Development of ASME Division 5 Code proposal on temperature limits for simplified design methods

Abstract

This report establishes proposed upper temperature limits for the ASME BP&V Code Section III, Division 5, Nonmandatory Appendix HBB-T design by elastic analysis provisions for bounding ratcheting strain and creep-fatigue damage in Class A high temperature nuclear reactor components. Limitations on the use of these design options are required because the design by elastic analysis methods rely on bounding theories that assume a non-unified, decoupled model of creep-plasticity. However, at high temperatures creep and plastic deformation become coupled and bounding theorems relying a decoupled material response may fail. The report describes a method for selecting appropriate upper temperature limits, demonstrates directly through a comparison to full inelastic simulations that the existing Code provisions can be nonconservative at high temperatures, and develops the requisite Code language required to implement the temperature limits in Section III, Division 5.

Development of the Technical Basis of a Unified Viscoplastic Model of 316H Stainless Steel for Incorporation into ASME Division 5

“…This means the material model must accurately predict cyclic inelastic deformation, even though the model need not explicitly represent damage as the damage calculation is done with a separate Code procedure. Previous work has demonstrated that above a certain threshold temperatures, established to be • C for 316H, a non-unified model decomposing inelastic deformation into separate rate-independent plasticity and rate-dependent creep contributions become unsuitable as creep and plasticity cannot be distinguished [10,11]. In this temperature regime a unified viscoplastic model is more appropriate.…”

Inelastic analysis procedure based on the Grade 91 unified viscoplastic constitutive model for ASME implementation

“…The draft guidance provides temperatures for each of the Class A materials above which creep and plasticity become indistinguishable. These temperatures are based on past DOE sponsored work [16,17].…”