Corrosion of Aluminum Fined Copper-Tube Heat Exchanger Coils

摘要

Aluminum finned copper-tube heat exchanger coils at an industrial facility experienced localized corrosion after a few months of operation. Initial testing indicated that the potential cause of corrosion was due to a process known as formicary corrosion. The source of the corrosion was investigated by performing air sampling of the location prior to and during the floor cleaning process as a way to determine whether the chemical cleaners used in the facility were potentially responsible for the accelerated corrosion. While some aggressive species were identified prior to the floor cleaning including formate, the measured levels of formate during the cleaning process were elevated from the initial baseline readings. Furthermore, acetate was not measured in the baseline readings, but was measured during the cleaning process. Two types of chemicals are used to clean the room containing the heat exchangers. Cleaner A is composed of two chemicals, one being alcohol based and the other chemical contains acetate groups. Cleaner B is composed of a long chained carbon molecule and oxygen organic component. Based on the air sampling results, the corrosivity of the two cleaners was examined. The experimental test consisted of filling a clean jar with the individual cleaning solutions diluted to ratios of either a 1:1, 6:1, or 12:1 with deionized water (DI). In addition, jars containing DI were used in the study. Copper tubes were maintained in the vapor space of the jars and exposed to a cyclic temperature between room temperature (≈24 °C) and 40 °C. The samples were exposed for 30 days. The results of the test showed minimal pitting on all samples, yet the material exposed to Cleaner A at a dilution ratio of 1:1 showed deep penetrating corrosion. The degradation was roughly halfway through-wall on the tubes exposed to the 1:1 Cleaner A to DI. From these results, it appears that the chemicals in the Cleaner A solution have the ability to lead to significant degradation in the copper tubing.