Microbiologically influenced corrosion inhibition of two marine structural steels caused by Halomonas titanicae in aerobic environments

Abstract

Corrosion is a global problem, especially in marine environments. The currently popular corrosion mitigation methods have the drawbacks of being costly, susceptible to environmental limitations, or causing environmental contamination. Microbiologically influenced corrosion inhibition (MICI), as a widespread phenomenon, can provide a new strategy utilizing bacteria to control corrosion. This study investigated the MICI mechanism of Halomonas titanicae on two marine structural steels (EH36-low alloy steel (E-LAS) (with copper) and Q235-carbon steel (Q-CS) (without copper)) in aerobic environments. Results show that the corrosion of E-LAS and Q-CS was both inhibited by H. titanicae in an aerobic enriched seawater. It was found that the aerobic respiration mode of H. titanicae was very different from its anaerobic respiration. The former respiration mode significantly reduced the dissolved oxygen (DO) concentrations in the medium. In addition, the DO levels in the biotic medium immersed with the two steels were similar, but the corrosion inhibition degree of E-LAS (22% drop) caused by H. titanicae was weaker than that of Q-CS (55% drop), indicating that the MICI mechanism of H. titanicae goes beyond simply reducing the DO concentration. The number of sessile cells on E-LAS was only 20% of that on Q-CS due to Cu in E-LAS, which led to a thinner extracellular polymeric substance (EPS) film and a corrosion product film with less Fe(II) content. This reduced the Rf values significantly. Therefore, the EPS and corrosion product films caused by H. titanicae aerobic respiration are also important in the corrosion inhibition process.