The long-term exposure of gas turbine vane and blade base alloys and a variety of protective coating systems to the effluent from a pressurized fluidized bed coal combustor has reached 4398 hours. After 4053 hours, FeCrAlY overlay coatings and platinum/rhodium-aluminide pack diffusion coatings show excellent resistance to corrosion attack at 1500/sup 0/F. Cobalt-base coatings are somewhat more susceptible to hot corrosion, and the unprotected nickel and cobalt-base alloys are most susceptible to corrosion, although corrosion rates have decreased to less than 1 mil/1000 hours for all materials at 1500/sup 0/F; i.e., corrosion penetration data is evolving parabolically. The three-stage cyclone cleanup system became severely distorted after approximately 5600 hours total service life. Distortion of the cyclones contributed to an increased dust loading to the material test sections, 110 to 250 ppM versus normal loadings of 30 to 90 ppM, for a period of about 75 hours. This increase in dust loading caused severe erosion of the airfoils in the high-velocity test section. Metal recession ranged 4 to 18 mils of leading edge loss on the impulse airfoils, and 11 to 27 mils of leading edge loss on the reaction airfoils. A new three-stage cyclone system was installed and dust loadings now range from 15 to 45 ppM.