EN 60544-5:2003

STANDARDElektrični izolacijski materiali – Ugotavljanje učinkov ionizirnega sevanja - 5. del: Postopki za ocenjevanje staranja med uporabo (IEC 60554-5:2003)Electrical insulating materials - Determination of the effects of ionizing radiation - Part 5: Procedures for assessment of ageing in service (IEC 60554-5:2003)©
Standard je založil in izdal Slovenski inštitut za standardizacijo. Razmnoževanje ali kopiranje celote ali delov tega dokumenta ni dovoljenoReferenčna številkaSIST EN 60544-5:2004(en)ICS29.035.01

EUROPEAN STANDARD
EN 60544-5 NORME EUROPÉENNE EUROPÄISCHE NORM
April 2003 CENELEC European Committee for Electrotechnical Standardization Comité Européen de Normalisation Electrotechnique Europäisches Komitee für Elektrotechnische Normung
Central Secretariat: rue de Stassart 35, B - 1050 Brussels
© 2003 CENELEC - All rights of exploitation in any form and by any means reserved worldwide for CENELEC members.
Ref. No. EN 60544-5:2003 E
ICS 17.240; 29.035.01
English version
Electrical insulating materials -
Determination of the effects of ionizing radiation Part 5: Procedures for assessment of ageing in service (IEC 60544-5:2003)
Matériaux isolants -
Détermination des effets
des rayonnements ionisants Partie 5: Procédures pour l'estimation
du vieillissement en service (CEI 60544-5:2003)
Elektroisolierstoffe -
Bestimmung der Wirkung
ionisierender Strahlung Teil 5 : Bewertungsverfahren für die Alterung während des Einsatzes (IEC 60544-5:2003)
This European Standard was approved by CENELEC on 2003-04-01. 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 Central Secretariat 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 Central Secretariat has the same status as the official versions.
CENELEC members are the national electrotechnical committees of Austria, Belgium, Czech Republic, Denmark, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Luxembourg, Malta, Netherlands, Norway, Portugal, Slovakia, Spain, Sweden, Switzerland and United Kingdom.

The text of document 15E/210/FDIS, future edition 1 of IEC 60544-5, prepared by SC 15E, Methods of test, of IEC TC 15, Insulating materials, was submitted to the IEC-CENELEC parallel vote and was approved by CENELEC as EN 60544-5 on 2003-04-01.
The following dates were fixed:
– latest date by which the EN has to be implemented
at national level by publication of an identical
national standard or by endorsement
(dop) 2004-01-01
– latest date by which the national standards conflicting
with the EN have to be withdrawn
(dow) 2006-04-01
Annexes designated "normative" are part of the body of the standard.
In this standard, annex ZA is normative. Annex ZA has been added by CENELEC. __________
Endorsement notice
The text of the International Standard IEC 60544-5:2003 was approved by CENELEC as a European Standard without any modification. __________

- 3 - EN 60544-5:2003
Annex ZA
(normative)
Normative references to international publications
with their corresponding European publications This European Standard incorporates by dated or undated reference, provisions from other publications. These normative references are cited at the appropriate places in the text and the publications are listed hereafter. For dated references, subsequent amendments to or revisions of any of these publications apply to this European Standard only when incorporated in it by amendment or revision. For undated references the latest edition of the publication referred to applies (including amendments). 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 1994 Electrical insulating materials - Determination of the effects of ionizing radiation Part 1: Radiation interaction and dosimetry
EN 60544-1 1994 IEC 60544-2 1991 Guide for determining the effects of ionizing radiation on insulating materialsPart 2: Procedures for irradiation and test
- - IEC/TR2 61244-1 1993 Determination of long-term radiation ageing in polymers Part 1: Techniques for monitoring diffusion-limited oxidation
- - IEC/TR2 61244-2 1996 Part 2: Procedures for predicting ageing at low dose rates
- - IEC/TR2 61244-3 1998 Long-term radiation ageing in polymersPart 3: Procedures for in-service monitoring of low-voltage cable materials
- -
NORMEINTERNATIONALECEIIECINTERNATIONALSTANDARD60544-5Première éditionFirst edition2003-02Matériaux isolants –Détermination des effets desrayonnements ionisants –Partie 5:Procédures pour l'estimationdu vieillissement en serviceElectrical insulating materials –Determination of the effects ofionizing radiation –Part 5:Procedures for assessmentof ageing in servicePour prix, voir catalogue en vigueurFor price, see current catalogue IEC 2003
Droits de reproduction réservés

