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.

Matériaux isolants électriques - 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.

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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
IEC 60544-5:2011
---------------------- Page: 1 ----------------------
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---------------------- Page: 2 ----------------------
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
---------------------- Page: 3 ----------------------
– 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 a

condition 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

---------------------- Page: 4 ----------------------
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

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between any IEC Publication and the corresponding national or regional publication shall be clearly indicated in

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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: 5 ----------------------
– 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 correct

understanding of its contents. Users should therefore print this document using a

colour printer.
---------------------- Page: 6 ----------------------
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.
---------------------- Page: 7 ----------------------
– 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 any
amendments) applies.

IEC 60544-1, Electrical insulating materials – Determination 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 61244-1, Determination of long-term radiation ageing in polymers – Part 1: Techniques

for monitoring diffusion-limited oxidation

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

for predicting ageing at low dose rates

IEC 60780, Nuclear power plants – Electrical equipment of the safety system – Qualification

---------------------- Page: 8 ----------------------
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 reactor
CBQ 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

---------------------- Page: 9 ----------------------
– 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 of

hydroperoxide 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 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.

---------------------- Page: 10 ----------------------
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 has its own advantages and limitations.

Selection of one or more of the methods will be dependent on the requirements of the

individual users.

Several approaches to ageing assessment in-service are described in this standard. These

are:

• identifying components of concern to prioritize the application of ageing management

programmes (see Clause 6);

• condition monitoring to assess the condition of materials which have aged for extended

time periods under actual use environments (see Clause 7);

• predictive modelling to use data from laboratory based accelerated ageing programmes to

estimate ageing under real-time ageing conditions (see Clause 8);

• sample deposit to provide samples for the measurement of ageing under real-time ageing

conditions (see Clause 9).
6 Identifying components of concern
6.1 General

Within a nuclear power plant there are many components containing polymeric insulating

materials, e.g. there are >1 000 km of electrical cables in a typical NPP. It is not practical to

assess the ageing of every individual component, and many will not be exposed to significant

environmental ageing conditions. It is therefore necessary to prioritize any ageing

management programme by identifying those components which are of most concern.
6.2 Priorities for ageing management

Not all components have the same priority for ageing management. In general, those

components performing safety functions during and following an accide
...

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