1998 Volume 47 Issue 7 Pages 468-475
Corrosions were found at the heat-exchanger made of Cu pipes which the reason why this trouble had estimated may be due to the microbially influenced corrosion (MIC). Laboratory measurements by the use of the same environments were planed. Underground water from the same plant was transferred to laboratory. Bacteria in the test solution was activated by the addition of small nutrients in the underground water. Cu samples were exposed to the test solution. After 2 weeks, a lot of pits occurred on the surface. On the other hand, pitting corrosion was not observed a test solution, which was sterilized by autoclaving. Culturing of bacteria residing in the underground water revealed 7 different species of bacteria. It was became that some 4 species of bacteria were killed by microbicidal activity of Cu ion. The residual 3 species were incubated separately in liquid culture. Next, this liquid culture was used as exposure test solution. Formation of biofilm on the Cu sample surface was observed when the samples were exposed in the test solution with the Staphylococcus sp. Under the biofilm, a lot of pits were occurred. It was became that the Staphylococcus sp. had an ability of proteinaceous fermentation. This fermentation produces ammonia. In conclusion, metallic Cu are corroded by the ammonia in the test solution. Corrosion path of Cu pipe by the underground water are discussed.