Abstract
There are cases of corrosion which are supposed to have been influenced by microbiological activities. It is not easy work to make the involvement of bacteria clear because of difficulties in reproducing the environmental conditions of the corrosion in question in laboratory tests. A case study introduced in this paper is a localized corrosion from cooling water environment on Ni-base alloy used in plate-type heat exchanger in chemical plants. It was made clear from observation of corrosion samples and through reproduction corrosion test in laboratory that some bacteria have contributed in causing the corrosion. With a series of laboratory tests, sterilization treatment of water was found quite effective to prevent bacteria-influenced corrosion and continuous application of biocide demonstrated a remarkable efficiency in preventing corrosion. The study results have already been adopted in actual plants and the corrosion in plate-type heat exchanger with Ni-base alloy have been largely prevented. No measurable shift of corrosion potential to noble side was observed by corrosion test. It is thought from the observation and examination above that the local environment in the plate had been severed by the influence of microbaiological activities.
