of environmental impact on the material. General and atmospheric corrosion develops on the surface of the wires [ 5 , 6 , 26 ]. Depending on the storage location, it had a different intensity—A and B wires in MAB were exposed to increased relative humidity, which was the reason for accelerating surface degradation.…”

“…Even assuming proper supervision of transport, warehousing and storage environmental influence on the wires is difficult to avoid. This is a threat especially in the extreme conditions prevailing in the maritime industry characterized by high humidity, the presence of salt and often variable temperature values [ 20 , 25 , 26 ].…”