| Spalled oxide particles and corrosion products released from the surface of steam generator materials cause various problems of accelerating stress corrosion cracking, denting, wastage, erosion of turbine, and decrease of thermal efficiency. Because the major part of exposed material surface in steam generator atmosphere is the surface of the steam generator tube, it is important to know the oxidation behavior of the tube material. The oxidation behavior of three kinds of Inconel alloys, i.e., Inconel 600, Inconel 690 and Incoloy 800 in air, pure water, and steam was studied and the oxide layers were analysed by SEM, EDX, X-ray diffractometer. And thermal diffusivities of Inconel alloys were measured by the laser flash method. Inconel 690 shows the best resistance to oxidation among the three alloys tested in static air, pure water, and steam. The good oxidation resistance of Inconel 690 is due to maintaining uniform Cr₂O₃ layer during the oxidation time. The thermal diffusivity decreases as the extent of oxidation increases. The thermal diffusivity of Inconel 600 oxidized at 500℃ for 3hours in static air decreases to 85% of that of non-oxidized specimen. The results of this study can be applied to the development of oxidation resistant materials of controlled Cr content. And the test data can be used as reference for the estimation of the amount of sludge, and as input data of steam generator design. |
|
