IEC/IEEE 62582-4:2022

IEC/IEEE 62582-4 ®
Edition 2.0 2022-11
REDLINE VERSION
INTERNATIONAL
STANDARD
colour
inside
Nuclear power plants – Instrumentation and control important to safety –
Electrical equipment condition monitoring methods –
Part 4: Oxidation induction techniques

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IEC/IEEE 62582-4 ®
Edition 2.0 2022-11
REDLINE VERSION
INTERNATIONAL
STANDARD
colour
inside
Nuclear power plants – Instrumentation and control important to safety –
Electrical equipment condition monitoring methods –
Part 4: Oxidation induction techniques
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 27.120.20
ISBN 978-2-8322-6032-6
– 2 – IEC/IEEE 62582-4:2022 RLV
© IEC/IEEE 2022
CONTENTS
FOREWORD . 4
INTRODUCTION . 7
1 Scope and object . 10
2 Normative references . 10
3 Terms and definitions . 10
4 Abbreviated terms and acronyms . 11
5 General description . 11
6 Applicability and reproducibility . 11
7 Measurement procedure . 12
7.1 Stabilisation of the polymeric materials . 12
7.2 Sampling. 12
7.2.1 General . 12
7.2.2 Sample requirements . 12
7.2.3 Precautions . 12
7.3 Sample preparation . 13
7.4 Instrumentation . 13
7.5 Calibration . 13
7.6 OIT measurement method . 13
7.6.1 Measurement procedure . 13
7.6.2 Temperature profile . 14
7.6.3 Gas flow . 15
7.6.4 Determining the value of oxidation onset . 15
7.6.5 Reporting . 16
7.7 OITP measurement method . 17
7.7.1 Measurement procedure . 17
7.7.2 Temperature profile . 17
7.7.3 Gas flow . 17
7.7.4 Determining the value of oxidation onset . 18
7.7.5 Reporting . 18
Annex A (informative) Interpretation of thermogram . 20
A.1 Interpretation of OIT thermograms . 20
A.2 Interpretation of OITP thermograms . 23
Annex B (informative) Example of a measurement report from OITP measurements
and OIT . 25
B.1 OITP measurements . 27
B.2 OIT measurements . 29
Annex C (informative) Influence of set temperature on the OIT value . 31
Bibliography . 32

Figure 1 – OIT measurement – Schematic of temperature and gas profile and
corresponding heat flow . 14
Figure 2 – Schematic showing the types of baselines (flat, sloping, endothermic dip,
melting endotherm) observed for OIT and OITP measurements . 15
Figure 3 – Schematic showing definition of onset value for OIT and OITP
measurements . 16

© IEC/IEEE 2022
Figure 4 – Schematic of the temperature for OITP measurements and the
corresponding heat flow . 17
Figure A.1 – Example of an OIT plot with clear baseline and onset . 20
Figure A.2 – Example of OIT plot with multiple onsets. 21
Figure A.3 – Example of OIT plot where the baseline is difficult to define . 22
–1
Figure A.4 – Example of OIT plot where heat flow is too low to use standard 0,1 W∙g
threshold . 22
Figure A.5 – Example of an OITP plot with a well-defined baseline and onset . 23
Figure A.6 – Example of an OITP plot for a semi-crystalline material showing a melting
endotherm prior to the oxidation onset . 24
Figure A.7 – Example of an OITP plot showing an endothermic dip immediately prior to
the oxidation onset . 24
Figure B.1 – Example of test plot .
Figure B.1 – Example of OITP test plot . 28
Figure B.2 – Example of OIT test plot . 30
Figure C.1 – Example of the influence of set temperature on the OIT value . 31

Table B.1 – Example of a measurement report from OITP . 27
Table B.2 – Example of a measurement report from OIT . 29

– 4 – IEC/IEEE 62582-4:2022 RLV
© IEC/IEEE 2022
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
NUCLEAR POWER PLANTS – INSTRUMENTATION AND CONTROL
IMPORTANT TO SAFETY – ELECTRICAL EQUIPMENT
CONDITION MONITORING METHODS –

