High Temperature Corrosion of Gas Turbine Materials with Ash Deposition in Methane Gas Combustion Environment

Beyond high temperature oxidation, sulfidation and molten salt corrosion, corrosion from ash/salt deposits has also been a serious problem for industrial gas turbine components such as nozzle guide vanes and rotor blades. This study focuses on hot corrosion behaviors caused by ash deposits on a nickel-based superalloy80H, a cobalt-based superalloy414, a CoNiCrAlY coating and a thermal barrier coating (TBC). Specimens were immersed in ashes and experiments were conducted in a methane gas combustion environment at 730°C, 850°C, and 950°C for 200h. Raw ash and synthetic ash were used for the ash deposition experiments. A coal gasification plant supplied the raw ash and the synthetic ash was combined artificially with Na₂SO₄, SiO₂, V₂O₅, NaCl, Fe₃O₄ and Fe₂O₃. To evaluate the accelerated corrosion effects of ash deposits, experiments were also conducted in the same combustion environment without ash deposition for 1000h. After these tests, cross sectional observations were made by a scanning electron microscope (SEM) and an electron probe micro analyzer (EPMA). Results showed that sulfur concentrated within the uncoated superalloy80H and superalloy414, and silicon invaded along the grain boundary of superalloy414.