SIST EN ISO 7441:1999

SLOVENSKI STANDARD
SIST EN ISO 7441:1999
01-oktober-1999
Korozija kovin in zlitin – Ugotavljanje kontaktne (na stiku dveh kovin) korozije s
preskušanjem v naravi (ISO 7441:1984)
Corrosion of metals and alloys - Determination of bimetallic corrosion in outdoor
exposure corrosion tests (ISO 7441:1984)
Korrosion von Metallen und Legierungen - Bestimmung der Kontaktkorrosion durch
Freibewitterungsversuche (ISO 7441:1984)
Corrosion des métaux et alliages - Détermination de la corrosion bimétallique par des
essais de corrosion en milieu extérieur (ISO 7441:1984)
Ta slovenski standard je istoveten z: EN ISO 7441:1995
ICS:
77.060 Korozija kovin Corrosion of metals
SIST EN ISO 7441:1999 en
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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SIST EN ISO 7441:1999

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SIST EN ISO 7441:1999

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SIST EN ISO 7441:1999

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SIST EN ISO 7441:1999
International Standard
INTt RNATIONAL ORGANIZATION FOR STANDARDIZATION.MEX~YHAPOAHAR OPTAHVl3AlJt’lfl I-IO CTAHAAPTM3AI.&IVl*ORGANlSATlON INTERNATIONALE DE NORMALISATION
Corrosion of metals and alloys - Determination of
bimetallic corrosion in outdoor exposure corrosion tests
Corrosion des m& taux et alliages - 06 termination de la corrosion bim&allique par des essais de corrosion en milieu extkieure
First edition - 1984-12-15
Ref. No. IS0 7441-1984 (E)
UDC 620.193.2 : 621.357.7
Descriptors : corrosion, metals, alloys, tests, determination, corrosion resistance, bimetallic corrosion tests, atmospheric corrosion.
Price based on 12 pages

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SIST EN ISO 7441:1999
Foreword
IS0 (the International Organization for Standardization1 is a worldwide federation of
national standards bodies (IS0 member bodies). The work of preparing International
Standards is normally carried out through IS0 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, govern-
mental and non-governmental, in liaison with ISO, also take part in the work.
Draft International Standards adopted by the technical committees are circulated to
the member bodies for approval before their acceptance as International Standards by
the IS0 Council. They are approved in accordance with IS0 procedures requiring at
least 75 % approval by the member bodies voting.
International Standard IS0 7441 was prepared by Technical Committee ISO/TC 156,
Corrosion of metals and alloys.
0 International Organization for Standardization, 1984
Printed in Switzerland

