Negligible creep temperature curve verification for steels 10CrMoV9-10 and X2CrMoNiMo17-12-2

A simplified methodology to define the negligible creep (TNEC) curves has been proposed for the CEN TC 54 WG CREEP for defining negligible creep temperature curves using standard tensile and the creep rupture properties. The method can potentially be implemented in the European standard EN-13445 for the design of unfired pressure vessels. The EN-13445 standard intends to include the NEC temperature curves for a number of steels (mainly ferritic and ferritic-martensitic). In this report the negligible creep curves for the F/M steel 10CrMo9-10 (Grade P22) and the austenitic steel X2CrNiMo17-12-2 (Grade 316L) are defined by limiting the allowable time in creep to 1/1000 of the corresponding time to rupture at the specified reference stress. The reference stress has been set at 2/3 Rp02 for the F/M steel and 1.35 Rp02 for the austenitic steel. The predicted curves are compared against creep strain data from the open literature and data from the European Creep Collaborative Committee (ECCC) Work Group I activities on robust creep strain modelling. For the case of X2CrNiMo17-12-2 steel the proposed negligible temperature curve is compared against the curve defined in the nuclear design rules RCC-MRx. The proposed methodology is based on the Wilshire equations: The time factor approach is shown to produce conservative TNEC curves for both steels and support the use of the methodology for generating TNEC curves for the EN13445 standard.