1994 年 43 巻 485 号 p. 203-209
The heating tubes, which operate under most adverse conditions of all boiler components, deserve exceptional care about their remaining service lifetime, with particular regard to accumulation of damage due to creep and progress of corrosion due to oxidation. The current practice of such evaluation is to perform appropriate destructive tests on the tubings sampled out of a bundle concerned, but the creep test does not return accurate enough estimates because the damage that has been accumulated in service is yet too small, giving rise to large scattering of data. In addition, there is a matter of rise of metal temperature due to internal formation of steam-induced oxide film, hence degradation of thermal conduction: since the metal temperature can exceed the initially set design operation temperature as the service is prolonged, this increment will have to be incorporated in the creep damage evaluation. Also, rise of effective stress arising from loss of wall thickness due to external formation of scale has to be considered. This report introduces a comprehensive damage assessment simulation program that takes these changes into account and discusses its authenticity on comparison with damage evaluation conducted by TEM.