Creep Remaining-Life Assessment of 2.25Cr-1Mo Steel Hot Reheat Steam Piping by Small Punch Test

Abstract

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.

Prediction of Graphitization Behavior during Long-Term Creep in Carbon Steels

“…As a result, the importance of the residual life evaluation of component materials, including graphitization risk assessment, is increasing because graphitization risk is enhanced when used for more than 10 5 hours. 7) The residual life can be evaluated by accelerated creep testing of miniature samples extracted from the component materials, 10,11) although shutdown of the operating plant is necessary for the sampling. Therefore, it is important to understand the graphitization risk conditions of carbon steels during the long-term operation to avoid of the unexpected failure due to the degraded mechanical properties of the component materials by graphitization with the minimum shutdown period.…”