DEVELOPMENT OF A REPRODUCIBLE SCREENING METHOD TO DETERMINE THE MECHANISM AND EFFECT OF ORGANIC ACIDS AND OTHER CONTAMINANTS ON THE CORROSION OF ALUMINUM-FINNED COPPER-TUBE HEAT EXCHANGE COILS

Abstract

Indoor corrosion failures of aluminum-finned copper-tube evaporator coils, and also in some systems without aluminum fins, is a menacing issue in the heating, ventilation, and air conditioning (HVAC) industry. Extensive laboratory testing has verified the development of a reproducible screening method to assess suspected contaminants of producing premature failures of copper tube resulting from a very localized form of corrosion known as “formicary corrosion” [a/k/a “ant nest corrosion”]. This paper provides a historical perspective on formicary corrosion and various mechanisms. BACKGROUND Indoor corrosion failures of aluminum-finned copper-tube evaporator coils, sometimes without aluminum fins, is a menacing issue in the heating, ventilation, and air conditioning (HVAC) industry. Of note, significantly from Japanese research, is the conclusion that approximately 10% of all premature failures of copper tube result from a very localized form of corrosion known as formicary or “ant nest” corrosion. Based on this fact alone, the HVAC industry worldwide has recognized that formicary corrosion, albeit not identified as such in most instances, accounts for many premature failures in copper products. Some geographic areas within the United States have experienced higher incidences of formicary corrosion than others, and likewise, some homes experience multiple failures while those around them appear immune. Failures typically manifest as leaks that form under the aluminum fin pack area of the evaporator coil within a few years of installation. A comprehensive study by Carrier (1) has identified this form of corrosion in most coil brands from all the major suppliers.