Analysis of Water Quality for Pitting Corrosion Risk of Copper Used in Heat Exchanger of Air Conditioner

The leakage accident of the water supply pipe and the pipe heat exchanger was the major problem [1, 2], which is attributed to the pitting corrosion of copper. The mechanism of the pitting corrosion of copper has been investigated widely [1-5]. Campbell [1, 3, 4] discussed the occurrence of the pitting corrosion of copper under flowing hard and soft water in the water pipes, indicating that the dissolution of copper was influenced by the water quality significantly.

In the present study, the pitting corrosion risk of copper used in the heat exchanger of air conditioner was investigated by the parameters of the water quality sampled by the copper heat exchanger of the air conditioner of all over the country in Japan. The parameters (pH, acid consumption, total hardness) and the concentrations of Cl^- and SO₄^2- of the sampled water were analyzed to construct two-dimensional phase diagrams. The polarization curve measurement was performed by three-electrode system. The working electrode (0.20 cm²) was the copper plate and the counter electrode was the platinum wire. The KCl-saturated silver/silver chloride electrode (SSE) was used as the reference electrode. The measurement was started from the rest potential to 1.0 V vs. SSE at 100 mV/min. All the potentials in this paper were referred to SSE. The compositions of test solution were determined by the results of the analysis for the sampled water from the copper heat exchanger of the air conditioner of all over the country in Japan. All measurements were made at 25 ^oC. The results of the two-dimensional phase diagrams and the electrochemical measurement were discussed in this paper.

Reference

[1] H. S. Campbell, Journal of Applied Chemistry, 4, 633 (1954).

[2] V. F. Lucey, British Corrosion Journal, 2, 175 (1967).

[3] H. S. Campbell, Water Treatment and Examination, 20, 11(1971).

[4] H. S. Campbell, Journal Institute of Metals, 77, 345 (1950).

[5] R. May, Journal Institute of Metals, 82, 65 (1953).