Investigation of the Influence of Proximal Radiation on the Thermal Stresses and Lifetime of Metallic Radiant Tubes in Radiation-Dominated Industrial Furnaces*

Abstract

Abstract The influence of surrounding (or proximal) radiation on radiant tubes inside a continuous hot-dip galvanizing line was investigated. The furnace chamber, the strip and the neighbouring tubes were considered as the surroundings. A coupled heat transfer model was developed and subsequently validated against experimental measurements. This model was used to calculate the radiation exchange between the tube and its surroundings, and to give the new temperature distribution on the tubes as its output. This result served as an input to an already validated FEM model, which was used to assess the creep behaviour and the corresponding stresses on the tube. Basis of the investigated setups were Alloy 602 p-type tubes operating under burner on/off firing. The results show an increase in creep deformation of the tube when the surroundings were taken into account. Highest creep deformations were observed for setups with a strip, even though these cases showed the lowest maximum tube temperatures. Furthermore, an opposing effect between creep deformation and stresses acting on the tube exists. This is supported by the fact that no definite pattern relating the creep and stresses of a tube was found. Local tube temperature gradients and transient cyclic loading due to burner on/off firing were observed to have a significant influence on the tube's service life.