1999 Volume 48 Issue 7 Pages 425-431
Copper tubes have been widely used for water supply and heat exchangers. In such systems copper tubes often suffer from type I pitting-corrosion. A mechanism of the type I pitting-corrosion on copper tubing has been presented, but a initiation mechanism of the pitting corrosion is still unknown. In this paper we aimed to clarify the initiation mechanism of the pitting corrosion.
Copper-tube specimens were immersed in a circulating solution. The solution had been used for heat exchangers at a Japanese factory where the water leakage occurred by the pitting corrosion on copper tubes. The solution contained tiny precipitates resulted from corrosion of galvanized steel pipe. During the immersion test changes in the surface state of a copper tube was analyzed by in situ RAMAN (in situ Raman Spectroscopy), SEM (Scanning Electron Microscope), EPMA (Electron Probe Microanalysis), AES (Auger, Electron Spectroscopy) and XPS (X-ray Photoelectron Spectroscopy).
The pitting corrosion was observed only in the test solution which had been used for heat exchangers. It was considered that Cu2O film on the copper-tube surface became less stable on which the tiny precipitates deposited, and that Cu2O film could not protect the copper-tube surface. It will be the cause why the type I pitting-corrosion occurred.