Copyright - all rights reservedAucune partie de cette publication ne peut être reproduite niutilisée sous quelque forme que ce soit et par aucun procédé,électronique ou mécanique, y compris la photocopie et lesmicrofilms, sans l'accord écrit de l'éditeur.No part of this publication may be reproduced or utilized in anyform or by any means, electronic or mechanical, includingphotocopying and microfilm, without permission in writing fromthe publisher.International Electrotechnical Commission,
3, rue de Varembé, PO Box 131, CH-1211 Geneva 20, SwitzerlandTelephone: +41 22 919 02 11
Telefax: +41 22 919 03 00
E-mail: inmail@iec.ch
Web: www.iec.chCODE PRIXPRICE CODEVCommission Electrotechnique InternationaleInternational Electrotechnical Commission

60544-5  IEC:2003– 3 –CONTENTSFOREWORD.7INTRODUCTION.111Scope and object.132Normative references.133Abbreviations.134Background.154.1Diffusion limited oxidation (DLO).154.2Dose rate effects (DRE).174.3Accelerated ageing.174.4Approaches to ageing assessment.195Condition monitoring techniques.195.1Introduction.195.2Establishment of correlation curves for CM methods.215.3Indenter.235.4Oxidation induction time (OIT).255.5Oxidation induction temperature (OITP).295.6Thermogravimetric analysis (TGA).315.7Density measurements.356Equipment deposit.396.1Requirements of a deposit.416.2Installation of an equipment deposit.416.3Testing of samples from the deposit.436.4Determination of sampling intervals.436.5Real-time aged equipment and operating experience.45Bibliography.63Figure 1 – Development of ageing data on changes in tensile elongation anda condition indicator (for example, indenter modulus) – Schematic.49Figure 2 – Correlation curve derived from data in Figure 1 – Schematic.51Figure 3 – Correlation curve for indenter modulus against tensile elongation fora CSPE cable jacket material [7].51Figure 4 – Typical force – Displacement curve from indenter measurements, showingdefinition of indenter modulus.53Figure 5 – Typical shape of thermogram from an OIT test, showing baseline and onsetdetermination (method B) – Schematic.53Figure 6 – Shape of thermogram from an OIT test with no well-defined baseline –Schematic.55Figure 7 – Shape of thermogram from an OIT test with multiple onsets – Schematic.55Figure 8 – Shape of thermogram from a typical OITP test on a semi-crystalline material(for example, XLPE) – Schematic.57Figure 9 – Shape of test data plot from a typical TGA test – Schematic.57Figure 10 – Example of correlation curve for TGA data against tensile elongation,for a PVC sheath material [7].59

60544-5  IEC:2003– 5 –Figure 11 – Reverse temperature effect during radiation ageing of XLPE cableinsulation material during radiation ageing at elevated temperature [20].59Figure 12 – Determination of lead times for a cable deposit – Schematic [21].61Table 1 – Recommended test parameter values for indenter measurements.47Table 2 – Recommended test temperatures for OIT measurements.47

60544-5  IEC:2003– 7 –INTERNATIONAL ELECTROTECHNICAL COMMISSION____________ELECTRICAL INSULATING MATERIALS –DETERMINATION OF THE EFFECTS OF IONIZING RADIATION –Part 5: Procedures for assessment of ageing in serviceFOREWORD1)The IEC (International Electrotechnical Commission) is a worldwide organization for standardization comprisingall national electrotechnical committees (IEC National Committees). The object of the IEC is to promoteinternational co-operation on all questions concerning standardization in the electrical and electronic fields. Tothis end and in addition to other activities, the IEC publishes International Standards. Their preparation isentrusted to technical committees; any IEC National Committee interested in the subject dealt with mayparticipate in this preparatory work. International, governmental and non-governmental organizations liaisingwith the IEC also participate in this preparation. The IEC collaborates closely with the InternationalOrganization for Standardization (ISO) in accordance with conditions determined by agreement between thetwo organizations.2)The formal decisions or agreements of the IEC on technical matters express, as nearly as possible, aninternational consensus of opinion on the relevant subjects since each technical committee has representationfrom all interested National Committees.3)The documents produced have the form of recommendations for international use and are published in the formof standards, technical specifications, technical reports or guides and they are accepted by the NationalCommittees in that sense.4)
In order to promote international unification, IEC National Committees undertake to apply IEC InternationalStandards transparently to the maximum extent possible in their national and regional standards. Anydivergence between the IEC Standard and the corresponding national or regional standard shall be clearlyindicated in the latter.5)
The IEC provides no marking procedure to indicate its approval and cannot be rendered responsible for anyequipment declared to be in conformity with one of its standards.6)
Attention is drawn to the possibility that some of the elements of this International Standard may be the subjectof patent rights. The IEC shall not be held responsible for identifying any or all such patent rights.International Standard IEC 60544-5 has been prepared by subcommittee 15E: Methods oftest, of IEC technical committee 15: Insulating materials.The text of this standard is based on the following documents:FDISReport on voting15E/210/FDIS15E/214/RVDFull information on the voting for the approval of this standard can be found in the report onvoting indicated in the above table.This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.IEC 60544 consists of the following parts, under the general title Electrical insulatingmaterials – Determination of the effects of ionizing radiation:Part 1: Radiation interaction and dosimetryPart 2: Procedures for irradiation and testPart 3: (now incorporated into Part 2)Part 4: Classification system for service in radiation environmentsPart 5: Procedures for assessment of ageing in service

