2009 Volume 58 Issue 6 Pages 214-220
A Ni-base alloy, UNS N07001, is generally used for power recovery turbine rotors for fluid catalytic cracking units of oil refinery equipment (FCC gas expander turbines). However, the alloy may suffer from sulfidation-corrosion caused by H2S and SO2 contained in the FCC exhaust gas. This paper describes the problem of high-temperature sulfidation-corrosion of FCC gas expander turbine rotors and the influence of the gas composition, temperature, and stress to the grain boundary sulfidation-corrosion behavior. In addition to explanation of the fracture mechanism of the gas expander turbine blades, countermeasures against high-temperature sulfidation-corrosion are introduced: Cr diffusion coating, a steam cooling system, and a sulfidation-corrosion resistant Ni-base alloy. The Cr diffusion coating is highly dimensionally accurate allowing use on close tolerance fitting parts with complicated profiles such as blades and disks and shows high sulfidation-corrosion resistance in the operating conditions of gas expanders. The developed sulfidation-corrosion resistant Ni-base alloy for FCC gas expander turbine rotors offers high-temperature strength equivalent to the conventional alloy, UNS N07001, with higher sulfidation-corrosion resistance.
