Abstract
Uniform oxidation is the most common type of corrosion of copper tubes in heat-exchanging refrigerating and air-conditioning units. Recently an unusual type of corrosion, “ant nest corrosion”, has been reported in such copper tubes at the final leakage test before shipment or a short time after installation. The corrosion is characterized by complicated microscopic caverns containing porous copper oxide connected by tunnels. The microcaverns have voids and cracks, and the surfaces of the copper tubes are tarnished dark-brown or red-brown without bulky corrosion products and show no obvious defects indicating the leaks. Sixty four cases of such premature failures of copper tubes discovered during the 11 years from 1978 to 1988 are listed in Table 1, including date of detection, application of copper tube, time to failure, wall thickness, location of attack, surface color and possible corrosives. Nomenclature for the localized corrosion and classification of different types of the ant nest corrosion with its size are also described. Nine typical structures of the ant nest corrosion are presented in the copper tubes for both air-conditioning units and simulation tests.
