IEC 60426:2007
(Main)Electrical insulating materials - Determination of electrolytic corrosion caused by insulating materials - Test methods
Electrical insulating materials - Determination of electrolytic corrosion caused by insulating materials - Test methods
IEC 60426:2007 determines the ability of insulating materials to produce electrolytic corrosion on metals being in contact with them under the influence of electric stress, high humidity and elevated temperature. The effect of electrolytic corrosion is assessed in one test by using consecutively two methods:
- visual semi-quantitative method consisting in comparing visually the corrosion appearing on the anode and cathode metal strips, with those given in the reference figures. This method consists of the direct visual assessment of the degree of corrosion of two copper strips, acting as anode and cathode respectively, placed in contact with the tested insulating material under a d.c. potential difference at specified environmental conditions. The degree of corrosion is assessed by visually comparing the corrosion marks on the anode and cathode metal strips with those shown in the reference figures;
- quantitative method, which involves the tensile strength measurement, carried out on the same anode and cathode metal strips after visual inspection.
An additional quantitative test method for determining electrolytic corrosion, which involves tensile strength measurement of copper wire, is described in the informative Annex C.
Matériaux isolants électriques - Détermination de la corrosion électrolytique en présence de matériaux isolants - Méthodes d'essais
La CEI 60426:2007 détermine la capacité des matériaux isolants à produire une corrosion électrolytique sur des métaux en contact avec eux, sous l'influence de contraintes électriques, d'une forte humidité et de températures élevées. L'effet de la corrosion électrolytique est apprécié d'après un seul essai, en utilisant successivement les deux méthodes suivantes:
- une méthode visuelle semi-quantitative qui consiste à comparer visuellement la corrosion qui apparaît sur les bandes métalliques pour l'anode et la cathode, à celles des figures de référence. Cette méthode consiste en l'appréciation visuelle directe du degré de corrosion de deux lames de cuivre, servant respectivement d'anode et de cathode, mises en contact avec le matériau isolant en essai et soumises dans des conditions d'environnement spécifiées à une différence de potentiel en courant continu. Le degré de corrosion est évalué en comparant visuellement les marques de corrosion constatées sur les bandes métalliques anode et cathode, à celles des figures de référence;
- une méthode quantitative, qui met en jeu des mesures de résistance à la traction, effectuées sur les mêmes bandes métalliques pour l'anode et la cathode, après inspection visuelle.
Une méthode d'essai quantitative supplémentaire en vue de déterminer la corrosion électrolytique, qui met en jeu des mesures de la résistance à la traction de fils de cuivre, est décrite dans l'Annexe informative C.
General Information
Standards Content (Sample)
INTERNATIONAL IEC
STANDARD 60426
Second edition
2007-01
Electrical insulating materials –
Determination of electrolytic corrosion
caused by insulating materials –
Test methods
Reference number
Publication numbering
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60000 series. For example, IEC 34-1 is now referred to as IEC 60034-1.
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INTERNATIONAL IEC
STANDARD 60426
Second edition
2007-01
Electrical insulating materials –
Determination of electrolytic corrosion
caused by insulating materials –
Test methods
© IEC 2007 ⎯ Copyright - all rights reserved
No part of this publication may be reproduced or utilized in any form or by any means, electronic or
mechanical, including photocopying and microfilm, without permission in writing from the publisher.
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Telephone: +41 22 919 02 11 Telefax: +41 22 919 03 00 E-mail: inmail@iec.ch Web: www.iec.ch
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– 2 – 60426 © IEC:2007(E)
CONTENTS
FOREWORD.4
INTRODUCTION.6
1 Scope.7
2 Normative references .7
3 Terms and definitions .7
4 General description of the test method .8
5 Test specimens .8
5.1 General .8
5.2 Cut surfaces of rigid materials (blocks, plates, sheets or semi-finished
materials) .9
5.3 Cast, moulding, injection and pressed materials .9
5.4 Cut surfaces of flexible films, foils and thin sheets.9
5.5 Adhesive tapes.10
5.6 Flexible sleeving and tubing .10
5.7 Lacquers and insulating varnishes.10
5.8 Cleanliness of contact surfaces .10
5.9 Number of test specimens .11
6 Test strips .11
6.1 General .11
6.2 Preparation of the test strips .11
6.3 Cleanliness of test strips .12
7 Test device.12
8 Test conditions .14
9 Test procedure .14
10 Evaluation .14
10.1 General evaluation .14
10.2 Visual inspection of the test strips .15
10.3 Tensile strength of test strips .15
11 Evaluation of corrosion on copper strips .16
12 Test report.17
Annex A (normative) Tables for the evaluation of corrosion on brass and aluminium
strips .18
Annex B (informative) Notes on visual evaluation .20
Annex C (informative) Copper wire tensile strength method .21
Figure 1 – Test specimen of rigid material, for example textile laminate.8
Figure 2 – Test specimen of flexible material, for example flexible films, foils etc.10
Figure 3 – Test strip.12
Figure 4 – Test device for determining electrolytic corrosion.13
Figure C.1 – Apparatus for determining electrolytic corrosion of rigid insulating material .23
Figure C.2 – Apparatus for determining electrolytic corrosion of flexible insulating material .23
60426 © IEC:2007(E) – 3 –
Table 1 – Degrees of corrosion of copper strips .16
Table A.1 – Degrees of corrosion of brass strips.18
Table A.2 – Degrees of corrosion of aluminium strips .19
– 4 – 60426 © IEC:2007(E)
INTERNATIONAL ELECTROTECHNICAL COMMISSION
___________
ELECTRICAL INSULATING MATERIALS −
DETERMINATION OF ELECTROLYTIC CORROSION CAUSED BY
INSULATING MATERIALS −
TEST METHODS
FOREWORD
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International Standard IEC 60426 has been prepared by IEC technical committee 112:
Evaluation and qualification of electrical insulating materials and systems.
This second edition cancels and replaces the first edition, published in 1973, and constitutes
a technical revision.