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SIST EN ISO 7441:1999
IS0 7441-1984 (E)
INTERNATIONAL STANDARD
Corrosion of metals and alloys - Determination of
bimetallic corrosion in outdoor exposure corrosion tests
1 Scope and field of application
The test specimens are assemblies in which one plate of metal
(coated metal) may act as the anode and two plates of a dif-
This International Standard specifies methods for the deter-
ferent metal (coated metal) as the cathode, thereby producing
mination of bimetallic corrosion of metals and alloys, and
an electrochemical cell in the presence of an electrolyte. (See
metals and alloys with metallic and non-metallic non-organic figures 1 and 2.)
coatings, in outdoor exposure corrosion tests.
Reference specimens are anodic plates exposed with the test
NOTE - In the text of this International Standard, the term “metal” is
specimens.
used for both metals and alloys, and the term “coated metal” for
metals and alloys with metallic and non-metallic non-organic coatings.
Control specimens are anodic plates which are kept under con-
ditions which prevent corrosion during the test period.
The methods are intended for the determination of the amount
and type of corrosion effect, arising in natural atmospheres,
The amount and type of corrosion effect is evaluated on the
caused by contact with different metals (coated metals), and
basis of:
for the evaluation of the effectiveness of bimetallic corrosion
protection treatments.
-
changes in surface appearance;
- depth and area of corrosion effect;
2 References
-
changes in mechanical properties;
I S 0 1456, Metallic coatings - Electroplated coatings of nickel
- loss in mass;
plus chromium.
-
other characteristics resulting from bimetallic cor-
I SO 2081, Metallic coatings - Electroplated coatings of zinc on
rosron.
iron or steel. 1)
The effectiveness of corrosion protection treatments may be
IS0 2082, Metallic coatings - Electroplated coatings of cad-
evaluated by applying coatings to the anodic or cathodic plates
mium on iron or steel.2)
or to the test specimen assembly, with the exception that elec-
trodeposited coatings shall not be applied to the test specimen
I SO 4540, Metallic coatings - Coatings cathodic to the sub-
assembly.
Rating of electroplated test specimens subjected to
strate -
corrosion tests.
Coated specimens should be tested simultaneously with
specimens without protective coatings.
IS0 4542, Metallic and other non-organic coatings - General
rules for stationary outdoor exposure corrosion tests.
3.2 The test conditions (macroclimatic region, type of at-
I S 0 6892, Metallic materials - Tensile testing.
mosphere and conditions for the location and exposure of
specimens at the atmospheric field stations) should be chosen
according to the expected conditions of service of articles,
joints and parts in which the contacted metals (coated metals)
3 General principles
will be used.
3.1 The test consists of simultaneous exposure of test
specimens and reference specimens at atmospheric field
3.3 Atmospheric field stations should be suitably equipped
stations and subsequent comparative evaluation of their cor-
and the equipment should comply with the requirements of
rosion resistance.
relevant International Standards. (See, for example, IS0 4542.)
1) At present at the stage of draft. (Revision of IS0 2081-1973.)
2) At present at the stage of draft. (Revision of IS0 20821973.)

