Effect of Water Vapor on High-Temperature Corrosion under Conditions Mimicking Biomass Firing

Abstract

The variable flue gas composition in biomass-fired plants, among other parameters, contributes to the complexity of high-temperature corrosion of materials. Systematic parameter studies are thus necessary to understand the underlying corrosion mechanisms. This paper investigates the effect of water (H2O) vapor content in the flue gas on the high-temperature corrosion of austenitic stainless steel (TP 347H FG) under laboratory conditions, to improve the understanding of corrosion mechanisms. Deposit-coated and deposit-free samples were isothermally exposed for 72 h in a synthetic flue gas atmosphere containing either 3 or 13 vol % H2O vapor. Comprehensive characterization of the corrosion products was carried out by the complementary use of microscopic, spectroscopic, and diffraction-based techniques. To evaluate the effect of the exposure time, results were compared to previous results with longer isothermal exposure over 168 h and indicated that the development of a Ni-rich layer as a result of selective attack was time-dependent. The increase in the water vapor decreased the measurable corrosion attack, and in addition, decreased sulfation was observed. Results from the current investigation and from previously reported findings suggest that an increase in the water vapor content will cause competitive adsorption on active sites.