Precision in the extrapolation of creep rupture data

To be able to determine the accuracy in the extrapolation of creep rupture data, expressions for estimating the error are presented. One expression is based on the statistical uncertainty in the least square fit to the data. This estimate can be considered as the minimum possible error that is prese nt in extrapolated values. Expressions for the upper limit of the error bas ed on linear as well as higher-order polynomials are derived. It is demonst rated that the expression based on linear extrapolation has a general appli cability and covers most cases of technical interest. Comparison to previou sly performed extrapolation analyses shows that the actual variation betwee n extrapolation methods lies in general between the least square error and the upper limit estimate. It is proposed that design values derived from ex trapolated creep rupture data should be reduced, with an additional data fa ctor if the estimated error in the extrapolation is larger than what is typ ical in the materials codes and standards. Values for these data factors ar e given.