Abstract
A small punch creep testing technique using miniaturized specimen with a dimension of 10 × 10 × 0.3^t mm has been demonstrated for evaluating change in creep property of high temperature components due to long-term service operation. This technique was applied to SUS 316 HTB secondary superheater boiler tube actually used for 100,600 h in a fossil power plant. The overall shapes of the creep curves determined by the small punch creep test were similar to those obtained from a conventional uniaxial creep test. That is, they exhibited clearly three creep stages. The extent of secondary creep stage and rupture time t_r decreased with a increase of testing load level. The creep rupture life of the service-exposed tube was shorter than that of the unexposed tube at a temperature of 650℃ and at high load levels, i.e. 338 N and 408 N. However, to the contrary, the former became longer than the latter at relatively low load levels, i.e. 234 N and 286 N. The difference in rupture life between them had a tendency to increase with a decrease of testing load level. These small punch creep behaviors of SUS 316 HTB superheater boiler tubes have been examined from a metallographic point of view.
