Creep stress calculation model for ethylene cracking furnace tubes under consideration of carburization

Ethylene cracking furnace tube is an important part of the furnace. Up to now, the studies show that the carburization is the main reason of the tube failure. According to the principle of carbon diffusion, the carburization concentration along tube wall is obtained by approximately simulation in the present paper. The volume expansion of the tube caused by carburization would make a change of the strain and stress fields. The relationship between the carbon content and the strain (or the stress) in the radial, circular and axial directions can be inferred based on the physical equations of symmetrical plane problem. Combining the stress condition by pressure, temperature and carburization, the creep stress calculation equations are derived. The results show that the carburization has a great influence on tube failure.