RADIANT TUBE

PURPOSE: To reduce thermal strain and prevent the generation of deformation or crack by a method wherein two kinds or more of heat resistant alloys, having different coefficients of linear thermal expansion, are used to reduce a difference between the coefficients of linear thermal expansion of radiant tubes at a combustion burner side and an exhaust gas side. CONSTITUTION: A radiant tube, having W-shape, is constituted of a first straight tube unit 1, a second straight tube unit 2, a third straight tube unit 3, a fourth straight tube unit 4, a first bent tube unit 5, a second bent tube unit 6, a third bent tube unit 7 and connecting parts 8 through welding. Both end parts of the radiant tube are fixed rigidly to the outer surface of a furnace wall 9. Accordingly, a temperature difference is generated between the high-temperature unit of a combustion burner 10 side and the low-temperature unit of exhaust gas 11 side whereby a difference of the length of thermal expansion of the radiant tube between the first straight tube unit 1 and the fourth straight tube unit 4 is generated thereby generating a thermal stress. Due to such a reason, two kinds or more of alloys having different coefficient of linear thermal expansion are used for the material of the heat resistant alloys constituting the radiant tubes to reduce the difference of the coefficient of linear thermal expansion due to the temperature difference.