It is known that one of the causes of pitting corrosion of copper tubes is residual carbon on the inner surface. It was confirmed that type I" pitting corrosion of the copper tube is suppressed by keeping the residual carbon amount at 2 mg/m 2 or less, which is lower than that of the type I' pitting corrosion, or by removing the fine particles that are the corrosion product of galvanized steel pipes. The developed water treatment chemical was evaluated using three types of copper tubes with residual carbon amounts of 0 mg/m 2 , 0.5 mg/m 2 , and 6.1 mg/m 2. The evaluation was conducted for three months in an open-circulation cooling water system and compared with the current water treatment chemical. Under the current water treatment chemical conditions, only the copper tube with a residual carbon amount of 6.1 mg/m 2 showed a significant increase in the natural corrosion potential after two weeks, and pitting corrosion occurred. No pitting corrosion and no increase in the natural corrosion potential were observed in any of the copper tubes that were treated with the developed water treatment chemical. In addition, the polarization curve was measured using the cooling water from this field test, and the anodic polarization of two cooling waters was compared. For copper tubes with a large amount of residual carbon, the current density near 0 mV vs. Ag/AgCl electrode (SSE) increased when the developed water treatment chemical was added.

The copper tubes of heat exchangers used in air conditioning and sanitation equipment have been reported to show type I pitting corrosion due to the synergistic effects of carbon film and water quality. To quantify the carbon film, the inner surfaces of the tubes after degreasing with acetone are dissolved with a mixture of nitric and hydrochloric acid to allow collection and analysis of the attached carbon. However, there are concerns about the difficulty and danger of the conventional procedure. Therefore, a simple method for quantifying carbon film is required. We reported a method for measuring the difference between the corrosion potentials on the inside with attached carbon film and outside with removed carbon film of copper tubes. However, data variation is observed in medium residual carbon, which is thought to be due to uneven carbon film. In this study, we examined the correlation between residual carbon and composition of surface for X-ray photoelectron spectroscopy (XPS) measurement. The results confirmed that the peak of C 1s increased and Cu 2p 3/2 decreased with increasing residual carbon. As the residual carbon and the integrated intensity at C 1s in the same way showed a linear relation, the residual carbon can be determined by the XPS measurement.

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Open Journal of Composite Materials a small amount of residual carbon (anode). In addition, the higher the area ratio of the carbon film was, the larger the galvanic current tended to be.

Corrosion has been reported to occur in the copper tubes of heat exchangers in multiple-circulation hot water supply systems. We have been investigating the applicability of high-strength Cu-0.65 mass% Sn-0.014 mass% Zr-0.020 mass% P alloy to counteract this corrosion. Immersion tests, electrochemical measurements, and field tests were performed. Excellent corrosion resistance of the alloy was established under conditions with flowing water due to the formation of composite films containing tin. The alloy is expected to be better than copper as a corrosion-resistant material for heat exchanger tubes.