VTT TECHNICAL RESEARCH CENTRE OF FINLAND LTD Creep and creep-fatigue VTT ProperScan HT Life
Creep? = time dependent deformation of solids at T ½ T m Important for: Design of high temperature applications Creep strength /stress for Time to rupture Time to 1% strain Weld strength factors (welds) Life management Creep damage accumulation Remaining life estimation Inspection scheduling Failure analysis Ends ultimately in failure (creep rupture) 11/12/2015 2
Creep limits life in design and service! 11/12/2015 3
High temperature materials mechanical testing facilities 16 single specimen creep testing machines (max 950 C) Uniaxial creep, notched bar, compact tension specimens 4 multi-specimen creep machines (4 specimens each) 3 servo-mechanical testing machines used for: Impression creep testing Creep-fatigue under four point bending Small punch 11/12/2015 4
Creep strain and creep to rupture Experimental evaluation: Multiaxial creep (notched bar), impression creep, small punch Creep strain and creep to rupture modelling In-house LCSP creep strain model Creep: Temperature compensated time to rupture for conventional T/P22 Temperature compensated creep to rupture and Wilshire model curve for nickel-base superalloy Creep strain and creep strain rate: VTT in-house LCSP-model High Ni (Kimura 2012) Creep: Temperature compensated time to rupture and model prediction for P91 11/12/2015 5
Stress (MPa) Utilization of creep models for case studies (Steam mixer 600 C / 100 000 h) FEA Uniaxial creep models: rupture, strain, cyclic loading 1000 EPRI raw data VGB raw data EN-10216 standard data Manson-Brown model Wilshire model EPRI weld data Multiaxial strain LIFE! 100 10 10 100 1000 10000 100000 1000000 11/12/2015 6 Time to rupture (h) Multiaxial constraint
Service exposure will degrade material and creep strength to limit life Gas turbine blades 11/12/2015 7 Boiler tube
Creep-fatigue testing Two-way pneumatic loading system (push / pull) based on bellows technology Enables creep fatigue crack initiation testing with strain or stress control, with or without hold periods The equipment can also be modified for creep-fatigue crack growth testing The bellows technology concept is capable of operating in a range of extreme conditions High temperature (up to 800ºC) Pressurized water or steam Super Critical Water (SCW) Irradiation environments 8
Creep-fatigue assessment for ultra high efficiency pf power plants Meeting the materials and Manufacturing Challenge for Ultra High Efficiency PF Power Plants with CCS The concept is to perform innovative demonstrations that will significantly contribute to the EU target to increase the efficiency in existing and new build pulverised coal power plants. This is necessary as the EC aims to capture and store CO 2 to reach a 20% CO 2 reduction in 2020. Demonstration of materials and coatings for boiler and mainstream pipework under Ultra-supercritical (USC) and current steam conditions. Demonstration of the mechanical integrity of the main steam pipe under USC conditions to a steam temperature of 750 C. Material testing and evaluation to study creep-fatigue properties of Ni-based superalloys. Creep-fatigue testing and material properties charazterization Creep-fatigue testing for parent material and cross-weld specimens A pre-creep exposure of 178MPa / 750 C / 3000h for selected specimens to demonstrate post service simulation Atlas of fractographs and micrographs Creep-fatigue modelling to support mechanical behaviour extrapolation to actual in-service periods The stress relaxation behaviour assessment and modelling The creep strain and creep to rupture modelling The creep-fatigue interaction 11/12/2015 9
Creep-fatigue assessment and modelling for nuclear applications Materials research project for European Gen IV prototypes: the LFR ETPP (European Technology Pilot Plant) Myrrha and the SFR Prototype ASTRID The modified 9Cr 1Mo (P91) steel is a candidate material for several components of the Generation IV nuclear reactors. Typical in-service conditions require operating temperatures between 400 C and 600 C, which means that the creep behaviour of these steels is of primary interest. In addition, the repeated start and stop-operations during service lead to loadings of creep fatigue type, with very long holding periods in combination with high frequency thermal loads. Improvement of selected rules and specifying the recommendations on the improved rules (in RCC-MRx, ASME III NH, BS-R5) for creep and creep-fatigue interaction for P91 components Creep-fatigue assessment according to methods defined in RCC-MRx, ASME III NH, and BS-R5 Robust models for creep-fatigue life assessment VTT in-house creep-fatigue model (the Φ-model) FEA assisted assessment of creep-fatigue rules to P91 components Additional qualification experiments to allow codification on P91 material and components Two-way pneumatic loading system (push / pull) based on bellows technology for creep-fatigue testing Enables testing in strain or stress control, with or without hold periods The concept is capable of operating in a range of extreme conditions High temperature (up to 800ºC) Pressurised water or steam, Super Critical Water (SCW) Irradiation environments 11/12/2015 10
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