IEC 60544-5:2022

Electrical insulating materials - Determination of the effects of ionizing radiation - Part 5: Procedures for assessment of ageing in service

IEC 60544-5:2022 is available as IEC 60544-5:2022 RLV which contains the International Standard and its Redline version, showing all changes of the technical content compared to the previous edition.IEC 60544-5:2022 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 document is aimed at providing methods for the assessment of ageing in service. The approaches discussed in Clause 5 through Clause 9 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 edition includes the following significant technical changes with respect to the previous edition:
- added recent references in 7.4 showing that some electrical condition monitoring methods show promising correlations with ageing;
- updated recommendations for implementation of a sample deposit in 9.2, installation of a sample deposit in 9.3 and testing of samples from the deposit in 9.4;
- updated list of references.

Matériaux isolants électriques - Détermination des effets des rayonnements ionisants - Partie 5: Procédures pour l'évaluation du vieillissement en service

IEC 60544-5:2022 est disponible sous forme de IEC 60544-5:2022 RLV qui contient la Norme internationale et sa version Redline, illustrant les modifications du contenu technique depuis l'édition précédente.L'IEC 60544-5:2022 traite des méthodes d'évaluation du vieillissement qui peuvent être appliquées aux composants à base de matériaux polymères (gaines et isolations de câble, joints en élastomère, revêtements polymères, garnitures) qui sont utilisés dans des environnements où ils sont exposés aux rayonnements. L'objet du présent document est de fournir des méthodes pour évaluer le vieillissement en service des matériaux. Les approches examinées dans les Articles 5 à 9 concernent les programmes d'évaluation de vieillissement fondés sur une surveillance de l'état (CM, Condition Monitoring), l'utilisation de dépôts d'échantillons dans des environnements sévères et l'échantillonnage de composants vieillis en temps réel. Cette édition inclut les modifications techniques majeures suivantes par rapport à l'édition précédente:
- des références récentes ont été ajoutées en 7.4 afin d'introduire des méthodes de surveillance de l'état qui montrent des corrélations prometteuses vis-à-vis du vieillissement;
- les recommandations ont été mises à jour pour la mise en œuvre d'un dépôt d'échantillons en 9.2, l'installation d'un dépôt d'échantillons en 9.3 et les essais sur les échantillons du dépôt en 9.4;
- la liste de références a été mise à jour.

General Information

• Status: Published
• Publication Date: 16-Jun-2022
• ICS: 17.240 - Radiation measurements
• ICS: 29.035.01 - Insulating materials in general
• Technical Committee: TC 112 - Evaluation and qualification of electrical insulating materials and systems
• Current Stage: PPUB - Publication issued
• Completion Date: 17-Jun-2022

Standards Content (sample)

IEC 60544-5
Edition 3.0 2022-06
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
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'évaluation du vieillissement en service
IEC 60544-5:2022-06(en-fr)
---------------------- Page: 1 ----------------------
THIS PUBLICATION IS COPYRIGHT PROTECTED
Copyright © 2022 IEC, Geneva, Switzerland

All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form

or by any means, electronic or mechanical, including photocopying and microfilm, without permission in writing from

either IEC or IEC's member National Committee in the country of the requester. If you have any questions about IEC

copyright or have an enquiry about obtaining additional rights to this publication, please contact the address below or

your local IEC member National Committee for further information.

Droits de reproduction réservés. Sauf indication contraire, aucune partie de cette publication ne peut être reproduite

ni utilisée sous quelque forme que ce soit et par aucun procédé, électronique ou mécanique, y compris la photocopie

et les microfilms, sans l'accord écrit de l'IEC ou du Comité national de l'IEC du pays du demandeur. Si vous avez des

questions sur le copyright de l'IEC ou si vous désirez obtenir des droits supplémentaires sur cette publication, utilisez

les coordonnées ci-après ou contactez le Comité national de l'IEC de votre pays de résidence.

