EN 60544-5:2012
(Main)Electrical insulating materials - Determination of the effects of ionizing radiation - Part 5: Procedures for assessment of ageing in service
Electrical insulating materials - Determination of the effects of ionizing radiation - Part 5: Procedures for assessment of ageing in service
IEC 60544-5:2011 covers ageing assessment methods which can be applied to components based on polymeric materials (e.g. cable insulation and jackets, elastomeric seals, polymeric coatings, gaiters) which are used in environments where they are exposed to radiation. The object of this standard is aimed at providing methods for the assessment of ageing in service. The approaches discussed in the following clauses cover ageing assessment programmes based on condition monitoring (CM), the use of sample deposits in severe environments and sampling of real-time aged components. This second edition cancels and replaces the first edition, published in 2003, and constitutes an editorial revision to align it with standards recently developed by SC 45A as well as with other parts in the IEC 60544 series.
Elektroisolierstoffe - Bestimmung der Wirkung ionisierender Strahlung - Teil 5: Bewertungsverfahren für die Alterung während des Einsatzes
Matériaux isolants - Détermination des effets des rayonnements ionisants - Partie 5: Procédures pour l'estimation du vieillissement en service
La CEI 60544-5:2011 couvre les méthodes d'évaluation du vieillissement pouvant être appliquées aux composants à base de matériaux polymères (par exemple, des gaines et isolations de câble, des joints en élastomère, des revêtements polymères, des gaines) qui sont utilisés dans des environnements où ils sont exposés aux rayonnements. L'objet de la présente norme est destiné à fournir des méthodes d'évaluation du vieillissement en service. Les approches examinées dans les articles qui suivent couvrent les programmes d'évaluation de vieillissement fondés sur le contrôle des conditions (CM), l'utilisation de dépôt d'échantillons dans des environnements sévères et l'échantillonnage de composants vieillis en temps réel. Cette deuxième édition annule et remplace la première édition, publiée en 2003, dont elle constitue une éditoriale révisée destinée à aligner ce document avec des normes récemment élaborées au sein du SC 45A, ainsi qu'avec d'autres parites de la série CEI 60544.
Električni izolacijski materiali - Ugotavljanje učinkov ionizirnega sevanja - 5. del: Postopki za ocenjevanje staranja med uporabo
Ta del standarda IEC 60544 zajema metode za ocenjevanje staranja, ki jih je mogoče uporabiti za dele na osnovi polimernih materialov (npr. izolacija in plašči kablov, elastomerna tesnila, polimerne prevleke, gamaše), ki se uporabljajo v okoljih, kjer so izpostavljeni sevanju. Namen tega standarda je zagotoviti metode za ocenjevanje staranja med uporabo. Pristopi, obravnavani v naslednjih točkah, zajemajo programe za ocenjevanje staranja na podlagi spremljanja stanja (CM), puščanja vzorcev v neugodnih okoljih in vzorčenje delov, staranih v realnem času.
General Information
Relations
Standards Content (Sample)
SLOVENSKI STANDARD
SIST EN 60544-5:2012
01-julij-2012
1DGRPHãþD
SIST EN 60544-5:2004
(OHNWULþQLL]RODFLMVNLPDWHULDOL8JRWDYOMDQMHXþLQNRYLRQL]LUQHJDVHYDQMDGHO
3RVWRSNL]DRFHQMHYDQMHVWDUDQMDPHGXSRUDERElectrical insulating materials - Determination of the effects of ionising radiation - Part 5:
Procedures for assessment of ageing in serviceElektroisolierstoffe - Bestimmung der Wirkung ionisierender Strahlung - Teil 5 :
Bewertungsverfahren für die Alterung während des Einsatzes
Matériaux isolants - Détermination des effets des rayonnements ionisants - Partie 5:
Procédures pour l'estimation du vieillissement en serviceTa slovenski standard je istoveten z: EN 60544-5:2012
ICS:
29.035.01 Izolacijski materiali na Insulating materials in
splošno general
SIST EN 60544-5:2012 en
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
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SIST EN 60544-5:2012
EUROPEAN STANDARD
EN 60544-5
NORME EUROPÉENNE
April 2012
EUROPÄISCHE NORM
ICS 17.240; 29.035.01 Supersedes EN 60544-5:2003
English version
Electrical insulating materials -
Determination of the effects of ionizing radiation -
Part 5: Procedures for assessment of ageing in service
(IEC 60544-5:2011)
Matériaux isolants - Elektroisolierstoffe -
Détermination des effets des Bestimmung der Wirkung ionisierender
rayonnements ionisants - Strahlung -
Partie 5: Procédures pour l'estimation du Teil 5: Bewertungsverfahren für die
vieillissement en service Alterung während des Einsatzes
(CEI 60544-5:2011) (IEC 60544-5:2011)
This European Standard was approved by CENELEC on 2012-01-18. CENELEC members are bound to comply
with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this European Standard
the status of a national standard without any alteration.Up-to-date lists and bibliographical references concerning such national standards may be obtained on
application to the CEN-CENELEC Management Centre or to any CENELEC member.This European Standard exists in three official versions (English, French, German). A version in any other
language made by translation under the responsibility of a CENELEC member into its own language and notified
to the CEN-CENELEC Management Centre has the same status as the official versions.
