An Overview of Metal Dusting in Synthesis Gas Environments

Abstract

This paper gives an overview of the different processes of metal dusting (MD) that operate on low and high alloyed iron and nickel base alloys exposed in CO+H2–containing environments with or without water vapour. MD of pure metals like iron and nickel occur with a solely carbon-induced corrosion mechanism. However, in high alloyed materials with strong oxide formers such as Cr and Al, a more complex MD-process takes place which involves both carbon and oxygen in close collaboration. The “alloyed” carbides, i.e normally Cr-containing carbides, formed in such materials are thermodynamically stable with respect to the carbon activity. However, in the reaction front of a MD-pit with non-protective spinel oxide, they destabilise and dissolve due to the influence of the low oxygen activity determined by CO-dissociation. Based on recent results in the field of MD a chart with tentative MD mechanisms is presented as a function of alloy composition and temperature.

An Expanded Model for the Pressure Effect in Metal Dusting of Mn-Containing Alloy 600 Based on Advanced Scale Characterization

“…This poses a severe problem for industrial applications which use carbonaceous gases at high temperatures. The general underlying mechanisms and conditions have been very well elucidated through the extensive work of the groups of Grabke [1], Young [2], Szakálos [3], and Natesan [4], among others. Indeed, the seminal work of Prof. David Young and colleagues on metal dusting is succinctly discussed in Chapter 9 of his outstanding book High-Temperature Oxidation and Corrosion of Metals, 2nd Edition [5].…”

“…Such materials are typically protected by an oxide scale, which grows at the relatively low O 2 partial pressures of the MD environment and forms a barrier against the high carbon activity of the gas and thus C transport into the alloy. Upon scale failure, MD in highly alloyed materials is caused by C diffusion into the subsurface zone, C oversaturation, and graphite formation [1][2][3][4]. Thus, the incubation time to pit formation strongly depends on the resistance of the oxide scale and therefore its chemical and mechanical integrity.…”