Rökkanaler av metall - korrosionsprovningsmetod med omväxlande förbränning av vedbränsle och lättolja

• This report presents the results of the STEM project number 11885-2. The aim of the project was to develop a corrosion test method for metal flue liners with alternating wood and oil burning. Indeed, the conditions gathered by the alternate use of wood and oil for combustion are considered to be severe for metal chimneys, because of the combination of low temperature corrosion (condensation corrosion) involving aggressive ions like chloride, corrosion promoting air pollutants as sulfur dioxide, and high temperature corrosion involving oxidation mechanisms. For the moment there exists no standard method at a European level for the testing of metal flue liners in the conditions named above. Moreover, the combination of oil and wood is becoming more and more common in private houses, especially in northern Europe (mostly Sweden and Finland). The tests performed in this project used partly light oil containing small amounts of sulfur, pellets, and a combination of pellets and light oil that was spiked with determined amounts of chloride and sulfur so that relative high concentrations of chloride and sulfur dioxide were obtained in the flue gas. In none of the six-weeks test performed corrosion could be observed on the metal flue liners of two stainless steels, namely ASTM 304 and 316 (corresponding to SS 2333 and SS 2343). Acceleration was obtained mainly by temperature cycling in that way that condensation corrosion was first initiated. Thereafter the condensate was evaporated and during this process the corrosion promoting contaminants in the condensate increased till the metal flue liner was completely dried. A condensation/drying up cycle lasted for half an hour The proposed test method, apart from having a too low acceleration factor, was found to be difficult to realize with regards to security and handling. Instead of increasing the acceleration factor by varying key parameters, which involves the risk of modifying the corrosion mechanisms compared to real conditions, another method is proposed to be developed in a future work. This unconventional and general method, developed originally by CSTB in France, is based on corrosion by condensate in controlled conditions. The method has shown promising results for some fuels, but needs further development to be used a European standard.

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