2000 Volume 49 Issue 10 Pages 612-618
In the simulated once-through type boiler feedwater under oxygenated treatment (OT) conditions, the fundamental corrosion characteristics of carbon steel for boiler tubes in fossil power plants were experimentally investigated, comparing with those under the all volatile treatment (AVT). The corrosion weight loss under the OT conditions was less than about 1/2 of that under the AVT condition. The dissolution ratio of the AVT scale (Fe3O4) into the high temperature AVT water showed the very large value of approximately 30%. On the contrary, the dissolution ratio of the OT scale (Fe3O4+α-Fe2O3) into the OT water was almost zero. The cross sectional morphology of OT oxide films showed the duplex structures consisting of the outer layer with the grain size of 1-2μm and of the inner layer with the grain size less than 0.1μm and also with thickness less than 1μm. These results indicate that the OT oxide film was very thin and tight in comparison with the AVT film.
From the view point of the above fundamental corrosion characteristics, it is suggested that the OT for the feedwater is superior to the AVT concerning the corrosion resistance of the carbon steel.