13th International Conference on Fracture June 16–21, 2013, Beijing, China -9- • Calculation of ductility-exhaustion-type strain-based creep damage tends to overestimate the creep fraction used per cycle when all inelastic strain during a hold period is counted. However, use of a modified stress ductility approach or equivalent appeared to provide the best method of assessment. • As an initial approach to component assessment it seems that application of an easy to use conservative method offers a practical way of undertaking bounding type calculations. Use of these approaches must consider lower bound materials data and simplified stress analysis for both parent and welds. • For second level assessments there are advantages to use of probabilistic assessment using validated inelastic analysis. Since this approach requires considerable effort on materials relationships and validation of models it will only be used for a very select number of components • As Power plant operation now involves an increasing range of cyclic operation, issues of creep and cyclic damage increasingly a concern. The following questions summarize topics of focus for EPRI: – How to predict field damage using available models/ methodologies? Required accuracy? Important attributes? – Monitoring. Need for instrumentation in performing a component assessment? – Availability of relevant materials data to assessment of an ageing plant (coal or HRSG pressure parts, rotors)? – Design. Can we improve on the design for cyclic high temperature service? Should there be design life based on hours, cycles, and oxidation? – What is required for practical component assessment? It is clear the groundwork laid by EPRI on creep-fatigue damage with the collaboration, assistance, and dedication of a large international experts group was a timely activity due to increased cyclic plant operation. While many tasks are now complete, more work is needed. The international group will continue to meet with key activities on completing standardization, developing creep-fatigue datasheets, and focusing on application case studies to improve component assessments. Acknowledgements Thanks to the support and contributions from the invited experts the discussions were successful in identifying key issues and perhaps more importantly developing solutions to these challenges. Support for this work has included the involvement of the following Bob Ainsworth, Dave Dean and Mike Spindler , British Energy (now EdF),UK; Ashok Saxina , Galgotias University, India (formerly University of Arkansas); Stuart Holdsworth, EMPA, Switzerland; Yukio Takahashi, CRIEPI, Japan; Bilal Dogan (formerly of GKSS and EPRI); Peter Skelton, consultant UK (formerly CEGB and Imperial College); Warwick Peyton, ANSTO, Australia; Toshimitsu A. Yokobori ,Tohoku University, Japan: Karl Maile and Andreas Klenk, MPA Stuttgart, Germany; Olivier Ancelet, CEA, France; Hellmuth Klingelhöffer, BAM, Germany; Fujimitsu Masuyama, Kyushu Institute of Technology, Japan; Andre Pineau, Ecole des Mines de Paris, France; Alfred Scholz, T.U. Darmstadt, Germany.
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