Abstract: This paper presents an investigation into the carburization and mechanical property testing of the inlet tube in the radiation section of an SL-Ⅰ ethylene cracking furnace in a petrochemical enterprise during its service life. The testing encompasses observation of carburization degree, scanning electron microscopy (SEM) observation, tensile test at room temperature and high temperature durability test. The results indicate that for the 25Cr35NiNb+MA inlet tube of SL-Ⅰ cracking furnace, the most serious carburizing part is 4~6 m away from the bottom of the furnace, and the maximum carburizing layer thickness of the inner wall of the inlet tubes after 4, 6 and 8 years of service accounts for 35%, 70% and 100% of the wall thickness respectively. The yield strength of the inlet tubes with 4, 6 and 8 years of service decreased by 4%, 10% and 17% respectively compared with the new furnace tubes not in service. The tensile strength decreased by 15%, 18% and 32% respectively. Elongation after fracture decreased by 59%, 68% and 82% respectively. The high temperature rupture time of inlet tubes with 4, 6 and 8 years of service decreased by about 64%, 77% and 88% respectively. To address the issues of carburization and mechanical performance degradation, the paper provides operational recommendations for the inlet tubes in the radiation section of SL-Ⅰ type ethylene cracking furnace.

Key words: ethylene cracking furnace, radiant section inlet tube, carburization, mechanical property