Abstract
Sulfur and water have a fundamental impact on the corrosion rate and potential failure of materials. It is therefore necessary to understand the mechanisms, rates, and potential means of transport, as well as the reactions of these elements with an alloy. This paper investigates the effect of water vapor in the initial stages of SO2 corrosion of an Fe-9Cr-0.5Mn model alloy at 650°C in situ under laboratory conditions using energy-dispersive x-ray diffraction analysis. Two separate experiments were run, one with a 99.5% Ar + 0.5% SO2 atmosphere and one with a 69.5% Ar + 0.5% SO2 + 30% H2O atmosphere. With a wet atmosphere, the alloy formed a scale with decreasing oxygen content towards the scale–alloy interface. Sulfides were identified above and below a (Fe, Cr)3O4 layer in the inner corrosion zone. In contrast to this, the overall scale growth was slower in a dry SO2 atmosphere.
Highlights
Ferritic–martensitic high-temperature alloys are state-of-the-art materials used for superheater tubes in coal, biomass, or cofired power plants.[1,2] The pipe materials P23, P91, P92, and VM12SH contain a minimum of 2% to 13% Cr by weight[3] to support the formation of protective Cr-rich oxide layers
This paper investigates the effect of water vapor in the initial stages of SO2 corrosion of an Fe-9Cr-0.5Mn model alloy at 650°C in situ under laboratory conditions using energy-dispersive x-ray diffraction analysis
The overall scale growth was slower in a dry SO2 atmosphere
Summary
Ferritic–martensitic high-temperature alloys are state-of-the-art materials used for superheater tubes in coal-, biomass-, or cofired power plants.[1,2] The pipe materials P23, P91, P92, and VM12SH contain a minimum of 2% to 13% Cr by weight[3] to support the formation of protective Cr-rich oxide layers. The harmful effect of water vapor at 1 bar on Fe-Cr alloys causes catastrophic breakaway oxidation of protective chromia (Cr2O3) scales.[9] Energy-dispersive x-ray diffraction (EDXRD) has been shown to be a powerful tool to follow the oxidation and sulfidation processes of materials at high temperatures in real time.[10,11] Based on this, the current work investigates the very early stages of oxidation and sulfidation of a ferritic 9 wt.% Cr-containing model alloy in SO2/H2O and SO2 atmospheres
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