60544-5  IEC:2003– 9 –The committee has decided that the contents of this publication will remain unchanged until2008. At this date, the publication will be•reconfirmed;•withdrawn;•replaced by a revised edition, or•amended.

60544-5  IEC:2003– 11 –INTRODUCTIONOrganic materials provide a significant proportion of insulations used in electrical systems.These materials are sensitive to the effects of irradiation and the response varies widelybetween different types. It is therefore important to be able to assess the degree ofdegradation of these insulating materials during their service lifetimes. This part of IEC 60544provides recommended procedures for monitoring ageing of insulating materials in service.There are a number of approaches to the assessment of ageing of polymer-based componentsexposed to radiation environments [1], [2]1. These are based on better understanding of thefactors affecting ageing degradation which has been developed over the last 15 years. In anuclear power plant, qualification programmes are normally used for selection of components,including those based on polymeric materials. These initial qualification procedures, such asIEEE-323 [3], were written before ageing was well understood. Most of the methods discussedin this document are therefore used to address the limitations of the initial qualificationprocess.This part is the fifth in a series dealing with the effect of ionizing radiation on insulatingmaterials.Part 1 (Radiation interaction) constitutes an introduction dealing very broadly with theproblems involved in evaluating radiation effects. It also gives a guide to dosimetryterminology, several methods of determining exposure and absorbed dose, and methods ofcalculating absorbed dose in any specific material from the dosimetry method applied.Part 2 (Procedures for irradiation and test) describes procedures for maintaining sevendifferent types of exposure conditions during irradiation. It also specifies the controls thatshall be maintained over these conditions so that when test results are reported, reliablecomparisons of material performance can be made. It also defines certain importantirradiation conditions and test procedures to be used for property change determinations andcorresponding end-point criteria.Part 3 has been incorporated into Part 2.Part 4 (Classification system for service in radiation environments) provides a recommendedclassification system for categorizing the radiation endurance of insulation materials.___________1 Figures in square brackets refer to the bibliography.

60544-5  IEC:2003– 13 –ELECTRICAL INSULATING MATERIALS –DETERMINATION OF THE EFFECTS OF IONIZING RADIATION –Part 5: Procedures for assessment of ageing in service1 Scope and objectThis part of IEC 60544 covers ageing assessment methods which can be applied tocomponents based on polymeric materials (for example, cable insulation and jackets,elastomeric seals, polymeric coatings, gaiters) which are used in environments where theyare exposed to radiation.The object of this part of IEC 60544 is to provide guidelines on the assessment of ageing inservice. The approaches discussed cover ageing assessment programmes based on conditionmonitoring (CM), the use of equipment deposits in severe environments and sampling of real-time aged components.2 Normative referencesThe following referenced documents are indispensable for the application of this document.For dated references, only the edition cited applies. For undated references, the latest editionof the referenced document (including any amendments) applies.IEC 60544-1:1994, Electrical insulating materials – Determination of the effects of ionizingradiation – Part 1: Radiation interaction and dissymmetryIEC 60544-2:1991, Electrical insulating materials – Determination of the effects of ionizingradiation – Part 2: Procedures for irradiation and testIEC/TR2 61244-1:1993, Determination of long-term ageing in polymers – Part 1: Techniquesfor monitoring diffusion-limited oxidationIEC/TR2 61244-2:1996, Determination of long-term ageing in polymers – Part 2: Proceduresfor predicting ageing at low dose ratesIEC/TR2 61244-3:1998, Long-term radiation ageing in polymers – Part 3: Procedures for in-service monitoring of low-voltage cable materials3 AbbreviationsBRButyl rubberBWRBoiling water reactorCMCondition monitoringCSPEChlorosulphonated polyethyleneDLODiffusion limited oxidationDREDose-rate effectDSCDifferential scanning calorimeterEPREthylene propylene rubberEPDMEthylene propylene diene copolymer

