Metal dusting on an alumina forming Ni-base alloy

• Published in: Corrosion science 2006-07, Vol.48 (7), p.1679-1695
• Main Authors: Szakálos, P., Lundberg, M., Pettersson, R.
• Format: Article
• Language: English
• Subjects: Alumina-formers; Applied sciences; Carburization; Corrosion; Corrosion environments; Diffusion; Discontinuous precipitation; Exact sciences and technology; Heat treatment; iron; Kinetics; Materials science; mechanisms; Metal dusting; Metals. Metallurgy; Micro-cracks; Ni-base alloy; Oxidation; Production techniques; Synthesis gas; TECHNOLOGY; TEKNIKVETENSKAP; Teknisk materialvetenskap; Thermochemical treatment and diffusion treatment
• ISSN: 0010-938X; 1879-0496; 1879-0496
• DOI: 10.1016/j.corsci.2005.05.023

A high-performance commercial alumina-forming Ni-base alloy was studied after a 2 years field exposure at 540 °C in a methanol plant with a gas composition of 10–20%CO and 20–40%H 2O, with some CO 2 and the remainder H 2. The same material was also used in laboratory studies performed at 650 °C using a gas mixture with higher CO and lower H 2O content; 50%CO + 3%H 2O + 47H 2 (carbon activity a c = 39). Post-exposure metallographic examinations together with thermodynamic calculations were used to identify and describe the metal dusting processes. A growth mechanism for metal dusting in nickel base alloys, which is independent of metal bulk diffusion, is identified. The process involves a separation of the carbon-saturated metal into a network of discontinuous precipitated carbides and a depleted Ni–austenite matrix followed by selective oxidation of the carbide network. The corrosion product consists of Cr-depleted Ni-particles, Cr-rich oxides and free carbon. The estimated metal dusting corrosion rate in the field exposure was 20–25 μm/year, based on metallography and it was correlated to a theoretical model based on boundary diffusion processes.