New approaches to determine negligible creep

Working group WG59 CEN/TC54 has drafted a CEN technical report on how to determine no- and negligible creep temperature limits to support EN 13445-3 (unfired pressure vessels). Presently the standard assumes "rule-of-thumb" values for no-creep temperatures of ferritic and austenitic steels, 375 degrees C and 425 degrees C correspondingly. It is though well known that the lower ferritic grades could be creeping below the limit temperature and creep strength enhanced ferritic steels may show significant creep at temperatures well beyond it. Similarly, austenitic steels; nickel and other alloys are likely to have an even wider range of limit temperatures. This paper describes the data assessments and test methods used to determine limit temperatures for a specific set of steels and comparisons are made to other standards and nuclear design codes. The new approaches are promoting iso-stress testing in the low temperature range and applying Wilshire equation assessments on historical data.