Controlling Factors of Localized Corrosion in Boiler Combustion Gas Environments

Abstract

Localized corrosion (LC) sometimes appears in boiler tubes exposed in severely corrosive combustion gases including Cl, S and O, but prediction and on-site maintenance of LC is actually difficult in many cases. Therefore understanding the cause of LC is considered to be important to maintain safety services and estimate lifetime in high temperature facilities. This LC occurs due to formation of partially different corrosive conditions due to fuels, condition of combustion, designing of boilers, and materials. In this paper, investigation results of macroscopic LC and influenced factors formed in actual boilers were described with the four cases of fossil fuel, biomass and WTE boilers, and also described against any coatings. Mechanisms of each LC were considered individually by using cut-off samples of damaged tubes, detailed analyses of corrosive environments and results of laboratory tests. From these considerations, protective oxide layers and not only static factors but also dynamic factors arising in operated conditions such as temperature and composition fluctuations were concluded to be important for the accurate lifetime evaluations of tube materials and coatings.