Cracking Cause of Radiant Tube in a Continuous Annealing Furnace

The radiant tube in a continuous annealing furnace cracked during service. The cracking causes of the radiant tube were analyzed by fracture macromorphology and micromorphology observation, chemical composition analysis, mechanical property test and force analysis. The results show that the combined action of high temperature creep and high temperature oxidation corrosion led to the failure of radiation tube in the continuous annealing furnace. Under low stresses and high temperatures, holes formed by grain boundary sliding grew and connected to form cracks; the pores formed by the rupture of the oxide film accelerated the combination and growth of cracks, and the cracks propagated fast under the creep stresses, finally leading to the failure of the radiant pipe. After long-term service in a high temperature environment, the inner wall of the radiant tube was seriously thinned by oxidation corrosion; the strength of the radiant tube was obviously lower than the standard value, and the bearing capacity decreased, which resulted in the initiation of cracks in the stress concentration area of the high temperature concentration area and the final failure of the radiant tube.