60544-5  IEC:2003– 15 –ETFEEthylene tetrafluoroethylene copolymerEVAEthylene vinyl acetate copolymerIMIndenter modulusLOCALoss of coolant accidentNBRNitrile rubberOITOxidation induction timeOIT/OITPOxidation induction temperaturePEPolyethylenePEEKPolyether ether ketonePPOPolyphenylene oxidePVCPolyvinyl chloridePWRPressurized water reactorSIRSilicone rubberTGAThermo-gravimetric analysisXLPECross-linked polyethyleneXLPOCross-linked polyolefin4 BackgroundThere are a number of alternative methods offered for ageing assessment as described intheir respective subclauses. Each of these methods has its own advantages and limitations.Selection of the appropriate method will be dependent on the requirements of the individualusers.There are a number of factors that need to be considered when assessing ageing of polymericcomponents in radiation environments. In the following subclauses, some of these factors arebriefly discussed and reference made to more detailed information. To accelerate radiation-ageing environments, the normal approach is to increase the radiation dose rate, oftencombined with an increase in temperature. The two most important potential complicationsarising from such increases involve diffusion limited oxidation (DLO), which is describedin 4.1, and chemical dose-rate effects (DRE), which are described in 4.2. The implications ofthese factors on the use and interpretation of CM techniques are also discussed. Acceleratedageing programmes briefly discussed in 4.3 and 4.4 introduce the approaches available forageing assessment in-service.4.1 Diffusion limited oxidation (DLO)When polymers are exposed to an oxygen-containing environment (for example, air), a certainamount of oxygen will be dissolved in the material. In the absence of oxygen-consumingreactions (oxidation), the amount of dissolved oxygen will be proportional to the oxygenpartial pressure surrounding the polymer (well known from Henry’s law). Ageing will lead tooxidation reactions in the polymer, whose rate will increase significantly as the dose rate andtemperature of ageing are increased. If the rate of consumption of dissolved oxygen in thepolymer is faster than the rate at which oxygen can be replenished by diffusion from thesurrounding air atmosphere, the concentration of dissolved oxygen in the interior regions willdecrease with time (the oxygen concentration at the sample surface will remain at itsequilibrium value). The reduction in internal oxygen concentration can lead to reduced ornegligable oxidation, which is referred to as diffusion limited oxidation.

60544-5  IEC:2003– 17 –The importance of this effect is dependent on the sample thickness (thinner samples givingsmaller DLO effects) and the ratio of the oxygen consumption rate to the oxygen permeabilitycoefficient P, which equals the product of the oxygen diffusion and solubility parameters.Accelerated radiation environments involve increases in dose rates, which increase theoxygen 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 willbecome more important as the dose rate is raised. These effects are described in more detailin IEC 61244-1.The effects of diffusion limited oxidation also need to be considered when carrying outcondition monitoring tests. This is not an issue for the many CM techniques which measureproperties at room temperature, such as those based on density and modulus measurements.On the other hand, several CM techniques such as oxidation induction time (OIT) andthermogravimetric analysis (TGA) use quite elevated temperatures during the measurements.For these techniques, it is quite possible to have DLO effects present during measurement ofthe CM parameter. DLO also needs to be addressed when developing correlation curves forcondition monitoring methods, to ensure that representative data are obtained for bothradiation and thermal ageing.4.2 Dose-rate effects (DRE)The existence of radiation dose-rate effects and methods for dealing with these effects aredescribed in IEC 61244-2. Generally, DRE are separated into two types. The first type, whichis commonly observed in accelerated radiation ageing experiments, is due to the DLO effectsdescribed above. These DLO-based effects represent a physical, geometry-dependent DRE.The second type concerns chemical DRE. Such chemically based DRE are much lesscommon. A documented case of chemical DRE is found in PVC and low-density polyethylenematerials, caused by the slow breakdown of hydroperoxide intermediate species in theoxidation reaction [4].4.3 Accelerated ageingAccelerated ageing programmes in the laboratory sometimes use acceleration factors muchlower than are normally used in equipment qualification. This may avoid some of the problemsassociated with diffusion limited oxidation and dose-rate effects. The ageing produced maythen be a better simulation of the long-term ageing that occurs under service conditions. Thedata that are obtained in accelerated ageing tests can be used with predictive models whichenable assessments to be made of the behaviour of the materials under service conditions.Accelerated ageing programmes normally require a matrix of test data to be generated over arange of environmental conditions as described in IEC 61244-2. As a minimum, data areneeded for at least three different dose rates at the normal operating temperature butadditional data on thermal ageing and radiation ageing at elevated temperature enables betteruse to be made of the available predictive modelling methods. The dose rates andtemperatures used for accelerated ageing shall be selected using the principles described inIEC 60544-2 to ensure that homogeneous oxidation occurs. For each environmental conditionused, test data need to be obtained at several different ageing times, the longest of whichshall be sufficient to introduce significant degradation. A typical test programme could take upto 18 months to complete, depending on the radiation resistance of the materials being tested.

