Heating tube for boilers and method of manufacturing the same

A method of manufacturing a coated heat transmitting tube for a boiler, comprising:

• forming a porous sprayed coating by thermally spraying a metal.multidot.alloy having higher high temperature oxidation resistance and corrosion resistance at high temperature as compared with a material of a heat transmitting tube onto a heat transmitting surface of the tube for contacting combustion gas;
• and
• contacting the porous sprayed coating with a gas comprising vanadium compound and sulfur compound at high temperature to form a heat shielding layer formed by impregnating pores of the porous sprayed coating with inorganic sintered fine particles comprising vanadium compound and sulfur compound.

A method of manufacturing a coated heat transmitting tube for a boiler having an excellent effect of controlling adhesion of deposition onto an inner wall face of the tube, comprising:

• forming a porous sprayed coating having a thickness of 30-1000 .mu.m and a porosity of 2-20%, the forming of the porous sprayed coating comprising thermally spraying a metal.multidot.alloy having higher high temperature oxidation resistance and corrosion resistance at high temperature as compared with a material of the heat transmitting tube onto a heat transmitting surface of the tube for contacting a combustion gas;
• and
• then contacting the porous sprayed coating with a gas comprising vanadium compound and sulfur compound at high temperature to form a heat shielding layer formed by impregnating pores of the porous sprayed coating with inorganic sintered fine particles comprising vanadium compound, sulfur compound, NiO, and crust-forming component.