Hot corrosion behaviour of HVAF coatings deposited on Fe[sbnd]25Cr[sbnd]20Ni support hanger material

Abstract

Fe[sbnd]25Cr[sbnd]20Ni cast alloy is used as the material of construction for support hangers in fired heaters of oil refineries. These hangers support heater tubes in the fired heaters and are susceptible to hot corrosion due to Na<inf>2</inf>SO<inf>4</inf> and V<inf>2</inf>O<inf>5</inf> containing corrosive ash, especially when low-grade fuels are burnt. API recommends 50Cr[sbnd]50Ni cast-alloy for constructing the support hangers in highly corrosive atmospheres which, is highly expensive as well as brittle. To overcome this problem, in this work, coatings of 50Cr[sbnd]50Ni and 20Cr[sbnd]80Ni were applied on Fe[sbnd]25Cr[sbnd]20Ni substrates by HVAF process. The coatings were characterized by: Optical Microscopy, SEM-EDS Analysis, XRD Analysis, and Raman Spectroscopy. To study the hot corrosion behaviour of these coated specimens, a cyclic hot-corrosion test was carried out at 700 °C using 20 % Na<inf>2</inf>SO<inf>4</inf>–80 % V<inf>2</inf>O<inf>5</inf> salt slurry. Along with the coated specimens, cast specimens of Fe[sbnd]25Cr[sbnd]20Ni and 50Cr[sbnd]50Ni were also subjected to the hot-corrosion test. Thus, Type-II hot corrosion behaviour of all four specimens were analyzed comparatively by weight-change measurements, cross-sectional metallography, SEM-EDS, XRD, and Raman-Spectroscopy. The Fe[sbnd]25Cr[sbnd]20Ni cast specimen displayed the least corrosion resistance. The corrosion resistance of the 50Cr[sbnd]50Ni coated specimen and the 50Cr[sbnd]50Ni cast specimen was found to be intermediate and quite comparable. 20Cr[sbnd]80Ni coated specimen recorded the best corrosion resistance. The corrosion mechanism and beneficial effects of high nickel-containing HVAF coatings against hot corrosion are presented. © 2024 Elsevier B.V.