Investigating the anti-coking behavior of diffusion aluminide coatings applied on HP steel

In the petrochemical industry and in the cracking process, during the reactions that lead to the production of such products as ethylene and propylene, unfavorable reactions are also formed, which cause the formation of coke in the furnace coils. Appropriate coating of the steel can increase the resistance to hot corrosion and high temperature oxidation, largely prevent coke deposition and result in longer life of the reactors. In this research, in order to increase the anti-coking ratio and improve the resistance to oxidation and carburization of HP-micro alloyed steel, aluminide diffusion coatings were investigated. First, the chemical composition of the substrate was determined by optical spectroscopy and, then, the aluminizing process was employed to create a diffusion coating. The coating operation was carried out at 1000 degrees C and a holding time of 5 hours. The results of the X-ray diffraction test on the aluminized sample indicated the presence of NiAl phase on the surface. In order to evaluate the resistance to coke deposition, the coking test was performed to determine the anti-coking ratio. The results showed that the aluminized specimens significantly prevented the formation of filamentary coke due to the presence of the protective oxide layer, while in the untreated steel, the initial filaments formed by the reaction of hydrocarbon and the active elements of the substrate in large amounts over the surface.