ISO 4540:1980

International Standard
INTERNATIONAL ORGANIZATION FOR STANDARDIZATION.MEXaYHAPOJlHAR OPrAHM3AUMR fl0 CTAHAAPTM3A~MMWIRGANISATION INTERNATIONALE DE NORMALISATION
Coatings cathodic to the Substrate -
Metallic coatings -
Rating of electroplated test specimens subjected to
corrosion tests
Cotation des bprouvettes ayant
- Depots electrolytiques cathodiques par rapport au m&al de base -
Re& temen ts /ne taffiques
recu un dep6t tilectrofytique, soumises aux essais de corrosion
First edition - 1980-10-01
UDC 621357.7 : 620.193
iii Ref. No. ISO 45404980 (E)
-
Descriptors : metal coatings, corrosion tests, classification, defects.
I
3
ii
-
Price based on 16 pages

---------------------- Page: 1 ----------------------
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of
national Standards institutes (ISO member bodies). The work of developing Inter-
national Standards is carried out through ISO technical committees. Every member
body interested in a subject for which a technical committee has been set up 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.
Draft International Standards adopted by the technical committees are circulated to
the member bodies for approval before their acceptance as International Standards by
the ISO Council.
International Standard ISO 4540 was developed by Technical Committee ISO/TC 107,
Meta//ic and other non-organic coatings, and was circulated to the member bodies in
March 1977.
lt has been approved by the member bodies of the following countries :
Australia India South Africa, Rep. of
Austria I reland Spain
Bulgaria Israel Sweden
Italy Switzerland
Canada
Czechoslovakia Japan Turkey
France Korea, Rep. of United Kingdom
Germany, F. R. Poland USA
Hungary Romania USSR
The member body of the following country expressed disapproval of the document on
tech nical grounds
Netherlands
International Organkation for Standardkation, 1980
0
Printed in Switzerland

---------------------- Page: 2 ----------------------
INTERNATIONAL STANDARD
ISO 4540-1980 (E)
Metallic coatings - Coatings cathodic to the Substrate -
Rating of electroplated test specimens subjected to
corrosion tests
1 Scope and field of application 2.2 The rating number assigned to the ability of the coating
to protect the Substrate from corrosion is called the “protec-
tion” rating .
1 .l This International Standard specifies a method of
evaluating the condition of electroplated test specimens that
have been exposed to corrosive environments for test pur- 2.3 The rating number assigned by the inspector’s judgment
poses. of the Overall appearance of the specimen, including all defects
caused by exposure (see the note), is called the “appearance”
lt is based on experience of the method with Standard rating.
10 cm x 15 cm test Panels, exposed on racks at outdoor test
sites in natura1 atmospheres. lt has also been used for rating
NOTE - Spetimens that are not “perfett” even before being exposed
similar Panels that have been subjected to accelerated tests, should normally be rejected (sec the note to clause 4).
such as those specified in ISO 3768, Meta//ic coatings -
Neutral salt Spray test INSS test), ISO 3769, Metallic coatings
2.4 The result of inspecting a specimen is recorded as two
-
Acetic acid salt Spray test (ASS test), ISO 3770, Metallic
numbers separated by an oblique stroke (/), the protection
coatings - Copper-accelerated acetic acid salt spra y test
number being given first.
(CASS test) and ISO 4541, Metallic and other non-organic
coatings - Corrodkote corrosion test (CORR test). Any
2.5 In addition to recording the numerical rating of a
modifications needed to adapt the method to rating actual pro-
specimen, the inspector should note the typeIs) and severity of
duction Parts are not considered in this International Standard.
defectls) contributing to the rating. This may be done by the
use of agreed Symbols for the most common defects (sec
1.2 This method is applicable only to decorative and protec-
annex A) and abbreviations for the degree or severity of these
tive coatings that are cathodic to the Substrate, for example
defects.
nicke1 plus chromium or topper plus nicke1 plus chromium on
steel or zinc die castings. lt is not intended for use with anodic
2.6 For the rating of purely protective (not decorative)
sacrificial coatings such as zinc and Cadmium on steel.
cathodic coatings, the “appearance number” may be omitted.
3 Types of defect
2 Principle
3.1 “Protection” defects (see annex A) include crater corro-
2.1 The rating method described in this International Stan-
sion, pinhole corrosion, corrosion products, blisters (see the
dard recognizes that typical decorative and protective deposits
note), and any other defects that involve basis metal corrosion.
such as nicke1 plus chromium, with or without a topper under-
coat, have two functions :
NOTE - Blisters on electroplated zinc alloy die castings usually signify
basis metal corrosion, but the inspector’s judgment may be required to
a) to protect the Substrate from corrosion and thus pre-
decide whether a blister does or does not arise at the Substrate-coating
vent degradation of appearance caused by basis metal cor-
interface.
rosion products, such as rust and rust stains;
3.2 “Appearance” defects include, in addition to those
b) to itself maintain a satisfactory appearance.
caused by basis metal corrosion, all defects that detract from
the appearance (i.e. the commercial acceptability) of the
Although these functions overlap, they tan be evaluated
specimen. Typical defects are surface pits, “crow’s feet”,
separately and it is frequently desirable to do so. Accordingly,
Cracks, surface stain, tarnish, etc.
this International Standard assigns separate ratings to
a) the appearance as affected by corrosion of the
3.3 Defects developing on exposure that indicate improper
Substrate;
preparation or electroplating shall be noted, but no attempt
should be made to rate test specimens showing major amounts
b) the appearance as affected by deterioration of the
of such defects. Peeling of the coating from the Substrate, or of
coating itself.
one coating from another, is the principal such defect.
1

