ISO 14993:2018

INTERNATIONAL ISO
STANDARD 14993
Second edition
2018-07
Corrosion of metals and alloys —
Accelerated testing involving cyclic
exposure to salt mist, dry and wet
conditions
Corrosion des métaux et alliages — Essais accélérés comprenant des
expositions cycliques à des conditions de brouillard salin, de séchage
et d'humidité
Reference number
©
ISO 2018
© ISO 2018
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ii © ISO 2018 – All rights reserved

Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 2
4 Test solution . 2
4.1 General . 2
4.2 Preparation of the sodium chloride solution . 2
4.3 pH adjustment . 2
5 Apparatus . 3
5.1 Component protection . 3
5.2 Exposure equipment . 3
6 Test specimens. 4
7 Arrangement of the test specimens . 4
8 Operating conditions . 5
9 Continuity of tests . 6
10 Duration of tests . 6
11 Treatment of test specimens after testing . 6
11.1 General . 6
11.2 Non-organic coated test specimens: metallic and/or inorganic coated . 6
11.3 Organic coated test specimens . 6
11.3.1 Scribed organic coated test specimens . 6
11.3.2 Organic coated but not scribed test specimens . 7
12 Evaluation of results . 7
13 Test report . 7
Annex A (informative) Typical apparatus for cyclic salt mist, dry and wet corrosion tests .9
Annex B (informative) Method for evaluation of the corrosivity of the apparatus .11
Annex C (normative) Preparation of test specimens with organic coatings for testing .13
Annex D (normative) Required supplementary information for testing test specimens with
organic coatings .14
Bibliography .15
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
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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 (see www .iso .org/directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
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.org/iso/foreword .html.
This document was prepared by Technical Committee ISO/TC 156, Corrosion of metals and alloys.
This second edition cancels and replaces the first edition (ISO 14993:2001), which has been technically
revised. The main technical changes are as follows:
— the document has been harmonized with ISO 9227;
— the terms and definitions clause has been added;
— the allowed range of mass loss of steel reference specimen has been changed.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www .iso .org/members .html.
iv © ISO 2018 – All rights reserved

Introduction
Corrosion of metallic materials with or without corrosion protection is influenced by many
environmental factors, the importance of which may vary depending on the type of metallic material
and the type of environment. It is impossible, therefore, to design accelerated laboratory corrosion
tests in such a way that all environmental factors influencing resistance to corrosion are taken into
account. Laboratory tests are, therefore, designed to simulate the effects of the most important factors
that enhance the corrosion of metallic materials.
The accelerated corrosion test method described in this document is designed to simulate and enhance
the environmental influence on a metallic material of exposure to an outdoor climate, where exposure
to salt-contaminated conditions occurs and may promote corrosion.
The test method involves cyclic exposure of test specimens to a mist of salt solution, to drying conditions
and to periods of high humidity. However, the method is mainly intended for comparative testing and
the results obtained do not permit far-reaching conclusions on the corrosion resistance of the tested
metallic material under the whole range of environmental conditions within which it may be used.
Nevertheless, the method provides valuable information on the performance of materials exposed to
salt-contaminated environments similar to those used in the test.
INTERNATIONAL STANDARD ISO 14993:2018(E)
Corrosion of metals and alloys — Accelerated testing
involving cyclic exposure to salt mist, dry and wet
conditions
WARNING — This document may involve hazardous materials, operations and equipment. It does
not purport to address all of the safety problems associated with its use. It is the responsibility
of the user of this document to establish appropriate safety and health practices.
1 Scope
This document specifies the apparatus and test procedure to be used in conducting accelerated
corrosion tests for the comparative evaluation of metallic materials with or without permanent
corrosion protection or temporary corrosion protection in salt-contaminated outdoor environments.
The test involves cyclic exposure of the specimens to neutral salt mist, “dry” and “wet” conditions. The
type of test specimen and the exposure period are not specified.
The particular advantages of this test over common accelerated tests such as the neutral salt spray
(NSS) test lie in its ability to better reproduce the corrosion that occurs in outdoor salt-contaminated
environments.
