For simplified design of components operating at high temperatures it is recommended to design in the No Creep (NC) or Negligible creep (NEC) temperature regimes of the material. In nuclear design rules (such as RCC-MRx), it is possible to disregard creep as design criterion during normal service operation if the temperature, stress and time limits for NEC are respected. It is a challenge to define these limits reliably in the temperature range where creep behavior (time to strain and/or rupture) is traditionally not tested. In the non-nuclear field the European standard EN-13445 for the design of unfired pressure vessels intends to include NEC temperature curves (TNEC) for a number of steels (austenitic, ferritic and ferritic-martensitic steels.). In this report the JRC contribution to the CEN/TC 54/WG CREEP activities are reported. A methodology originated from the FP7 MATTER project is here used for defining the TNEC curves for X10CrMoVNb9-1 (Grade 91) and 10CrMo910 (Grade 22) steels with the limited data available in the material standard EN 10028. The TNEC is successfully determined and validated by the MATTER results for X10CrMoVNb9-1 steel. The TNEC curves are shown to be independent of product form (thickness of pipes). Also the curves are almost identical for both assessed steels. The change in yield and tensile strength seemingly compensates for the change in rupture strength. The approach can now be used for defining the NEC of other steels tabulated in the standards.JRC.F.4 - Innovative Technologies for Nuclear Reactor Safet
