Corrosion mechanisms and models for flue gas corrosion in aluminium heat exchangers

In the recent years condensing wall-hung gas-fired boilers have become the benchmark product in their class of appliances for residential heating with fossil fuels. Due to the compact construction of the heat exchanger, its narrow gas channels are easily clogged by corrosion products which represent an unavoidable side-effect of dew point corrosion. As a result, the clogged heat exchanger can give rise to malfunctioning of the condensing boiler, which should be avoided. The additional heat from the flue gas is being reused by the condensing boiler, as it flows through the heat exchanger. Condensation of combustion products from natural gas occurs where the temperature locally drops below the dew point of the gas mixture, which yields a flim of acidic solution on each surface of the boiler heat exchanger that is exposed to the flue gas flow during the boiler's burning cycles. The concentration of this acidic condensate changes according to the temperature gradient along the heat exchanger, which leads to various corrosion mechanisms. The final target of the experimental investigation was the determination of the main parameters affecting the dew point corrosion rates on the heat exchanger fins. A dew point corrosion setup has been developed to simulate the real conditions in the flue gas. In order to understand the dew point corrosion behavior, the factors that influence the acid condensation rate and corrosion rate according to the temperature gradient are focused on. A dew point corrosion setup has been developed to simulate the real conditions in the flue gas.