SIST EN ISO 7441:2015

SLOVENSKI STANDARD
SIST EN ISO 7441:2015
01-marec-2015
1DGRPHãþD
SIST EN ISO 7441:1999
Korozija kovin in zlitin – Ugotavljanje kontaktne (na stiku dveh kovin) korozije s
preskušanjem v naravi (ISO 7441:2015)
Corrosion of metals and alloys - Determination of bimetallic corrosion in outdoor
exposure corrosion tests (ISO 7441:2015)
Korrosion von Metallen und Legierungen - Bestimmung der Kontaktkorrosion durch
Freibewitterungsversuche (ISO 7441:2015)
Corrosion des métaux et alliages - Détermination de la corrosion bimétallique par des
essais de corrosion en milieu extérieur (ISO 7441:2015)
Ta slovenski standard je istoveten z: EN ISO 7441:2015
ICS:
77.060 Korozija kovin Corrosion of metals
SIST EN ISO 7441:2015 en
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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SIST EN ISO 7441:2015

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SIST EN ISO 7441:2015

EUROPEAN STANDARD
EN ISO 7441

NORME EUROPÉENNE

EUROPÄISCHE NORM
January 2015
ICS 77.060 Supersedes EN ISO 7441:1995
English Version
Corrosion of metals and alloys - Determination of bimetallic
corrosion in atmospheric exposure corrosion tests (ISO
7441:2015)
Corrosion des métaux et alliages - Détermination de la Korrosion von Metallen und Legierungen - Bestimmung der
corrosion bimétallique par des essais d'exposition de Kontaktkorrosion durch Freibewitterungsversuche (ISO
corrosion atmosphérique (ISO 7441:2015) 7441:2015)
This European Standard was approved by CEN on 15 November 2014.

CEN 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 CEN-CENELEC Management Centre or to any CEN 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 CEN member into its own language and notified to the CEN-CENELEC Management Centre has the same
status as the official versions.

CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia,
Finland, Former Yugoslav Republic of Macedonia, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania,
Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and United
Kingdom.





EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION

EUROPÄISCHES KOMITEE FÜR NORMUNG

CEN-CENELEC Management Centre: Avenue Marnix 17, B-1000 Brussels
© 2015 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 7441:2015 E
worldwide for CEN national Members.

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SIST EN ISO 7441:2015
EN ISO 7441:2015 (E)
Contents Page
Foreword .3
2

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SIST EN ISO 7441:2015
EN ISO 7441:2015 (E)
Foreword
This document (EN ISO 7441:2015) has been prepared by Technical Committee ISO/TC 156 “Corrosion of
metals and alloys” in collaboration with Technical Committee CEN/TC 262 “Metallic and other inorganic
coatings” the secretariat of which is held by BSI.
This European Standard shall be given the status of a national standard, either by publication of an identical
text or by endorsement, at the latest by July 2015, and conflicting national standards shall be withdrawn at the
latest by July 2015.
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent
rights. CEN [and/or CENELEC] shall not be held responsible for identifying any or all such patent rights.
This document supersedes EN ISO 7441:1995.
According to the CEN-CENELEC Internal Regulations, the national standards organizations of the following
countries are bound to implement this European Standard: Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech
Republic, Denmark, Estonia, Finland, Former Yugoslav Republic of Macedonia, France, Germany, Greece,
Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal,
Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and the United Kingdom.
Endorsement notice
The text of ISO 7441:2015 has been approved by CEN as EN ISO 7441:2015 without any modification.

3

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SIST EN ISO 7441:2015

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SIST EN ISO 7441:2015
INTERNATIONAL ISO
STANDARD 7441
Second edition
2015-01-15
Corrosion of metals and alloys —
Determination of bimetallic corrosion
in atmospheric exposure corrosion
tests
Corrosion des métaux et alliages — Détermination de la corrosion
bimétallique par des essais d’exposition de corrosion atmosphérique
Reference number
ISO 7441:2015(E)
©
ISO 2015

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SIST EN ISO 7441:2015
ISO 7441:2015(E)