60544-5  IEC:2003– 19 –The type of data required in the test matrix will be determined by the type of component beingevaluated. The types of test parameters which are appropriate are given in IEC 60544-2 forvarious types of polymeric material.Analysis of the data generated in the experimental test matrix in terms of predictive modellingmethods is described in detail in IEC 61244-2 for three different predictive models which arecurrently available.4.4 Approaches to ageing assessmentTwo approaches to ageing assessment in service are described in this part of IEC 60644.These are–condition monitoring using non-destructive test methods,–sampling of materials from an equipment deposit.Condition monitoring techniques are used to assess the condition of materials which haveaged for extended time periods under actual use environments, such as in nuclear powerplants, accelerators, reprocessing plants, etc. The approach makes use of non-destructive ormicro-sampling test methods which have been shown to correlate well with ageingdegradation. Condition monitoring methods are described in detail in Clause 5.The use of samples from an equipment deposit in the plant is an alternative approach toassessment of ageing in service. This makes use of samples specifically installed in the plantfor destructive testing as part of an ageing management programme. This approach isdescribed in detail in Clause 6.5 Condition monitoring techniques5.1 IntroductionThere exists a wide range of methods which have been evaluated for condition monitoring ofpolymeric components, particularly for cable materials [5], [6]. Of the many methodsexamined, only a few have been identified as being potentially suitable for practical use.These are summarized in IEC 61244-3. For these methods, data correlating the monitoringparameter with degradation of the polymeric component have been built up and the practicallimitations explored over the last few years. The most developed methods are as follows.–Indenter–Oxidation induction time (OIT)–Oxidation induction temperature (OITP)–Thermogravimetric analysis (TGA)–DensityThe recommended test procedures for each of these techniques are given in 5.3 to 5.7,respectively.Condition monitoring in ageing assessment can be used in a number of ways, ranging fromshort-term trouble-shooting to long-term on-going qualification programmes. In short-termtests, the emphasis of condition monitoring tends to be on identifying the extent of a problemor in demonstrating that a problem does not exist. For example, the indenter has been usedto determine the extent of damage to cables from degradation arising from damaged

