Research on the mechanical property deterioration and the creep damage for the in-serviced heating furnace tubes

Long term exposition and high temperature in the petrochemical industry pose challenges for metal materials, especially for the AISI 1020 steel, which is a type of carbon structural steel. The creep damage is therefore particularly important. However, few researches focus on this type of material owing to the limit service temperature is not high. In this paper, the study focuses on AISI 1020 steel furnace tubes service that have been in service for over 20 years at 218 ^oC. Microstructural observations and mechanical properties tests are conducted on the tubes. The results indicated that the furnace tube exhibited pearloid spheroidisation after service. The hardness of the lower section of the tube characterized by a large grain size was below 140 HV_0.3. Compared with a new furnace tube, the ultimate tensile strength (UTS) of the furnace tube after service decreased by 18.93%、23.56% and 6.93% at room temperature, 600 °C, and 650 °C, respectively. The carbides in the furnace tube mainly include Fe₃C and Cr₇C₃. At a given stress level, the steady-state creep rate increases with increasing temperature, and the creep life decreases. Such results provide a theoretical basis for designing and manufacturing furnace tubes in similar working conditions, controlling material deterioration, and developing preventive measures.