DEFINING A NEGLIGIBLE CREEP TEMPERATURE CURVE FOR GR. 91 STEEL

Time independent rules for design can be applied if the design temperature of a component is restricted below the negligible creep temperature (TNEC). The TNEC curve describes the time and temperature limits below which accumulated creep strain and damage is insignificant at a specified reference or design stress. For the ferritic/martensitic steel Gr. 91 (X10CrMoVNb9-1) there is currently no TNEC curve available in the nuclear design code RCC-MRx. In this paper the TNEC curve for Gr.91 is defined using a new methodology developed in the European FP 7 project MATTER. The TNEC curve is based on time to 0.2% creep strain data. Supporting test data from low temperature (375-500 °C) creep and tensile tests are presented and assessed. The TNEC curve can alternatively be constructed by using time factor corrected creep rupture data. These time factors can be used for evaluating the safety against significant creep at both reference and design stress. The presented methodology is will be used for determination of TNEC curves for the next revision of the EN-13445.JRC.G.I.4-Nuclear Reactor Safety and Emergency Preparednes