VC-20-005 -- Development of a New Accelerated Corrosion Test for All-Aluminum Microchannel and Tube and Fin Heat Exchangers--Part II: Chamber Study (RP-1645)

A new accelerated corrosion test was designed and implementedto assess corrosion resistance of all-aluminum microchannelheat exchangers. The chemical composition and pH ofcorrosive electrolytes were selected based on the InternationalOrganization for Standardization’s (ISO) Standard 9223,Corrosion of Metals and Alloys—Corrosivity of Atmospheres—Classification, Determination and Estimation, forsimulating various corrosive environments in an commerciallyavailable corrosion test chamber (ISO 2012). Temperature,duty cycle of wetting/drying cycles, and corrosive electrolyteconcentration as variables were studied at high and low levels.Four sets of tests were conducted on ten heat exchangersamples in each test. Chilled water was circulated in five of theten samples (except in the first run) for 2500 hours, and heatexchangers were removed periodically to assess for perforationusing a leak test. No leaks were detected after 2500 hoursfor any of the tested heat exchangers. However, pittingtendency was observed and quantified by pit density, pit depth,and pit area using optical microscopy. Plots of number of pitsand tables of pit depth and pit area are presented for each setof test runs. As expected, pitting tendencies exhibited certainvariance from one sample to the next depending on samplelocation inside the corrosion chamber. Heat exchangersamples exposed to corrosive agents that experienced wet/drycycles with chilled-water circulations showed higher numberof pits compared to their counterparts with no chilled-watercirculation. The bottom rows of most heat exchanger samplesshowed more severe pitting and damage due to accumulationof corrosive agents.