The main changes with respect to the previous edition are listed below:
• experience has indicated the need for improved description of the experimental method. It
describes a revised procedure for the visual and tensile strength test method that
overcomes the limitations of the first edition;
• one older method of the first edition has partly been maintained in the informative annex.
60426 © IEC:2007(E) – 5 –
The text of this standard is based on the following documents:
FDIS Report on voting
112/45/FDIS 112/55/RVD
Full information on the voting for the approval of this standard can be found in the report on
voting indicated in the above table.
This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.
A bilingual version of this publication may be issued at a later date.
The committee has decided that the contents of this publication will remain unchanged until
the maintenance result 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.
– 6 – 60426 © IEC:2007(E)
INTRODUCTION
Electrical insulating materials at high atmospheric humidity and under influence of electric
stress may cause corrosion of metal parts being in contact with them. Such electrolytic
corrosion is dependent upon the composition of the insulating material and the character of
the metal; it is influenced by temperature, relative humidity, nature of the voltage and the time
of exposure. Direct voltage produces much more rapid and extensive corrosion than alterna-
ting voltage. Corrosion is more pronounced at the positive electrode.
Not only copper but also most other metals, except the noble metals such as platinum or gold,
are subject to electrolytic corrosion. Electrolytic corrosion, however, is usually determined
with insulating materials in contact with copper, brass or aluminium. Copper, however, is a
basic metal and most frequently used in electrotechnical, teletechnical and electronic
equipment, especially for current conducting parts and therefore it was chosen as a basic test
metal. Other metals may be used when needed for special purposes, but the results may
differ from those described in this method.
Electrolytic corrosion may cause open-circuit failure in electrical conductors and devices. It
may promote low resistance leakage path across or through electrical insulation and the
products of corrosion may otherwise interfere with the operation of electrical devices, i.e. may
prevent operation of contacts, etc.
Electronic equipment operating under conditions of high humidity and elevated temperature
may be particularly subjected to failure from electrolytic corrosion. Therefore, the selection of
insulating materials, which do not produce electrolytic corrosion, is important for such
applications.
The test method described in this second edition replaces two separate methods of the first
edition – visual and tensile strength method. The former tensile strength method of the first
edition, using copper wires, has been maintained in an informative annex. It must be
emphasized that the advantage of this new method is that the same strip used for visual
inspection is next used for the tensile strength test in opposite to the method described in the
first edition. Therefore the correlation between tensile strength and visual examination is more
obvious.
60426 © IEC:2007(E) – 7 –
ELECTRICAL INSULATING MATERIALS −
DETERMINATION OF ELECTROLYTIC CORROSION CAUSED BY
INSULATING MATERIALS −
TEST METHODS
1 Scope
This standard determines the ability of insulating materials to produce electrolytic corrosion
on metals being in contact with them under the influence of electric stress, high humidity and
elevated temperature.
The effect of electrolytic corrosion is assessed in one test by using consecutively two
methods:
• visual semi-quantitative method consisting in comparing visually the corrosion appearing
on the anode and cathode metal strips, with those given in the reference figures.
This method consists of the direct visual assessment of the degree of corrosion of two
copper strips, acting as anode and cathode respectively, placed in contact with the tested
insulating material under a d.c. potential difference at specified environmental conditions.
The degree of corrosion is assessed by visually comparing the corrosion marks on the
anode and cathode metal strips with those shown in the reference figures;
• quantitative method, which involves the tensile strength measurement, carried out on the
same anode and cathode metal strips after visual inspection.
An additional quantitative test method for determining electrolytic corrosion, which involves
tensile strength measurement of copper wire, is described in the informative Annex C.
2 Normative references
The following referenced documents are indispensable for the application of this document.
For dated references, only the edition cited applies. For undated references, the latest edition
of the referenced document (including any amendments) applies.
IEC 60068-3-4:2001, Environmental testing – Part 3-4: Supporting documentation and
guidance – Damp heat tests
IEC 60454-2:⎯, Pressure-sensitive adhesive tapes for electrical purposes – Part 2: Methods
of test
3 Terms and definitions
For the purposes of this document the following terms and definitions apply:
3.1
electrolytic corrosion
kind of galvanic corrosion caused by joint action of external source of d.c. potential and some
substances included in some organic materials in presence of high humidity and elevated
temperature
—————————
To be published
– 8 – 60426 © IEC:2007(E)
3.2
test strip
a) positive
a metal strip connected with positive pole of direct current source which forms the anode
in the contact system: metal – insulating material
b) negative
a metal strip connected with negative pole of direct current source which forms the
cathode in the contact system: metal – insulating material
3.3
surface of contact
a) of tested material
part of insulating material specimen which is in direct contact with metal strips
b) of metal strip
part of metal strip (positive or negative) which is in direct contact with insulating material
specimen
4 General description of the test method
The test consists of applying specified environmental conditions and a d.c. potential
difference to two parallel copper strips 3 mm apart, acting as the anode and the cathode
respectively. The insulating material under test (test specimen) is placed across these two
strips. In order to obtain a good and uniform contact between the metal strips and the material
under test, the test specimen is pressed to the strips by a cylindrical loading tube.
5 Test specimens
5.1 General
The preparation of the specimens depends on the type of material and the form in which it is
supplied. The shape and dimensions of the test specimen are shown in Figure 1. Procedures
for the preparation of the test specimen are reported beneath (5.2 to 5.7).
Dimensions in millimetres
Surface of contact
4,0 ± 0,1
40 ± 1
IEC 122/07
Figure 1 – Test specimen of rigid material, for example textile laminate
10,0 ± 0,5
60426 © IEC:2007(E) – 9 –
5.2 Cut surfaces of rigid materials (blocks, plates, sheets or semi-finished materials)
The test specimens shall be cut out or machined from the tested material to a thickness of
4 mm, by means of a dry method without the use of cutting oils or lubricants and without
overheating or damaging them. It is recommended to take several test specimens from
various layers of the product.
It is permissible to use the test specimens of thickness smaller than 4 mm, but not smaller
than 2 mm.
