W. Wang, W. Schmid, W. Fürbeth
Proc. EUROCORR 2013, Estoril/P (2013)
Condensing boilers can achieve high level of efficiency by using the waste heat in the flue gases to pre-heat the cold water entering the boiler. During this process, acidic condensate is produced in the heat exchangers and flue gas ducts. The condensate leaves the system through a drain system.
The heat exchangers and drain systems are contaminated and/or clogged with corrosion products easily. Due to the acidic condensate corrosion the compact constructions of heat exchangers with narrow gas channels are clogged easily. Therefore this is an urgent problem especially for new boiler models that will reach the market in the following years. For this purpose a better understanding of the underlying processes leading to corrosion and contamination/clogging of systems should be obtained.
The corrosion behaviour and microstructure of Al230 alloy which is used in this project have been investigated. The microstructure of original and corroded sample surfaces was studied using scanning electron microscopy (SEM), energy dispersive spectroscopy (EDX) and electron probe micro-analysis (EPMA). The initial obtained results of immersion tests have confirmed former investigations: the corrosion rate increases with time and acid concentration, and slightly increases with temperature; the Al matrix is easier to be dissolved in the acidic solution, which makes the latticed Si phase exposed to the surface as black residue.