This document is applicable to
— metals and their alloys,
— metallic coatings (anodic and cathodic),
— conversion coatings,
— anodic oxide coatings, and
— organic coatings on metallic materials.
NOTE Methods of test for coatings to determine their resistance, in the presence of scribe marks through
to the substrate, to various cyclic corrosion conditions which include the condensation of water on the test
specimens during periods of humidity are given in ISO 11997-1.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements 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.
ISO 1514, Paints and varnishes — Standard panels for testing
ISO 2808, Paints and varnishes — Determination of film thickness
ISO 4623-2:2016, Paints and varnishes — Determination of resistance to filiform corrosion — Part 2:
Aluminium substrates
ISO 8044, Corrosion of metals and alloys — Basic terms and definitions
ISO 17872, Paints and varnishes — Guidelines for the introduction of scribe marks through coatings on
metallic panels for corrosion testing
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 8044 and the following apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https: //www .iso .org/obp
— IEC Electropedia: available at http: //www .electropedia .org/
3.1
reference material
material with known test performance
3.2
reference specimen
portion of the reference material (3.1) that is to be exposed with the intention to check the reproducibility
and repeatability of the test results for the test cabinet in use
3.3
test specimen
specific portion of the samples upon which the testing is to be performed
3.4
substitute specimen
specimen made of inert materials (such as plastic or glass) used for the substitute of a test specimen (3.3)
4 Test solution
4.1 General
Instructions for the preparation and use of a neutral sodium chloride solution are given in 4.2 and 4.3.
4.2 Preparation of the sodium chloride solution
Dissolve a sufficient mass of sodium chloride in distilled or deionized water with a conductivity no
higher than 20 μS/cm at 25 °C ± 2 °C to produce a concentration of 50 g/l ± 5 g/l. The sodium chloride
concentration of the sprayed solution collected shall be 50 g/l ± 5 g/l. The specific gravity range for a
50 g/l ± 5 g/l solution is 1,029 to 1,036 at 25 °C.
The sodium chloride shall not contain a mass fraction of the heavy metals of copper (Cu), nickel (Ni) and
lead (Pb) in total more than 0,005 %. It shall not contain a mass fraction of sodium iodide more than
0,1 % and a mass fraction of total impurities more than 0,5 %, calculated for dry salt.
NOTE Sodium chloride with anti-caking agents can act as corrosion inhibitors or accelerators. A useful
sodium chloride salt grade is a grade named Ph. Eur/USP or JIS, ACS.
4.3 pH adjustment
Adjust the pH of the salt solution so that the pH of the sprayed solution collected within the test cabinet
is 6,5 to 7,2 at 25 °C ± 2 °C. Check the pH using electrometric measurement. Measurements of pH
shall be done using electrode suitable for measuring in weakly buffered sodium chloride solutions in
deionized water. Make any necessary corrections by adding hydrochloric acid, sodium hydroxide or
sodium bicarbonate solution of analytical grade.
NOTE Possible changes in pH can result from loss of carbon dioxide from the solution when it is sprayed.
Such changes can be avoided by reducing the carbon dioxide content of the solution by, for example, heating it
to a temperature greater than 35 °C before it is placed in the apparatus, or by making the solution from freshly
boiled water.
2 © ISO 2018 – All rights reserved

5 Apparatus
5.1 Component protection
All components in contact with the salt mist spray or the test solution shall be made of, or lined with,
materials which are resistant to corrosion by the test solution and which do not influence the corrosivity
of the sprayed test solution.
The supports for the test specimen shall be constructed such that different substrate types do not
influence each other. It shall also be constructed so that the supports themselves do not influence the
test specimens.
5.2 Exposure equipment
5.2.1 Test cabinet, that meets the conditions of homogeneity and distribution of the spray. Due to the
limited capacity of test cabinets smaller than 0,4 m , the effect of the loading of the test cabinet on the
distribution of the spray and temperature shall be carefully considered. The solution shall not be sprayed
directly onto test specimens but rather spread throughout the test cabinet so that it falls naturally down
on them. The upper parts of the test cabinet shall be designed so that drops of sprayed solution formed
on its surface do not fall on the specimens being tested.