The contact surface of the test specimen shall be smoothed using abrasive paper. Care
should be taken to keep parallelism of the opposite surfaces of the test specimen, in order to
assure a good contact of the test specimen to the metal strips. The surface of contact should
not show any flaws, cracks, inclusions or bubbles.
The abrasive paper shall not contain any contaminations causing a bad corrosion index, for
example halogen components.
5.3 Cast, moulding, injection and pressed materials
From insulating materials delivered in the form of liquid resin, moulding powder or granules,
the test specimens shall be made in shapes and dimensions as shown in Figure 1. The
specimens shall be made by casting or pressing in a special mould, following exactly the
technological instruction recommended by the manufacturer of the tested material.
The test specimen and surface of contact shall be prepared as given in 5.2.
5.4 Cut surfaces of flexible films, foils and thin sheets
Test specimens of these products shall be made up in layers to form small packs placed
between suitable holding plates of insulating material not causing electrolytic corrosion itself,
for example polymethylmethacrylate (Plexiglas® ). The preferred thickness of holding plates
is 1 mm ± 0,2 mm.
The thickness of a pack should be approximately of 4 mm or 2 mm, depending on the
thickness of the tested foils. The value of 4 mm is recommended in the case of the single foil
thickness being less than 2 mm and more than 0,5 mm, whereas that one of 2 mm is
recommended if the single foil thickness is less than 0,5 mm.
These test blocks shall be compressed with screws made of the same material as holding
plates and then machined to the appropriate shape as shown in Figure 2. The material to be
tested should protrude 0,2 mm to 0,5 mm beyond the holding plates.
—————————
Plexiglas® is an example of a suitable product available commercially. This information is given for the
convenience of users of this document and does not constitute an endorsement by IEC of this product.
– 10 – 60426 © IEC:2007(E)
Dimensions in millimetres
Holding plates
Surface of contact
1,0 ± 0,2
2 or 4
40 ± 1
IEC 123/07
Figure 2 – Test specimen of flexible material, for example flexible films, foils etc.
Apart from this, the particulars given in 5.2 apply.
5.5 Adhesive tapes
For adhesive tapes the method of Clause 7 of IEC 60454-2 is recommended.
5.6 Flexible sleeving and tubing
Sleeving and tubing (both varnished fabric and extruded) are slit open, so as to make flat
sheets, which can then be prepared as for films (see 5.4).
5.7 Lacquers and insulating varnishes
The lacquer or insulating varnish to be tested shall be applied in the manner recommended by
the manufacturer to the surface of a test specimen of shape as shown in Figure 1 and
described in 5.2. The base material of the test specimen shall be a corrosion free plastic such
as polymethylmethacrylate.
In case of solvent incompatibility or a baking temperature being too high for the base material,
another suitable base material such as cast, hot cured corrosion free epoxy resin or glass
shall be used. If the lacquer or insulating varnish is designed to contribute freedom from
corrosion to another material, a test specimen of that material shall be used.
The tested lacquer or varnish shall be sprayed, dipped or otherwise coated to the desired
thickness and baked, if necessary, as specified or according to the directions of the
manufacturer.
If the thickness of coating is not determined by specification or direction of the manufacturer,
it shall be of (30 ± 10) μm.
5.8 Cleanliness of contact surfaces
When preparing and handling the test specimens, any soiling of the test surfaces, for example
by perspiration from the hands, shall be avoided. The specimens shall be touched only with a
pair of tweezers or with protecting gloves made of materials free from corrosion (e.g.
polyethylene). After the test specimens have been machined or cut, their surfaces shall be
cleaned with a soft brush. Before cleaning, the brush shall be rinsed in ethanol (96 %) and
then dried.
10,0 ± 0,5
0,2 to 0,5
60426 © IEC:2007(E) – 11 –
After the cleaning procedure, the surface of contact shall not show any foreign particles,
residues of oil or grease, no mould residues, etc.
5.9 Number of test specimens
At least five test specimens made from the same material shall be tested at the same time.
A specific sampling procedure may be desired. If necessary, such a sampling procedure
should be specified and used.
6 Test strips
6.1 General
The test strips shall be made of 0,1 mm thick, semi-hard copper of purity 99,9 Cu. Their
dimensions are 10 mm wide and 200 mm long. The test strips shall be flat, without bends and
burrs at the edges as well as any other mechanical defects or impurities on the test surface,
which may have influence on the test results.
NOTE Test strips of brass or aluminium can be made in the same way.
6.2 Preparation of the test strips
From each new reel of strip (sold as a semi-finished product) the first several decimetres of
the strip shall be rejected and then the suitable number of strip segments, each 200 mm long,
shall be cut-off.
Copper strips shall be degreased with a low boiling point organic solvent (e.g. acetone or
hexane) and then etched. Etching shall be carried out at laboratory temperature, with a
solution of the following composition: sulphuric acid (1,82) with a mass fraction of 73 %, nitric
acid (1,33) with a mass fraction of 26 %, sodium chloride with a mass fraction of 0,5 % and
hard carbon black with a mass fraction of 0,5 %. The time of etching shall be between 20 s to
60 s. All strips, which are destined for one set of testing, shall be etched at the same time.
The coarseness of the strip surface can be controlled by adjustment of the etching time until
the copper strip has an even dull sheen. The strips shall then be washed in distilled water,
then dipped in ethanol and dried with blotting paper.
NOTE Unevenness of the surface of the strip may influence the discolouration and may lead to a wrong
evaluation. A surface, which is evenly dull, shows a discolouration of greater intensity than a surface, which is
slightly corroded, semi-dull or brilliant.
After degreasing and etching, both ends of the strip shall be reeled loose to the shape as
shown in Figure 3.
So prepared test strips shall be immediately (within 20 min) mounted in the test device, ready
for the test procedure, as shown in Figure 4.
– 12 – 60426 © IEC:2007(E)
Dimensions in millimetres
25 ± 2
IEC 124/07
Figure 3 – Test strip
6.3 Cleanliness of test strips
After degreasing and etching, the strips should not be touched with bare hands. When
handling the strips, a pair of tweezers should be used and the reeling of the ends of the test
strip should be done using protective gloves.