CENELEC members are the national electrotechnical committees of Austria, Belgium, Bulgaria, Croatia, Cyprus,
the Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy,
Latvia, Lithuania, Luxembourg, Malta, the Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia,
Spain, Sweden, Switzerland, Turkey and the United Kingdom.CENELEC
European Committee for Electrotechnical Standardization
Comité Européen de Normalisation Electrotechnique
Europäisches Komitee für Elektrotechnische Normung
Management Centre: Avenue Marnix 17, B - 1000 Brussels
© 2012 CENELEC - All rights of exploitation in any form and by any means reserved worldwide for CENELEC members.
Ref. No. EN 60544-5:2012 E---------------------- Page: 3 ----------------------
SIST EN 60544-5:2012
EN 60544-5:2012 - 2 -
Foreword
The text of document 112/171/CDV, future edition 2 of IEC 60544-5, prepared by IEC TC 112,
"Evaluation and qualification of electrical insulating materials and systems", was submitted to the
IEC-CENELEC parallel vote and approved by CENELEC as EN 60544-5:2012.The following dates are fixed:
(dop) 2012-10-18
• latest date by which the document has
to be implemented at national level by
publication of an identical national
standard or by endorsement
(dow) 2015-01-18
• latest date by which the national
standards conflicting with the
document have to be withdrawn
This document supersedes EN 60544-5:2003.
EN 60544-5:2012 constitutes an editorial revision to align it with standards recently developed by SC 45A
as well as with other parts in the EN 60544 series.Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CENELEC [and/or CEN] shall not be held responsible for identifying any or all such patent
rights.Endorsement notice
The text of the International Standard IEC 60544-5:2011 was approved by CENELEC as a European
Standard without any modification.In the official version, for Bibliography, the following note has to be added for the standard indicated:
IEC 60544-4 NOTE Harmonized as EN 60544-4.---------------------- Page: 4 ----------------------
SIST EN 60544-5:2012
- 3 - EN 60544-5:2012
Annex ZA
(normative)
Normative references to international publications
with their corresponding European publications
The following documents, in whole or in part, are normatively referenced in this document and are
indispensable for its application. For dated references, only the edition cited applies. For undated
references, the latest edition of the referenced document (including any amendments) applies.