COPYRIGHT PROTECTED DOCUMENT
© ISO 2015
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized otherwise in any form
or by any means, electronic or mechanical, including photocopying, or posting on the internet or an intranet, without prior
written permission. Permission can be requested from either ISO at the address below or ISO’s member body in the country of
the requester.
ISO copyright office
Case postale 56 • CH-1211 Geneva 20
Tel. + 41 22 749 01 11
Fax + 41 22 749 09 47
E-mail copyright@iso.org
Web www.iso.org
Published in Switzerland
ii © ISO 2015 – All rights reserved

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SIST EN ISO 7441:2015
ISO 7441:2015(E)

Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Overview and comparison of methods . 2
5 Preparation of specimens . 3
5.1 Types of specimens . 3
5.1.1 General. 3
5.1.2 Rectangular plates . 3
5.1.3 Wire on bolt . . 8
5.2 Number and marking of specimens . 9
6 Exposure of specimens . 9
7 Evaluation of specimens .10
7.1 General .10
7.2 Evaluation based on mass loss .10
7.3 Other evaluation methods applicable for rectangular plates .10
7.3.1 Evaluation based on visual examination .10
7.3.2 Evaluation based on mechanical properties .11
7.4 Calculation of bimetallic effect .11
8 Test report .12
Bibliography .14
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SIST EN ISO 7441:2015
ISO 7441:2015(E)

Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
through ISO technical committees. Each member body interested in a subject for which a technical
committee has been established has the right to be represented on that committee. International
organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.
ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2. www.iso.org/directives
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of any
patent rights identified during the development of the document will be in the Introduction and/or on
the ISO list of patent declarations received. www.iso.org/patents
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation on the meaning of ISO specific terms and expressions related to conformity
assessment, as well as information about ISO’s adherence to the WTO principles in the Technical
Barriers to Trade (TBT) see the following URL: Foreword - Supplementary information
The committee responsible for this document is ISO/TC 156, Corrosion of metals and alloys.
This second edition cancels and replaces the first edition (ISO 7441:1984), which has been technically
revised.
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SIST EN ISO 7441:2015
ISO 7441:2015(E)

Introduction
Bimetallic corrosion occurs when a metal in electrical contact with a more noble metal corrodes at a
higher rate than it would in the same environment but without this contact.
Bimetallic corrosion in the atmosphere, in contrast to that in electrolytes, is characterized by a large
potential drop between the anode and the cathode. Therefore, bimetallic corrosion is usually limited to
[1]
a distance within about 0,5 cm from the point of contact .
The determination of bimetallic corrosion in atmospheric exposure tests can be made with several
methods, each with its own advantages. Three standardized tests are compared and described in this
International Standard:
— rectangular plates;
— washers;
— wire on bolt.
The standard starts with an overview and comparison of the three methods, with the purpose of aiding
the selection of an appropriate test method. Test procedures for the rectangular plate and washer test
are included in this standard since no independent standard describes these methods while those who
wish to use the wire on bolt test need to consult ASTM G116 for a complete description of the method.
The standard describes how to derive the bimetallic effect, which is a relative measure of the bimetallic
corrosion of a metal compared to the corrosion of the same metal but without the bimetallic effect. A
high galvanic effect does not necessarily mean that the bimetallic corrosion rate is high. Therefore,
valuable complementary information is the classification of the corrosivity of the test site according to
[2]
ISO 9223 .
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SIST EN ISO 7441:2015

