Corrosion of SUS304 Stainless Steel Pipe Induced by Manganese Oxide Deposition

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In order to understand the corrosion phenomenon of a 304 type stainless steel pipe that was used in a water filtration plant, the water inside the pipe was analyzed, and the distribution of corrosion location, the shape of corrosion pit as well as the corrosion morphology were observed. Besides, the potential of the corroded pipe in fresh water was measured. It was found that crevice corrosion occurred not only near welds but also at base metal and the flange of the pipe, although the chloride ion concentration in the water was less than 30ppm. Manganese oxide was observed on the inner surface of the pipe, which made the potential of the pipe higher than ER, CREV of 304 stainless steel, and thus induced the corrosion of the pipe. The manganese oxide was believed to result from oxidizing of Mn2+ in the water by chloric disinfectant. The shape of corrosion pit and its corrosion morphology in this investigation are similar to those observed at corrosion pit of MIC (microbiological induced corrosion) of stainless steels, which suggests that it is difficult to determine MIC from only the pitting shape and corrosion morphology.
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