IEC Secretariat Tel.: [phone]
3, rue de Varembé [e-mail]
CH-1211 Geneva 20 www.iec.ch
Switzerland
About the IEC

The International Electrotechnical Commission (IEC) is the leading global organization that prepares and publishes

International Standards for all electrical, electronic and related technologies.
About IEC publications

The technical content of IEC publications is kept under constant review by the IEC. Please make sure that you have the

latest edition, a corrigendum or an amendment might have been published.

IEC publications search - webstore.iec.ch/advsearchform IEC Products & Services Portal - products.iec.ch

The advanced search enables to find IEC publications by a Discover our powerful search engine and read freely all the

variety of criteria (reference number, text, technical publications previews. With a subscription you will always

committee, …). It also gives information on projects, replaced have access to up to date content tailored to your needs.

and withdrawn publications.
Electropedia - www.electropedia.org
IEC Just Published - webstore.iec.ch/justpublished
The world's leading online dictionary on electrotechnology,
Stay up to date on all new IEC publications. Just Published
containing more than 22 300 terminological entries in English
details all new publications released. Available online and
and French, with equivalent terms in 19 additional languages.
once a month by email.
Also known as the International Electrotechnical Vocabulary
(IEV) online.
IEC Customer Service Centre - webstore.iec.ch/csc
If you wish to give us your feedback on this publication or
need further assistance, please contact the Customer Service
Centre: [e-mail].
A propos de l'IEC

La Commission Electrotechnique Internationale (IEC) est la première organisation mondiale qui élabore et publie des

Normes internationales pour tout ce qui a trait à l'électricité, à l'électronique et aux technologies apparentées.

A propos des publications IEC

Le contenu technique des publications IEC est constamment revu. Veuillez vous assurer que vous possédez l’édition la

plus récente, un corrigendum ou amendement peut avoir été publié.
Recherche de publications IEC - IEC Products & Services Portal - products.iec.ch

webstore.iec.ch/advsearchform Découvrez notre puissant moteur de recherche et consultez

La recherche avancée permet de trouver des publications IEC gratuitement tous les aperçus des publications. Avec un

en utilisant différents critères (numéro de référence, texte, abonnement, vous aurez toujours accès à un contenu à jour

comité d’études, …). Elle donne aussi des informations sur adapté à vos besoins.
les projets et les publications remplacées ou retirées.
Electropedia - www.electropedia.org
IEC Just Published - webstore.iec.ch/justpublished
Le premier dictionnaire d'électrotechnologie en ligne au
Restez informé sur les nouvelles publications IEC. Just
monde, avec plus de 22 300 articles terminologiques en
Published détaille les nouvelles publications parues.
anglais et en français, ainsi que les termes équivalents dans
Disponible en ligne et une fois par mois par email.
19 langues additionnelles. Egalement appelé Vocabulaire
Electrotechnique International (IEV) en ligne.
Service Clients - webstore.iec.ch/csc
Si vous désirez nous donner des commentaires sur cette
publication ou si vous avez des questions contactez-nous:
[e-mail].
---------------------- Page: 2 ----------------------
IEC 60544-5
Edition 3.0 2022-06
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
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'évaluation du vieillissement en service
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 17.240; 29.035.01 ISBN 978-2-8322-3826-4

Warning! Make sure that you obtained this publication from an authorized distributor.

Attention! Veuillez vous assurer que vous avez obtenu cette publication via un distributeur agréé.