7 Test device
The test device shall be made of materials not causing corrosion, for example of
polymethylmethacrylate (Plexiglas® ). The test device shall enable simultaneous testing of
all test specimens processed from one batch of insulating material (no less than five
specimens).
The pressure of the test specimen onto the test strips shall be 10 N/cm . The pressure is
achieved by setting a cylindrical tube (made from materials not causing corrosion) on the test
specimen and filled with the appropriate amount of lead shot, to assure the desired pressure.
The recommended test device is shown in Figure 4.
—————————
Plexiglas® is an example of a suitable product available commercially. This information is given for the
convenience of users of this document and does not constitute an endorsement by IEC of this product.
∼5
60426 © IEC:2007(E) – 13 –
+ – – +
Detail A Detail A
Side view Front view
+ –
Detail A Detail A
Side view Front view
1 cylindrical tubes (loading tubes) 2 supporting frame
3 test specimens (insulatin material) 4 metal test strips
5 connecting terminals 6 copper electrodes
IEC 125/07
Figure 4 – Test device for determining electrolytic corrosion
Before beginning each test a
...
IEC 60426 ®
Edition 2.0 2007-01
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Electrical insulating materials – Determination of electrolytic corrosion caused
by insulating materials – Test methods
Matériaux isolants électriques – Détermination de la corrosion électrolytique en
présence de matériaux isolants – Méthodes d’essais
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IEC 60426 ®
Edition 2.0 2007-01
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Electrical insulating materials – Determination of electrolytic corrosion caused
by insulating materials – Test methods
Matériaux isolants électriques – Détermination de la corrosion électrolytique en
présence de matériaux isolants – Méthodes d’essais
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
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U
CODE PRIX
ICS 17.220.99; 29.035.01 ISBN 978-2-88910-192-4
– 2 – 60426 © IEC:2007
CONTENTS
FOREWORD.4
INTRODUCTION.6
1 Scope.7
2 Normative references .7
3 Terms and definitions .7
4 General description of the test method .8
5 Test specimens .8
5.1 General .8
5.2 Cut surfaces of rigid materials (blocks, plates, sheets or semi-finished
materials) .9
5.3 Cast, moulding, injection and pressed materials .9
5.4 Cut surfaces of flexible films, foils and thin sheets.9
5.5 Adhesive tapes.10
5.6 Flexible sleeving and tubing .10
5.7 Lacquers and insulating varnishes.10
5.8 Cleanliness of contact surfaces .10
5.9 Number of test specimens .11
6 Test strips .11
6.1 General .11
6.2 Preparation of the test strips .11
6.3 Cleanliness of test strips .12
7 Test device.12
8 Test conditions .14
9 Test procedure .14
10 Evaluation .14
10.1 General evaluation .14
10.2 Visual inspection of the test strips .15
10.3 Tensile strength of test strips .15
11 Evaluation of corrosion on copper strips .16
12 Test report.17
Annex A (normative) Tables for the evaluation of corrosion on brass and aluminium
strips .18
Annex B (informative) Notes on visual evaluation .20
Annex C (informative) Copper wire tensile strength method .21
Figure 1 – Test specimen of rigid material, for example textile laminate.8
Figure 2 – Test specimen of flexible material, for example flexible films, foils etc.10
Figure 3 – Test strip.12
Figure 4 – Test device for determining electrolytic corrosion.13
Figure C.1 – Apparatus for determining electrolytic corrosion of rigid insulating material .23
Figure C.2 – Apparatus for determining electrolytic corrosion of flexible insulating material .23
60426 © IEC:2007 – 3 –
Table 1 – Degrees of corrosion of copper strips .16
Table A.1 – Degrees of corrosion of brass strips.18
Table A.2 – Degrees of corrosion of aluminium strips .19
– 4 – 60426 © IEC:2007
INTERNATIONAL ELECTROTECHNICAL COMMISSION
___________
ELECTRICAL INSULATING MATERIALS –
DETERMINATION OF ELECTROLYTIC CORROSION
CAUSED BY INSULATING MATERIALS –
TEST METHODS
FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
all national electrotechnical committees (IEC National Committees). The object of IEC is to promote
international co-operation on all questions concerning standardization in the electrical and electronic fields. To
this end and in addition to other activities, IEC publishes International Standards, Technical Specifications,
Technical Reports, Publicly Available Specifications (PAS) and Guides (hereafter referred to as “IEC
Publication(s)”). Their preparation is entrusted to technical committees; any IEC National Committee interested
in the subject dealt with may participate in this preparatory work. International, governmental and non-
governmental organizations liaising with the IEC also participate in this preparation. IEC collaborates closely
with the International Organization for Standardization (ISO) in accordance with conditions determined by
agreement between the two organizations.
2) The formal decisions or agreements of IEC on technical matters express, as nearly as possible, an international
consensus of opinion on the relevant subjects since each technical committee has representation from all
interested IEC National Committees.
3) IEC Publications have the form of recommendations for international use and are accepted by IEC National
Committees in that sense. While all reasonable efforts are made to ensure that the technical content of IEC
Publications is accurate, IEC cannot be held responsible for the way in which they are used or for any
misinterpretation by any end user.
4) In order to promote international uniformity, IEC National Committees undertake to apply IEC Publications
transparently to the maximum extent possible in their national and regional publications. Any divergence
between any IEC Publication and the corresponding national or regional publication shall be clearly indicated in
the latter.
5) IEC itself does not provide any attestation of conformity. Independent certification bodies provide conformity
assessment services and, in some areas, access to IEC marks of conformity. IEC is not responsible for any
services carried out by independent certification bodies.
6) All users should ensure that they have the latest edition of this publication.
7) No liability shall attach to IEC or its directors, employees, servants or agents including individual experts and
members of its technical committees and IEC National Committees for any personal injury, property damage or
other damage of any nature whatsoever, whether direct or indirect, or for costs (including legal fees) and
expenses arising out of the publication, use of, or reliance upon, this IEC Publication or any other IEC
Publications.
8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
indispensable for the correct application of this publication.
9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of
patent rights. IEC shall not be held responsible for identifying any or all such patent rights.
