Modelling hot corrosion in industrial gas turbines

Abstract Gas turbines are a critical component within combined cycle power systems that are being developed to generate electricity more cleanly and efficiently from solid fuel sources, that include coal and biomass. The use of such fuels, to produce fuel gases, increases the potential for significant corrosion and erosion damage to gas turbine blades and vanes. This paper addresses the modelling and prediction of type II hot corrosion in industrial gas turbines within the aim of given acceptable and predictable lifetimes. A matrix of corrosion tests have been undertaken using the ‘deposit recoat’ test procedure, with samples cooled periodically to re-apply controlled amounts of salt deposit. Deposited salt was 4/1 mole fraction of Na2SO4 and K2SO4, with deposited fluxes of 0, 1.5, 5.0 and 15.0 μg/cm2/h. Samples of polycrystalline (IN738 and IN792) and single crystal superalloys (CMSX4 and SC2B) were exposed for test durations of 500 and 1000 h at 700°C in a variety of gas compositions, consisting of air+50–500 vppm SO2+0–500 vppm HCl+0–5 vol% H2O. Section loss data has been measured, using precision optical metrology and analysed statistically. Models have been developed that predict section loss as a function of salt deposition rate and gas composition to precisions of ±20 mm loss, with 95% confidence (2×standard deviation).