---------------------- Page: 3 ----------------------
ISO 4540-1980 (EI
4 Preparation for and manner of inspection
TABLE - Protection rating versus area of defect
NOTE - It may sometimes be necessary to expose specimens for test, Area of defect
1
Rating
even though they are defective in certain respects before exposure. In %
that case, an inspection shall be made and the findings recorded before
the specimens are exposed.
No defect 10
< 0,l 9
> 0,l < 0,25 8
Spetimens may be inspected on the exposure racks or
4.1
may be removed to a more suitable location if necessary. > 0,25 < 0,5 7
Lighting during inspection shall be as nearly uniform as possi-
> 0,5 G l,o 6
ble; direct reflection from sun or clouds shall be avoided, and
> l,o d 2,5 5
various angles of inspection shall be tried to ensure that defects
show up. > 2,5 < 5 4
> 5 < 10 3
> 10 < 25 2
4.2 If the condition of the specimens allows, they shall be in-
> 25 < 50 1
spected in the uncleaned condition. If dirt, salt deposits, etc.,
make it impractical to inspect them, specimens may be
> 50 0
1
sponged with a mild soap Solution followed by a water rinse,
but no pressure should be exerted in this procedure as this
would tend to upgrade the rating by, for example, cleaning off
5.1.1 Stritt application of the equation given in 5.1 would
the corrosion products. Spetimens should be allowed
to dry
lead to ratings greater than 10 for specimens with extremely
before they are inspected.
small defective areas. Rating 10, accordingly, is arbitrarily
assigned to a specimen with no defects.
4.3 Defects to be noted and taken into account in rating
specimens include only those that tan be seen by the unaided
5.1.2 If desired, fractional ratings between 9 and 10 may be
eye. (“Unaided eye” includes wearing of correctional glasses, if
assignated to Panels judged better than 9 but not perfett. Frac-
the inspector normally wears them.)
tional ratings below 9, although normally not especially useful,
may be assigned if desired.
Optical aids may be used to identify or study defects, after they
have been detected by the unaided eye.
5.2 As an aid in judging the defective area, Standards of com-
parison consisting of Photographs of Panels and dot Charts are
4.4 Edge defects, occurring within 6 mm of the edges of a
reproduced in annex B.The Standards represent as nearly as
specimen, may be noted in the description, but are not nor-
possible the maximum amount of corrosion permissible for a
mally counted in arriving at the numerical rating. Similarly, con-
given rating; there is a Standard for each rating 1 to 9. A
tact and rack marks, mounting holes, etc., shall be disre-
specimen worse than the Standard for rating 1 is assigned a
garded.
rating of 0.
The types of corrosion defects normally encountered differ ac-
4.5 Rubbing, polishing, etc., of the surface of the specimen
cording to the type of atmospheric exposure. Typical
may be desirable to study one or another aspect of its con-
decorative deposits exposed to marine atmospheres often tend
dition. Such a procedure shall be confined to the minimum area
to fail by crater corrosion, whereas, in industrial atmospheres,
absolutely necessary for the purpose, preferably not more than
they are more likely to exhibit pinhole corrosion. The latter at-
1 cm2 of a 10 cm x 15 cm specimen.
mosphere also tends to be more severe with regard to degrada-
tion of the coating System, but somewhat less severe with
regard to basis metal corrosion. For this reason, the same stan-
5 Assignment of protection rating dard comparison photogaphs or Charts are not suitable for use
at all types of locations. Photographs are more helpful in
assessing specimens exposed to marine atmospheres, whereas
5.1 The numerical rating System is based on the area covered
dot Charts are more suitable for industrial atmospheres. (See
by protection defects and is given by the following equation :
annex B.)
R = 3 (2 - log 10 4
where 5.3 In rating any given specimen, it is recommended that the
appropriate series of Standards, i.e. Photographs or dot Charts,
R is the rating; be placed beside it, and the basis metal corrosion defects be
matched as nearly as possible with one of the Standards. If the
specimen is somewhat better than Standard (X), but not as
A is the percentage of the total area covered by defects.
good as Standard (X + 11, it is rated (XI; if somewhat worse
R is rounded off to the nearest whole number, as indicated in than Standard (XI but not as bad as Standard (X - l), it is
the following table. rated (X - 1).
2

---------------------- Page: 4 ----------------------
ISO 4540-1980 (EI
A penalty of 1 or 2 Points (rating numbers) is assigned for ap-
5.4 If a large group of specimens is being inspected at one
pearance defects classified as slight. One penalty Point is
time, it is recommended that they be assessed individually as
assigned if the defects tan be classified as very slight, two if
in 5.3, but when the entire group has been rated, the individual
slight.
ratings should be reviewed to make sure that the ratings
assigned actually reflect their relative merits. This review acts
NOTE - If fractional rating was used for the protection number, this
as a check on individual ratings and aids in ensuring that the in-
would result in a fractional appearance rating; in that case the frac-
spector’s judgment or frame of reference has not changed dur-
tional appearance rating should be rounded to the next lower whole
ing the course of the inspection, owing to fatigue, Change in
number.
lighting conditions, haste to finish the job, or other Causes. One
method of facilitating this comparison is to remove individual
specimens from their racks and place them beside other
6.3.2 Defects moderately damaging include the same types as
specimens. lt may be advisable to arrange all of th
...