On rare occasions, pitting corrosion occurs over a short period of time in copper tubes used as heat transfer tubes in open cooling water systems in air conditioning systems etc. It was supposed that deposits were one of the causes of the pitting corrosion of copper tubes. Therefore, the influence that various deposits gave to pitting corrosion of copper tubes was evaluated. Macro-cell tests that reproduced the state that deposits appeared in the defect of residual free carbon on copper tubes were examined. The results showed that rust of steel had a much greater effect for the corrosion than deposits of calcium carbonate, silica, calcium silicate, and so on. It was thought that the reason was that the formation of the oxide film on copper surface was obstructed by the rust of steel. One of the reasons is that the pH of rust of steel is slightly low. It was found that the oxide film forming on the copper surface in advance suppressed the influence on corrosion of the deposition of the rust of steel.
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