® Registered trademark of the International Electrotechnical Commission
Marque déposée de la Commission Electrotechnique Internationale
---------------------- Page: 3 ----------------------
– 2 – IEC 60544-5:2022 © IEC 2022
CONTENTS

FOREWORD ........................................................................................................................... 4

INTRODUCTION ..................................................................................................................... 6

1 Scope .............................................................................................................................. 7

2 Normative references ...................................................................................................... 7

3 Terms, definitions and abbreviated terms ........................................................................ 7

3.1 Terms and definitions .............................................................................................. 7

3.2 Abbreviated terms ................................................................................................... 7

4 Background ..................................................................................................................... 8

4.1 General ................................................................................................................... 8

4.2 Diffusion-limited oxidation (DLO)............................................................................. 8

4.3 Dose rate effects (DRE) .......................................................................................... 9

4.4 Accelerated radiation ageing ................................................................................... 9

4.5 Accelerated thermal ageing ..................................................................................... 9

5 Approaches to ageing assessment ................................................................................ 10

6 Identifying components of concern ................................................................................ 10

6.1 General ................................................................................................................. 10

6.2 Priorities for ageing management .......................................................................... 10

6.3 Environmental monitoring ..................................................................................... 10

6.4 Localized severe environments ............................................................................. 11

6.5 Worst case components ........................................................................................ 11

7 Condition monitoring techniques .................................................................................... 11

7.1 General ................................................................................................................. 11

7.2 Establishing correlation curves for CM methods .................................................... 11

7.3 CM methods ......................................................................................................... 12

7.4 Using CM for short-term troubleshooting ............................................................... 12

7.5 Using CM for long-term degradation assessment .................................................. 14

8 Predictive modelling ...................................................................................................... 15

9 Sample deposit .............................................................................................................. 16

9.1 General ................................................................................................................. 16

9.2 Requirements of a deposit .................................................................................... 16

9.3 Pre-ageing samples for a deposit .......................................................................... 16

9.4 Installation of a sample deposit ............................................................................. 17

9.5 Testing of samples from the deposit ...................................................................... 17

9.6 Determination of sampling intervals ...................................................................... 17

9.7 Real time aged materials ...................................................................................... 18

Annex A (informative) Example of a CM correlation curve .................................................... 19

Annex B (informative) Use of a deposit ................................................................................ 20

B.1 Typical sample in a deposit ................................................................................... 20

B.2 Typical testing schedule for a deposit ................................................................... 20

Bibliography .......................................................................................................................... 21

Figure 1 – Development of ageing data on changes in tensile elongation and a

condition indicator (e.g. indenter modulus) – Schematic representation ................................ 13

Figure 2 – Correlation curve derived from data in Figure 1 – Schematic representation ........ 14

Figure 3 – Estimation of elongation from a correlation curve ................................................. 15

---------------------- Page: 4 ----------------------
IEC 60544-5:2022 © IEC 2022 – 3 –

Figure 4 – Modification of sampling interval dependent on values of the CM indicator –

Schematic representation ..................................................................................................... 18

Figure A.1 – Correlation curve for indenter modulus against tensile elongation for a

CSPE cable jacket material [24] ............................................................................................ 19

---------------------- Page: 5 ----------------------
– 4 – IEC 60544-5:2022 © IEC 2022
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.

IEC 60544-5 has been prepared by IEC technical committee TC 112: Evaluation and

qualification of electrical insulating materials and systems. It is an International Standard.

This third edition cancels and replaces the second edition published in 2011. This edition

constitutes a technical revision.

This edition includes the following significant technical changes with respect to the previous

edition:

a) added recent references in 7.4 showing that some electrical condition monitoring methods

show promising correlations with ageing;

b) updated recommendations for implementation of a sample deposit in 9.2, installation of a

sample deposit in 9.3 and testing of samples from the deposit in 9.4;
c) updated list of references.
---------------------- Page: 6 ----------------------
IEC 60544-5:2022 © IEC 2022 – 5 –
The text of this International Standard is based on the following documents:
Draft Report on voting
112/523/CDV 112/553/RVC

Full information on the voting for its approval can be found in the report on voting indicated in

the above table.
The language used for the development of this International Standard is English.

This document was drafted in accordance with ISO/IEC Directives, Part 2, and developed in

accordance with ISO/IEC Directives, Part 1 and ISO/IEC Directives, IEC Supplement, available

at www.iec.ch/members_experts/refdocs. The main document types developed by IEC are

described in greater detail at www.iec.ch/standardsdev/publications.