Part 4: Oxidation induction techniques

FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
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© IEC/IEEE 2022
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– 6 – IEC/IEEE 62582-4:2022 RLV
© IEC/IEEE 2022
IEC/IEEE 62582-4 was prepared by subcommittee 45A: Instrumentation, control and electrical
power systems of nuclear facilities, of IEC technical committee 45: Nuclear instrumentation, in
cooperation with Nuclear Power Engineering Committee of the IEEE, under the IEC/IEEE Dual
Logo Agreement between IEC and IEEE. It is an International Standard.
This document is published as an IEC/IEEE Dual Logo standard.
This second edition cancels and replaces the first 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) Consideration of publication of IEC/IEEE 60780-323;
b) An example added in Annex B and update;
c) Annex C added.
The text of this International Standard is based on the following IEC documents:
Draft Report on voting
45A/1435/FDIS 45A/1445/RVD
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 the rules given in the ISO/IEC Directives, Part 2,
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 of IEC/IEEE 62582 series, under the general title Nuclear power plants –
Instrumentation and control important to safety – Electrical equipment condition monitoring
methods, can be found on the IEC website.
The IEC Technical Committee and IEEE Technical Committee have 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.
IMPORTANT – The "colour inside" logo on the cover page of this document indicates that it
correct understanding of its
contains colours which are considered to be useful for the
contents. Users should therefore print this document using a colour printer.

© IEC/IEEE 2022
INTRODUCTION
a) Technical background, main issues and organisation of this standard
This part of IEC/IEEE 62582 specifically focuses on oxidation induction methods for condition
monitoring for the management of ageing of electrical equipment installed in nuclear power
plants. The methods are primarily suited to samples taken from materials that are polyolefin-
based, but they can also be used for some materials based on ethylene-propylene polymers
and for some ethylene vinyl acetate materials.
This part 4 of IEC/IEEE 62582 is the fourth part of the IEC/IEEE 62582 series. It contains
detailed descriptions of condition monitoring based on oxidation induction measurements.
IEC/IEEE 62582 series is issued with a joint logo which makes it applicable to the management
of ageing of electrical equipment qualified to IEEE as well as IEC Standards.
Historically, IEEE Std 323-2003 introduced IEC/IEEE 60780-323 includes the concept and role
that condition based qualification could be used in equipment qualification as an adjunct to
qualified life. In equipment qualification, the condition of the equipment for which acceptable
performance was demonstrated is the qualified condition. The qualified condition is the
condition of equipment, prior to the start of a design basis event, for which the equipment was
demonstrated to meet the design requirements for the specified service conditions.
Significant research has been performed on condition monitoring techniques and the use of
these techniques in equipment qualification as noted in NUREG/CR-6704, Vol. 2 (BNL-NUREG-
52610) JNES-SS-0903, 2009 and IAEA-TECDOC-1825:2017.
It is intended that this document be used by test laboratories, operators of nuclear power plants,
systems evaluators, and licensors.
b) Situation of the current standard in the structure of the IEC SC 45A standard series
IEC/IEEE 62582-4 is the third level IEC SC 45A document tackling the specific issue of
application and performance of oxidation induction measurements in the management of ageing
of electrical instrument and control equipment in nuclear power plants.
IEC/IEEE 62582-4 is to be read in association with IEC/IEEE 62582-1, which provides
background and guidelines for the application of methods for condition monitoring of electrical
equipment important to safety of nuclear power plants.
For more details on the structure of the IEC SC 45A standard series, see item d) of this
introduction.
c) Recommendations and limitations regarding the application of this standard
It is important to note that this document establishes no additional functional requirements for
safety systems.
d) Description of the structure of the IEC SC45A standard series and relationships with
other IEC documents and other bodies documents (IAEA, ISO)
The top-level document of the IEC SC 45A standard series is IEC 61513. It provides general
requirements for I&C systems and equipment that are used to perform functions important to
safety in NPPs. IEC 61513 structures the IEC SC 45A standard series.
IEC 61513 refers directly to other IEC SC 45A standards for general topics related to
categorisation of functions and classification of systems, qualification, separation of systems,

