A Fresh Look at the Mechanism of Corrosion in Boilers

Block specimen, hydrogen effusion, and model boiler experiments have shown that mild steel, after a brief period of “flash” oxidation immediately following immersion in aqueous solution, either corrodes relatively slowly with the formation of a thin, corrosion-resistant magnetite film, or corrosion proceeds rapidly with the development of a non-protective accumulation of iron oxide. In the latter case, film-destructive mechanisms induced experimentally by combinations of high temperature, stress, and quite high concentrations of hydroxide alkalinity or ferrous chloride have produced examples of generalized severe metal loss, pitting, heavy oxide accumulation, and hydrogen damage remarkably similar to corrosion manifestations responsible for metal failure in real boilers.