International Standard IEC 60426 has been prepared by IEC technical committee 112:
Evaluation and qualification of electrical insulating materials and systems.
This second edition cancels and replaces the first edition, published in 1973, and constitutes
a technical revision.
The main changes with respect to the previous edition are listed below:
• experience has indicated the need for improved description of the experimental method. It
describes a revised procedure for the visual and tensile strength test method that
overcomes the limitations of the first edition;
• one older method of the first edition has partly been maintained in the informative annex.
60426 © IEC:2007 – 5 –
This bilingual version, published in 2010-01, corresponds to the English version.
The text of this standard is based on the following documents:
FDIS Report on voting
112/45/FDIS 112/55/RVD
Full information on the voting for the approval of this standard can be found in the report on
voting indicated in the above table.
The French version of this standard has not been voted upon.
This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.
The committee has decided that the contents of this publication will remain unchanged until
the maintenance result 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.
– 6 – 60426 © IEC:2007
INTRODUCTION
Electrical insulating materials at high atmospheric humidity and under influence of electric
stress may cause corrosion of metal parts being in contact with them. Such electrolytic
corrosion is dependent upon the composition of the insulating material and the character of
the metal; it is influenced by temperature, relative humidity, nature of the voltage and the time
of exposure. Direct voltage produces much more rapid and extensive corrosion than alterna-
ting voltage. Corrosion is more pronounced at the positive electrode.
Not only copper but also most other metals, except the noble metals such as platinum or gold,
are subject to electrolytic corrosion. Electrolytic corrosion, however, is usually determined
with insulating materials in contact with copper, brass or aluminium. Copper, however, is a
basic metal and most frequently used in electrotechnical, teletechnical and electronic
equipment, especially for current conducting parts and therefore it was chosen as a basic test
metal. Other metals may be used when needed for special purposes, but the results may
differ from those described in this method.
Electrolytic corrosion may cause open-circuit failure in electrical conductors and devices. It
may promote low resistance leakage path across or through electrical insulation and the
products of corrosion may otherwise interfere with the operation of electrical devices, i.e. may
prevent operation of contacts, etc.
Electronic equipment operating under conditions of high humidity and elevated temperature
may be particularly subjected to failure from electrolytic corrosion. Therefore, the selection of
insulating materials, which do not produce electrolytic corrosion, is important for such
applications.
The test method described in this second edition replaces two separate methods of the first
edition – visual and tensile strength method. The former tensile strength method of the first
edition, using copper wires, has been maintained in an informative annex. It must be
emphasized that the advantage of this new method is that the same strip used for visual
inspection is next used for the tensile strength test in opposite to the method described in the
first edition. Therefore the correlation between tensile strength and visual examination is more
obvious.
60426 © IEC:2007 – 7 –
ELECTRICAL INSULATING MATERIALS –
DETERMINATION OF ELECTROLYTIC CORROSION
CAUSED BY INSULATING MATERIALS –
TEST METHODS
1 Scope
This standard determines the ability of insulating materials to produce electrolytic corrosion
on metals being in contact with them under the influence of electric stress, high humidity and
elevated temperature.
The effect of electrolytic corrosion is assessed in one test by using consecutively two
methods:
• visual semi-quantitative method consisting in comparing visually the corrosion appearing
on the anode and cathode metal strips, with those given in the reference figures.
This method consists of the direct visual assessment of the degree of corrosion of two
copper strips, acting as anode and cathode respectively, placed in contact with the tested
insulating material under a d.c. potential difference at specified environmental conditions.
The degree of corrosion is assessed by visually comparing the corrosion marks on the
anode and cathode metal strips with those shown in the reference figures;
• quantitative method, which involves the tensile strength measurement, carried out on the
same anode and cathode metal strips after visual inspection.
An additional quantitative test method for determining electrolytic corrosion, which involves
tensile strength measurement of copper wire, is described in the informative Annex C.
2 Normative references
The following referenced documents are indispensable for the application of this document.
For dated references, only the edition cited applies. For undated references, the latest edition
of the referenced document (including any amendments) applies.
IEC 60068-3-4:2001, Environmental testing – Part 3-4: Supporting documentation and
guidance – Damp heat tests
IEC 60454-2:⎯, Pressure-sensitive adhesive tapes for electrical purposes – Part 2: Methods
of test
3 Terms and definitions
For the purposes of this document the following terms and definitions apply.
3.1
electrolytic corrosion
kind of galvanic corrosion caused by joint action of external source of d.c. potential and some
substances included in some organic materials in presence of high humidity and elevated
temperature
—————————
To be published.
– 8 – 60426 © IEC:2007
3.2
test strip
a) positive
a metal strip connected with positive pole of direct current source which forms the anode
in the contact system: metal – insulating material
b) negative
a metal strip connected with negative pole of direct current source which forms the
cathode in the contact system: metal – insulating material
3.3
surface of contact
a) of tested material
part of insulating material specimen which is in direct contact with metal strips
b) of metal strip
part of metal strip (positive or negative) which is in direct contact with insulating material
specimen
4 General description of the test method
The test consists of applying specified environmental conditions and a d.c. potential
difference to two parallel copper strips 3 mm apart, acting as the anode and the cathode
respectively. The insulating material under test (test specimen) is placed across these two
strips. In order to obtain a good and uniform contact between the metal strips and the material
under test, the test specimen is pressed to the strips by a cylindrical loading tube.
5 Test specimens
5.1 General
The preparation of the specimens depends on the type of material and the form in which it is
supplied. The shape and dimensions of the test specimen are shown in Figure 1. Procedures
for the preparation of the test specimen are reported beneath (5.2 to 5.7).
Dimensions in millimetres
Surface of contact
4,0 ± 0,1
40 ± 1
IEC 122/07
Figure 1 – Test specimen of rigid material, for example textile laminate
10,0 ± 0,5
60426 © IEC:2007 – 9 –
5.2 Cut surfaces of rigid materials (blocks, plates, sheets or semi-finished materials)
The test specimens shall be cut out or machined from the tested material to a thickness of
4 mm, by means of a dry method without the use of cutting oils or lubricants and without
overheating or damaging them. It is recommended to take several test specimens from
various layers of the product.
