Corrosion of Aluminum-fin, Copper-tube Heat Exchange Coils

Over the past several years the HVAC industry has experienced a large increase in instances of leaks in the central portion of aluminum-finned, coppertube heat exchange coils. These leaks are characterized as being very small in size and very high in numbers within a single coil. There are many chemical species that can cause these coil leaks, including chlorides from pool chemicals and clothes washing, sulfur from tap water, lubricants and nearby industries, and ammonia compounds from cleaners or nearby industries. However this recent increase in reported coil leaks is being attributed to a newly discovered class of corroding agents. These are low molecular weight organic acids such as acetic acid and formic acid. This paper gives some background information on leak causes and then presents the diagnostic procedures typically used to determine these causes. Results of some of these analyses are also presented. As many of these procedures are new and often company-specific, there are no accepted industry standard procedures to test process chemicals or application contaminants for copper tube corrosion potential. Industry supported research has begun to develop a bench test for this