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Engineering Tools for Robust Creep Modeling

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Engineering Tools for Robust Creep Modeling VTT CREATES BUSINESS FROM TECHNOLOGY Technologyandmarketforesight•Strategicresearch•Productandservicedevelopment•IPRandlicensing Dissertation VTT PUBLICATIONS 728 •Assessments,testing,inspection,certification•Technologyandinnovationmanagement•Technologypartnership • • • VTT PUBLICATIONS 728 ENGINEERING Creep models are needed for design and life management of structural components operating at high temperatures. The determination of creep properties require long- term testing often limiting the amount of data. It is of considerable interest to be able to reliably predict and extrapolate long term creep behavior from relatively small sets of creep data. In this thesis tools have been developed to improve the TOOLS reliability of creep rupture, creep strain and weld strength predictions. Much of the resulting improvements and benefits are related to the reduced requirements for FOR supporting creep data. The simplicity and robustness of the new tools also make them easy to implement in analytical and numerical solutions. Creep models for ROBUST selected high temperature steels and OFP copper are presented. CREEP MODELING Stefan Holmström Engineering Tools for Robust Creep Modeling ISBN 978-951-38-7378-3 (soft back ed.) ISBN 978-951-38-7379-0 (URL: http://www.vtt.fi/publications/index.jsp) ISSN 1235-0621 (soft back ed.) ISSN 1455-0849 (URL: http://www.vtt.fi/publications/index.jsp) VTT PUBLICATIONS 728 Engineering Tools for Robust Creep Modeling Stefan Holmström Dissertation for the degree of Doctor of Science in Technology to be pre- sented with due permission of the Faculty of Engineering and Architecture, The Aalto University School of Science and Technology, for public exami- nation and debate in K216 at Aalto University (Otakaari 4, Espoo, Finland) on the 5th of February, 2010, at 12 noon. ISBN 978-951-38-7378-3 (soft back ed.) ISSN 1235-0621 (soft back ed.) ISBN 978-951-38-7379-0 (URL: http://www.vtt.fi/publications/index.jsp) ISSN 1455-0849 (URL: http://www.vtt.fi/publications/index.jsp) Copyright © VTT 2010 JULKAISIJA – UTGIVARE – PUBLISHER VTT, Vuorimiehentie 5, PL 1000, 02044 VTT puh. vaihde 020 722 111, faksi 020 722 4374 VTT, Bergsmansvägen 5, PB 1000, 02044 VTT tel. växel 020 722 111, fax 020 722 4374 VTT Technical Research Centre of Finland, Vuorimiehentie 5, P.O. Box 1000, FI-02044 VTT, Finland phone internat. +358 20 722 111, fax + 358 20 722 4374 Technical editing Mirjami Pullinen Edita Prima Oy, Helsinki 2010 Stefan Holmström. Engineering Tools for Robust Creep Modeling [Virumismallinnuksen uudet mene- telmät]. Espoo 2010. VTT Publications 728. 94 p. + 53 p. Keywords creep, strain, damage, modeling, steel, OFP copper Abstract High temperature creep is often dealt with simplified models to assess and pre- dict the future behavior of materials and components. Also, for most applications the creep properties of interest require costly long-term testing that limits the available data to support design and life assessment. Such test data sets are even smaller for welded joints that are often the weakest links of structures. It is of considerable interest to be able to reliably predict and extrapolate long term creep behavior from relatively small sets of supporting creep data. For creep strain, the current tools for model verification and quality assurance are very limited. The ECCC PATs can be adapted to some degree but the uncer- tainty and applicability of many models are still questionable outside the range of data. In this thesis tools for improving the model robustness have been devel- oped. The toolkit includes creep rupture, weld strength and creep strain model- ing improvements for uniaxial prediction. The applicability is shown on data set consisting of a selection of common high temperature steels and the oxygen-free phosphorous doped (OFP) copper. The steels assessed are 10CrMo9-10 (P22), 7CrWVMoNb9-6 (P23), 7CrMoVTiB10-10 (P24), 14MoV6-3 (0.5CMV), X20CrMoV11-1 (X20), X10CrMoVNb9-1 (P91) and X11CrMoWVNb9-1-1 (E911). The work described in this thesis has provided simple yet well performing tools to predict creep strain and life for material evaluation, component design and life assessment purposes. The uncertainty related to selecting the type of material model or determining weld strength factors has been reduced by the selection procedures and by linking the weld behavior to the base material mas- ter equation. Much of the resulting improvements and benefits are related to the reduced requirements for supporting creep data. The simplicity and robustness of the new tools also makes them easy to implement for both analytical and nu- merical solutions. 3 Stefan Holmström. Engineering Tools for Robust Creep Modeling [Virumismallinnuksen uudet mene- telmät]. Espoo 2010. VTT Publications 728. 