Failure Analysis on Perforation of Cr28Ni48W5 Alloy Heat Radiant Tube

An electric radiant tube in continuous annealing furnace was manufactured by using Cr28Ni48W5 heat resistant alloy with the built-in electric resistance bars of 0Cr27Al7Mo2 supported by the insulation of high-temperature ceramic disk. The radiant tube was found to be perforated during the annual routine inspection. In this study, a failure analysis of the radiant tube was performed by carefully visual inspection of the failed tube, scanning electron microscopy observation of perforation samples, and energy-dispersive X-ray spectroscopy analysis of the tube metals and oxide scales. The used materials were prepared by centrifugal casting. The analysis showed that there exhibited the microstructure characteristic of melting and solidification near the perforation hole, and the serious oxidation had occurred. It is inferred that under the condition of prolonged high-temperature heating, the creep deformation caused the electric resistance bar bend to contact the tube inner surface, and then electrical discharge took place and further melted the tube inner matrix through continuous heating by the release of electrical arc.