It is permissible to use the test specimens of thickness smaller than 4 mm, but not smaller
than 2 mm.
The contact surface of the test specimen shall be smoothed using abrasive paper. Care
should be taken to keep parallelism of the opposite surfaces of the test specimen, in order to
assure a good contact of the test specimen to the metal strips. The surface of contact should
not show any flaws, cracks, inclusions or bubbles.
The abrasive paper shall not contain any contaminations causing a bad corrosion index, for
example halogen components.
5.3 Cast, moulding, injection and pressed materials
From insulating materials delivered in the form of liquid resin, moulding powder or granules,
the test specimens shall be made in shapes and dimensions as shown in Figure 1. The
specimens shall be made by casting or pressing in a special mould, following exactly the
technological instruction recommended by the manufacturer of the tested material.
The test specimen and surface of contact shall be prepared as given in 5. 2 .
5.4 Cut surfaces of flexible films, foils and thin sheets
Test specimens of these products shall be made up in layers to form small packs placed
between suitable holding plates of insulating material not causing electrolytic corrosion itself,
for example polymethylmethacrylate (Plexiglas® ). The preferred thickness of holding plates
is 1 mm ± 0,2 mm.
The thickness of a pack should be approximately of 4 mm or 2 mm, depending on the
thickness of the tested foils. The value of 4 mm is recommended in the case of the single foil
thickness being less than 2 mm and more than 0,5 mm, whereas that one of 2 mm is
recommended if the single foil thickness is less than 0,5 mm.
These test blocks shall be compressed with screws made of the same material as holding
plates and then machined to the appropriate shape as shown in Figure 2. The material to be
tested should protrude 0,2 mm to 0,5 mm beyond the holding plates.
—————————
Plexiglas® is an example of a suitable product available commercially. This information is given for the
convenience of users of this document and does not constitute an endorsement by IEC of this product.
– 10 – 60426 © IEC:2007
Dimensions in millimetres
Holding plates
Surface of contact
1,0 ± 0,2
2 or 4
40 ± 1
IEC 123/07
Figure 2 – Test specimen of flexible material, for example flexible films, foils etc.
Apart from this, the particulars given in 5 . 2 a ppl y.
5.5 Adhesive tapes
For adhesive tapes the method of Clause 7 of IEC 60454-2 is recommended.
5.6 Flexible sleeving and tubing
Sleeving and tubing (both varnished fabric and extruded) are slit open, so as to make flat
sheets, which can then be prepared as for films (see 5. 4) .
5.7 Lacquers and insulating varnishes
The lacquer or insulating varnish to be tested shall be applied in the manner recommended by
Figure 1 and
the manufacturer to the surface of a test specimen of shape as shown in
described in 5.2. The base material of the test specimen shall be a corrosion free plastic such
as polymethylmethacrylate.
In case of solvent incompatibility or a baking temperature being too high for the base material,
another suitable base material such as cast, hot cured corrosion free epoxy resin or glass
shall be used. If the lacquer or insulating varnish is designed to contribute freedom from
corrosion to another material, a test specimen of that material shall be used.
The tested lacquer or varnish shall be sprayed, dipped or otherwise coated to the desired
thickness and baked, if necessary, as specified or according to the directions of the
manufacturer.
If the thickness of coating is not determined by specification or direction of the manufacturer,
it shall be of (30 ± 10) μm.
5.8 Cleanliness of contact surfaces
When preparing and handling the test specimens, any soiling of the test surfaces, for example
by perspiration from the hands, shall be avoided. The specimens shall be touched only with a
pair of tweezers or with protecting gloves made of materials free from corrosion (e.g.
polyethylene). After the test specimens have been machined or cut, their surfaces shall be
cleaned with a soft brush. Before cleaning, the brush shall be rinsed in ethanol (96 %) and
then dried.
10,0 ± 0,5
0,2 to 0,5
60426 © IEC:2007 – 11 –
After the cleaning procedure, the surface of contact shall not show any foreign particles,
residues of oil or grease, no mould residues, etc.
5.9 Number of test specimens
At least five test specimens made from the same material shall be tested at the same time.
A specific sampling procedure may be desired. If necessary, such a sampling procedure
should be specified and used.
6 Test strips
6.1 General
The test strips shall be made of 0,1 mm thick, semi-hard copper of purity 99,9 Cu. Their
dimensions are 10 mm wide and 200 mm long. The test strips shall be flat, without bends and
burrs at the edges as well as any other mechanical defects or impurities on the test surface,
which may have influence on the test results.
NOTE Test strips of brass or aluminium can be made in the same way.
6.2 Preparation of the test strips
From each new reel of strip (sold as a semi-finished product) the first several decimetres of
the strip shall be rejected and then the suitable number of strip segments, each 200 mm long,
shall be cut-off.
Copper strips shall be degreased with a low boiling point organic solvent (e.g. acetone or
hexane) and then etched. Etching shall be carried out at laboratory temperature, with a
solution of the following composition: sulphuric acid (1,82) with a mass fraction of 73 %, nitric
acid (1,33) with a mass fraction of 26 %, sodium chloride with a mass fraction of 0,5 % and
hard carbon black with a mass fraction of 0,5 %. The time of etching shall be between 20 s to
60 s. All strips, which are destined for one set of testing, shall be etched at the same time.
The coarseness of the strip surface can be controlled by adjustment of the etching time until
the copper strip has an even dull sheen. The strips shall then be washed in distilled water,
then dipped in ethanol and dried with blotting paper.
NOTE Unevenness of the surface of the strip may influence the discolouration and may lead to a wrong
evaluation. A surface, which is evenly dull, shows a discolouration of greater intensity than a surface, which is
slightly corroded, semi-dull or brilliant.
After degreasing and etching, both ends of the strip shall be reeled loose to the shape as
shown in Figure 3.
So prepared test strips shall be immediately (within 20 min) mounted in the test device, ready
for the test procedure, as shown in Figure 4.
