Abstract
The films formed on boiler tube steels are investigated and the corrosion resistances of the films formed are evaluated in this work. Corrosion potential measurements are conducted in simulated AVT (All Volatile Treatment) waters at 308K for 100h on STB410 carbon steel, STBA24 low-alloy steel and SUS304 stainless steel, which are used as the boiler tube steels in thermal power plants. Four kinds of the simulated AVT waters, i.e., the base water and the waters added with chloride and sulfate ions, are used in the tests. After corrosion potential measurements the films formed on the steels are observed with SEM (Scanning Electronic Microscope) and are analyzed with XPS (X-ray Photoelectron Spectroscopy). Anodic polarization behaviors of the materials with the films formed are also investigated in the same test waters. In all of the test waters, STB410 steel exhibits base corrosion potentials, while STBA24 and SUS304 steels show nobler. It is found that the films formed on STB410 steel consist of Fe-oxides and the films formed on STBA24 and SUS304 steels contain stable Cr-oxides. In this work, it is confirmed that the STBA24 and SUS304 steels show better corrosion resistances to the anions such as chloride and sulfate ions in the simulated AVT waters at 308K by virtue of the passive films.