NOTE When an international publication has been modified by common modifications, indicated by (mod), the relevant EN/HD
applies.Publication Year Title EN/HD Year
IEC 60544-1 - Electrical insulating materials - Determination EN 60544-1 -
of the effects of ionizing radiation -
Part 1: Radiation interaction and dosimetry
IEC 60544-2 - Guide for determining the effects of ionizing - -
radiation on insulating materials -
Part 2: Procedures for irradiation and test
IEC 60780 - Nuclear power plants - Electrical equipment of - -
the safety system - Qualification
IEC/TR 61244-1 - Determination of long-term radiation ageing in - -
polymers -
Part 1: Techniques for monitoring diffusion-
limited oxidation
IEC/TR 61244-2 - Determination of long-term radiation ageing in - -
polymers -
Part 2: Procedures for predicting ageing at low
dose rates
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SIST EN 60544-5:2012
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SIST EN 60544-5:2012
IEC 60544-5
Edition 2.0 2011-12
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Electrical insulating materials – Determination of the effects of ionizing
radiation –
Part 5: Procedures for assessment of ageing in service
Matériaux isolants électriques – Détermination des effets des rayonnements
ionisants –
Partie 5: Procédures pour l'estimation du vieillissement en service
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
PRICE CODE
INTERNATIONALE
CODE PRIX S
ICS 17.240; 29.035.01 ISBN 978-2-88912-836-5
® Registered trademark of the International Electrotechnical Commission
Marque déposée de la Commission Electrotechnique Internationale
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SIST EN 60544-5:2012
– 2 – 60544-5 IEC:2011
CONTENTS
FOREWORD ........................................................................................................................... 3
INTRODUCTION ..................................................................................................................... 5
1 Scope and object .............................................................................................................. 6
2 Normative references ....................................................................................................... 6
3 Terms and definitions ....................................................................................................... 7
4 Background ...................................................................................................................... 7
4.1 General ................................................................................................................... 7
4.2 Diffusion limited oxidation (DLO) ............................................................................. 7
4.3 Dose rate effects (DRE) .......................................................................................... 8
4.4 Accelerated radiation ageing ................................................................................... 8
4.5 Accelerated thermal ageing ..................................................................................... 9
5 Approaches to ageing assessment ................................................................................... 9
6 Identifying components of concern ................................................................................... 9
6.1 General ................................................................................................................... 9
6.2 Priorities for ageing management ............................................................................ 9
6.3 Environmental monitoring ...................................................................................... 10
6.4 Localized severe environments ............................................................................. 10
6.5 Worst case components ........................................................................................ 10
7 Condition monitoring techniques ..................................................................................... 10
7.1 General ................................................................................................................. 10
7.2 Establishing correlation curves for CM methods .................................................... 11
7.3 CM methods .......................................................................................................... 11
7.4 Using CM for short-term troubleshooting ............................................................... 11
7.5 Using CM for long-term degradation assessment ................................................... 13
8 Predictive modelling ....................................................................................................... 14
9 Sample deposit ............................................................................................................... 15
9.1 General ................................................................................................................. 15
9.2 Requirements of a deposit ..................................................................................... 15
9.3 Pre-ageing samples for a deposit .......................................................................... 15
9.4 Installation of an sample deposit ........................................................................... 15
9.5 Testing of samples from the deposit ...................................................................... 16
9.6 Determination of sampling intervals ....................................................................... 16
9.7 Real time aged materials ....................................................................................... 17
Annex A (informative) Example of a CM correlation curve .................................................... 18
Annex B (informative) Use of a deposit ................................................................................ 19
Bibliography .......................................................................................................................... 20
Figure 1 – Development of ageing data on changes in tensile elongation and acondition indicator (e.g. indenter modulus) – Schematic........................................................ 12
Figure 2 – Correlation curve derived from data in Figure 1 – Schematic ................................ 13
Figure 3 – Estimation of elongation from a correlation curve ................................................. 14
Figure 4 – Modification of sampling interval dependent on values of the CM indicator ........... 17
Figure A.1 – Correlation curve for indenter modulus against tensile elongation for a
CSPE cable jacket material [18] ............................................................................................ 18
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60544-5 IEC:2011 – 3 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
ELECTRICAL INSULATING MATERIALS –
DETERMINATION OF THE EFFECTS OF IONIZING RADIATION –
Part 5: Procedures for assessment of ageing in service
FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
all national electrotechnical committees (IEC National Committees). The object of IEC is to promote
international co-operation on all questions concerning standardization in the electrical and electronic fields. To
this end and in addition to other activities, IEC publishes International Standards, Technical Specifications,
Technical Reports, Publicly Available Specifications (PAS) and Guides (hereafter referred to as “IEC
Publication(s)”). Their preparation is entrusted to technical committees; any IEC National Committee interested
in the subject dealt with may participate in this preparatory work. International, governmental and non-
governmental organizations liaising with the IEC also participate in this preparation. IEC collaborates closely
with the International Organization for Standardization (ISO) in accordance with conditions determined by
agreement between the two organizations.2) The formal decisions or agreements of IEC on technical matters express, as nearly as possible, an international
consensus of opinion on the relevant subjects since each technical committee has representation from all
interested IEC National Committees.3) IEC Publications have the form of recommendations for international use and are accepted by IEC National
Committees in that sense. While all reasonable efforts are made to ensure that the technical content of IEC
Publications is accurate, IEC cannot be held responsible for the way in which they are used or for any
misinterpretation by any end user.4) In order to promote international uniformity, IEC National Committees undertake to apply IEC Publications
transparently to the maximum extent possible in their national and regional publications. Any divergence
between any IEC Publication and the corresponding national or regional publication shall be clearly indicated in
the latter.5) IEC itself does not provide any attestation of conformity. Independent certification bodies provide conformity
assessment services and, in some areas, access to IEC marks of conformity. IEC is not responsible for any
services carried out by independent certification bodies.6) All users should ensure that they have the latest edition of this publication.
