AN INVESTIGATION OF METAL DUSTING CORROSION OF ALLOYS 602CA AND 800 FML Mulaudzi1 2 3 LA Cornish1 2 GA Slabbert1 3 MJ Papo2 3 & J Zhang4 1 School of Chemical and Metallurgical Engineering University of the Witwatersrand 2 DST/NRF Centre of Excellence in Strong Materials hosted by the University of the Witwatersrand Johannesburg South Africa 3 Advanced Materials Division Mintek Randburg South Africa 4 School of Materials Science and Engineering The University of New South Wales Sydney Australia Corresponding Author: marandelam@mintek.co.za Abstract Metal dusting is a severe form of corrosion in which iron steels Ni- and Co-based alloys disintegrate into metal or carbide particles in a coke deposit when exposed to strongly carburising gases (carbon activity aC > 1) at elevated temperatures (400-800°C). Chromium-containing alloys can form a protective chromia scale to resist metal dusting. However extensive chromium carbide precipitation results in the depletion of chromium to such an extent that the protective chromia scale is not maintained and therefore metal dusting occurs. The dusting for these alloys is normally in the form of pitting where the original material transforms into a dust or coke of graphite and nanocrystalline-sized oxide particles. The mechanisms leading to metal dusting depend on the substrate material (e.g. Fe Ni Ni-based alloys austenitic and ferritic steels). The metal dusting phenomenon occurs in many petrochemical processes and it is therefore of great significance to the industry because of costly replacement of the metal dusted plant components and the associated downtime. The mechanistic studies of metal dusting processes and associated filamentous carbon formation were carried out in Alloys 602CA and 800 under a simulated metal dusting environment (18.9 vol% CO–79.1 vol% H2–2 vol% H2O). Alloy 800 is an austenitic iron-based alloy containing 32 Ni 21 Cr and about 0.1 C (wt%) whereas alloy 602CA is a nickel-based alloy containing 25 Cr 9.5 Fe 2.2 Al and 0.18 C (wt%). Reaction kinetics and product characterisations of both alloys were studied by weight loss/gain measurement visual examination optical microscopy scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDX) X-ray diffraction (XRD) and Raman and Mössbauer spectroscopy. The results have shown that alloy 602CA is more resistant to metal dusting than Alloy 800. Visual examination and SEM surface analysis showed that alloy 800 suffered metal dusting attack at an early exposure reaction period. The amount of coke deposits was found to increase on Alloy 800 with increased exposure from 96h to 720h. X-ray diffraction from the reacted surface identified graphite and austenite for both alloys and some iron oxides/spinel for Alloy 800. The different dusting behaviours of two alloys were discussed based on the effect of alloy composition on carbon diffusion and product formation.