Coking and Dusting of Fe–Ni Alloys in CO–H2–H2O Gas Mixtures

Abstract

Metal dusting of Fe-Ni alloys was investigated in a CO-H 2 -H 2 O-Ar gas corresponding to a C = 19.6 at 650°C. Thermogravimetric analysis showed that increasing the nickel content in the alloy decreased the initial rate of carbon uptake. A uniform Fe 3 C scale formed on pure iron, a layer with mixed structures of Fe 3 C, c and a-Fe developed on ferritic Fe-5Ni, and small amounts of Fe 3 C developed at the surface of an austenite layer grown on two-phase (a + c) Fe-10Ni. At nickel levels above 10%, no carbide appeared. These observations are shown to be broadly consistent with local equilibrium according to the Fe-Ni-C phase diagram. However, the failure of higher nickel austenitic alloys to form the (Fe,Ni) 3 C expected at high carbon activities indicates a barrier to nucleation and growth of this phase. Graphite deposition was catalysed by (Fe,Ni) 3 C on ferritics and by the metal itself on austenitics. The rates of carbon deposition on Fe-60Ni corresponded to the existence of three parallel and independent paths: the synthesis gas, the Boudouard and the carbon methanation reactions.

Recent advances in understanding metal dusting: A review

“…Thermodynamic calculation [20] shows that (Fe,Ni) 3 C formation is not thermodynamically hindered on high nickel content alloys. As is nonetheless evident, carburisation becomes very slow at high alloy nickel levels, and direct graphite deposition is favoured.…”

“…Differentiation then C for austenite in equilibrium with unit carbon activity [20] yields for the rate of sorption…”

“…Temperature cycling exposure conditions were used to promote spallation and [20] cracking of the protective chromia scales developed by these alloys. Metal wastage rates for the copper-free alloys of 304SS, 310SS and 800H are shown in Fig.…”

“…The present paper reviews a series of investigations into the detailed mechanism of metal dusting of ferritic and austenitic alloys. Particular attention is directed to the role of cementite and the microprocesses of nanoparticle formation and underlying metal destruction [16][17][18][19][20][21]. This work was carried out using surface observation, metallographic cross-section analysis and electron microscopic examination of coke deposits at different stages of the reaction.…”

Metal dusting behaviour of several nickel‐ and cobalt‐base alloys in COH2H2O atmosphere

“…Metal dusting is a catastrophic form of high temperature corrosion in which carbon-supersaturated gas degrades iron-, nickel-and cobalt-base alloys into a dust of carbon and particulate metal or metal carbides [1][2][3][4][5][6][7][8][9][10][11][12][13]. Two mechanisms have been proposed according to whether or not metastable carbide forms.…”