Study On Preparation Of Anti-coking And Anti-carburizing Coating And Performance Evaluation

Coking and carburizing phenomenon are the worldwide problems that exist during ethylene production process in the oil industry. The coke adheres to the walls and inhibits heat transfer from the burners to the gas mixture, also cause a reduction of tube diameter, causing a higher pressure drop. Using coating techniques to inhibition coking is an effective measure to extend the decoking cycle and the life of the furnace tube.According to the problems of the ethylene cracking furnace tube, the coating structures were designed in this paper. The Al-Si-Cr coatings were prepared on the surface of Cr35Ni45alloy by pack cementation processes, and optimizing the process. The results showed that the Al-Si-Cr coatings with a thickness of about130μm and obtained have a multiple layers with dense structure, consisting of an outer layer composed of aluminum-silicon-rich compounds and inner layer composed of chromium-silicon-rich compounds. Coatings preparation process has no obvious effect on the microstructure of matrix, and the tensile test showed that the tensile strength of the material is still in accordance with the requirements of the standard.The anti-coking properties were studied by coking experiments based on light naphtha, the results showed that the coating had excellent coking inhibiting properties and inhibited the catalytic coking effectively. The rate of coke inhibition was up to72.5%, and after three times decoking test, its rate was61.1%at least.The carburizing experiment tested in CH4-H2atmosphere, its anti-carburizing performance was analyzed by means of the optical microscope, SEM, XRD. The results showed that the Al-Si-Cr coating carburizing weight gain was significantly less than the uncoated specimens after carburizing for120h, the uncoated specimen microstructure changes obviously, the skeleton tissue morphology and grain boundary carbides disappear out of peeling, and the coating specimen internal microstructure found no significant change, indicating that Al-Si-Cr coating has excellent properties of anti-carburizing.