Carburizing Injury Research Of HPM Cracking Furnace Tube

Ethylene production plant is an important equipment for the petrochemical industry, cracking furnace is the key device in ethylene production equipment. The operating condition of ethylene cracking furnace is extremely harsh, the ethylene cracking furnace tubes has to withstand high temperatures, carburizing, coking and thermal fatigue effects and often prone to injury furnace tube. With high temperature, carburization, coking and thermal fatigue effects, ethylene cracking furnace tube furnace tubes are often prone to injury, carburizing is one of the main causes which lead to the early failure of tube furnace. The early damage of the furnace tube can cause serious effects to the safety and reliability of the cracking furnace. The failure damage of cracking furnace can not only cause an unplanned stop of cracking furnace, which will affect the normal operation of the cracking furnace. meanwhile the cracking furnace tube is very expensive, it will increase the cost and delay the production in case of replacing the furnace tube, which will lead to reduce the economic benefits of the ethylene plant. More serious consequence is that it willendanger the safety of life and property of the people. Therefore, the safety and reliability of the pyrolysis furnace tube has been more and more widely appreciated.This article focuses on the rolling internal orthoptera radiant tubes which has serves five-year in the SC-1cracking furnace. The study includes:Detecting and analyzing the degree of carburizing of different pipe sections; Variation of the tube microstructure after high temperature service; The mechanism of oxidative and carburizing damage of the furnace tube; Changes of mechanical properties at normal temperature; The numerical simulation for carburizing process of the furnace based on finite element analysis software. The main conclusions are as follows:After about five year of service, various parts of HPM furnace tubes have different degrees of carburizing. The diffusion layer of inner tube orthoptera bump is thicker. The uneven distribution of temperature can cause the vary degree of carburizing furnace tubes.After high temperature serving, there will be precipitation of carbides in the microstructure. There will precipitate M23C6carbide in the area of non-carburizing, the precipitation of M23C6occurs early in carburizing parts, and will gradually transform into M7C3carbides as the carbon content increases. The carbides at the grain boundary gradually become coarse linear as the carbon content increases, and the carbides gradually become blocky in the grain.There occurres oxidative damage at the inner and outer walls of the furnace tube, and apprears decarburization in the damaged area. The Cr and Si oxides are formed at the grain boundaries. Chromium oxide film formed on the outermost layer, which causes the diffusion of the chromium at the grain boundary near the surface to the surface layer. With the reconstruction and peeling of the surface oxide layer, it will lead to chromium depletion of the grain boundary near the surface.After the service adifferent degree of embrittlement occurs in the furnace. With the carburized layer thickness increases, the number of thermal fatigue reduces sharply, the impact toughness and tensile strength reduces, and the fatigue crack initiate in the carburizing layer of inner wall the in priority.During the numerical simulation of carburizing process of the furnace tube, when outer surface decarburization is not considered, furnace carbon concentration distribution trend toward a horizontal line. When outer surface decarburization is considered, the carbon concentration profile will eventually become a nearly linear parabolic ramp to reach steady state.