Development of the Test Solution for Rapidly Evaluating the Corrosion Resistance of Copper Tubes and Investigation for Effectiveness of the Initial Treatment on the Corrosion Resistance

Abstract

Copper tubes are used in heat exchangers of refrigerators and air conditioning units. However, in some cases, the mechanically processed locations of copper tubes experience pitting corrosion. Therefore, a test scheme to rapidly evaluate the corrosion resistance of copper tubes at such sections and the effectiveness of the "initial treatment" on the corrosion have been investigated. "Initial treatment" is one of the chemical treatments that improves the corrosion resistance of copper tubes. The corrosion of the copper tube was investigated by observing the surface after immersing the copper tube in various solutions containing hydrogen peroxide, chloride, sulfate, benzotriazole and bicarbonate for one day. The test solution that contained a combination of hydrogen peroxide H2O2 10 mg/L, chloride ion Cl-300 mg/L, sulfate ion SO4 2-300 mg/L and benzotriazole 10 mg/L could replicate the actual aspects of corrosion on the copper tubes for a day. In this solution the corrosion of copper tubes was concentrated at the mechanically processed sections. The results indicated the high tendency of corrosion at the mechanically processed sections. The improvement of corrosion resistance at such sections by initial treatment was also confirmed in the test solution. Additionally, it was found that the corrosion resistance of copper tubes at mechanically processed section was weaker as the residual carbon content increased.