The size and shape of the test cabinet shall be such that during periods of exposure to salt mist spray,
the collection rate of solution in the test cabinet is within the limits specified in 8.2.
NOTE A schematic diagram of one possible design of test cabinet and associated apparatus for salt mist
cyclic corrosion testing is shown in Annex A.
5.2.2 Humidity and temperature control system, that maintains the test cabinet and its contents
at the specified temperature and humidity (see 8.1). The temperature shall be measured at a position at
least 100 mm from walls and radiant heat sources.
5.2.3 Spraying device, for spraying the salt solution during periods of exposure to salt mist spray
comprising a supply of air at controlled pressure, a reservoir containing the solution to be sprayed and
one or more atomizers.
The compressed air supplied to the atomizers shall be passed through a filter to remove all traces
of oil or solid matter and shall be at an overpressure of 70 kPa to 170 kPa. The pressure is typically
98 kPa ± 10 kPa but can vary depending on the type of test cabinet and atomizer used.
5.2.4 Air saturator, consisting of a saturation tower containing hot water at a temperature higher
than that of the test cabinet. In order to prevent evaporation of water from the sprayed droplets, the air
shall be humidified before entering the atomizer, by passage through this tower.
During periods of exposure to the salt mist, the appropriate temperature depends on the pressure used
and on the type of atomizer nozzle and shall be adjusted so that the rate of collection of spray in the test
cabinet and the concentration of the collected spray are kept to within the specified limits (see 8.2). The
level of water shall be maintained automatically to ensure adequate humidification.
The atomizers shall be made of inert material, e.g. glass or plastic materials. Baffles may be used to
prevent direct impact of spray on the test specimens and the use of adjustable baffles is helpful in
obtaining constant distribution of spray within the test cabinet. The level of the salt solution in the
supply tank shall be maintained automatically to ensure constant spray delivery throughout the test.
5.2.5 Collecting devices, at least two, consisting of clean funnels with a collecting area of approximately
80 cm made of glass or other chemically inert material, with the stems inserted into graduated cylinders
or other similar containers. The purpose of the collecting devices is to confirm that the collection rate
is within specified limits (see 8.2). They shall be placed in the zone of the test cabinet where the test
specimens are placed, one close to the spray inlet and one remote from an inlet and in such a way that
only spray, and not the liquid falling from specimens or from parts of the test cabinet, is collected.
5.2.6 Air dryer, comprising a heating device and fan to supply dried air of the specified humidity
during “dry” periods (see Table 1).
5.2.7 Exhaust system, by which air is exhausted from the test cabinet. It shall not be influenced by the
back pressure of the atmosphere when the air is released at a point outside the building.
6 Test specimens
6.1 The number and type of test specimens, their shape and their dimensions, shall be selected in
accordance with the specification for the material or product being tested. When not specified, these
parameters shall be mutually agreed between the interested parties. Unless otherwise specified or agreed,
test specimens with an organic coating to be tested shall be made from burnished steel conforming
with ISO 1514, and of approximate dimensions 150 mm × 100 mm × 1 mm. Annex C describes how test
specimens with organic coatings shall be prepared for testing. Annex D gives supplementary information
that shall be supplied, as appropriate, for testing test specimens with organic coatings.
6.2 The test specimens shall be thoroughly cleaned before testing, if not otherwise specified. The
cleaning method employed shall depend on the nature of the material, its surface and the contaminants
and shall not include the use of any abrasives or solvents which may attack the surface of the specimens.
Care shall be taken that test specimens are not re-contaminated after cleaning by careless handling.
6.3 If the test specimens are cut from a larger coated sample, cutting shall be carried out in such a way
that the coating is not damaged in the area adjacent to the cut. Unless otherwise specified, the cut edges
shall be adequately protected by coating them with a suitable material, which remains stable under the
conditions of the test, such as paint, wax or adhesive tape.
7 Arrangement of the test specimens
7.1 The test specimens shall be placed in the test cabinet so that they are not in the direct path of spray
from the atomizer.
7.2 If the test cabinet is not full of test specimens, it is recommended to
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