Hot-corrosion (turbine)

Hot corrosion is accelerated high-temperature attack on turbine blades and nozzle guide vanes when molten salt deposits, mainly sodium sulfate and vanadium pentoxide, dissolve the protective oxide layer. Sodium chloride from marine air reacts with sulfur from the fuel to form Na2SO4, while vanadium in residual fuel forms V2O5; both deposit on hot-section parts. Type I attack runs at 800 to 950 degrees C with broad oxidation; Type II runs at about 670 to 750 degrees C as localized pitting. It strikes gas turbines and the exhaust valves and turbine wheels of diesels on heavy fuel. Fuel treatment to limit sodium and vanadium is the main defense.