Abstract
Ant-nest corrosion is a specific type of premature failure (2-3 months) of copper tubes used in air-conditioning units causing the loss of refrigerant liquid and the consequent environment pollution. It is known that attack requires the simultaneous presence of moisture, oxygen and a corrodent, usually an organic acid, such as formic, acetic, propionic or butyric acid or other volatile organic substances like methanol, ethanol, formaldehyde or acetoaldehyde. Approximately 10% of all premature failures of copper tubes used in the heating, ventilation and air-conditioning (HVAC) industry are the result of ant-nest corrosion. This type of corrosion usually occurs in thin-wall copper pipes, especially when copper is de-sulphurised, and is known by several names: formicary corrosion, unusual corrosion, branched pits, pinhole corrosion, etc.
Highlights
In air-conditioning applications, premature failure of copper tubing frequently occurs due to pitting corrosion after a short period in service (2-3 months) and even during post-installation leakage tests or during degreasing and stamping processes
It has been suggested that this type of corrosion may be caused by the decomposition products of chlorinated organic solvents used in degreasing, cleaning and picking treatments of the copper tubes during manufacturing or joining processes, or by certain types of synthetic lubricant oils used during the copper tubing stamping process[1-8, 11 and 12]
The aim of this paper is to review the bibliography in this area, describing copper corrosion originated by carboxylic organic acid in simulated environments; the sources of organic acid emissions and generation; and the current state of knowledge on the mechanism of initiation of copper ant-nest corrosion
Summary
In air-conditioning applications, premature failure of copper tubing frequently occurs due to pitting corrosion after a short period in service (2-3 months) and even during post-installation leakage tests or during degreasing and stamping processes This unusual type of localised corrosion in thin-walled tubes has been described in the bibliography as ant-nest (formicary) corrosion[1,2,3,4,5,6,7,8]. It has been suggested that this type of corrosion may be caused by the decomposition products of chlorinated organic solvents used in degreasing, cleaning and picking treatments of the copper tubes during manufacturing or joining processes, or by certain types of synthetic lubricant oils used during the copper tubing stamping process[1-8, 11 and 12] These copper oxide deposits serve as a nutrient for the decomposition process by providing oxygen for chemical reactions to take place. The aim of this paper is to review the bibliography in this area, describing copper corrosion originated by carboxylic organic acid in simulated environments; the sources of organic acid emissions and generation; and the current state of knowledge on the mechanism of initiation of copper ant-nest corrosion
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