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In order to investigate the adaptability of small punch (SP) creep testing technique to the remaining-life assessment, the SP creep test was carried out with 2.25Cr-1Mo steel hot rehear steam piping, which had been actually used in a fossil power plant for long periods of time. The SP load (F) was converted to the stress (σ) by three different equations, which were derived based on the displacement to maximum load in the SP test (u m ) and the deflection to minimum deflection rate in the SP creep test (u min ) for correlating the SP creep rupture data with the uniaxial ones. The experimental results showed that the SP creep rupture time of specimen removed at around outer surface of piping tended to be slightly shorter than those taken at around inner surface and center. It was also found that the SP creep rupture data were relatively in good agreement with the uniaxial ones by converting F to σ with the equations, and the creep remaining-life was well predicted by the extrapolation of short-term SP creep rupture data. The highest prediction accuracy was obtained by using the equation derived from the SP test result, that is, u m . Consequently, it was confirmed that the SP testing technique could be a strong tool for creep remaining-life assessment of boiler piping.

Electrochemical material characterization method was applied to the creep specimens of 12%Cr ferritic steel to evaluate the changes in precipitates during creep. Experimental results revealed that the peak current densities “Ip1” and “Ip2” appeared at specific potentials during anodic polarization curve measurement in 1M-KOH solution. These peak current densities corresponded to the selective dissolution of several kinds of precipitates, respectively. The Ip2, which reflected the amount of M23C6 and Laves phase, increased more siginificantly with creep than thermal aging. On the other hand, the effect of applied stress was not reflected on the change in Ip1, although it increased with thermal aging and creep as well as the Ip2.

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