Abstract: The protective properties of the oxide layer of TP347H high temperature superheater tube were analyzed in this study. The formation and exfoliation mechanism of the oxide layer was researched. The microstructure of the oxide layer of TP347H high temperature superheater tube was observed by scanning electron microscope(SEM) and the morphological features of it was also analyzed. The concentrations of alloy elements in the section of internal tube were quantitatively analyzed using energy dispersive system(EDS). The results showed that:The formation mechanism of oxide layer were mainly steam oxidation mechanism and oxygen oxidation mechanism. When the pipe had enough content Cr,to ensure the normal internal and external diffusion conditions,and the Fe-Cr spinel was formed,even the protective layer of Cr₂O₃ was formed. The oxide skin damage and exfoliation is mainly due to the oxygen oxidation mechanism. When the steam environment containing excess oxygen,dissolved oxygen as oxidant and it happened oxygen reaction with Fe-Cr spinel and Cr₂O₃ chromium layer. That destroy the structure and composition of Fe-Cr spinel,Cr₂O₃ chromium layer,so that the oxide layer loss of protective effect. The formation and exfoliation of oxide scale is mainly based on the mechanism of steam oxidation,the mechanism of oxygen oxidation and the mechanism of oxygen oxidation. The three mechanisms explain the whole process of the formation,growth and exfoliation of oxide skin.

Key words: TP347H steel, high temperature superheater tube, oxide layer, steam oxidation, oxygen oxidation, oxygen peroxidation, mechanism study