Abstract
Microbiologically influenced corrosion (MIC) is the rapid deterioration of structural materials induced by the action of microorganisms in an environment. Microbial adhesion and proliferation on the material surface are precursors to corrosion initiation, and if the material is stainless steel, its open-circuit potential can be ennobled. Therefore, extensive biofilm formation on metal surfaces and the ennoblement of the open-circuit potential of corrosion-resistant steels are recognized as indicators of MIC.
Numerous laboratory-scale studies have been conducted on the correlation between microbial adhesion on materials and initiation of MIC. However, only few studies have been conducted on the correlation between metallurgical factors of structural materials and the amount of microbes or flora on the material surface in actual environments.
We conducted systematic research focused on material types or alloying elements to investigate how such metallurgical factors affect microbial activity in the field. The corrosion behavior was examined using corrosion engineering methods such as potential measurement and weight loss evaluation. Thereafter, the amounts of microbes and flora adhering to copper, carbon steel, and stainless steel coupons in freshwater were determined using a genetic analysis method. Material analysis indicated that the no rapid change in potential over time was observed for the copper specimen, which ranged from −10 to 60 mV. Moreover, minimal surface stains such as slime was observed on the surface of the copper specimen when compared to the carbon steel surface, which exhibited significant amounts of rust within one month of exposure. Microbial analysis also showed a remarkable decrease in the concentration of bacteria on the surface of the copper specimen over time. These results indicate the considerable potential for the use of copper in practical environments. Thus, this study has captured the growth of microorganisms and the transition of microbial community structure reflecting nutrient requirements in parallel with the process of corrosion induction in an actual environment.
This Paper was Originally Published in Japanese in J. Japan Institute of Copper 60 (2021) 150–156. The captions of Table 1, Table 2, Fig. 3, Fig. 4 and Fig. 5 are slightly modified.
This plot shows the principal coordinates analysis (PCoA) based on the weighted UniFrac distances of 16S rRNA genes in each community structure. The UniFrac distance is a metric distance based on the phylogenetic distances of OTUs observed in microbial communities. In this PCoA plot, the OFHC copper samples are clearly located away from the water and deposit samples, i.e., the sediments in the aerobic pool. This result suggests that a special microbial community structure is formed on the surface of the OFHC copper specimens. Conversely, the microbial community on the SPCC-SB surface showed similar α-diversity to that of the water samples, whereas the β-diversity analysis showed that the microbial community structure clearly differed from that of environmental water, deposit/aerobic pool sediments, and the attachments on OFHC copper.
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