– 12 – 60426 © IEC:2007
Dimensions in millimetres
25 ± 2
IEC 124/07
Figure 3 – Test strip
6.3 Cleanliness of test strips
After degreasing and etching, the strips should not be touched with bare hands. When
handling the strips, a pair of tweezers should be used and the reeling of the ends of the test
strip should be done using protective gloves.
7 Test device
The test device shall be made of materials not causing corrosion, for example of
polymethylmethacrylate (Plexiglas® ). The test device shall enable simultaneous testing of
all test specimens processed from one batch of insulating material (no less than five
specimens).
The pressure of the test specimen onto the test strips shall be 10 N/cm . The pressure is
achieved by setting a cylindrical tube (made from materials not causing corrosion) on the test
specimen and filled with the appropriate amount of lead shot, to assure the desired pressure.
The recommended test device is shown in Figure 4.
—————————
Plexiglas® is an example of a suitable product available commercially. This information is given for the
convenience of users of this document and does not constitute an endorsement by IEC of this product.
∼5
60426 © IEC:2007 – 13 –
+ – – +
Detail A Detail A
Side view Front view
+ –
Detail A Detail A
Side view Front view
1 cylindrical tubes (loading tubes) 2 supporting frame
3 test specimens (insulatin material) 4 metal test strips
5 connecting terminals 6 copper electrodes
IEC 125/07
Figure 4 – Test device for determining electrolytic corrosion
Before beginning each test and mounting test specimens, the test device shall be cleaned in
order to remove any corrosive residues from the previous test. Metal contacting parts shall be
carefully degreased and cleaned. Other parts of the test apparatus shall be carefully wiped
with a cloth damped with ethanol.
In the test device, a cylindrical tube presses a test specimen against two adjacent copper
electrodes 10 mm in width, arranged 4 mm apart. The two test strips are placed between the
test surface of the specimen and along two copper electrodes, as shown in Figure 4 (Detail A).
– 14 – 60426 © IEC:2007
8 Test conditions
The tests shall be carried out in a conditioning chamber under the following severities:
• temperature: (55 ± 1) °C;
• relative humidity: (93 ± 2) %;
• duration of the test: (240 ± 2) h.
A direct voltage source of (120 ± 5) V, for example a dry battery, shall be used. If a rectifier is
used, the permissible superimposed alternating voltage ripple may not amount to more than
1 % of the total voltage.
The methods enabling accurate temperature and humidity control have been described in
IEC 60068-3-4.
9 Test procedure
The test specimens shall be placed in the test device together with the copper test strips as
described in Clause 7. The copper electrodes of the device (see Figure 4) shall not be
contaminated at the surfaces being in contact with the copper strips (e.g. by corrosion
residues).
At least five test specimens of the same insulating material shall be mounted in the test
device.
The test device with the test specimens and test strips shall be placed in the conditioning
chamber. A direct voltage of (120 ± 5) V shall be applied to the terminals of the test device for
(240 ± 2) h, provided that no other time is specified in relevant specifications.
Before inserting in the conditioning chamber, the test device with the test specimens and test
strips shall be heated to a temperature about (5 ± 1,0) K higher than that of the chamber
temperature, in order to prevent condensation on the surface.
During the test and at the end of the test, the applied voltage shall be measured at the
terminals located on the test device (see Figure 4, Detail A, front view) to ensure that the
voltage value has been maintained within the specified limits.
At the end of the test period, the voltage shall be disconnected and the test device shall be
removed from the conditioning chamber and cooled to room temperature.
The test strips shall be carefully removed from the test device and examined visually and then
the tensile strength shall be measured.
NOTE It is not permitted to store the test strips after the test procedure. Both visual inspection and tensile
strength measurement shall be performed immediately (within 30 min) after removing test strips from the test
chamber.
10 Evaluation
10.1 General evaluation
The general evaluation of the electrolytic corrosion consists of two combined estimations:
a) visual inspection – qualitative evaluation,
b) tensile strength measurement – quantitative evaluation.
60426 © IEC:2007 – 15 –
As a first evaluation a visual inspection is carried out and then a tensile strength measure-
ment is made on the same strip. The results of both inspections give a general evaluation of
the test.
NOTE Instead of copper strips, other test metals may be used, such as brass and aluminium. The corrosion
indices of evaluation for brass and aluminium strips are given in Annex A (Tables A.1 and A.2).
10.2 Visual inspection of the test strips
The strips (negative and positive) shall be examined on the side that was in direct contact
with the test surface of the specimen.
The inspection of the test metal surfaces should be done (with a bare eyes or) using a
magnifying glass with 5 magnifications.
The appearance of the positive and negative pole strips shall be compared to Table 1 and
described in corrosion indexes given in this table. For each polarity, the symbol representing
the most unfavourable corrosion index of the five strips is taken as the characteristic
corrosion index of the material.
NOTE In the event of marked variations in the results obtained, the test should be repeated to discover whether
preparation or execution of the test was inadequate or whether the differing results are due to inhomogeneities in
the material under test.
10.3 Tensile strength of test strips
At least five samples of unexposed strips shall be tested for tensile strength to determine the
comparative factor F . None of the individual values obtained shall vary from the mean value
by more than 2 %. If the unexposed strip fails to meet this requirement, then five additional
specimens shall be tested. None of the second five tests shall vary from the mean value by
more than 2 %. In case the variation is more than 2 %, the strips used for testing shall be
rejected and a new reel of strip shall be used.
After exposure and visual inspection, the test strips shall be carefully unreeled. Then the
tensile strength F of the positive polarity test strips shall be determined in the same way as
for the unexposed strips.
NOTE The measurement of tensile strength of the negative strips is a useful, but not necessary check. The
decrease of tensile strength of the negative strips usually differs by not more than 1 % from the mean value of the
unexposed strips.
The corrosion liability of the specimen under test is calculated as follows:
F −F
0 1
Corrosion liability factor: K = × 100
F
where
F is the tensile strength mean value of the unexposed strips;
F is the tensile strength mean value of the strips with positive polarity determined after
moisture and voltage exposure in the conditioning chamber.
