A Laboratory Study of High-Temperature Corrosion on Fireside Surfaces of Coal-Fired Steam Generators

Three experimental approaches gave significant information on high-temperature fireside corrosion: 1 Sodium and potassium chlorides, injected through a gas flame, were deposited as such and then converted to sulfates on an iron surface. 2 Samples of mixed alkali and iron sulfates first showed decomposition and then formed melts at temperatures as low as 1070 deg F. This temperature is within the range that might be expected for fireside surface temperatures on superheater and reheater tubes of large steam generators. 3 Alkali metal chlorides and sulfates, in partial coverage of metal disks and in a flue gas atmosphere, formed fused deposits at temperatures as low as 900 deg F. Complex alkali iron sulfates may cause corrosion either by direct electrolytic corrosion or by altering the normally protective iron oxide scale so that the metal is exposed to direct oxidative corrosion.