7) No liability shall attach to IEC or its directors, employees, servants or agents including individual experts and
members of its technical committees and IEC National Committees for any personal injury, property damage or
other damage of any nature whatsoever, whether direct or indirect, or for costs (including legal fees) and
expenses arising out of the publication, use of, or reliance upon, this IEC Publication or any other IEC
Publications.8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
indispensable for the correct application of this publication.9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of
patent rights. IEC shall not be held responsible for identifying any or all such patent rights.
International Standard IEC 60544-5 has been prepared IEC technical committee TC 112:
Evaluation and qualification of electrical insulating materials and systems.This second edition cancels and replaces the first edition, published in 2003, and constitutes
an editorial revision to align it with standards recently developed by SC 45A as well as with
other parts in the IEC 60544 series.The text of this standard is based on the following documents:
CDV Report on voting
112/171/CDV 112/191/RVC
Full information on the voting for the approval of this standard can be found in the report on
voting indicated in the above table.---------------------- Page: 9 ----------------------
SIST EN 60544-5:2012
– 4 – 60544-5 IEC:2011
This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.
A list of all parts in the IEC 60544 series, published under the general title Electrical
insulating materials – Determination of the effects of ionizing radiation, can be found on the
IEC website.The committee has decided that the contents of this publication will remain unchanged until
the stability date indicated on the IEC web site under "http://webstore.iec.ch" in the data
related to the specific publication. At this date, the publication will be• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
IMPORTANT – The 'colour inside' logo on the cover page of this publication indicates
that it contains colours which are considered to be useful for the correctunderstanding of its contents. Users should therefore print this document using a
colour printer.---------------------- Page: 10 ----------------------
SIST EN 60544-5:2012
60544-5 IEC:2011 – 5 –
INTRODUCTION
Organic and polymeric materials provide a significant proportion of the insulation used in
electrical systems. These materials are sensitive to the effects of irradiation and the response
varies widely between different types. It is therefore important to be able to assess the degree
of degradation of these insulating materials during their service lifetimes. This part of
IEC 60544 provides recommended procedures for assessing ageing of insulating materials in
service.There are a number of approaches to the assessment of ageing of polymer-based
components exposed to radiation environments [1–4] . These are based on the better
understanding of the factors affecting ageing degradation which has been developed over
several decades. In nuclear power plants, qualification programmes are normally used for
selection of components, including those based on polymeric materials. These initial
qualification procedures, such as IEEE-323 [5] and IEEE-383 [6], were originally written
before there was sufficient understanding of ageing mechanisms. Most of the methods
discussed in this part of IEC 60544 are therefore used to supplement the initial qualification
process.This part is the fifth in a series dealing with the effect of ionizing radiation on insulating
materials.Part 1 (Radiation interaction and dosimetry) constitutes an introduction dealing very broadly
with the problems involved in evaluating radiation effects. It also provides guidance to
dosimetry terminology, several methods of determining exposure and absorbed dose, and
methods of calculating absorbed dose in any specific material from the dosimetry method
applied.Part 2 (Procedures for irradiation and test) describes procedures for maintaining seven
different types of exposure conditions during irradiation. It also specifies the controls that
should be maintained over these conditions so that when test results are reported, reliable
comparisons of material performance can be made. In addition, it defines certain important
irradiation conditions and test procedures to be used for property change determinations and
corresponding end-point criteria.Part 3 has been incorporated into the second edition of IEC 60544-2.