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SIST EN ISO 7441:2015
INTERNATIONAL STANDARD ISO 7441:2015(E)
Corrosion of metals and alloys — Determination of
bimetallic corrosion in atmospheric exposure corrosion
tests
1 Scope
This International Standard specifies and compares methods for the determination of bimetallic
corrosion of metals and coated metals in atmospheric exposure corrosion tests.
NOTE In the text of this International Standard, the term “metal” is used for both metals and alloys, and the
term “coated metal” for metals and alloys with metallic and non-metallic inorganic coatings.
The methods are intended for the determination of the amount and type of corrosion effect, arising in
natural atmospheres, caused by contact with different metals.
2 Normative references
The following documents, in whole or in part, are normatively referenced in this document and are
indispensable for its application. For dated references, only the edition cited applies. For undated
references, the latest edition of the referenced document (including any amendments) applies.
ISO 1456, Metallic and other inorganic coatings — Electrodeposited coatings of nickel, nickel plus chromium,
copper plus nickel and of copper plus nickel plus chromium
ISO 2081, Metallic and other inorganic coatings — Electroplated coatings of zinc with supplementary
treatments on iron or steel
ISO 7599, Anodizing of aluminium and its alloys — General specifications for anodic oxidation coatings on
aluminium
ISO 6892-1, Metallic materials — Tensile testing — Part 1: Method of test at room temperature
ISO 8044, Corrosion of metals and alloys — Basic terms and definitions
ISO 8407, Corrosion of metals and alloys — Removal of corrosion products from corrosion test specimens
ISO 8565, Metals and alloys — Atmospheric corrosion testing — General requirements
ISO 15510, Stainless steels — Chemical composition
ASTM G116, Standard Practice for Conducting Wire-on-Bolt Test for Atmospheric Galvanic Corrosion
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 8044 and the following apply.
3.1
test specimens
specimens that are exposed for evaluation of bimetallic corrosion caused by contact with different
materials
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SIST EN ISO 7441:2015
ISO 7441:2015(E)

3.2
reference specimens
specimens prepared, exposed and evaluated in the same configuration and design as the test specimens
but not subject to bimetallic corrosion, for example by being in contact with an inert non-conductive
material or the same material, instead of the different material
3.3
standard specimens
specimens used to determine the corrosivity of the test environment in absence of bimetallic corrosion
3.4
control specimens
specimens prepared and evaluated in the same way as test specimens but, instead of being exposed in
the test environment, stored under controlled conditions which prevent corrosion
4 Overview and comparison of methods
The determination of bimetallic corrosion in atmospheric exposure tests can be made with several
methods. Three of these methods are compared and described in this International Standard:
— rectangular plates;
— washers;
— wire on bolt.
An overview and comparison of methods are shown in Table 1. Each configuration has its own advantages
and the selection of method shall be based on the needs of the test programme. The main advantage
with rectangular plate test is the possibility of evaluating the mechanical properties. The washer test
is the only method where it is not necessary to know in advance which material is the anode. The short
exposure time is the main advantage of the wire on bolt test.
Table 1 — Comparison of rectangular plates, washers and wire on bolt for conducting test
assessing bimetallic corrosion in the atmosphere
Effect Rectangular plates Washers Wire on bolt
Sensitivity
a
≥ 1 year ≥ 1 year > 90 days
(exposure time)
Material limitation None None Wire anode
Anode/cathode Necessary to know in advance Not necessary to know in Necessary to know in
which material is the anode advance which material is advance which material is
the anode the anode
Evaluation method(s) Mass loss Mass loss Mass loss
Mechanical properties
Mechanical Can be difficult to maintain Can be difficult to main- Can be difficult to main-
electrical contact between pan- tain electrical contact tain enough wire tension
els throughout the exposure between panels through- without causing wire
test. out the exposure test. fracture
Crevice corrosion Crevice corrosion can be a Crevice corrosion can be a Lower risk that crevice
problem problem corrosion will be a prob-
lem
a
A shorter duration of exposure is permissible under certain conditions, see Clause 6.
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SIST EN ISO 7441:2015
ISO 7441:2015(E)

