ASME Section III Design-By- Analysis Criteria Concepts and Stress Limits 1

The ASME Section III design-by-analysi

Recommended Revisions to Nuclear Piping Thermal Expansion Stress Limits

Piping thermal expansion stress limits for ASME Section III Class 2 and 3 piping are directly based on the original thermal expansion rules for B31.1 piping published in 1955. Temperature limits for B31 piping are much higher than for Class 2/3 nuclear piping. The fundamental concern in 1955 for piping design was to prevent cyclic creep strains, and the thermal expansion rules were based on a strain range criterion. Fatigue was also a concern, and a stress-range reduction factor for cyclic conditions was incorporated into the strain-based rule. The history and development of the B31.1 thermal expansion rules are summarized. After review of the technical basis, it becomes evident that the nuclear Class 2/3 rules can be simplified and improved by changing to an explicit fatigue-based rule rather than the strain-based rule of B31.1. Recommended Section III code revisions are provided with discussion of related technical issues.</jats:p

The 2011 Forum on Appropriate Criteria and Methods for Seismic Design of Nuclear Piping

A summary of The 2011 SEC Forum on Appropriate Criteria and Methods for Seismic Design of Nuclear Piping is provided. This forum session was the fifteenth in a series that was started in 1992. In the 2011 forum, the main topic of discussion was “Seismic Response Behavior of Piping”. The ASME Section III code for design of nuclear piping allows significant material plasticity at the Level D (SSE) limits. Test results from the EPRI/NRC Piping and Fitting Dynamic Reliability Program were reviewed including the failure modes of collapse versus fatigue. The Section III seismic stress limits were reviewed. The main discussion was on predicting fatigue life for an SSE including the effect of ratchet strains on fatigue life.</jats:p

Commentary on Class 2/3 Piping Rules

Much of the piping in a nuclear plant is designed to the ASME Boiler and Pressure Vessel Code, Section III, Class 2 or 3 requirements. The Code rules are given in NC/ND-3600 of Section III. These rules were developed from the B31.1 rules, and incorporated into Section III 1971 for nuclear components. However, the Class 2/3 piping Code requirements have changed significantly since that time. There is not a criteria document available from ASME that describes the Class 2/3 piping rules. The purpose of this paper is to provide background information and a discussion of the Code stress limits so that the piping analyst can properly interpret the meaning of the Code requirements.</jats:p

The 2009 Forum on Seismic Design of Piping Systems for the Year 2010

A summary of The 2009 Forum on Seismic Design of Piping Systems for the Year 2010 is provided. This forum session was the thirteenth in a series that was started in 1992. Previously, the title was Appropriate Criteria and Methods for Seismic Design of Nuclear Piping. In this 2009 forum, the main topic of discussion was “Dynamic Response Behavior of Piping.” Test results from three experimental programs were reviewed. The Berkeley NL vibration tests, the University of Liverpool vibration tests, and the EPRI/NRC Piping and Fitting Dynamic Reliability Program. The self-limiting nature of piping response by inelastic energy absorption is obvious from the experimental data.</jats:p