Abstract
Metal dusting is a localized degradation that occurs in environments containing carbon and hydrogen compounds, but almost no oxygen. Metal dusting was observed in the inlet tube of a heat exchanger unit, where the high temperature reaction gas is employed for getting high temperature water steam. Alloy 800 was used for inlet tube manufacturing. Analysis of surface contaminants showed two forms of carbon in it: very fine globular, very probably amorphous and rod-like, which could be crystalline. Preferential diffusion of carbon through the broken oxide surface layer leads to precipitation of secondary phases and dusting of metal.

Key words
metal dusting, metallography, diffusion, hardness

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