Corrosion Behavior of Copper and its Welds by Bacteria in Underground Water(Materials, Metallurgy & Weldability)

概要

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Microbiologically Influenced Corrosion (MIC) was suspected in the corrosion failure of heat exchanger copper piping, carrying groundwater. Laboratory simulation studies were planned to find out the mechanism of corrosion. Ground water from the same plant was transferred to the laboratory aseptically and used for the experiment. Bacteria in the test solution were activated by the addition of low concentrations of nutrients. Cu samples were exposed to the test solution. After 2 weeks, many corrosion sites were observed on the surface in the form of pitting. On the other hand, pitting corrosion was not observed on exposure to sterile test solution. Culturing of bacterial strains in the ground water revealed 7 different species. Four of them were susceptible to microbicidal activity of copper. The remainder of them were incubated separately in liquid medium and exposure studies were conducted. Formation of biofilm on copper coupons was observed when they were exposed to the test solution with Staphylococcus sp. Under the biofilm, many corrosion sites in the form of pitting could be seen. Staphylococcus sp. are capable of fermentation of protein and thereby the production of ammonia. It is concluded that the copper coupons were corroded by ammonia in the test solution. The corrosion mechanism of copper pipe in ground water is discussed with reference to available literature.
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