The central value of the corrosion liability factor K of the specimen tested is determined as a
mean value of the tensile strength decrease by at least five positive strips, expressed in
percentage. The calculated factor K is compared with the corresponding range of corrosion
liability factors given in Table 1 (if needed, with the factors given in evaluation Tables A.1 and
A.2, for brass and aluminium strips respectively).
– 16 – 60426 © IEC:2007
11 Evaluation of corrosion on copper strips
Table 1 – Degrees of corrosion of copper strips
Negative pole strip Positive pole strip Tensile strength General
corrosion liability evaluation
Description Illustration Visual Description of Illustration Visual
factor
of visual appearance corrosion visual appearance corrosion
K %
index index
No change K 1 No change A 1 Not
K ≤ 3
or appearance of or appearance of corrosive
slight ground colour slight ground colour
on the contact on the contact
surface with surface with
specimen specimen
3< K <15
Dark-brown or black K 2 Brown tarnish or A 2 Slightly
spots cover up to single rose-coloured corrosive
50 % of contact etching spots cover
surface; on the to 50 % of contact
remaining no change surface
or slight
discolouration
Black spots cover K 3 50 % to 100 % of A 3 15< K ≤ 30 Corrosive
the whole or a contact surface
prevailing part of the covered by brown
contact surface, as (brick-red) deposit or
well on the other rosy etching spots;
side of the strip possible appearance
of green spots
K > 30
Intense black spots K 4 Total contact surface A 4 Strongly
spread wide over the covered by thick corrosive
contact surface and brown deposit or
on the other side of deep etched (rose-
the strip; the black coloured) or great
or brown spots may amount of green
not appear on the corrosion products;
contact surface possibility of cross-
etching of the strip
60426 © IEC:2007 – 17 –
12 Test report
The test report should include at least the following information:
– designation of the material tested (name, type and form);
– thickness and dimension of the material from which the specimens were made;
– type of the metal strip (if other than copper);
– position of test specimen in material;
– test device (if other than described in Clause 7);
– the severities of the test, as described in Clause 8;
– duration of the test, as described in Clauses 8 and 9;
– number of the test specimens;
– the individual corrosion indexes (visual and tensile strength) obtained for each specimen;
– special or additional observations;
– any deviation from the conditions specified in this method;
– date of the test.
– 18 – 60426 © IEC:2007
Annex A
(normative)
Tables for the evaluation of corrosion on brass and aluminium strips
Table A.1 – Degrees of corrosion of brass strips
Negative pole strip Positive pole strip Tensile strength General evaluation
corrosion liability
Description of Illustration Visual corrosion Description of Illustration Visual corrosion
factor
visual appearance index visual appearance index
K %
No change or slight K 1 No change A 1 K ≤ 3 Not corrosive
discolouration or appearance of
slight discolouration
Dark-brown spots K 2 Slight red colouring A 2 3 < K < 15 Slightly
cover up to 50 % of (incipient corrosive
contact surface dezincification)
and/or brown spots
cover up to 50 % of
contact surface
Black spots cover up K 3 Red colouring and A 3 15 < K ≤ 30 Corrosive
to 100 % of the possible occurrence
contact surface and of white deposit on
possible also on the 50 % to 100 %
reverse side of the of contact surface
strip
Continuous black K 4 Strong red colouring A 4 K > 30 Strongly
colouring extending (advanced corrosive
beyond the area of dezincification) on
the contact surface total contact surface
and and possible
also on the reverse occurrence of white
side of the strip or black deposit
60426 © IEC:2007 – 19 –
Table A.2 – Degrees of corrosion of aluminium strips
Negative pole strip Positive pole strip Tensile strength General evaluation
corrosion liability
Description of visual Illustration Visual Description of visual Illustration Visual
factor
appearance corrosion appearance corrosion index
K %
index
No change K 1 No change A 1 K ≤ 3 Not corrosive
White spots cover K 2 Slight etching in form A 2 3 < K < 15 Slightly
predominating part of of white spots or white corrosive
contact area deposit cover up to
50 % of the contact
surface
Thin white deposit on K 3 Predominating part of A 3 Corrosive
15 < K ≤ 30
whole contact area,
contact surface area
which may extend covered by white
beyond this area and deposit of corrosion
also on the reverse products of aluminium
side of the strip and single pitting holes
Thick white deposit of K 4 The whole area of the A 4 K > 30 Strongly
corrosion products of contact surface is corrosive
aluminium covers the covered by thick white
whole area of contact deposit of corrosion
surface extending far products of aluminium
beyond this area. On also extending beyond
the reverse side great the contact area and a
white spots great number of deep
and thick white deposit pitting, some
penetrating the strip
– 20 – 60426 © IEC:2007
Annex B
(informative)
Notes on visual evaluation
If slight electrolytic corrosion occurs with non-ferrous metals, discolourations appear; on brass
for example, brown, black or red (dezincification). In the case of heavy electrolytic corrosion,
green discolourations appear at the positive pole. These green discolourations are more
dangerous because they indicate electrolytic erosion of the metal at the positive pole which,
in the case of wires in coils for instance, initiates destruction as a result of reduction in
diameter.
The cut edges of laminates and other insulating materials usually produce more corrosion
than the moulded surface of such materials with its high resin content or the surface obtained
by varnishing or coating with better insulating materials. This indicates that embedded paper
or fabrics, glass mats, wood flour and other fillers can also be responsible for the process of
electrolysis. The test method thus makes primary provision that the cut edge of the insulating
materials be used as the test surface. To ensure that, as far as possible, all embedded
materials are included in the test of the cut surfaces, the test face should be made smooth
and flat, by milling for example. If cut by scissors, the test variability caused by the resultant
rough edges of the test specimens would be too great.
As impurities such as chlorine ions produced by perspiration assist electrolytic processes, the
testing surfaces should not be touched with the fingers after preparing the specimens.
Further treatment can also reduce the surface quality of insulating materials in respect to the
process of electrolysis. To permit a description of the quality of the surface, if necessary,
particulars relating to the test of the surface have also b
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