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 document will remain unchanged until the

stability date indicated on the IEC website under webstore.iec.ch in the data related to the

specific document. At this date, the document will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
---------------------- Page: 7 ----------------------
– 6 – IEC 60544-5:2022 © IEC 2022
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], [2], [3], [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 the

selection of components, including those based on polymeric materials. These initial

TM 2 TM 2

qualification procedures, such as IEEE Std 323 -1974 [5] and IEEE Std 383 -1974 [6],

were originally written before there was sufficient understanding of ageing mechanisms. Most

of the methods discussed in this document are therefore used to supplement the initial

qualification process.

This document is the fifth in a series dealing with the effect of ionizing radiation on insulating

materials.

IEC 60544-1 (Radiation interaction and dosimetry) constitutes an introduction dealing very

broadly with the problems involved in evaluating radiation effects. It also provides guidance on

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.

IEC 60544-2 (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.

IEC 60544-3 has been withdrawn and incorporated into the second edition of IEC 60544-2.

IEC 60544-4 (Classification system for service in radiation environments) provides a

recommended classification system for categorizing the radiation endurance of insulation

materials.
___________
Numbers in square brackets refer to the Bibliography.

IEEE Std 323-1974 and IEEE Std 383-1974 are now withdrawn and have been superseded by more recent

revisions.
---------------------- Page: 8 ----------------------
IEC 60544-5:2022 © IEC 2022 – 7 –
ELECTRICAL INSULATING MATERIALS –
DETERMINATION OF THE EFFECTS OF IONIZING RADIATION –
Part 5: Procedures for assessment of ageing in service
1 Scope

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 document is aimed at providing methods for the assessment of ageing in

service. The approaches discussed in Clause 5 through Clause 9 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 are referred to in the text in such a way that some or all of their content

constitutes requirements of this document. For dated references, only the edition cited applies.

For undated references, the latest edition of the referenced document (including any

amendments) applies.

IEC 60544-2, Electrical insulating materials – Determination of the effects of ionizing radiation

on insulating materials – Part 2: Procedures for irradiation and test

IEC TS 61244-1, Determination of long-term radiation ageing in polymers – Part 1: Techniques

for monitoring diffusion-limited oxidation

IEC TS 61244-2, Determination of long-term radiation ageing in polymers – Part 2: Procedures

for predicting ageing at low dose rates
3 Terms, definitions and abbreviated terms
3.1 Terms and definitions
No terms and definitions are listed in this document.

ISO and IEC maintain terminological databases for use in standardization at the following

addresses:
• IEC Electropedia: available at http://www.electropedia.org/
• ISO Online browsing platform: available at http://www.iso.org/obp
3.2 Abbreviated terms
BWR boiling water reactor
CBQ condition-based qualification
CM condition monitoring
CSPE chlorosulphonated polyethylene
DBE design basis event
---------------------- Page: 9 ----------------------
– 8 – IEC 60544-5:2022 © IEC 2022
DLO diffusion-limited oxidation
DRE dose rate effect
EPR ethylene propylene rubber
EQ environmental qualification
NPP nuclear power plant
OIT oxidation induction time
OITP oxidation induction temperature
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 4.2 through 4.5, 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 (DLO), 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 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. For more detail about these effects, IEC TS 61244-1 shall be consulted.

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

---------------------- Page: 10 ----------------------
IEC 60544-5:2022 © IEC 2022 – 9 –

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 TS 61244-2. This standard shall be consulted for more detail about these

effects. 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 of hydroperoxide

intermediate species in the oxidation reaction [9]. The existence of such chemical DRE shall be

checked at the start of any accelerated ageing programme. If there are no data available in the

literature for the specific materials of interest, this can be checked by including tests at low

dose rates in the 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 TS 61244-2. As a minimum, data are needed for

at least three 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 for

accelerated 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.

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

materials and components.
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 have been exposed to accelerated thermal ageing shall be allowed to stabilize

before any CM tests are carried out. Some polymeric materials
...