2005 Volume 54 Issue 3 Pages 120-123
We performed the electrochemical experiments, such as measurements of polarization curves, corrosion potentials and constant-potential holding tests, using copper tubes with/without residual carbon film under water with/without nitrite inhibitor taken from the heat storage plants working in Tokyo. The polarization curve under the water with nitrite inhibitor shows the passivation from -950mV to 120mV (Ag/AgCl), while the one under the water without inhibitor does not show the passivation. The passive current density of the copper tube with residual carbon film is higher than that of the copper tube without carbon film. In the constant-potential holding test at 200mV for 168h, the current density at 168h was 20μA/cm2 under the water without inhibitor and 0μA/cm2 with inhibitor. After the constant-potential holding test, the surface of specimens in the water without inhibitor were covered with the oxide films and patinas. The surface of specimens in the water with inhibitor remained the bright metallic color and had spottily some patinas. Under these patinas, the pitting corrosion has slightly occurred.