A procedure for extended extrapolation of creep rupture data

To be able to perform extended extrapolation of creep rupture data, i.e., extrapolation by more than a factor of three in time, a new procedure is proposed. A free temperature model for the time-temperature parameter is used that provides a high degree of flexibility. Postassessment tests are formulated to verify that the chosen time-temperature parameter has sufficient stability. In the analysis, criteria are introduced for the position of the predicted creep rupture curve in relation to the scatter band of data as well as criteria on derivatives of the predicted creep rupture curves. The procedure has been applied successfully to five common creep-resistant pressure vessel steels: one low-alloy steel (2Cr 1Mo) and four austenitic stainless steels: 304H, 316, 253MA, and 800H. The small deviations between the full datasets and strongly culled sets demonstrate the validity of the proposed procedure.