Investigation on Carburization during the Repeated Coking and Decoking Process

In this work, stainless steel blank tube and TiN-coated tube obtained by atmospheric-pressure chemical vapor deposition were used to explore the carburization during the repeated coking and decoking process. Various analytical techniques including scanning electron microscopy, energy-dispersive X-ray spectroscopy, and Raman spectroscopy were applied to analyze the morphology, composition, and type of coke. To protect the pipeline, the on-line decoking method was used to determine the amount of coke. During the coking experiment, it was observed that carburization and metal outdiffusion occurred on the inner surface of the microchannel by scanning the cross section of reaction sheets. Moreover, the coke mass of the blank tube in the next coking experiment increased evidently after the previous coking and decoking cycle. However, under the same experimental condition, TiN coatings transforming into TiO2–TiCxNy–TiN multilayer films could still maintain anticoking performance because it alleviated the carburization and metal outdiffusion.