– 8 – IEC/IEEE 62582-4:2022 RLV
© IEC/IEEE 2022
defence against common cause failure, software aspects of computer-based systems, hardware
aspects of computer-based systems, and control room design. The standards referenced
directly at this second level should be considered together with IEC 61513 as a consistent
document set.
At a third level, IEC SC 45A standards not directly referenced by IEC 61513 are standards
related to specific equipment, technical methods, or specific activities. Usually these
documents, which make reference to second-level documents for general topics, can be used
on their own.
A fourth level extending the IEC SC 45A standard series, corresponds to the Technical Reports
which are not normative.
IEC 61513 has adopted a presentation format similar to the basic safety publication IEC 61508
with an overall safety life-cycle framework and a system life-cycle framework and provides an
interpretation of the general requirements of IEC 61508-1, IEC 61508-2 and IEC 61508-4, for
the nuclear application sector. Compliance with IEC 61513 will facilitate consistency with the
requirements of IEC 61508 as they have been interpreted for the nuclear industry. In this
framework IEC 60880 and IEC 62138 correspond to IEC 61508-3 for the nuclear application
sector.
IEC 61513 refers to ISO as well as to IAEA 50-C-QA (now replaced by IAEA GS-R-3) for topics
related to quality assurance (QA).
The IEC SC 45A standards series consistently implements and details the principles and basic
safety aspects provided in the IAEA code on the safety of NPPs and in the IAEA safety series,
in particular the Requirements NS-R-1, establishing safety requirements related to the design
of Nuclear Power Plants, and the Safety Guide NS-G-1.3 dealing with instrumentation and
control systems important to safety in Nuclear Power Plants. The terminology and definitions
used by SC 45A standards are consistent with those used by the IAEA.
The IEC SC 45A standard series comprises a hierarchy of four levels. The top-level documents
of the IEC SC 45A standard series are IEC 61513 and IEC 63046.
IEC 61513 provides general requirements for instrumentation and control (I&C) systems and
equipment that are used to perform functions important to safety in nuclear power plants
(NPPs). IEC 63046 provides general requirements for electrical power systems of NPPs; it
covers power supply systems including the supply systems of the I&C systems.
IEC 61513 and IEC 63046 are to be considered in conjunction and at the same level. IEC 61513
and IEC 63046 structure the IEC SC 45A standard series and shape a complete framework
establishing general requirements for instrumentation, control and electrical power systems for
nuclear power plants.
IEC 61513 and IEC 63046 refer directly to other IEC SC 45A standards for general
requirements for specific topics, such as categorization of functions and classification of
systems, qualification, separation, defence against common cause failure, control room design,
electromagnetic compatibility, human factors engineering, cybersecurity, software and
hardware aspects for programmable digital systems, coordination of safety and security
requirements and management of ageing. The standards referenced directly at this second level
should be considered together with IEC 61513 and IEC 63046 as a consistent document set.
At a third level, IEC SC 45A standards not directly referenced by IEC 61513 or by IEC 63046
are standards related to specific requirements for specific equipment, technical methods, or
activities. Usually these documents, which make reference to second-level documents for
general requirements, can be used on their own.

© IEC/IEEE 2022
A fourth level extending the IEC SC 45 standard series, corresponds to the Technical Reports
which are not normative.
The IEC SC 45A standards series consistently implements and details the safety and security
principles and basic aspects provided in the relevant IAEA safety standards and in the relevant
documents of the IAEA nuclear security series (NSS). In particular this includes the IAEA
requirements SSR-2/1 , establishing safety requirements related to the design of nuclear power
plants (NPPs), the IAEA safety guide SSG-30 dealing with the safety classification of structures,
systems and components in NPPs, the IAEA safety guide SSG-39 dealing with the design of
instrumentation and control systems for NPPs, the IAEA safety guide SSG-34 dealing with the
design of electrical power systems for NPPs, the IAEA safety guide SSG-51 dealing with human
factors engineering in the design of NPPs and the implementing guide NSS17 for computer
security at nuclear facilities. The safety and security terminology and definitions used by the
SC 45A standards are consistent with those used by the IAEA.
IEC 61513 and IEC 63046 have adopted a presentation format similar to the basic safety
publication IEC 61508 with an overall life-cycle framework and a system life-cycle framework.
Regarding nuclear safety, IEC 61513 and IEC 63046 provide the interpretation of the general
requirements of IEC 61508-1, IEC 61508-2 and IEC 61508-4, for the nuclear application sector.
In this framework, IEC 60880, IEC 62138 and IEC 62566 correspond to IEC 61508-3 for the
nuclear application sector.
IEC 61513 and IEC 63046 refer to ISO 9001 as well as to IAEA GSR part 2 and IAEA GS-G-3.1
and IAEA GS-G-3.5 for topics related to quality assurance (QA).
At level 2, regarding nuclear security, IEC 62645 is the entry document for the IEC/SC 45A
security standards. It builds upon the valid high level principles and main concepts of the
generic security standards, in particular ISO/IEC 27001 and ISO/IEC 27002; it adapts them and
completes them to fit the nuclear context and coordinates with the IEC 62443 series. At level 2,
IEC 60964 is the entry document for the IEC/SC 45A control rooms standards, IEC 63351 is the
entry document for the human factors engineering standards and IEC 62342 is the entry
document for the ageing management standards.
NOTE 1 It is assumed that for the design of I&C systems in NPPs that implement conventional safety functions (e.g.
to address worker safety, asset protection, chemical hazards, process energy hazards) international or national
standards would be applied.
NOTE 2 IEC TR 64000 provides a more comprehensive description of the overall structure of the IEC SC 45A
standards series and of its relationship with other standards bodies and standards.