5 Preparation of specimens
5.1 Types of specimens
5.1.1 General
When determining the risk of bimetallic corrosion, depending on the particular test, the specimens
will not only suffer from increased corrosion due to bimetallic effects. For example, in the wire on bolt
test the wire tension may influence the outcome of the test depending on the particular application.
Therefore, several types of specimens (test specimens, reference specimens, standard specimens and
control specimens) as defined in Clause 3 are needed depending on the purpose of the test programme.
NOTE Comparison of effects of test and reference specimens gives the relative risk of bimetallic corrosion
but reference specimens are generally not suitable for evaluation of the absolute corrosion attack when there
is no risk of bimetallic corrosion due to the particular design of the specimens. For evaluation of the absolute
attack standard specimens are more suitable. Flat or irregularly shaped specimens can be used, as described
in ISO 8565, depending on the intended use of the tested material. For example, hanging wires can be used as
standard specimens for the wire on bolt test but flat panels can also be used if they are easily obtained and more
closely resembles the shape of the intended use.
Control specimens shall be used if evaluation of mechanical properties is part of the test programme.
Unless otherwise stated, the material, dimensions, direction of cutting, method of surface treatment
and other parameters of anodic plates of test specimens, reference specimens and control specimens
shall be the same.
5.1.2 Rectangular plates
The test specimens shall be as shown in Figure 1 or Figure 2.
NOTE 1 The configuration shown in Figure 1 cannot be used for evaluation based on mass loss. The configuration
shown in Figure 2 cannot be used for evaluation based on mechanical properties.
Anodic plates shall have a thickness of 1 mm to 6 mm and their length shall be suitable for tensile testing
in accordance with ISO 6892-1.
Cathodic plates shall have thickness of 1 mm to 6 mm. In the case of precious metals, cathodic plates can
consist of a foil covering a plate of inert material, such as plastic material. In this case, the foil and inert
material assembly shall have a thickness of 1 mm to 6 mm.
If it is not known which of the metals constituting the test specimen is nobler, each metal shall be tested
in one complete set of specimens as the anode, and in the other, as the cathode.
The surfaces of specimens shall be free from visible defects, such as non-uniformity of rolling, scale,
exfoliation, cracks, pores, blisters, scratches and dents. If there are no visual surface defects, as detected
with the naked eye, specimens shall be tested with the surface in the condition as delivered or after
treatment, as recommended for the articles concerned. If defects are removed by mechanical means,
the surface roughness of specimens, including cut edges, shall at least be better than 2,5 µm, a surface
roughness of 0,4 µm to 0,5 µm is recommended.
The surface conditions, including cut edges, of coated metallic plates shall be in accordance with ISO 1456,
ISO 2081 or ISO 7599 or other appropriate international, national or regional standards depending on
the specific coatings in question.
If a metal is tested in contact with a coated metal, damage to, or absence of, the coating is permissible
only on the cut edges of anodic plates.
Washers and sleeves shall be used to insulate bolts from the metallic plates. The contact between
two plates of metal shall be achieved by pressure. Ceramics or other insulating materials which are
not susceptible to creep or degradations over extended periods of time are recommended as washer
materials. Sleeves of polyethylene or polypropylene are recommended.
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SIST EN ISO 7441:2015
ISO 7441:2015(E)

The bolts shall be tightened firmly until good electrical contact is achieved between the plates.
Insufficient torque will cause too high a resistance between the washers, and too much torque will crack
the bushing. The torque applied while tightening the bolts shall be the same for all specimens, a value of
−1
about (1,0 ± 0,1) N m being typical. Otherwise, a good rule of thumb is to tighten until all components
are in contact and then tighten an additional one quarter turn. After assembly, the electrical insulation
(>10 kΩ) of the bolt from the washers and the electrical contact (<1 Ω) between the plates shall be
verified with a resistance meter.
These electrical resistance checks should be repeated if assemblies are dry in connection with site
visits. If the resistance increases or if there are other indications of relaxation, the bolts should be re-
tightened without disturbing the assemblies. The reason for loss of contact could be that solid corrosion
products accumulate between the washers pushing them apart. Another reason could be the relaxation
of the non-metallic components caused by long term stress leading to creep.
Metallic bolts and washers shall be made of stainless steel of grade 1.4301/X5CrNi18-10/304 or higher
chromium grades, see ISO 15510.
Specimens shall be examined for conformity to the requirements above by visual inspection and
appropriate measurements.
Immediately before testing, the surfaces of the specimens and other parts of the assemblies shall be
degreased using organic solvents, for example ethanol, white spirit.
After degreasing, the specimens shall be handled only by the cut edges and when wearing cotton or
rubber gloves.
After degreasing, test specimens and reference specimens, the corrosion behaviour of which is to be
determined by mass loss, shall be kept in desiccators containing a desiccant (for example silica gel) for
not less than 24 hours.
In preparing specimens a thin layer of an organic coating, glue, varnish or lacquer, such as cellulose
acetate dissolved in acetone, is recommended to prevent crevice corrosion. This coating shall be applied
to the degreased surface of the anodic plate in such a way as to seal completely the gap between the
anode and cathode plates without projecting beyond the cathode plate. The dry coating thickness shall
not exceed 10 µm. This coating shall not cover the area adjacent to bolt holes, in order to allow contact
between the metallic plates when they are assembled.
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SIST EN ISO 7441:2015
ISO 7441:2015(E)

