Using a steam corrosion testing apparatus operating under almost the same steam conditions as those in actual boilers, the influences of temperature and pressure (especially above critical pressure) on steam corrosion were investigated for austenitic heat-resisting steels such as SUS 347HTB, 17-14CuMo, and the newly-developed 20Cr-25Ni and 22Cr-35Ni steels for advanced fossil steam plants.
Corrosion loss in weight increases with increase in steam pressure and temperature. Increasing Cr and Ni content improve the corrosion resistance. Concentration of Cr in inner scale, (Cr, Fe)2O3, increases with Cr content of steel. This causes the higher resistance to steam corrosion. A Ni-enriched layer formed at the Cr2O3/metal interface contributes to the improvement of steam corrosion resistance. The Ni concentration in the layer becomes higher as steels contain higher Ni. Structural investigation of the scale cross sections shows that considerably large amounts of voids and cavities are produced in the scale of SUS 347HTB and 17-14CuMo steels corroded in steam at high temperature and pressure.
