Materials at High Temperature Vol 21, Issue 1, 2004
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Use of advanced creep data for assessment of plant life and safety
R. A. Ainsworth
British Energy Generation Ltd, Gloucester, UK
Traditionally, design of components required to operate at high temperature has needed only limited creep data. Typically, creep rupture data and isochronous stress-strain curves have been sufficient. However, modern design approaches and assessments of operating plant using fitness-for-service procedures may require significantly more information. This paper describes these data requirements and addresses the issues of advanced constitutive equations and data for crack growth assessments in some detail.
Keywords: creep data, plant life, plant safety
Creep rupture and ductility of as-manufactured and service-aged nickel alloy IN617 materials and welds
David Allen1 Jean-Pierre Keustermans2, Sigrid Gijbels2 and Valerio Bicego3
1Power Technology, Powergen, UK
2Laborelec, Belgium
3CESI, Italy
This paper describes an ECCC Working Group 3C project on the creep performance of IN617 parent material and fabrication and repair welds in as-manufactured, aged, and service exposed conditions. The aims were to provide data for design of high temperature plant, to investigate the effects of service ageing, and to clarify the potential risk of relaxation cracking should an as-welded weldment enter service. A multi-member Italian consortium undertook creep testing of a new IN617 parent and weld, while Laborelec carried out parallel testing on an ex-service IN617 weld from a GT combustion system component provided by Powergen. The project also included comparison tests on the new weld after thermal pre-ageing to simulate service conditions at both moderate and higher temperatures. The results show that IN617 welds are weaker in creep than the parent material. Pre-ageing at high temperature causes a slight reduction in creep strength, but pre-ageing at a more moderate temperature actually causes a slight increase. Plain bar testing showed that IN617 weld metal can exhibit intergranular creep failure with fairly low ductility. However, notched bar testing of the ex-service material showed some evidence of notch strengthening in the weld metal and heat-affected zone, suggestive of a moderately low risk of creep brittle weld relaxation cracking in this material.
Keywords: creep rupture and ductility, nickel alloy IN617
Developments in assessing creep behaviour and creep life of components
P. Auerkari1, T.B. Brown2, S. Holdsworth3, R. Hales4, A. Klenk5 ,R. Patel6,
A. Thomas7, A. Tonti8 and T. Vilhelmsen9
1VTT, Finland,
2Mitsui Babcock, UK
3Alstom Power, UK
4ETD, UK
5MPA Stuttgart, Germany
6British Energy, UK
7SPG, Germany
8ISPESL, Italy
9Elsam, Denmark
Assessment of components for behaviour and life in the creep regime can arise both for as-new and inservice structures. The latter is generally more demanding, not only because of material ageing and possible growth of damage, but also due to frequently limited input information and less specific normative framework than for design. Regardless of whether the component has been observed (or assumed) to contain defects or not, the assessment procedures and the background tools have been developing considerably from the time when currently operating vintage components were first taken to service. The Working Group on Components of ECCC/AC is preparing overviews of the current methods and experience on component assessment. This effort is supported by application examples on component assessment and validation testing, as well the field experience from ex-service components.
Keywords: creep behaviour, creep life
The use of advanced-creep data for new plant development and design, and for the exploitation of new materials
C. Berger, M. Schwienheer and A. Scholz
Institute of Materials Technology, Darmstadt University of Technology, Germany
Advanced design methods contribute to the effective long term operation of high temperature components and guarantee low technical risk and high economical advantages. Along with the generation of advanced creep data, modelling and scatterband analyses are necessary to generate design curves and lower bound properties inclusive. Besides, in order to develop life prediction methods variable creep experiments lead to properties for single-stage and multi-stage loading. Further, the knowledge of multiaxial creep behaviour is of high future interest. The development of methods to transfer uniaxial material properties to multi-axial loading situations is a current challange. Different methods are established in order to describe creep crack initiation as well as crack propagation. A knowledge of the influence of creep processes on tolerance to pre-existing defects promotes the long term usability of components.
