ISO 9223:2012

INTERNATIONAL ISO
STANDARD 9223
Second edition
2012-02-01
Corrosion of metals and alloys —
Corrosivity of atmospheres —
Classification, determination and
estimation
Corrosion des métaux et alliages — Corrosivité des atmosphères —
Classification, détermination et estimation

Reference number
©
ISO 2012
©  ISO 2012
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ii © ISO 2012 – All rights reserved

Contents Page
Foreword . iv
Introduction . v
1  Scope . 1
2  Normative references . 1
3  Terms and definitions . 2
4  Symbols and abbreviated terms . 2
4.1  Symbols . 2
4.2  Abbreviated terms . 3
5  Category of corrosivity of the atmosphere . 3
6  Classification of corrosivity of the atmosphere . 3
7  Corrosivity determination based on corrosion rate measurement of standard specimens . 4
8  Corrosivity estimation based on environmental information . 4
8.1  Corrosivity estimation — General . 4
8.2  Normative corrosivity estimation based on calculated first-year corrosion losses . 5
8.3  Informative corrosivity estimation based on description of exposure conditions . 6
Annex A (informative) Sources of uncertainty associated with the determination and estimation of
atmospheric corrosivity . 7
Annex B (informative) Characterization of the atmosphere in relation to its corrosivity . 9
Annex C (informative) Description of typical atmospheric environments related to the estimation
of corrosivity categories . 13
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 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.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.
The main task of technical committees is to prepare International Standards. Draft International Standards
adopted by the technical committees are circulated to the member bodies for voting. Publication as an
International Standard requires approval by at least 75 % of the member bodies casting a vote.
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.
ISO 9223 was prepared by Technical Committee ISO/TC 156, Corrosion of metals and alloys.
This second edition cancels and replaces the first edition (ISO 9223:1992), which has been technically revised.
iv © ISO 2012 – All rights reserved

Introduction
Metals, alloys and metallic coatings can suffer atmospheric corrosion when their surfaces are wetted. The
nature and rate of the attack depends upon the properties of surface-formed electrolytes, particularly with
regard to the level and type of gaseous and particulate pollutants in the atmosphere and to the duration of
their action on the metallic surface.
The character of the corrosion attack and the corrosion rate are consequences of the corrosion system, which
comprises the metallic materials, the atmospheric environment, technical parameters and operation conditions.
The corrosivity category is a technical characteristic which provides a basis for the selection of materials and
protective measures in atmospheric environments subject to the demands of the specific application,
particularly with regard to service life.
Data on the corrosivity of the atmosphere are essential for the development and specification of optimized
corrosion protection for manufactured products.
The corrosivity categories are defined by the first-year corrosion effects on standard specimens as specified in
ISO 9226. The corrosivity categories can be assessed in terms of the most significant atmospheric factors
influencing the corrosion of metals and alloys.
The measurement of relevant environmental parameters is specified in ISO 9225.
The ways of determining and estimating the corrosivity category of a given location according to this
International Standard and the relationships among them are presented in Figure 1. It is necessary to
distinguish between corrosivity determination and corrosivity estimation. It is also necessary to distinguish
between corrosivity estimation based on application of a dose-response function and that based on
comparison with the description of typical atmospheric environments.
This International Standard does not take into consideration the design and mode of operation of the product,
which can influence its corrosion resistance, since these effects are highly specific and cannot be generalized.
Steps in the choice of optimized corrosion protection measures in atmospheric environments are defined in
ISO 11303.
Figure 1 — Classification of atmospheric corrosivity

vi © ISO 2012 – All rights reserved

INTERNATIONAL STANDARD ISO 9223:2012(E)

