Evaluation of ECSC studies on residual life

Directorate-General For Research And Innovation

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Environmental research

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• Sciences et techniques

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• Publié par: DIRECTORATE-GENERAL-FOR-RESEARCH-AND-INNOVATION
• Nombre de lectures: 11
• Langue: English
• Poids de l'ouvrage: 4 Mo

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Commission of the European Communities
technical steel research
Properties and service performance
EVALUATION OF ECSCSTUDIES
ON RESIDUAL LIFE
Report
EUR 9878 EN
Blow-up from microfiche original Commission of the European Communities
technical steel research
Properties and service performance
EVALUATION OF ECSC-STUDIES
ON RESIDUAL LIFE
CF. ETIENNE
TNO
METAALINSTITUUT
Postbus 541
NL-7300 AM APELDOORN
Contract No 7210-ZZ/439
SYNTHESIS REPORT
Directorate-General
Science, Research and Development
1985 EUR 9878 EN Published by the
COMMISSION OF THE EUROPEAN COMMUNITIES
Directorate-General
Information Market and Innovation
L-2920 LUXEMBOURG
LEGAL NOTICE
Neither the Commission of the European Communities nor any person acting
on behalf of then is responsible for the use which might be made of
the following information
>ECSC-EEC-Euratom, Brussels· Luxembourg III
EVALUATION OF ECSC-STUDIES ON RESIDUAL LIFE
Summary V
Résumé IX
Zusammenfassung XIII
1 . Introduction 1
2. Procedures for characterization of high temperature materials and for
residual life assessment 5
(i) procedures based on nondestructive methods
(ii)s based on creep measurements 7
(iii) general procedures for residual life assessment 9
3. ECSC-studies on residual life 11
3.1. Survey of ECSC-studies
3.2. Characteristical physical and mechanical properties 15
(i) yield strength and hardness
(ii) number of cycles-to-failure in low cycle fatigue test 17
(iii) density8
(iv) electrical resistivity, thermal conductivity, Young's
modulus and magnetic properties 20
(v) fracture mechanicals such as JT and crack
c
opening displacement1
(vi) internal friction stress3
(vii) small angle neutron scattering 24
3.3· Creep at varying temperature and stress; validity of the life
fraction rule 26
(i) the life fraction rule
(ii) two stage creep tests and post-service exposure creep
tests
(iii) rectangular cyclic creep tests with varying temperature
and stress9 IV
3.4. Microstructural behaviour 32
(i) deformation and dislocation structures 33
(ii) degradation of bainitic structures4
(iii) changes in chemical content of the carbides
(iv) types of precipitations5
(v) quantification of precipitations 3
(vi) width of precipitaton free zones along the grain
boundaries 37
(vii) cavities8
(viii) microcracks 43
3.5. Cavitation growth and life prediction 4
(i) cavity nucleation and cavity growth
(ii) life prediction from cavitation growth9
3.6. Influence of residual elements 51
3.7. Other aspects
(i) techniques for monitoring creep deformation in
components3
(ii) nondestructive testing techniques4
(iii) strain analysis
(iv) behaviour of weldments 55
(v) environmental factors; creep-fatigue interactions 55
4. Evaluation of different test methods in ECSC-studies with respect
to residual life assessment7
5. Further needs of supporting research 62
Acknowledgement 65
References6
Tables (with captions in French and German) 71
Figures (withs in French and) 82 EVALUATION OF ECSC-STUDIES ON RESIDUAL LIFE
SUMMARY
The assessment of the residual life of high temperature installations
operating in the creep regime is of importance from an economical and a
safety point of view.
It comes into being as soon as a component of a high temperature
installation has to be inspected or the design life will be exceeded.
Such an assessment should preferably be based on a simple procedure where
the expired and/or the residual life can be determined by the measurement of
a single parameter. Otherwise, the decision on further use of an
installation has to be based on a combination of information from
nondestructive methods and the experience on the longterm behaviour gathered
from destructive testing methods.
Most available measuring techniques have the disadvantage of being not
sensitive enough or having a limited validity e.g. for a particular material
or for specific conditions. The proposed procedures for the assessment of
residual life are either too complex or too simple and often too much time
consuming. The complexity of the subject is perfectly illustrated by the new
British Standard (PD6510:1983) in which not a procedure but rather a
description of all the relevant subjects related to residual life assessment
is presented.
In the framework of ECSC Steel Research a number of research projects has
been performed dealing with the important aspects of residual life. The aim
of these projects was to contribute to the knowledge of the behaviour of
structural steels at high temperatures, on the basis of which better
procedures for the residual life assessment could be established.
In this paper a survey is given of the problems related to residual life
assessment and of the results obtained in eight projects sponsored by ECSC
which have been evaluated in comparison with results from literature.
The main conclusions of the evaluation are that there does not exist an
uniquely applicable method of residual life assessment and that such an VI -
assessment can only be based on the thorough evaluation of all the relevant
information.
In the different projects an enormous quantity of relevant information has
been gathered. The final reports should be consulted for essential details
of these studies.
In this summary a rough indication of the different aspects related to
residual life assessment will be given:
- Lowering the residual element content has an improving effect on creep
ductility of some ferritic steels, especially in coarse grained material
from heat affected zones in weldments.
- Qualitative and quantitative metallographic characterization of material
from components have been studied in several projects.
- Including microstructural examination in residual life assessment offers
the possibility to verify the virgin condition of the material, to verify
the recorded time-temperature history and to get information with respect
to residual ductility.
- An analysis has been proposed for predicting rupture life behaviour of any
material which fails by an intergranular failure mechanism. The model is
based on information with respect to the nucleation kinetics of cavities
and the growth rate of the cavities for the steel under discussion. On
this basis a method to predict the residual life of a component might come
into being.
- To verify the validity of the life fraction rule a large number of creep
rupture experiments under conditions of varying stress or temperature have
been performed on material in the as-delivered condition and on material
from components. On this basis a modified life fraction rule could be
established in which the steel type, the variation in stress or
temperature and the sequence of these variations are taken into account.
- From several considerations it became clear that the residual ductility is
a very important criterion for assessing the further use of high
temperature installations. For the moment creep rupture ductility is the
most secure measure for this residual ductility, but there is a need for a
faster relevant test method.
- In the projects a large number of characteristical properties have been
tested on their efficiency to describe the exhaustion of the material.
Most of these properties deliver additional information for the
characterization of the material, but they are not (yet) able to produce VII
direct information for residual life assessment. This holds - with
different limitations - for density, number of cycles to failure in low
cycle fatigue test, electrical resistivity, magnetic properties, small
angle neutron scattering, internal friction stress etc.
- For some testing methods more research is necessary before an evaluation
of the capability with respect to residual life assessment can be given
(especially for a fracture mechanics approach measuring crack opening
displacement or J and crack growth rate of material from components).
c
The attempt to evaluate the numerous studies on residual life has drawn the
attention to some related aspects:
- the need of internationally accepted definitions of concepts,
- the necessity to distinguish between general or limited applicability of
derived results,
- the lack of practical conclusions about the acceptability of using
components within the third creep regime.
Moreover, the evaluation of the ECSC-projects confronts us with further
needs of supporting research before a definitive procedure for the
assessment of residual life of high temperature installations can be
established. Aspects deserving special attention are indicated in the last
chapter.
Because of the large effort that will be involved in dealing with all these
aspects, a concerted action is proposed to fix priorities, to define
experimental programmes and to coordinate the execution of agreed
programmes. In the author's opinion the most important items for further
research are related to residual ductility and to strain analysis,
particularly with respect to tran