Hot Corrosion of Gas Turbine Components

Hot corrosion is the accelerated rate of oxidation of coatings and substrates, which occurs when a condensed phase is present on the surface. The major constituent of the corrosive deposit is sodium sulfate, although when fuels other than light distillates are employed, the deposit can contain various amounts of vanadium pentaoxide, an impurity present in many heavy distillates and most residual oils. Other corrodents that can be present in varying concentrations are lead, carbon and alkali halides. The coatings employed to extend the life of gas turbine alloys, and the alloys themselves exhibit varying degrees of resistance to hot corrosion. In our study of the “Parameter Monitoring for Corrosion Control of Utility Gas Turbines” we are determining the relative effect of each of the aforementioned corrodents with respect to simple aluminides, overlay coatings and precious metal coatings on three nickel base superalloys and one cobalt base superalloy. Although these studies are being conducted over the temperature range from 1500 to 1800°F, this presentation primarily emphasizes the completed high temperature results with some examples of the ongoing lower temperature studies.