Preoxidation Film and Its Anticoking Behavior on an Optimized HP40Nb Alloy with Al, Zr, Y Addition

To reduce the coking of steam-cracking furnace tubes, an anticoking oxide film is formed by preoxidation. In this paper, the effect of the preoxidation process on the oxidation behavior of Fe-35Ni-25Cr alloy is studied, and its coking resistance is analyzed. The results show that oxidized at 650 °C; the oxidation product is M2O3; After oxidation at 1000 °C, the oxide layer is three layers of spinel, Cr-rich M2O3, and Al2O3. After two steps of oxidation, the oxidation products are spinel, Al-rich M2O3 and Al2O3. The coking resistance of the oxide film is analyzed. The results show that the surface coking amount of oxide film formed by two-step oxidation method is the least. The oxide layer formed by oxidation at 1000 °C has a spalling phenomenon. More coke is deposited on the surface of the preoxidized film at 650 °C, while filamentous coke appears on the surface of the unoxidized alloy.