Oxidation behavior and performance deterioration of cracking furnace tubes in service

In recent years, the centrifugal casting material Cr35Ni45Nb has been widely used in cracking furnace tubes. The common failure forms in the service process are carburizing cracking, bending, bulging, creep cracking, thermal fatigue cracking, thermal shock cracking, and oxidation, among which the inner wall oxidation and carburization of cracking furnace tubes cause the largest proportion of material failure. In this paper, we will discuss the inner wall oxidation behavior of cracking furnace tubes and its influence on the lasting strength of the furnace tubes. Several groups of endurance tests were designed for service furnace tubes, and the oxidation characteristics, oxide film rupture damage, and its influence on the endurance life of furnace tubes in different service times were analyzed by means of XRD, SEM, and so on. The results show that the oxide layer of the furnace tube is divided into two layers, the outer layer is repeatedly destroyed and rebuilt. With the continuous evolution of material structure, its properties also deteriorate, and its tensile strength, yield strength, elongation, and durable life all decrease significantly.