OCR Text |
Show 7 Next, as shown in Fig.3 (b), the stress occurring in the radiant tube in 100 hours after it has been raised to the temperature of 900°C is seen to increase two to three times in the No.2 bend and No.3 bend. These increases are attributed to downward movement of the No.1 straight tube due to creep deformation,which applied loading to the No.2 bend and No.3 bend. This also suggested that downward pressure from the No.1 straight tube induces deformation in the other straight tubes, causing further deformation of the radiant tube. The extent of deformation owing to the above-mentioned mechanism is seen to coincide with the result of the deformation tests on stainless steel SUS304, as shown in Fig.4. 30~---------------------------------------~ ,.-.. E ~ 20 c: o +"' C'O E ~ o ~ 10 c Calculated \ I_ Measurement Deformation :C ~ O~~ ___ L-~ ___ L-~ ___ L-~ ___ ~~~ o 50 100 Creep Time (hr.) Fig.4. Creep deformation of radiant tube Thus, to prevent crack and deformation in the No.1 straight tube,it is very important to reduce l:l T and to minimize local temperature gradients. Concretely, it is desirable to avoid local overheating by optimizing the design of the burner. The results of the analysis of the thremal stress |