Part 4 (Classification system for service in radiation environments) provides a recommended
classification system for categorizing the radiation endurance of insulation materials.
___________Figures in square brackets refer to the bibliography.
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SIST EN 60544-5:2012
– 6 – 60544-5 IEC:2011
ELECTRICAL INSULATING MATERIALS –
DETERMINATION OF THE EFFECTS OF IONIZING RADIATION –
Part 5: Procedures for assessment of ageing in service
1 Scope and object
This part of IEC 60544 covers ageing assessment methods which can be applied to
components based on polymeric materials (e.g. cable insulation and jackets, elastomeric
seals, polymeric coatings, gaiters) which are used in environments where they are exposed to
radiation.The object of this standard is aimed at providing methods for the assessment of ageing in
service. The approaches discussed in the following clauses cover ageing assessment
programmes based on condition monitoring (CM), the use of sample deposits in severe
environments and sampling of real-time aged components.2 Normative references
The following documents, in whole or in part, are normatively referenced in this document and
are indispensable for its application. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including anyamendments) applies.
IEC 60544-1, Electrical insulating materials – Determination of the effects of ionizing radiation
– Part 1: Radiation interaction and dosimetryIEC 60544-2, Guide for determining the effects of ionizing radiation on insulating materials –
Part 2: Procedures for irradiation and testIEC 61244-1, Determination of long-term radiation ageing in polymers – Part 1: Techniques
for monitoring diffusion-limited oxidationIEC 61244-2, Determination of long-term radiation ageing in polymers – Part 2: Procedures
for predicting ageing at low dose ratesIEC 60780, Nuclear power plants – Electrical equipment of the safety system – Qualification
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60544-5 IEC:2011 – 7 –
3 Terms and definitions
For the purposes of this document, the following abbreviations, taken from IEC 60780, apply.
BWR Boiling water reactorCBQ Condition based qualification
CM Condition monitoring
CSPE Chlorosulphonated polyethylene
DBE Design basis event
DLO Diffusion limited oxidation
DRE Dose rate effect
DSC Differential scanning calorimeter
EPR Ethylene propylene rubber
EQ Environmental qualification
EVA Ethylene vinyl acetate copolymer
IM Indenter modulus
LOCA Loss of coolant accident
NPP Nuclear power plant
OIT Oxidation induction time
OITP Oxidation induction temperature
PE Polyethylene
PVC Polyvinyl chloride
PWR Pressurized water reactor
TGA Thermo-gravimetric analysis
VVER Water-cooled, water-moderated energy reactor (type of pressurized water reactor developed
by Russia)XLPE Cross-linked polyethylene
4 Background
4.1 General
There are a number of factors that need to be considered when assessing ageing of polymeric
components in radiation environments. In the following clauses some of these factors are
briefly discussed and references made to more detailed information.To accelerate radiation-ageing environments, the normal approach is to increase the radiation
dose rate, often combined with an increase in temperature. The two most important potential
complications arising from such increases involve diffusion-limited oxidation, which is
described in 4.2, and chemical dose rate effects (DRE), which are described in 4.3. The
implications of these factors on the use and interpretation of condition monitoring (CM)
techniques are also discussed. Accelerated ageing programmes are briefly discussed in 4.4
and 4.5.4.2 Diffusion limited oxidation (DLO)
When polymers are exposed to an oxygen-containing environment (e.g. air), some oxygen will
be dissolved in the material. In the absence of oxygen-consuming reactions (oxidation), the
amount of dissolved oxygen will be proportional to the oxygen partial pressure surrounding
the polymer (well known from Henry’s Law). Ageing will lead to oxidation reactions in the
polymer, whose rate will increase significantly as the dose rate and temperature of ageing are
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– 8 – 60544-5 IEC:2011
increased. If the rate of consumption of dissolved oxygen in the polymer is faster than the rate
at which oxygen can be replenished by diffusion from the surrounding atmosphere, the
concentration of dissolved oxygen in the interior regions will decrease with time (the oxygen
concentration at the sample surface will remain at its equilibrium value). The reduction in
internal oxygen concentration can lead to reduced or negligible oxidation, referred to as
diffusion limited oxidation.The importance of this effect is dependent on the sample thickness (thinner samples giving
smaller DLO effects) and the ratio of the oxygen consumption rate to the oxygen permeability
coefficient P, which is the product of the oxygen diffusion and solubility parameters.