– 10 – IEC/IEEE 62582-4:2022 RLV
© IEC/IEEE 2022
NUCLEAR POWER PLANTS – INSTRUMENTATION AND CONTROL
IMPORTANT TO SAFETY – ELECTRICAL EQUIPMENT
CONDITION MONITORING METHODS –

Part 4: Oxidation induction techniques

1 Scope and object
This part of IEC/IEEE 62582 specifies methods for condition monitoring of organic and
polymeric materials in instrumentation and control systems using oxidation induction techniques
in the detail necessary to produce accurate and reproducible measurements. It includes the
requirements for sample preparation, the measurement system and conditions, and the
reporting of the measurement results.
The different parts of IEC/IEEE 62582 are measurement standards, primarily for use in the
management of ageing in initial qualification and after installation. IEC/IEEE 62582-1 includes
requirements for the application of the other parts of the IEC/IEEE 62582 series and some
elements which are common to all methods. Information on the role of condition monitoring in
the qualification of equipment important to safety is found in IEEE Std 323 IEC/IEEE 60780-
323.
2 Normative references
There are no normative references in this document.
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO, IEC and IEEE 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
• IEEE Standards Dictionary Online: available at http://dictionary.ieee.org
3.1
Oxidation induction time
OIT
relative measure of a stabilised material’s resistance to oxidative decomposition, determined
by the calorimetric measurement of the time interval to the onset of exothermic oxidation of the
material at a specified temperature in an oxygen atmosphere, under atmospheric pressure
Note 1 to entry: OIT is expressed in minutes (min).
3.2
Oxidation induction temperature
OITP
calorimetric measurement of the temperature of the onset of exothermic oxidation of the
material when subjected to a specified heating rate in an oxygen atmosphere, under
atmospheric pressure
Note 1 to entry: OITP is expressed in degrees Celsius (°C).

© IEC/IEEE 2022
4 Abbreviated terms and acronyms
CSPE chlorosulphonated polyethylene
DSC differential scanning calorimeter
EPDM ethylene propylene diene monomer
EPR ethylene propylene rubber
EVA ethylene vinyl acetate
OIT oxidation induction time
OITP oxidation induction temperature
PE polyethylene
PEEK poly ether ether ketone
PVC poly vinyl chloride
STA simultaneous thermal analyzer
XLPE cross-linked polyethylene
5 General description
Oxidation induction methods are based on the detection of the oxidation exotherm that occurs
when a sample is heated in the presence of oxygen. This exotherm is sensitive to the level of
degradation in some organic and polymeric materials and can be used as an indicator of ageing.
There are two oxidation induction methods available, based on the time required to reach the
onset of oxidation at a constant temperature (oxidation induction time – OIT) or based on the
temperature at the onset of oxidation during a constant temperature ramp rate (oxidation
induction temperature – OITP). The two methods are complementary, in that OITP is often
effective in those materials where OIT is difficult to determine. OIT and OITP decrease with
increasing degradation. The methods are generally related to the amount of antioxidants
present in the material. As degradation proceeds, these antioxidants are depleted. For material
without antioxidants OIT is not suitable, but OITP may give a useful result. In general, OIT and
OITP are used to measure the thermal stability of polymers under isothermal (OIT) and dynamic
(OITP) heating conditions in oxygen.
6 Applicability and reproducibility
The oxidation induction method is primarily suited to samples taken from materials (such as
cable jackets or insulation) that are polyolefin-based (e.g. PE, XLPE). It can also be used for
some materials based on ethylene-propylene polymers (e.g. EPR, EPDM) and for some
ethylene vinyl acetate (EVA) materials. Oxidation Induction techniques may not be applicable
to high temperature polymers in some cases. It is not applicable to high temperature polymers,
such asPEEK. The method can be applied to other materials but problems with interpretation
of the results may reduce the effectiveness of the test.
The method is generally not suitable for chlorinated polymers (e.g. PVC, CSPE) because of the
corrosive degradation products evolved during the measurements, which can damage the
instrument. For these materials, smaller sample masses (1 mg to 2 mg) may enable the method
to be used with care. In addition, some modern systems are designed with features that protect
the equipment from volatile off gases. To determine if the equipment is protected or if additional
protective components are needed, consult the equipment manufacturer.
The method is not suitable for field use in the nuclear power plant but uses samples taken from
the plant, which are then measured in the laboratory. Each OIT measurement in the laboratory
can take up to 90 min to complete for unaged samples, decreasing for heavily aged samples,
whereas OITP measurements typically take 30 min to 40 min.

