Corrosion of carbon steel under sequential aerobic–anaerobic environmental conditions

• Under oxygen supply conditions, steel developed iron oxide surface deposits.
• Sequential aerobic–anaerobic conditions lead to the formation of protective layer.
• Under direct anaerobic conditions, the mackinawite corrosion layer was less protective.
• The corrosion rate depends on the structural properties of the corrosion products.

We investigated sequential aerobic and anaerobic microbiologically induced corrosion of carbon steel to simulate deep geological disposal conditions. Under limited oxygen supply, lepidocrocite and magnetite corrosion products formed on the steel coupon, while under continuous oxygen supply, a mixture of lepidocrocite, maghemite and magnetite was identified. Upon oxygen consumption and establishment of sulphidogenic conditions, due to sulphate-reducing bacteria activity, all these oxides disappeared via transformation into pyrrhotite. Corrosion rate of steel in direct anaerobic cultures was higher than that of steel initially corroded in aerobic condition, suggesting a protective role of corrosion product layer formed under sequential aerobic–anaerobic conditions.