The mechanistic studies of metal dusting processes and associated filamentous carbon formation were carried out in Alloys N06025 (Ni-based) and N08800 (austenitic Fe-based) under a simulated metal dusting environment (18.9 vol% CO–79.1 vol% H2–2 vol% H2O) at 650oC. Reaction kinetics and product characterisation of alloys N06025 and N08800 were studied by weight loss/gain measurement, visual examination, optical microscopy, scanning electron microscopy with energy dispersive X-ray analysis (SEM-EDX) and X-ray diffraction (XRD). The results showed that alloy N06025 is more resistant to metal dusting than Alloy N08800. Visual examination and scanning electron microscopy (SEM) surface analysis showed that alloy N08800 suffered metal dusting attack at an early exposure reaction period. The amount of coke deposits was found to increase on Alloy N08800 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 N08800. The different dusting behaviours of two alloys were discussed based on the effect of alloy composition on carbon diffusion and product formation.
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).1 The dusting of these alloys is normally in the form of pitting where the original material transforms into a dust of coke or 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).2 Metal dusting occurs in many petrochemical processes and is thus of great significance to the industry because of costly replacement of the metal dusted plant components and the associated downtime.