94 s. + liitt. 53 s. Keywords creep, strain, damage, modeling, steel, OFP copper Tiivistelmä Rakenteiden suunnitteluun ja elinikäennusteisiin käytetyt kuumalujien terästen lujuusarvot ja hitsien lujuuskertoimet pohjautuvat virumiskoetuloksiin, joita on varsinkin pitkäaikaisina käytettävissä usein vain niukasti. Sen vuoksi on erityi- sen tärkeää, että koetuloksiin sovitetut materiaalimallit ovat taloudellisia, tarkko- ja ja luotettavia erityisesti ekstrapoloitaessa pidemmille käyttöajoille. Tässä väitöstyössä on kehitetty uusia malleja työkaluiksi virumismurtolujuu- den, hitsien lujuuskertoimien ja virumisvenymän luotettavaan määrittämiseen sekä virumiseliniän ennustamiseen erityisesti tapauksissa, joissa mallinnuksen tueksi on käytettävissä niukasti virumiskoetuloksia. Uusien mallien suoritusky- kyä on testattu eurooppalaisessa vertailututkimuksessa, jossa ne ennustivat yk- sin-kertaisesta muodostaan huolimatta venymiä tarkemmin kuin aiemmat ja huomattavasti monimutkaisemmat virumismallit. Uusia malleja on työssä sovel- lettu OFP-kuparille ja ferriittisille teräksille 10CrMo9-10 (P22), 7CrWVMoNb9- 6 (P23), 7CrMoVTiB10-10 (P24), 14MoV6-3 (0.5CMV), X20CrMoV11-1 (X20), X10CrMoVNb9-1 (P91) ja X11CrMoWVNb9-1-1 (E911). Materiaali- malleja on myös sovitettu numeerisen suunnittelun työkaluihin (COMSOL ja ABAQUS) ja verifioitu pitkään käytössä olleen hitsatun putkiyhteen elinikätar- kastelulla. Väitöstyön tuloksena kehitettyjä malleja ja menetelmiä voivat soveltaa korke- an lämpötilan rakenteiden suunnittelijat ja eliniän hallinnan asiantuntijat helpot- tamaan ja tarkentamaan virumiskäyttäytymisen ennustamista. Työn keskeinen anti on kehitettyjen menetelmien tarjoama vähentynyt materiaalidatan tarve ja mallien yksinkertainen rakenne, joka helpottaa niiden hyödyntämistä sekä ana- lyyttisissä että numeerisissa ratkaisuissa. 4 Preface This work has been carried out at VTT, financially supported by the Academy of Finland grant 117700 with prof. Kim Wallin acting as instructor. It has been supervised by prof. Hannu Hänninen, head of laboratory of Engineering Materi- als at Helsinki University of Technology (HUT). Prof. Hänninen is greatly ac- knowledged for his valuable input in the finalization stage of the thesis and for arranging a place at HUT to escape the hectic work surroundings of VTT. A substantial part of the research gone into the development of the creep mod- els and modeling tools has been done over several years within many VTT pro- jects, both national and international. Projects like Extreme (internal VTT), Aloas (RFCS), LC-Power & Life-Power (Tekes financed), The Värmeforsk pro- ject on Creep damage development in welded X20 and P91 components and the LEIA / PIKE projects, to name a few, have contributed to this thesis. The European Creep Collaborative Committee (ECCC) has been a valuable supply of interesting challenges, creep expertise, relevant feed-back, active sup- port, friendship and an invaluable source of creep data that would not have been accessible without the ECCC WG1 network lead by Dr. Stuart Holdsworth. The Japanese creep data produced and freely distributed by NIMS has also been a valuable source of high quality data. The work done on the OFP copper for nu- clear waste canisters has been part of the national projects LEIA / PIKE, funded by the public Nuclear Waste Management Program in Finland (KYT). Special thanks go of course to the co-authors of the publications incorporated in this thesis. Also my team, “Materials performance for combustion systems”, has given me great support and has shown incredible patience and has not complained over sloppily done administrative tasks during the final stages of this work. Finally, I would like to thank my wife and children for their valuable support and understanding when my eyes have glazed over at home, in the car or at some social event, brooding over some nutty creep modeling detail. 5 Contents Abstract ................................................................................................................. 3 Tiivistelmä ............................................................................................................. 4 Preface.................................................................................................................. 5 Research hypothesis and original features........................................................... 7 List of abbreviations and symbols....................................................................... 11 1. Introduction ................................................................................................... 15 2. General aspects on creep data, modeling and design ................................. 18 2.1 Creep testing....................................................................................................................
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