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Show 4 problems require replacement of radiant tube. Therefore, prevention of radiant tube deformation and crack is necessary for stabilizing the operation and reducing the costs associated with radiant tube replacement. The limit of heat resistance of the radiant tubes can be evaluated on the basis of high temperature strength characteristics of the radiant tube material, the difference between the peak and average temperature of the radiant tubes(hereinafter called "/1T "), and the level of stress to which the radiant tubes are exposed. In improving the heat resistance of the radiant tubes, in other words, there are three possible means, namely, the method of improving the high temperature strength of the radiant tube materi a 1, the method of reduc i ng the /1 T, and the method of reduci ng the stress to which the radiant tube is exposed, as shown in Fig.2. Stress on Radiant Tube (R/T) Average Temp. (2) Reduction of the Maximum Temperature ..c +-' C> s::: F----I-~ CD '+-' en ..c +-' g»~--~ CD '+-' L-.:II::~_~ ___ R/T Temp. en (1) Imp rovement of Mate ria I Strength ..c +-' g~--~ Q) '+-' en L.-..Z..---X-_...J..-__ R/T Temp. (3) Reduction of Thermal Stress ..c +-' g>t----~ CD '+-' en '----X.---K._-L-----'-__ R/T Temp. Fig.2 Improving methods of heat resistance of radiant tube The material of radiant tubes is generally an alloy steel containing expensive chromium and nickel as its main components. Even assuming it is |