High Temperature Damage Analysis Of Radiant Tubes Using In Continuous Annealing Furnace

Radiation tubes are widely used in annealing furnace, heating furnace and other industrial heating device of steel manufacture, chemical and thermoelectric industry. Its security and stability during long-term service is an important factor to ensure the whole equipment to run safely and steadily. If the radiant tube suffers premature severe deformation or rupture, it will have a great impact on its function to perform and the quality of the products, and causes significant economic losses.Research on material damage of the severely deformed radiation tube after two years of high temperature service in continuous annealing furnace of Baosteel company was performed in order to determine the mechanism of deformation and rupture occurred in the service process. Analysis results showed that the coarsening of the second phase occurred under long-term high temperature service, changes in morphology of microstructure of the radiant tube materials included coarsening and mergers of secondary precipitation and transformation of the skeleton-like primary carbide to chain-like second phase at the grain boundary; In oxidizing combustion atmosphere, the inner wall of the radiant tube suffered serious oxidation attack. Cracking and spalling of the oxide scale, and large number of voids at the grain boundary formed by oxidation caused the effective thickness thinning of the pipe wall; It was found that nitridation phenomenon occurred at the inner and outer walls of the radiant tube serviced in N2containing atmosphere. Nitrogen led to transformation of M23C6to M2(C,N) and M6(C,N), and further coarsening of the second phase. The mechanical properties assessment on the high temperature damage of the material founded that voids and cracks formed in oxidation corrosion process led to serious material damage, and the hardness decreased significantly; The coarsening of the second phase under high temperature aging and nitridation led to hardness increase, high temperature rupture strength and creep performance degradation, and increased susceptibility to brittle fracture during room temperature and high temperature service.Damage and deterioration phenomenon of the heat resistant steel radiant tube in industrial applications is usually complex. It is not only to analyze and assess the relevant reaction mechanism using the thermodynamic and kinetic analysis, but further to propose approaches to delay or prevent the reaction. It was found that continuous and dense oxide film can significantly affect the degree of oxidation corrosion of materials at the radiation tube wall. Oxidation and subsurface deterioration processes under protection were slow and showed a uniform distribution. Nitridation was significantly reduced and the second phase coarsening was inhibited. The content of the last part of this paper is about the control method of the high temperature corrosion and deformation of the heat resisting steel radiant tube after the above-mentioned material degradation analysis, which provides a theoretical basis for the actual operation on improvement and maintaining of the radiant tube device.