60544-5  IEC:2003– 21 –thermal insulation on a steam line near a cable run in a BWR nuclear power plant. By carryingout indenter measurements along this cable, it was possible to obtain a profile of thedamaged area.In some cases, the use of design criteria (for example, calculation of self-heating of powercable from current loading) can be very conservative, indicating that a power cable should beshowing significant degradation. Checks on the component using CM methods can be used todemonstrate that the materials have not degraded to the extent predicted, avoidingunnecessary replacement.Condition monitoring methods can also be used in on-going test programmes which can spanthe lifetime of the plant. Typical uses of CM methods in such programmes are as follows:–trending of component condition relative to a qualified condition determined during initialequipment qualification procedures;–comparison of condition monitoring data with predictive modelling, based on acceleratedageing data in the laboratory and a knowledge of the environmental conditions seen by thecomponent;–monitoring of components in an equipment deposit located in a severe environment in theplant (most frequently used for cables and electrical components).5.2 Establishment of correlation curves for CM methodsIn order to use condition monitoring methods it is important to develop correlation curvesbetween the monitoring parameter measured and the prime indicator of degradation orfunctionality. For polymeric cable materials, the prime indicator of degradation is generallyconsidered to be tensile elongation at break, since electrical properties do not generallychange significantly before physical failure of the cable. In seal materials, compression sethas proved to be a useful indicator of the degradation in sealing properties introduced byageing. Suitable degradation parameters for other components are given in IEC 60544-2.Correlation curves are determined by measurements of the prime indicator and the relevantCM parameter on samples aged under identical conditions, as shown schematically inFigure 1. The measurements should cover a range of degradation levels, from the unagedcondition to a severely degraded condition. It is recommended that at least five sets of data atdifferent ageing times are used in establishing the correlation curve (Figure 2).Correlation curves are normally established using accelerated testing. Such tests shall becarried out using the procedures described in IEC 60544-2. Alternatively, correlation curvescan be established as part of the equipment deposit procedure for ageing assessment, asdescribed in Clause 6.An example, for a CSPE cable material (Figure 3), shows the correlation between indentermeasurements and changes in the tensile elongation at break obtained during an acceleratedageing programme [7]. A good correlation has been obtained for both radiation and thermalageing of this CSPE material. Condition monitoring measurements in-plant on this materialusing the indenter could be compared with the predicted degradation to enable residual lifeto be estimated. The predicted degradation would be obtained from use of ageing models(such as those described in IEC 61244-2), combined with knowledge of the environmentalconditions in plant.

60544-5  IEC:2003– 23 –5.3 IndenterThe indenter is an instrument that determines a parameter related to the compressivemodulus of a polymer. By driving an instrumented probe of known shape into the surface ofthe polymer and monitoring, the load exerted is measured [8]. The indenter was developedspecifically for evaluation of cable materials but has also been applied to degradation ofelastomeric seals [9]. The indenter modulus (IM) is determined from the slope of the forceversus penetration curve, typically for indenter forces up to 15 N maximum. This is shownschematically in Figure 4.The value of the indenter modulus is dependent on the probe dimensions. The probe shape isa truncated cone, whose tip diameter shall be stated in the test report.5.3.1 Test methodFor laboratory measurements using the indenter, a cable sample shall have a minimum lengthof 100 mm. For field measurements of cable materials using the indenter, the location shall beselected to enable at least three tests to be carried out, either around the circumference ofthe cable or along its length. The sample to be tested shall be free of surface debris anddeposits. If the sample has such deposits, it shall be wiped clean using a damp cloth.Solvents shall not be used for cleaning.The sample shall be clamped in the test jaw so that it is held firmly but not compressed. Themaximum force and probe speed are set using the instrument software. Recommended valuesfor these test parameters for different polymer types are given in Table 1. For field tests, aminimum of three tests shall be made, either around the circumference or along the length ofthe samples. Multiple tests shall not be carried out at the same location. For laboratorymeasurements, it is recommended that three tests shall be carried out around thecircumference of the sample and repeated in at least two locations along the sample.5.3.2 Analysis of test dataThe data generated during the indenter test consist of probe force versus displacementvalues. The indenter modulus (IM) is defined for a specific force range asIM = (F1 – F2)/(d1 – d2)where F1 and F2 are the force values and d1 and d2 are the corresponding displacementvalues over a force range covering the initial linear part of the force-displacement curve(see Figure 4). Recommended force ranges for analysis of different polymer types are givenin Table 1.5.3.3 ReportThe test report shall include the following details:–the test instrument used;–probe tip dimensions;–the sample tested;–the location of the test positions within that sample;–test temperature;–probe speed;–force range used for analysis;–values of the indenter modulus for each test, together with the mean value and standarddeviation.

