Abstract
Since tubes, used in superheater or reheater of thermal power plant boiler, are used at an elevated temperature for a long period of time, occurring of creep damage and oxidation thinning are concerned. Although it is important to grasp a temperature in use for securing the soundness of equipment, since number of tube is large and installed in the furnace, it is difficult to carry out a temperature measurement by thermocouple etc. It has been reported, when the low alloy steel (2.25Cr-1Mo, STBA24) widely used for piping or tube is exposed to elevated temperature for long term, the area (PFZ, Precipitates Free Zone) in which carbide disappeared near the grain boundary will be formed, and from measurement of PFZ width, it is possible to presume the mean operating temperature in period of use. The above-mentioned technique is applied to boiler tube scrap wood, and tried to presume operating temperature. Moreover, technique of presuming the residual life of tube from the presumed temperature, in consideration of oxidation thinning, is developed.
