Filtration–UV irradiation as an option for mitigating the risk of microbiologically influenced corrosion of subsea construction alloys in seawater

The effect of filtration-UV irradiation of seawater on the biofilm activity on several offshore structural alloys was evaluated in a continuous flow system over 90 days. Biofilms ennobled the electrode potential by +400–500 mV within a few days of exposure to raw untreated seawater. Filtration-UV irradiation of the seawater delayed the ennoblement of the steels for up to 40 days and lowered localized corrosion rates in susceptible alloys. Ennobling biofilms were composed of microbial cells, diatoms and extracellular polymeric substances and the bacterial community in biofilms was affected by both the alloy composition and seawater treatment

Use of an Electrochemical Split Cell Technique to Evaluate the Influence of Shewanella oneidensis Activities on Corrosion of Carbon Steel

Microbially induced corrosion (MIC) is a complex problem that affects various industries. Several techniques have been developed to monitor corrosion and elucidate corrosion mechanisms, including microbiological processes that induce metal deterioration. We used zero resistance ammetry (ZRA) in a split chamber configuration to evaluate the effects of the facultatively anaerobic Fe(III) reducing bacterium Shewanella oneidensis MR-1 on the corrosion of UNS G10180 carbon steel. We show that activities of S. oneidensis inhibit corrosion of steel with which that organism has direct contact. However, when a carbon steel coupon in contact with S. oneidensis was electrically connected to a second coupon that was free of biofilm (in separate chambers of the split chamber assembly), ZRA-based measurements indicated that current moved from the S. oneidensis-containing chamber to the cell-free chamber. This electron transfer enhanced the O2 reduction reaction on the coupon deployed in the cell free chamber, and consequently, enhanced oxidation and corrosion of that electrode. Our results illustrate a novel mechanism for MIC in cases where metal surfaces are heterogeneously covered by biofilms

Monitoring of anaerobic microbially influenced corrosion via electrochemical frequency modulation

Electrochemical frequency modulation (EFM) is a rather novel technique to monitor corrosion rates in situ, providing direct access to Tafel slopes with only minor polarization. So far EFM has been applied mainly for electrochemical corrosion monitoring in purely chemical corrosion systems with predominant uniform corrosion, but it has also great potential for monitoring microbially influenced corrosion (MIC). Thus, in this study MIC induced by different cultures of sulfate-reducing bacteria (SRB) was monitored with EFM, and compared to results from linear polarization resistance (LPR) and measurements of the free corrosion potential E-corr. The electrochemical results obtained in small scale bioreactors with a three electrode setup were complemented by chemical analysis and SEM observations. SRB featuring high corrosion rates were compared to non-corrosive but still H-2-consuming control SRB, sterile controls and abiotic sulfide corrosion controls. Corrosion rates determined with EFM and LPR were accurate and precise in all cases as long as the system was based on uniform corrosion. However with the onset of localized corrosion both methods fail to predict accurate rates. Unlike other electrochemical corrosion rate measurements, EFM has the advantage to provide indicating ratios in the current response at different frequencies, so-called causality factors, which allow identifying changes in the corrosion system and therefore assessing the accurateness of the obtained results. As a consequence EFM is a promising electrochemical corrosion monitoring technique for MIC in fundamental and applied studies. (c) 2013 Elsevier Ltd. All rights reserved