60544-5  IEC:2003– 25 –5.3.4 ReproducibilityThe reproducibility of indenter measurements between laboratories has been evaluated ininterlaboratory tests on a range of cable materials. Typically, IM values can be measuredwithin ±5 % to ±10 % of the mean value, depending on the material. The IM values obtainedcan also be affected by the ambient temperature at which the tests are carried out. This isparticularly important for PVC, EVA and CSPE materials but is less important for EPR, EPDM,XLPE and PE materials for temperatures in the range 16 °C to 24 °C [10].5.3.5 LimitationsIndenter modulus (IM) is a good indicator of degradation in many of the polymers used inradiation environments. Good correlation data have been demonstrated for EPR, EPDM,CSPE, PVC, EVA and neoprene-based cable materials, and fluoropolymer and EPDM sealmaterials. The standard technique does not work well for XLPE-based cable materials.The instruments commercially available are primarily aimed at testing of cable materials andtherefore are mainly suitable for components with a cylindrical geometry with diameters in therange of 5 mm to 30 mm. Wires as small as 3 mm in diameter can be measured but thevariability in modulus values tends to be higher than in the larger diameters.For cables in plant, normally only the jacket material is accessible for testing. It is not alwayspossible to infer the degradation state of the insulation from the measured degradation of thejacket material. For many cables, there is little correlation between the degradation ofinsulation and jacket materials [2].5.4 Oxidation induction time (OIT)Oxidation induction tests utilize micro-samples of material which can be taken from thecomponent (for example, cable jacket material) without affecting functionality. These testsutilize thermal analysis using commercial differential scanning calorimetry (DSC) equipment todetermine either an oxidation induction time at constant temperature, or an oxidationinduction temperature (OITP) at a constant temperature ramp rate. The two methods arecomplementary, in that OITP is often effective in those materials where OIT is difficult todetermine. The OI time decreases with increasing degradation of the material.5.4.1 Test method for OIT testsThe test sample should consist of 8 mg to 10 mg of material. This could be a surface scrapingfrom a cable jacket material or a slice through an insulation sample. The sample shall bechopped into pieces with a maximum dimension of approximately 0,5 mm or sieved through a40-mesh grid. The sample pieces should be placed in a pan suitable for the instrument beingused. An aluminium pan with a mesh lid is recommended. An identical empty pan shall beused as the control sample. Temperature calibration of the DSC instrument shall be carriedout prior to running OIT tests. The calibration method shall span the temperature range usedin the OIT tests.In OIT tests, the sample temperature is increased rapidly to the test temperature in nitrogenat a flow rate of 50 ml/min. The recommended temperature ramp rate is 50 °C/min up to 10 °Cbelow the test temperature and then 5 °C/min up to the test temperature. Suggested testtemperatures for different polymer types are given in Table 2. This temperature is normallyselected to give an OIT value of 60 min to 90 min for unaged material. Once the test

60544-5  IEC:2003– 27 –temperature has been achieved and stabilized, then the gas flow through the test cell isswitched to oxygen and the time required for the onset of oxidation is monitored [11]. Thisonset is characterized by a rapid exothermic heat flow from a flat baseline. At least three OITtests should be carried out from the same sample batch. The stabilization time at the testtemperature before switching to oxygen should be kept the same for each test. A hold time of2 min is recommended.5.4.2 Analysis of OIT testsThe test data consist of a plot of the heat flow through the sample pan as a function of time.The onset of oxidation is indicated by an exothermic heat flow relative to the baseline, asshown in Figure 5. Calculation of the onset time is carried out by the instrument softwareusing one of two methods.Method A – The point of maximum heat flow is determined and a tangent drawn to this pointon the thermogram. The onset time is defined as the time difference from the start of oxygenflow and where the tangent intersects the baseline.Method B – The tangent to the curve is drawn at a specific threshold value relative to thebaseline. The onset time is defined as the time difference between the start of oxygen flowand where the tangent intersects the baseline. Threshold values used for this method ofanalysis are typically 0,5 W/g to 1 W/g.5.4.3 Reporting of OIT testsThe test report shall include the following details:–instrument used;–sample mass;–isothermal temperature used;–temperature ramp rates used to reach the test temperature;–hold time before switching to oxygen flow;–gas flow rate;–method used for analysis;–OIT value for each of the samples tested;–examples of the thermograms.5.4.4 Reproducibility of OIT testsTypically, variations of ±5 % to ±10 % of the mean value are observed in OIT measurements [11].In practice, there can be problems with interpretation of the thermograms for some materials.It is often difficult to define a flat baseline from which to measure a threshold for the oxidationonset (Figure 6). Also in some materials, multiple onsets are observed making selection of theappropriate onset more difficult (Figure 7).