Keywords: creep strain, creep ductility, creep equations, scatterband assessment, multiaxiality, stress relaxation, creep crack initiation and propagation, pre-existing defects
Creep strength and ductility of 9 to 12% chromium steels
J. Hald
Elsam/Energy E2/IPL-Materials Technology, TU Denmark
The present paper focuses in on long-term creep properties of parent material of the new 9-12%Cr creep resistant steels, P91, E911 and P92 developed for use in advanced ultrasupercritical power plants. These steels have been at the center of activities in the ECCC Working Group 3A (WG3A) “Ferritic Steels”, which covers creep data development and analysis for parent materials and welds of all ferritic creep resistant steels ranging from low alloy steels up to 12%Cr steels. The opinions stated in the paper represent the views of the author rather than the whole ECCC WG3A group.
Keywords: creep strength, ductility, 9-12% chromium steels
Developments in the assessment of creep strain and ductility data
Stuart Holdsworth
ALSTOM Power, Rugby CV21 2NH, UK
Developments in the use of creep crack initiation for design and performance assessment
A. Klenk1, F. Mueller2, D. Dean3 and R.D. Patel3
1Materialpruefungsanstalt (MPA), University of Stuttgart, Germany
2Institut fuer Werkstoffkunde (IfW) Darmstadt, Germany
3British Energy, UK
In large components such as rotors defects due to manufacturing processes have to be taken into account and crack assessments based on findings of non-destructive evaluation are necessary. Similar approaches are used in remaining life estimations. The Time Dependent Failure Assessment Diagram (TDFAD) approach is currently being developed within the R5 procedures as an alternative to conventional methods for predicting incubation and the early stages of creep crack growth. A similar Two Criteria Diagram approach has been developed independently in Germany to assess creep crack incubation in ferritic steels. Both approaches have been investigated in a study initiated by ECCC Working Group 1.2 “Creep Crack Initiation”. Calculations and parameters used for the analysis such as reference stresses and fracture mechanics parameters have been compared for two materials, a ferritic 1CrMoV steel and an austenitic steel of type 316H.
Keywords: creep crack initiation, failure assessment diagram, two criteria diagram
Introduction to ECCC and activities of the project Advanced Creep
G. Merckling
Istituto Scientifico Breda, Milan, Italy
The European Creep Collaborative Committee was founded in 1991/2 by European industrial and research organisations to harmonise and exchange scientific activities in the field of long duration creep. Now-a-days, due to the reduced availability of industrial and public funding the Europe wide collaboration has a particular weight in optimising the available testing and development resources. ECCC, supported by the EC Thematic Network Advanced Creep, 14 nations and nearly 50 organisations, actually runs Working Groups dealing with creep data generation and assessment procedures (WG1 and subgroups), with creep data collation, assessment and testing program co-ordination for ferritic and martensitic steels (WG3.A), austenitic steels (WG3.B), superalloys (WG3.C) and with creep behaviour of components (WG4). Several of these activities introduced harmonised common views into European and International Standards.
Keywords: European Creep Collaborative Committee
The multiaxial and uniaxial creep ductility of Type 304 steel as a function of stress and strain rate
M. W. Spindler
British Energy, Assessment Technology Group, Barnett Way, Barnwood, Gloucester GL4 3RS, UK, E-mail mike.spindler@british-energy.com
Calculations of creep damage under conditions of strain control are often carried out using a ductility exhaustion approach. Issue 3 of the R5 procedure uses a ductility exhaustion approach to calculate creep damage, in which the ductility is a function of creep strain rate and temperature. However, recent studies have shown that the prediction of creep damage in creep-fatigue tests is improved when the creep ductility is considered to be a function of stress, creep strain rate and temperature. The aim of this paper is to describe the development of a new model for the effect of multiaxial states of stress on creep ductility which is intended for use with a creep damage model in which the creep ductility is a function of stress, creep strain rate and temperature.
Keywords: multiaxial and uniaxial creep ductility, Type 304 steel, stress and strain rate