Abstract: The high-temperature oxidation behavior of X80 pipeline steel was studied systematically by the thermogravimetric analysis. The oxidation weight gain， morphologies of the oxide scale and the distribution of alloying elements at the oxide/substrate interface at different temperatures were analyzed. The results show that in the range of 700~1200℃， the curves of oxidation weight gain of X80 steel follow the parabolic law and the thickness of the oxide scale increases with the temperature， especially when the temperature is higher than 800℃， owing to the phase transformation in the substrate. The oxide scale of X80 steel has a typical three-layer structure at high temperature， consisting of the outer thin Fe₂O₃ layer， the middle Fe₃O₄ layer and the inner FeO layer with the coarse columnar. Also， there is an internal oxidation layer with fine grains formed near the steel substrate. The internal oxidation layer suppresses the interdiffusion of iron and oxygen ions， and improves the high-temperature corrosion resistance of X80 pipeline steel.

Key words: X80 pipeline steel, oxide scale, ion diffusion, phase transformation, internal oxidation