Accelerated radiation environments involve increases in dose rates, which increase the
oxygen consumption rate. If the temperature remains constant as the dose rate is increased,
the oxygen permeability coefficient will be unchanged. This means that DLO effects will
become more important as the dose rate is raised. These effects are described in more detail
in IEC 61244-1.The effects of DLO may also need to be considered when carrying out CM measurements.
This is not an issue for the many CM techniques which measure properties at ambient
temperature, such as those based on density and modulus measurements. On the other hand,
several CM techniques such as oxidation induction time (OIT) and thermogravimetric analysis
(TGA) use quite elevated temperatures during the measurements. For these techniques, it is
quite possible to have DLO effects present during measurement of the CM parameter. For this
reason, detailed test methods for CM have been developed [8] to ensure that the sample
preparation and test procedure avoid DLO effects. DLO shall be addressed when developing
correlation curves for CM methods, to ensure that representative data are obtained for both
radiation and thermal ageing.4.3 Dose rate effects (DRE)
The existence of radiation dose-rate effects and methods for dealing with these effects are
described in IEC 61244-2. Generally, DRE are separated into two types. The first type, which
is commonly observed in accelerated radiation-ageing experiments, is due to the DLO effects
described in 4.2. These DLO-based effects represent a physical, geometry-dependent DRE.
The second type, of interest to the current discussion, concerns chemical DRE. Such
chemically based DRE are much less common. A documented case of chemical DRE is found
in PVC and low density polyethylene materials, caused by the slow breakdown ofhydroperoxide intermediate species in the oxidation reaction [10]. The existence of such
chemical DRE shall be checked at the start of any accelerated ageing programme.4.4 Accelerated radiation ageing
Accelerated ageing programmes in the laboratory tend to use acceleration factors much lower
than are normally used in equipment qualification. This may avoid some of the problems
associated with DLO and DRE. The ageing produced may then be a better simulation of the
long term ageing that occurs under service conditions. The data that are obtained in
accelerated ageing tests can be used with predictive models to enable assessments to be
made of the behaviour of the materials under service conditions.Accelerated ageing programmes require a matrix of test data to be generated over a range of
environmental conditions as described in IEC 61244-2. As a minimum, data are needed for at
least 3 different dose rates at the normal operating temperature but additional data on thermal
ageing and radiation ageing at elevated temperature enables better use to be made of the
available predictive modelling methods. The dose rates and temperatures used foraccelerated ageing should be selected using the principles described in IEC 60544-2 to
ensure that homogeneous oxidation occurs. For each environmental condition used, test data
shall be obtained at several different ageing times, the longest of which should be sufficient to
introduce significant degradation. A typical test programme could take more than 18 months
to complete, dependent on the radiation resistance of the materials being tested.
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60544-5 IEC:2011 – 9 –
The data required in the test matrix are determined by the type of component being
evaluated. The appropriate test parameters are given in IEC 60544-2 for various types of
polymeric material.4.5 Accelerated thermal ageing
When carrying out thermal ageing as part of an accelerated ageing programme, it is important
that an appropriate value of the activation energy is used in assessing the temperature and
timescale of the accelerated test. In some materials, the ageing mechanism at high
temperatures is different to that which would occur under plant conditions and in many
materials the activation energy decreases significantly at lower temperatures [10,11].
Samples which been exposed to accelerated thermal ageing shall be allowed to stabilize
before any CM tests are carried out. Some polymeric materials are hygroscopic and show a
marked dependence of their properties on the moisture content [8]. This is primarily of
concern for a few materials used in older nuclear plant, but may also be important for those
CM methods that are sensitive to the moisture content of the material.5 Approaches to ageing assessment
There are a number of complementary methods available for ageing assessment as described
in their respective clauses. Each of these methods...
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