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SIST EN ISO 7441:1999
IS0 7441-1984 (E)
4 Specimens Specimens shall be identified by marking. Such marking
4.6
shall include the characteristics and agreed designation of the
tested anodic and cathodic metal (coated metal), in accordance
4.1 The test specimens shall be as shown in figure 1 or
with an inventory of specimens (see annex A) and serial
figure 2. numbers assigned to the metallic plates. The marking may be
made with a stamp or using indelible paint or by drilling notches
Anodic plates may be up to 6 mm thick and their length shou Id
on the face of each metallic plate of the specimen.
be suitable for tensile testing In a ccordance with IS0 6892.
The designation of a metal (coated metal) shall be marked in
the top left-hand corner and the serial number in the top right-
Cathodic plates shall have a thickness of 1 to 6 mm. In the case
hand corner of anodic and cathodic plates.
of precious metals, cathodic plates may comprise a foil cover-
ing a plate of inert material, such as a plastic material ; the con-
Areas bearing markings made by mechanical means shall be
tact between two plates of metal should be achieved by
protected by water-resistant varnishes. The markings should be
pressure. The thickness should not be less than 1 mm.
legible and durable throughout the period of test.
If it is not known which of the metals (coated metals) con-
stituting the test specimen is nobler, each metal (coated metal)
4.7 Washers and sleeves shall be used to insulate bolts from
should be tested in one complete set of specimens as the
the metallic plates and to avoid pressing metallic plates
anode, and in the other, as the cathode.
together during the period of test. Ceramics or other insulating
materials which are not susceptible to creep or degradations
The presence of gaps and crevices between anodic and
over extended periods of time are recommended as washer
cathodic plates should be minimized and such clearances
materials. Sleeves of polyethylene or polypropylene are recom-
should not exceed 0,02 mm. When assembling the test
mended.
specimens, the maximum value of the torque applied while
tightening the bolts should be more than 5,0 N. m. Metallic bolts and washers shall be made of 18-8 or higher
chromiu m gra des of stainless steel.
4.2 The surfaces of specimens shall be free from visible
4.8 The number of test specimens, reference specimens and
defects, such as non-uniformity of rolling, scale, exfoliation,
control specimens removed for inspection at any one time shall
cracks, pores, blisters, scratches, dents.
be not less than three.
If there are no surface defects, specimens shall be tested with
If mechanical tests are not required by the test programme, the
the surface in the condition as delivered or after treatment, as
number of control specimens may be decreased to three per
recommended for the material (articles) concerned.
lot.
If defects are removed by mechanical means, the surface
roughness (I?,) of test specimens, reference specimens and
5 Preparation of specimens for test
control specimens, including cut edges, shall be within the
range 0,75 to 2,5 pm.
5.1 Test specimens, reference specimens and control speci-
mens shall be examined for conformity to the require-
4.3 The surface finish (including cut edges) of metallic plates
ments of clause 4 by visual examination and appropriate
(coated metals) shall be in accordance with appropriate lnter-
measurements.
national Standards, for example IS0 1456, IS0 2081, IS0 2082.
If a metal is tested in contact with a coated metal, damage to,
5.2 Immediately before testing, the surfaces of specimens
or absence of, the coating is permissible only on the cut edges
shall be degreased using organic solvents, for example ethanol,
of anodic plates.
white spirit.
After degreasing, the specimens shall be handled only by the
cut edges and when wearing cotton (or rubber) g oves.
4.4 The evaluation of bimetallic corrosion resistance accord-
ing to all criteria except loss in mass shall be carried out using
specimens as shown in figure 1.
5.3 After degreasing, test specimens and reference speci-
mens, the corrosion behaviour of which is to be evaluated by
The evaluation of bimetallic corrosion resistance according to
loss in mass, shall be kept in desiccators containing a desiccant
all criteria except changes in mechanical properties shall be car-
(for example silica gel) for not less than 24 h. They shall then be
ried out using specimens as shown in figure 2.
weighed to the nearest 0,000 1 g.
The material, dimensions, direction of cutting, method of
4.5 5.4 Control specimens shall be stored throughout the test
surface treatment and other parameters of anodic plates of test period under conditions which prevent corrosion, for example
specimens, reference specimens and control specimens shall in desiccators or in polyethylene bags containing a desiccant
be the same. (silica gel) at a relative humidity of less than 50 %.
2

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SIST EN ISO 7441:1999
IS0 7441-1984 0
the test specimen in the zone of bimetallic corrosion. The zone
Control specimens made from metals susceptible to natural
of bimetallic corrosion is the total area of the anodic plate, of
ageing should be stored only for evaluation of changes in
width 10 mm, adjacent to the zone of the direct contact with
mechanical properties.
the cathodic plates.
5.5 In preparing specimens a thin layer of an organic coating,
Evaluations of bimetallic corrosion resistance by change in sur-
glue, varnish or lacquer, such as cellulose acetate dissolved in
face appearance and by the amount and type of corrosion ef-
acetone, is recommended to prevent crevice corrosion. This
fect shall be carried out separately for the marked (face) and
coating should be applied to the degreased surface of the
unmarked (reverse) sides of the specimens.
anodic plate in such a way as to seal completely the gap be-
The result of the test shall be taken as the average value of the
tween the anode and cathode plates without projecting beyond
corrosion increase index (indices) determined for three or more
the cathode plate. The dry coating thickness should not exceed
specimens.
10 pm. This coating should not cover the area adjacent to bolt
holes, in order to allow contact between the metallic plates
when they are assembled.
7.2 Evaluation based on change in surface
appearance
Transition resistance between cathodic and anodic plates
should be kept constant throughout the period of test.
7.2.1 Specimens chosen for inspection, either during or on
completion of the test, shall be examined visually in daylight or
in artificial diffused light. Optical instruments may be used if
6 Procedure
this is specified in the test programme.
6.1 Test specimens and reference specimens shall be ex-
7.2.2 The following changes in surface appearance shall be
posed to the outdoor atm
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