Corrosion of metals and alloys — Corrosivity of atmospheres —
Classification, determination and estimation
1 Scope
This International Standard establishes a classification system for the corrosivity of atmospheric environments.
It
 defines corrosivity categories for the atmospheric environments by the first-year corrosion rate of
standard specimens,
 gives dose-response functions for normative estimation of the corrosivity category based on the
calculated first-year corrosion loss of standard metals, and
 makes possible an informative estimation of the corrosivity category based on knowledge of the local
environmental situation.
This International Standard specifies the key factors in the atmospheric corrosion of metals and alloys. These
are the temperature-humidity complex, pollution by sulfur dioxide and airborne salinity.
Temperature is also considered an important factor for corrosion in areas outside the temperate macroclimatic
zone. The temperature-humidity complex can be evaluated in terms of time of wetness. Corrosion effects of
other pollutants (ozone, nitrogen oxides, particulates) can influence the corrosivity and the evaluated one-year
corrosion loss, but these factors are not considered decisive in the assessment of corrosivity according to this
International Standard.
This International Standard does not characterize the corrosivity of specific service atmospheres,
e.g. atmospheres in chemical or metallurgical industries.
The classified corrosivity categories and introduced pollution levels can be directly used for technical and
economical analyses of corrosion damage and for a rational choice of corrosion protection measures.
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.
ISO 8044, Corrosion of metals and alloys — Basic terms and definitions
ISO 9224, Corrosion of metals and alloys — Corrosivity of atmospheres — Guiding values for the corrosivity
categories
ISO 11844-1, Corrosion of metals and alloys — Classification of low corrosivity of indoor atmospheres —
Part 1: Determination and estimation of indoor corrosivity
ISO 11844-2, Corrosion of metals and alloys — Classification of low corrosivity of indoor atmospheres —
Part 2: Determination of corrosion attack in indoor atmospheres
ISO 11844-3, Corrosion of metals and alloys — Classification of low corrosivity of indoor atmospheres —
Part 3: Measurement of environmental parameters affecting indoor corrosivity
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 8044 and the following apply.
3.1
corrosivity of atmosphere
ability of the atmosphere to cause corrosion in a given corrosion system
3.2
category of corrosivity of atmosphere
standardized rating of corrosivity of atmosphere in relation to the one-year corrosion effect
3.3
type of atmosphere
characterization of the atmosphere on the basis of appropriate classification criteria other than corrosivity or of
complementary operation factors
EXAMPLE Rural, urban, industrial, marine, chemical, etc.
3.4
temperature-humidity complex
combined effect of temperature and relative humidity on the corrosivity of the atmosphere
3.5
time of wetness
period when a metallic surface is covered by adsorptive and/or liquid films of electrolyte to be capable of
causing atmospheric corrosion
3.6
pollution level
numbered rank based on quantitative measurements of specific chemically active substances, corrosive
gases or suspended particles in the air (both natural and the result of human activity) that are different from
the normal components of the air
3.7
category of location
conventionally defined typical exposure conditions of a component or structure
EXAMPLE Exposure in the open air, under shelter, in a closed space, etc.
3.8
dose-response function
relationship derived from results of field tests for calculation of corrosion loss from average values of
environmental parameters
4 Symbols and abbreviated terms
4.1 Symbols
r Corrosion rate for the first year of atmospheric exposure
corr
T Air temperature
2 © ISO 2012 – All rights reserved

P SO deposition rate
d 2
P SO concentration
c 2

S Cl deposition rate
d
 Time of wetness
4.2 Abbreviated terms
C Atmospheric corrosivity category
RH Relative humidity
5 Category of corrosivity of the atmosphere
The corrosivity of the atmosphere is divided into six categories (see Table 1).
Table 1 — Categories of corrosivity of the atmosphere
Category Corrosivity
C1 Very low
C2 Low
C3 Medium
C4 High
C5 Very high
CX Extreme
6 Classification of corrosivity of the atmosphere
The corrosivity of atmospheric environments shall be classified either by determination of the corrosivity in
accordance with Clause 7 or, where this is not possible, by estimation of the corrosivity in accordance with
Clause 8. Both methods of the corrosivity evaluation represent a generalized approach and are characterized
by some uncertainties and limitations.
A corrosivity category determined from the first-year corrosion loss reflects the specific environmental situation
of the year of exposure.
A corrosivity category estimated from the dose-response function reflects the statistical uncertainty of the
given function.
A corrosivity category estimated using the informative procedure based on the comparison of the local
environmental conditions with the description of typical atmospheric environments can lead to
misinterpretations. This approach is to be used if experimental data are not available.
Annex A defines uncertainties related to the determination and normative estimation of atmospheric corrosivity
categories.
Detailed classification of low corrosivity of indoor atmospheres covering the corrosivity categories C1 and C2
in terms of this International Standard is specified in ISO 11844-1, ISO 11844-2 and ISO 11844-3.
7 Corrosivity determination based on corrosion rate measurement of standard
specimens
Numerical values of the first-year corrosion rates for standard metals (carbon steel, zinc, copper, aluminium)
are given in Table 2 for each corrosivity category. One-year exposure tests should start in the spring or
autumn. In climates with marked seasonal differences, a starting time in t
...