Microstructure and Growth Mechanism of the Oxide Scale Formed on HR3C at the Steam Side in Ultra Supercritical (USC) Units

The structure, morphology and elemental micro-distributions of the steam side oxide scale of the HR3C reheater tubes after operation for 5400 h and 23400 h, respectively, in Huaneng Yuhuan Power Plant were studied. It was found that with the advance of oxidation process, the steam side oxide scale of HR3C tubes developed from a double-layer structure to a four-layer structure and the Cr-depleted zone was the shortcut for the growth of the oxide scale. The growth mechanism of the steam side oxide scale on HR3C was also discussed.