Relationship between activity of sessile microorganisms and microbial corrosion of stainless steels in seawater

摘要

Type 316L stainless steel (SS) specimens were exposed to natural seawater at various seasons. The concentration of H_2O_2 in native biofilms formed on the specimens was detected after the exposures and open circuit potentials (OCP) for the specimens were also measured. At a summer season, the concentration of H_2O_2 was higher than 10ppm and OCP were nobler than +0.6V vs. SHE. On the other hand, H_2O_2 concentration was lower than 1ppm and OCP were less noble than +0.3V vs. SHE at a winter season. The specimens were moved to synthetic seawater, to which Catalase or Peroxidase was dosed, and H_2O_2 in native biofilms was disintegrated. The ennoblement of OCP was canceled by disintegrating H_2O_2. Natural seawater was pumped through type 316L tubes. After the water flowing process, the inner surfaces of the sample tubes were observed with a fluorescence microscope, and the numbers of viable bacteria, as well as the numbers of inviable bacteria, were counted. The deposits on the surfaces, including the biofilms, were removed and the surfaces were observed with a laser microscope. More corrosion pits were observed on the surfaces of the sample tube, on that there were a larger number of viable bacteria than on the surfaces of the other sample. Therefore, the initiation of pitting on type 316L SS exposed to natural seawater is assumed to be under the influence of the density of viable bacteria on the surfaces.