Analysis of creep stress-strain relationships is made for horizontally supported furnace tubes including the effect of tube weight and internal pressure. Steady-state creep effects through the tube wall due to axially symmetrical heal input are also analyzed for these conditions. The original Bailey approach to the pressure problem only is extended to the larger scope undertaken. Maximum permissible tube spans are derived based on accepted criteria for creep stress and deflections.
The results of this work indicate that maximum allowable tube spans may often be theoretically increased beyond present usual design limits except for a few specific materials and instances where short spans are required at very high temperatures. In actual tube design, consideration should be given to experience in operation of any particular type of furnace so that secondary effects may be minimized. Increased economies in costs and flexibility in furnace layout as well as rational span determination are expected from use of these results.