Radiant tubes of a continuous annealing furnace at Mobarakeh Steel Company failed after a fraction of service life. The tubes have manufactured from INCONEL alloy 601 superalloy. In this study, a failure analysis of radiant tubes were performed by careful visual iection of the failed tubes, scanning electron microscopy observation of near crack region samples, energy dispersive X-ray spectroscopy and X-ray diffractometer analysis of tube metals and oxide scales. The temperature distribution for study-state heat transfer and the structural stresses induced by weight of tube material have studied in this paper. Finite element method (FEM) has employed to compute the effect of temperature increasing on tube service life and define the critical regions. Because of it is important to investigate the propagation method of creep cracking behavior. Therefore, in this article the Erickson machine employed to opening the secondary cracks in a sample of the failed zone. The creep-crack propagation method has studied with scanning electron. SEM fractography have used for study the fracture surfaces of unfailed sample produced by tensile test. Further more to evaluate the distribution of hardness in samples, micro hardness test has used. The results showed that the cracks growth is occurring in grain boundary precipitates. Although the fracture surfaces of unfailed sample reveals ductile fracture. Besides the experimental results of micro hardness test showed a high difference between matrix and precipitates. Due to cracks, propagation occurred between ductile matrixes and hard precipitates. The experimental results showed that the mode of tube failure was a combination of creep damage and high temperature oxidation attack leading to cracking. Significant growth of precipitates of carbide has also observed in the failed zones which results in the drastic reduction of material ductility and propagation of creep cracking. The simulation results showed that damaged region in radiant tubes is susceptible to high temperature creep. Tube failure occurred because of bending in tube length that may be responsible for subsequent hot-spots formation and high temperature oxidation, and verified experimental results. Moreover, simulation displayed that modification in radian tube installation is necessary and utilization of supports in specific locations can be extended creep life. Keywords: failure, radiant tube, creep, oxidation, finite element method
