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

Abstract

The metal dusting behaviour of total 11 nickel-and cobalt-base alloys at 680 8C in a gas of 68%CO-31%H 2 -1%H 2 O (a C ¼ 19.0, p O 2 ¼ 5.4 Â 10 À25 atm) was investigated. All samples were electropolished and reacted in a thermal cycling apparatus. On the basis of their reaction kinetics, these alloys can be classified into three groups: the first, with rapid carbon uptake and significant metal wastage, consists of alloys of relatively high iron content (AC 66, 800H and NS-163); the second, with intermediate rates, consists of some Co-base alloys (HAYNES 188, HAYNES 25 and ULTIMET) and the third, with very low reaction rates, consists of nickel-base alloys with high chromium levels (601, HAYNES HR 160, 230, G-35 and EN 105). An external chromia scale protected group 3 alloys from carburization and dusting. However, this protective scale was damaged and not rehealed for group 1 and group 2 alloys, allowing carbon attack. In all cases, coke deposited on the surface with two typical morphologies: filaments and graphite particle clusters. Subsurface spinel formation in high iron-content alloys led to rapid dusting due to the significant volume expansion. Alloy carbon permeability was calculated from a simple law of mixtures, and shown to correlate reasonably well with initial dusting rate except for one cobalt-base alloy in which iron spinel formation was significant.

Scaling up the Process of Catalytic Decomposition of Chlorinated Hydrocarbons with the Formation of Carbon Nanostructures

“…During this period, the carbon corrosion of the metal surface, the formation of microsized domains, and the appearance of the active particles catalyzing the growth of carbon fibers take place [23,44]. In the case of chlorine-containing medium, the induction period is significantly shortened if compared with other carburizing atmospheres [24,31] and does not exceed tens of minutes. After the induction period, the stage of intensive carbon deposition goes on (Figure 2).…”

“…In this case, the initial alloy samples undergo rapid disintegration under the action of an aggressive chlorine-containing medium. This phenomenon is well-known in the literature under the name of metal dusting (MD) [24,25]. In industry, the MD process is negatively associated with the destruction of metal reactors and pipelines [26][27][28][29].…”