– 12 – IEC/IEEE 62582-4:2022 RLV
© IEC/IEEE 2022
Measurements of OIT typically have a standard deviation of 5 % to 10 % of the mean value
whereas measurements of OITP typically have a standard deviation of 1 % to 3 % of the mean
value, both within the same laboratory and between different laboratories. Some of this variation
arises from inhomogeneity of the sample materials, which becomes significant when making
condition measurements on samples whose mass is very low. OITP measurements are usually
more reproducible than OIT measurements but require baseline data for interpretation of the
changes.
7 Measurement procedure
7.1 Stabilisation of the polymeric materials
An appropriate time period shall be allowed for the polymeric materials in recently manufactured
equipment to stabilise before any condition monitoring or accelerated ageing programmes are
carried out. The time period over which the polymeric materials stabilise is normally dependent
on the processing additives and polymer composition. If manufacturers’ stabilisation time data
are not available, a period of 6 months shall be allowed.
7.2 Sampling
7.2.1 General
Measurements of OIT or OITP provide information on the status of the equipment only at the
specific location which has been sampled. The selection of the sample locations for condition
monitoring shall be made based on the environmental conditions in representative areas during
plant operation. It is important that these locations represent as wide a range of ageing
conditions as possible with special consideration given to locations where ageing conditions
could be severe, e.g. hotspots. The location of the sampling and available information about
the environmental time history at the sample location selected shall be documented.
7.2.2 Sample requirements
To enable up to 5 measurements to be made on one specific sample, a minimum of 50 mg of
material is needed. The material to be sampled shall be cleaned of surface debris. No solvents
shall be used to clean the surface. Samples typically may take the form of slivers or scrapings
of material taken from the surface of a cable jacket or a thin slice through insulation at a
termination. The location of the sampling position shall be noted, including its radial distribution
(i.e. whether it is a surface sample or a through thickness slice).
When sampling dual layer materials, e.g. cables, it shall be clear in the report how the samples
have been obtained. The measured value will be dependent on the proportion of each layer
included in the sample tested. For this reason, it is recommended that the layers are not mixed
when technically possible.
Sampling and measurement procedures shall comply with local instructions, taking into account
the safety of personnel and equipment
Care shall be taken to avoid unsuitable conditions in storage during the time period between
sampling and measurements. It is recommended that samples be stored in the dark at
temperatures not exceeding 25 °C and at humidity conditions within 45 % and to 75 %.
7.2.3 Precautions
When taking samples for OIT/OITP in the field, the equipment shall be visually inspected before
and after the sampling in order to document that the equipment is not damaged.
If samples are to be taken from operational equipment in plant, the impact of such sampling on
future operational use and qualification of such equipment shall be evaluated prior to sampling.

