Corrosion of steels and irons immersed in natural seawater for up to 600 years

Marine immersion corrosion observations for archaeological and other data, including from shipwrecks, wrought iron anchors and cast iron bridge piers are used to estimate corrosion losses in natural unpolluted coastal and near-coastal seawaters for exposures up to about 600 years. Empirical functions for the development of corrosion loss with time were then developed, standardized to 20˚C mean seawater temperature. The resulting slightly non-linear corrosion loss trend, represented by a modified form of the power law, is consistent with Phase 4 of the previously proposed bi-modal corrosion model. These observations support the notion that the rate of long-term corrosion is controlled by outward diffusion, through the rust layers, of gaseous hydrogen generated by the cathodic hydrogen evolution reaction under predominantly anaerobic corrosion conditions. The power-law trend also provides good extrapolation from shorter- term data. For practical purposes for exposures < 100 years in seawaters with mean temperature around 20˚C, a linear model, with longer-term corrosion rate 0.06 mm/y at 20˚C, is sufficiently accurate.

In situ corrosion of canister materials in bentonite: the IC-A experiment at Mont Terri

Since 2012, a long-term in situ corrosion experiment (IC-A) has been conducted in the Mont Terri Underground Research Laboratory in Switzerland. The aims of the project with international partners are to confirm the long-term anaerobic corrosion rate of carbon steel and copper in compacted bentonite under repository-relevant environmental conditions, to gather in situ corrosion data supporting canister lifetime predictions, to provide confirmation of the effect of the bentonite buffer on microbial activity and microbially influenced corrosion, and to study the effects of welding (steel) and deposition technique (copper) on the corrosion properties of these candidate materials for disposal canisters. To date, carbon steel and cold sprayed and electrodeposited copper coatings have been retrieved after different exposure periods up to 3 years and characterised to establish the composition of the corrosion product, the morphology of the corroded surface, and to measure the rate of corrosion. For carbon steel specimens, a complex corrosion product was identified, consisting predominantly of magnetite. Low average anaerobic corrosion rates were measured for carbon steel and a very modest amount of alteration was identified on copper. The density and the initial form of the bentonite had a small influence on the rate of corrosion, across all materials.

Nitrite as a causal factor for nitrate-dependent anaerobic corrosion of metallic iron induced by Prolixibacter strains

Microbially influenced corrosion (MIC) may contribute significantly to overall corrosion risks, especially in the gas and petroleum industries. In this study, we isolated four Prolixibacter strains, which belong to the phylum Bacteroidetes, and examined their nitrate-respiration- and Fe0-corroding activities, together with two previously isolated Prolixibacter strains. Four of the six Prolixibacter strains reduced nitrate under anaerobic conditions, while the other two strains did not. The anaerobic growth of the four nitrate-reducing strains was enhanced by nitrate, which was not observed in the two nitrate-non-reducing strains. When the nitrate-reducing strains were grown anaerobically in the presence of Fe0 or carbon steel, the corrosion of the materials was enhanced by more than 20-fold compared to that in aseptic controls. This enhancement was not observed in cultures of the nitrate-non-reducing strains. The oxidation of Fe0 in the anaerobic cultures of nitrate-reducing strains occurred concomitantly with the reduction of nitrite. Since nitrite chemically oxidized Fe0 under anaerobic and aseptic conditions, the corrosion of Fe0- and carbon-steel by the nitrate-reducing Prolixibacter strains was deduced to be mainly enhanced via the biological reduction of nitrate to nitrite, followed by the chemical oxidation of Fe0 to Fe2+ and Fe3+ coupled to the reduction of nitrite.

Research on the St3 Carbon Steel Corrosion in the Presence of Microorganisms Isolated from the Groundwater at the Yeniseyskiy Site

The paper presents the experimental study exploring the corrosion of carbon steel St3 samples in the presence of a microbiological community sampled at the Yeniseiskiy site and the microbiota of bentonite clays. Depending on the conditions, an average 3—30-fold increase in the corrosion rate of steel was observed due to the biogenic and biogenic-mediated processes. The maximum steel degradation effect was observed at a temperature of 50°C in the presence of sulfate ions under conditions being considered optimal for sulfate-reducing bacteria. The developed steel corrosion model was used to determine the activation energy of the aerobic and anaerobic corrosion process.