Corrosion behavior of ferritic steels on the air sides of boiler tubes in a steam/air dual environment

The corrosion behavior of heat resistant ferritic steels for boiler tubes in a steam/air dual environment simulating the non heated areas at 823, 873 and 923 has been investigated. Corrosion rates of the ferritic steels on the air sides under a condition of steam/air dual environment are increased more significantly than these in simple air conditions because the permeation hydrogen from steam sides. Corrosion morphology on the air sides closely resembles that on the steam sides, namely, a two-layered oxide scale is formed. However, Fe2O3 is observed in the outermost layer of the scale. The inner scales on the air sides are found to grow parabolically with time for all steels tested. The hydrogen permeation current measurements show that the amount of permeated hydrogen from the steam sides decreases parabolically with time, and also decrease, with increasing Cr contents in the steels.