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VTT TECHNICAL RESEARCH CENTRE OF FINLAND LTD
Creep and
creep-fatigue
VTT ProperScan® HT Life
2 11/12/2015 2
Creep?
= time dependent deformation of solids at T ≥ ½·Tm
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)
3 11/12/2015 3
Creep limits life in design and service!
4 11/12/2015 4
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
5 11/12/2015 5
High Ni
(Kimura 2012) Temperature compensated creep
to rupture and Wilshire model
curve for nickel-base superalloy
Creep strain and creep strain rate:
VTT in-house LCSP-model
Creep: Temperature
compensated time to rupture
for conventional T/P22
Creep: Temperature
compensated time to rupture
and model prediction for P91
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
6 11/12/2015 6
Utilization of creep models for case studies (Steam mixer 600°C / 100 000 h)
Multiaxial strain
LIFE !
Uniaxial creep models:
rupture, strain, cyclic loading
10
100
1000
10 100 1000 10000 100000 1000000
Time to rupture (h)
Str
es
s (
MP
a)
EPRI raw data
VGB raw data
EN-10216 standard dataManson-Brown model
Wilshire model
EPRI weld data
Multiaxial constraint
FEA
7 11/12/2015 7
Service exposure will degrade material and
creep strength to limit life
Gas turbine blades
Boiler tube
8
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
9 11/12/2015 9
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 CO2 to reach a 20% CO2 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 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
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
10 11/12/2015 10
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.
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
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
TECHNOLOGY FOR BUSINESS
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