Evaluation of metal dusting of nickel-chromium-iron based alloys in a laboratory environment
Master Thesis
2006
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University of Cape Town
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Abstract
The deposition of carbon from a carbon-rich environment onto structural materials is prevalent in petrochemical and chemical industries such as in the production of syngas, iron reduction plants, petroleum refineries, carbon dioxide cooled nuclear plants, fuel cells using molten salts and hydrocarbons, and the recycle-gas loop equipment of coal-gasification units. The consequence of carbon deposition is a metal related degradation phenomenon known as "Metal dusting". Metal dusting results in rapid material wastage and/or thinning of material, producing hemispherical pits and grooves as the affected material disintegrates into a mixture of carbon and metal particles. The aim of this study was to elucidate material factors that cause or contribute to metal dusting. This was achieved by refurbishing the in-built metal dusting rig to carry out experimental tests on a laboratory scale. The objectives of this research were to simulate a metal dusting environment, characterize the resistance of various alloys to metal dusting, and to evaluate the effects of surface treatment and temperature on metal dusting. Metal dusting was induced on a wide variety of nickelbased and iron-based alloys which were capable of forming chromium oxide scales in a flowing CO-HrH20 atmosphere at 650°C and 500°C. Some of the alloys were heat treated at 850°C for an hour prior to exposure and others were ground to 600 grit SiC. Some degree of metal dusting attack was observed for all alloys tested except for an alloy with high chromium and nickel content. The results indicated that metal dusting is much more aggressive at lower temperatures than at high temperatures. It was also observed that the surface working of the alloys had a very significant effect to metal dusting resistance as well as the amount of scale forming elements additions and the presence of certain carbides forming elements. The preheat treatment seemed not to have a Significant effect on the resistance to metal dusting.
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Includes bibliographical references (leaves 115-120).
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Marekwa, M. 2006. Evaluation of metal dusting of nickel-chromium-iron based alloys in a laboratory environment. University of Cape Town.