Initiation of Metal-Dusting Pits and a Method to Mitigate Metal-Dusting Corrosion

Initiation of metal dusting was studied by scanning-electron microscopy and Raman spectroscopy. A copper-indicator method was developed to identify locations that are easily attacked by metal dusting. The effect of surface scratches on metal dusting was investigated. Alloy 800 specimens from a hydrogen-reformer plant were analyzed. The alloy developed a nonprotective oxide scale in which the major phase was \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$Fe_{1+x}Cr_{2-x}O_{4}$$\end{document} spinel with a high Fe content. The initiation of metal-dusting pits occurs when channels form through the oxide scale for the transfer of carbon. The channels can be blocked by short exposure of the metal-dusted alloy surface to an oxidizing environment. Metal-dusting corrosion could be mitigated by selection of alloys with long incubation time and by minimizing and/or slowing the pit-growth rate using an intermediate oxidation treatment at an appropriate temperature and in an appropriate environment for a relatively short time.