Dimensions in millimetres
10
A - A
5
7
1 6
2
8
1 2 3
9
A
A
4
25
75
150 - 240
Key
1 anodic plate 6 washer, thickness 1 mm, diameter 16 mm
2 cathodic plate 7 insulating washer, thickness 1 mm to 3 mm, diameter 18 to
20 mm
3 microsections 8 insulating sleeve
4 tensile test specimen 9 nut
5 bolt 8 mm × 40 mm
Figure 1 — Example of test specimen used for evaluations based on criteria other than mass
loss
© ISO 2015 – All rights reserved 5
90
1 - 6
50
70

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SIST EN ISO 7441:2015
ISO 7441:2015(E)

Dimensions in millimetres
2 3
1
4
5
6
A - A
7
110
70
50
A
A
2 8
Key
1 anodic plate 5 insulating washer, thickness 1 to 3 mm, diameter 18 to 20 mm
2 cathodic plate 6 insulating sleeve
3 bolt 8 mm × 40 mm 7 nut
4 washer, thickness 1 mm, diameter 8 microsections
16 mm
Figure 2 — Example of test specimen for evaluation based on criteria other than mechanical
properties
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65
1 - 6
25

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SIST EN ISO 7441:2015
ISO 7441:2015(E)

The components specifications used to construct the specimen assemblies for this test is shown in
Table 2 and Figure 3. Washer dimensions are critical to maintaining the 1:1 area ratio fixed by the
geometry. Thickness shall be adjusted by surface grinding, if required.
Table 2 — Dimensions of components for the washer assembly
Thickness/length Inside diameter Outside diameter
Component Designation
mm mm mm
Bolt 40 — — M6S M5 × 40 A4
Washer — 4,9 15,9 —
Polymer bushing 11,1 5,2 7,9 —
Polymer washer (small) 3,2 8,3 19,0 —
Metal A washers (small) 1,6 8,3 25,4 —
Metal B washers (small) 1,6 8,3 30,0 —
Metal A washers (large) 1,6 8,3 33,5 —
Metal B washers (large) 1,6 8,3 36,6 —
Polymer washer (large) 3,2 8,3 35,6 —
Washer — 4,9 15,9 —
Lock washers — 4,9 — —
Nut — — — M6M M5 A4
1
6
2
7
3
4
8
5
9
10
Key
1 bolt 6 washer
2 polymer washer 7 metal A washer
3 metal B washer 8 polymer bushing
4 polymer washer 9 washer
5 lock washer 10 angle support
Figure 3 — Schematic completed washer assembly
The bolts, end washers, lock washers and nuts can be made of any material provided that the material
will not degrade in the atmosphere for the duration of the exposure.
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SIST EN ISO 7441:2015
ISO 7441:2015(E)

Washers shall not be made by punching directly to the final dimensions, as this introduces a deformed
area near the edge. Washers can be made by first punching out discs a minimum of 3 mm diameter
oversize and machining to final dimensions, then drilling holes in the disk centres.
The surfaces of specimens shall be free from visible defects, such as non-uniformity of rolling, scale,
exfoliation, cracks, pores, blisters, scratches and dents. If there are no visual surface defects, as detected
with the naked eye specimens shall be tested with the surface in the condition as delivered or after
treatment, as recommended for the articles concerned. If defects are removed by mechanical means,
the surface roughness of specimens, including cut edges, shall at least be better than 2,5 µm, a surface
roughness of 0,4 µm to 0,5 µm is recommended.
Additional washers of the anode material shall be prepared to enable the construction of reference
assemblies, where all four washers are made of the anode material and exposed under identical
conditions to the test assemblies. The reference assemblies are used to assess non-galvanic effects.
All parts shall be thoroughly cleaned and degreased before assembly. After degreasing, the washers
shall only be handled by the edges while wearing clean, cotton or rubber gloves.
If the relationship between the anode and the cathode of the materials is not known at the start of
the test, the inner washers shall be weighe
...