Size effect studies of the creep behaviour of a pressure vessel steel at temperatures from 700 to 900 °C

Characterization of the creep properties of heat resistant 9–12% chromium steels by miniature specimen testing

“…At the lowest test temperature of 700 1C the trend additionally depended on the initial stress level. The stress variation with values ranging from 10 MPa to 30 MPa was much higher in [31] than in our experiments; it may be anticipated that this could explain why no stress dependence of rupture time was observed in the present work. Similarly, the elongation at fracture and creep rate minima were also found to depend on specimen size, with the latter exhibiting differences of more than one order of magnitude [31].…”

“…The stress variation with values ranging from 10 MPa to 30 MPa was much higher in [31] than in our experiments; it may be anticipated that this could explain why no stress dependence of rupture time was observed in the present work. Similarly, the elongation at fracture and creep rate minima were also found to depend on specimen size, with the latter exhibiting differences of more than one order of magnitude [31]. The reported variations do not clearly correspond to our findings, as the elongations were consistently found to be larger in the smaller specimens and enhanced or reduced creep rate minima were obtained depending on test temperature.…”

“…The authors point out that no single general trend could be derived from earlier literature findings and, consequently, available explanations remained on the level of plausibility [31]. In the experimental part of their work, the creep behavior of a pressure vessel steel was examined in argon atmospheres, comparing results of 5 mm and 20 mm gauge length diameter specimens.…”

“…A more recent study of creep specimen size effects was performed by Krompholz and Kalkhof [31] in the framework of an Euratom project. The authors point out that no single general trend could be derived from earlier literature findings and, consequently, available explanations remained on the level of plausibility [31].…”

“…As a first effect, it was shown in [31] that time to rupture and especially time to reach 5% elongation depended on specimen size, yielding deviations up to a factor of 10. Similarly to the present results, the trend towards longer/shorter life of small specimens depended on the applied temperature.…”