Microbiologically influenced corrosion of copper - exposure, remedial treatment and ways to avoid it

摘要

A rare type of uniform corrosion is the microbiologically influenced corrosion (MIC) of copper. In Germany it could be characterized by a high copper content of water samples ("blue water phenomenon") and large tenorite layers on the internal surface of copper tubes. The drinking waters used are soft alkaline surface waters. In two private houses, mean copper values of approx. 3.5 mg/l were observed after 24 hours of stagnation. Consumers have never been at risk because the milky blue green water indicated that something was wrong. In one case, black solids were also found in the water samples and identified as tenorite. It was shown that thermal disinfection decreases the copper levels for some days (maximum 20 days). Comparisons of old and new installations demonstrated that only new zones of an installation could be affected, but never those where the normal malachite layer was formed. On the basis of this knowledge a remedial treatment could be developed by (1) removing existing layers and (2) avoiding long stagnation periods in such cleaned or in new installations. Pitting corrosion in horizontal tubes, often a secondary effect of MIC and caused by the settling down of corrosion products, never appears in these objects where the installation was regularly flushed immediately after MIC was identified.