Draft Rules for Alloy 617 Creep-Fatigue Design Using an EPP+SMT Approach

Abstract

The report describes an improved new creep-fatigue design method for structural components in high temperature nuclear service. The new method uses an integrated elastic-perfectly plastic (EPP) analysis and Simplified Model Test (SMT) approach that greatly simplifies the design process by avoiding the separate evaluation of creep and fatigue damages and eliminating the requirement of stress classification. The report includes draft design rules, presented in a format compatible with an ASME nuclear Code Case, as well as a commentary on the rules and the validation of the rules using pressurized SMT (p-SMT) test data. Areas of potential improvement have been identified for further evaluation. The report also develops EPP+SMT design charts for Alloy 617 at temperatures between 800°C and 950°C by extrapolating high strain range, short hold test data to low strain range and long hold times, typical for structural components in high temperature nuclear service. The design charts are currently limited to 10,000 cycles to avoid excessive extrapolation outside the test database. More robust alternate extrapolation procedures will be considered in future work. The report includes several verification problems comparing the new EPP+SMT design method with current ASME creep-fatigue design methods. The comparison demonstrates that the EPP+SMT method significantly reduces the over-conservatism in current methods. Finally, the report includes a fully-documented sample problem with multiple load cases detailing the application of proposed EPP+SMT design rules.

High-Temperature Creep Test Suite for Grizzly

“…The header model is considered to operate at a constant pressure of 7.5 MPa and 600 • C. The operating time of 5 years is considered in this analysis [32 ].…”

“…Figure 10: Variation of temperature in the inner tube of the hot duct during the accident and emergency shutdown, based on a transient heat transfer analysis reported in[32 ].…”

Report on FY 2023 Research and Development on Specially Designed Creep-fatigue Experiments on Alloy 617 in Support of Improving Creep-fatigue Evaluation Approaches

“…Approaches to account for the primary-load effect on SMT design curves were discussed in Barua et al (2020Barua et al ( , 2021, and the results show that the EPP strain range analysis procedure naturally captures the primary pressure effect. Barua et al (2020Barua et al ( , 2021 also demonstrated that the EPP+SMT methodology is much simpler to execute than conventional CF damage analyses through multiple sample problems. The remaining critical factors in finalizing the SMT-based design curves are the methods for extrapolating the design curves to the low strain range region and with longer hold times (such as long hold time of 1,000 h) that are prototypical of plant operations.…”

An extrapolation method for strain ranges and hold times in developing the EPP+SMT creep-fatigue design curves for Alloy 617

“…The reduction of SMT CF life because of primary load was found to be dependent on strain ranges and elastic follow-up factors. Approaches to account for the primary-load effect on SMT design curves were discussed in Barua et al (2020Barua et al ( , 2021, and the results show that the EPP strain range analysis procedure naturally captures the primary pressure effect. Barua et al (2020Barua et al ( , 2021 also demonstrated that the EPP+SMT methodology is much simpler to execute than conventional CF damage analyses through multiple sample problems.…”