© IEC/IEEE 2022
NOTE Where removal of material from operational equipment is considered detrimental to
qualification or future use, the equipment should be removed from service or repaired according
to the utility’s local procedures to ensure that qualification is maintained.
7.3 Sample preparation
Samples for each OIT or OITP measurement shall be in the range 10 mg ± 2 mg in weight
5 mg ± 1 mg in mass. Some older, less sensitive equipment may require the use of larger
samples. In this case, 10 mg ± 1 mg of material should be used for the measurements.
Regardless of which value is used, the mass of the sample in each measurement should be
consistent. Each sample shall be chopped or ground into pieces with max dimensions of 1 mm.
It is recommended that the chopped sample should be screened with a mesh to provide a
particle size not greater than 0,85 mm as consistent sample preparation is important to enable
reproducible oxidation of the sample during measurement. The chopped or granular sample
shall be placed into a sample pan appropriate to the instrument being used and packed to
achieve a good contact to the sample pan.
The sample pans shall be of aluminium, ceramic, or platinum and be open or have lids with
holes or mesh to allow free access for oxygen during the measurement. A minimum of three
samples shall be measured. If the results of measurements on three samples have a standard
deviation > 10 % of the mean value for OIT or > 3 % of the mean value for OITP, an additional
two samples should be measured if sufficient material is available. Out of these five
measurements the highest and lowest will be removed and use the mean value of the remaining
three samples.
NOTE 1 If smaller sample weights mass needs to be used, e.g. for chlorinated materials, this
should be noted in the measurement report.
NOTE 2 If the results of measurements on three samples have a standard deviation >10 % of the mean value for
OIT or >3 % of the mean value for OITP, an additional two samples should be measured.
7.4 Instrumentation
The instrument used for oxidation induction measurements shall be capable of determining
exotherms in the sub-milliwatt range, e.g. a differential scanning calorimeter (DSC),
simultaneous thermal analyzer (STA), or differential thermal analyzer (DTA). It shall be capable
of maintaining an isothermal stability of ± 0,3 °C over the duration of the measurement, typically
up to 90 min. The temperature ramp rate shall be programmable.
The instrument shall allow purging of the sample chamber with specific gases at a controllable
rate. The distance between the gas-switching point and the instrument cell needs to be kept as
short as possible, with a dead time of less than 1 min, to minimise the switching volume.
−1
, the dead volume shall be less than 75 ml.
Accordingly, for a flow rate of 75 ml∙min
For analysis purposes, the difference in heat flow between a reference pan and the sample pan
as a function of time (for OIT measurements) or temperature (for OITP measurements) shall be
measured.
7.5 Calibration
The instrument shall be calibrated according to the manufacturer’s recommendations and the
relevant QA (quality assurance) procedure, using a suitable calibration standard for the
temperature ranges being used (e.g. lead/indium/tin). Measurement of a reference sample shall
be carried out prior to each batch of OIT or OITP measurements to verify this calibration.
7.6 OIT measurement method
7.6.1 Measurement procedure
The measurement procedure is illustrated in Figure 1. It includes the following steps.

– 14 – IEC/IEEE 62582-4:2022 RLV
© IEC/IEEE 2022
−1
• The sample is heated in nitrogen at a rate of temperature rise of 50 °C ∙min until 10 °C
−1
below the set temperature T . The ramp rate is then reduced to 5 °C∙min to reach the
set
set temperature.
• The sample is then held for 2 min at the set temperature in nitrogen after which the
atmosphere in the instrument is switched to oxygen.
• The oxidation exotherm is detected by a rapid increase in heat flow.
• The time from switching the atmosphere to oxygen until the sample starts oxidising is
determined. This time is the oxidation induction time.

Figure 1 – OIT measurement – Schematic of temperature
and gas profile and corresponding heat flow
7.6.2 Temperature profile
The reproducibility of OIT measurements is dependent on using a standardised thermal history.
T for OIT measurements shall be 210 °C, provided that the oxidation induction time for
set
unaged material is at least 30 min. The OIT value is highly dependent on T selected, see
set
example in Annex C. If the OIT is less than 30 min for unaged material, then T shall be
set
© IEC/IEEE 2022
reduced in 10 °C increments until the OIT is > 30 min. If the OIT is > 90 min for unaged material,
then T shall be increased in 10 °C increments until the OIT is < 90 min. Once the value of
set
T has been selected for a specific material, the same value shall be used for all subsequent
set
measurements on that material.
NOTE OIT > 90 min for unaged material is acceptable provided that the heat flow observed during the oxidation
exotherm is sufficient to exceed the required threshold value (see 7.6.4.2).
7.6.3 Gas flow
−1 −1
The flow rate for oxygen during OIT tests shall be 75 ml∙min ± 25 ml∙min . The flow rate for
nitrogen during the initial phase of OIT tests is not critical but it is recommended that
−1 −1
75 ml∙min ± 25 ml∙min be used.
NOTE Oxidation induction measurements can be affected by the oxygen flow rate used during the tests. For low
−1
flow rates (< 50 ml∙min ), this can result in increased induction times in OIT tests. For the range of flow rates from
−1 −1
50 ml∙min to 100 ml∙min , oxidation induction times are not strongly dependent on the oxygen flow rate.
7.6.4 Determining the value of oxidation onset
7.6.4.1 Definition of the baseline
The threshold for oxidation induction is measured relative to a baseline, as shown in Figure 2.
There will usually be a period of constant heat flow p
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