60544-5  IEC:2003– 29 –5.4.5 Limitations of OIT testsFor those materials such as some XLPE and EPR, which give well-defined single onsets anda good baseline, OIT tests are a useful method of condition monitoring. The OI timedecreases with increasing degradation of the material. OIT tests can be used for PVC andother chlorinated materials, such as CSPE and neoprene, but the degradation productsgenerated during the test are corrosive and are likely to damage the test instrument.For these materials, smaller sample mass (1 mg to 2 mg) enable the OIT test to be usedwith care.For cables in plant, normally only the jacket material is accessible for testing except atterminations. It is not always possible to infer the degradation state of the insulation from themeasured degradation of the jacket material. For many cables, there is little correlationbetween the degradation of insulation and jacket materials [2].5.5 Oxidation induction temperature (OITP)Oxidation induction tests utilize micro-samples of material which can be taken from thecomponent (for example, cable jacket material) without affecting functionality. These testsutilize thermal analysis using commercial differential scanning calorimetry equipment todetermine either an oxidation induction time (OIT) at constant temperature, or an oxidationinduction temperature (OITP) at a constant temperature ramp rate. The two methods arecomplementary, in that OITP is often effective in those materials where OIT is difficult todetermine. The OITP decreases with increasing degradation.5.5.1 Test method for OITP testsSample preparation is the same as for OIT tests (see 5.4.1). In OITP tests, the sampletemperature is ramped at a constant rate in flowing oxygen. A ramp rate of 10 °C/min isrecommended. The onset of oxidation is shown by an exothermic heat flow from a flatbaseline, but unlike in the OIT tests, physical transitions such as melting of semi-crystallinefractions are also observed (Figure 8). The OITP test shall be run from the same startingtemperature for each test. At least three OITP tests shall be carried out from the same samplebatch. Temperature calibration of the DSC instrument shall be carried out prior to runningOITP tests. The calibration method shall span the temperature range used in the OITP tests.5.5.2 Analysis of OITP testsThe test data consist of a plot of the heat flow through the sample pan as a function oftemperature. The onset of oxidation is indicated by an exothermic heat flow relative to thebaseline, as shown in Figure 8. Calculation of the onset temperature is carried out by theinstrument software using one of two methods.Method A – The point of maximum heat flow is determined and a tangent drawn to this pointon the thermogram. The onset temperature is defined as the temperature at which the tangentintersects the baseline.Method B – The tangent to the curve is drawn at a specific threshold value relative to thebaseline. The onset temperature is defined as the temperature at which the tangent intersectsthe baseline. Threshold values used for this method of analysis are typically 0,5 W/g to 1 W/g.

60544-5  IEC:2003– 31 –5.5.3 Reporting of OITP testsThe test report shall include the following details:–the instrument used;–sample mass;–gas flow rate;–temperature ramp rate;–starting temperature;–the method used for analysis;–OITP value for each of the samples tested.5.5.4 Reproducibility of OITP testsVariations of ±2 °C are typically seen in OITP measurements for those materials that show aclear onset [10]. As in OIT tests, there are sometimes problems of interpretation, particularlyin defining the baseline, but these are less of a problem in OITP tests.5.5.5 Limitations of OITP testsOITP tests have shown a good correlation with ageing degradation for a number of materialtypes, good results being obtained with XLPE, EPR, EVA, PEEK and butyl rubber based cablematerials. OITP tests can be used for PVC and other chlorinated materials, such as CSPEand neoprene, but the degradation products generated during the test are corrosive and arelikely to damage the test instrument. For these materials, smaller sample mass (1 mg to 2 mg)enable the OITP test to be used with care.For cables in plant, normally only the jacket material is accessible for testing except atterminations. It is not always possible to infer the degradation state of the insulation from themeasured degradation of the jacket material. For many cables, there is little correlationbetween the degradation of insulation and jacket materials [2].5.6 Thermogravimetric analysis (TGA)Like oxidation induction tests, thermogravimetric analysis utilizes micro-samples of materialwhich can be taken from the component without affecting functionality. These tests usecommercial thermal analysis equipment to monitor the mass loss in the sample as the sampletemperature is ramped up at a constant rate. The absolute values obtained in the TGA testsare dependent on the oxygen content in the sample chamber, with higher onset values beingobserved with lower oxygen content. The TGA temperature tends to decrease with increasingradiation degradation.5.6.1 Test method for TGA testsSample preparation is the same as for OIT tests (see 5.4.1). The sample temperature isramped at a constant rate in flowing oxygen. The recommended ramp rate is 10 °C/min andoxygen flow rate shall be 50 ml/min. At least three tests shall be carried out for each samplebatch, using the same start temperature for each test. Temperature calibration of the TGAinstrument shall be carried out prior to running TGA tests. The calibration method shall spa
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