ISO 19735:2023

INTERNATIONAL ISO
STANDARD 19735
First edition
2023-12
Corrosion of metals and alloys —
Corrosivity of atmospheres —
Mapping areas of increased risk of
corrosion
Corrosion des métaux et alliages — Corrosivité des atmosphères —
Cartographie des zones présentant un risque accru de corrosion
Reference number
© ISO 2023
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ii
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Mapping of corrosivity . 2
4.1 Dose-response functions . 2
4.2 Environmental data used as input to dose-response functions . 2
4.3 Transformation of the environmental data to a common grid system . 2
4.4 Calculation and presentation of corrosion . 2
5 Mapping of lifetime. 3
6 Mapping of corrosion cost .3
7 Mapping errors .4
Annex A (informative) ISO 9223 dose-response functions . 5
Annex B (informative) ICP materials functions . 6
Annex C (informative) Example of environmental data sources . 8
Annex D (informative) Procedure for calculation of lifetimes . 9
Bibliography .10
iii
Foreword
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iv
Introduction
Corrosion maps have become more frequent, and to ensure transparency and ease of comparison of
corrosion maps, this work was initiated.
This document describes procedures for calculating corrosivity maps based on arrays of environmental
data organised in a grid and using a dose-response function. Corrosivity maps based on dose-response
functions can be very useful for illustrating geographical variations, trends in time and the relative
importance of different underlying parameters (climate, pollution) and to communicate these results to
those not working in the field of corrosion. The result for an individual grid cell of a corrosivity map is,
however, very uncertain. If a corrosivity assessment for a single location is needed, it is recommended
to also consider direct measurements of corrosion according to ISO 9223.
v
INTERNATIONAL STANDARD ISO 19735:2023(E)
Corrosion of metals and alloys — Corrosivity of
atmospheres — Mapping areas of increased risk of
corrosion
1 Scope
This document gives guidelines for producing corrosivity maps and maps related to increased risk of
corrosion in outdoor open atmospheres, but not sheltered or semi-sheltered positions.
The maps are calculated based on environmental data using specific relationships, so-called
dose-response functions. Other means of producing corrosivity maps, for example using detailed
measurements of corrosion and subsequent interpolation of measured corrosion values, are not within
the scope of this document.
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 9223:2012, Corrosion of metals and alloys — Corrosivity of atmospheres — Classification,
determination and estimation
ISO 9224:2012, Corrosion of metals and alloys — Corrosivity of atmospheres — Guiding values for the
corrosivity categories
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
3.1
dose-response function
relationship derived from results of field tests for calculation of corrosion loss from average values of
environmental parameters
Note 1 to entry: The term is commonly used for all functions, including those where it is not mathematically
correct to denote the combination of time and pollution by the word “dose”.
4 Mapping of corrosivity
4.1 Dose-response functions
For worldwide corrosivity mapping of carbon steel, zinc, copper and aluminium (C1-C5 and CX), dose-
response functions given in ISO 9223 should be used. Other functions can also be used for comparison
purposes.
NOTE 1 The error associated with estimation of corrosivity categories using dose-response functions is
always higher compared to direct measurements and can lead to significant over or under estimation.
For mapping regions, countries or local areas other dose-response functions can be used.
NOTE 2 Several dose-response functions are available, and examples are given in Annex A and Annex B.
Dose-response functions should be derived from a statistical analysis of field exposure data collected
according to the procedures given in ISO 8565.
The dose-response functions used shall be clearly indicated in the map or map legend. If dose-response
functions are not derived from a statistical analysis of field exposure data, this shall be mentioned. This
is also the case if dose-response functions based on field data are altered or if several functions based
on different field exposure data are combined.
NOTE 3 It is permissible to simplify a dose-response function before its use by inserting a constant instead of
an environmental parameter if it can be clearly motivated by an error analysis. This can, for example, be done
with respect to temperature, if the mapped area is local with a small variation in temperature compared to other
parameters.
4.2 Environmental data used as input to dose-response functions
Data used as input to dose-response functions shall be based on annual averages or longer time spans.
The respective years(s) for the data shall be clearly indicated in the map or map legend.
It is recommended to use the same time period for all data, but exceptions can be made. One example is
if a map series is produced with the purpose of illustrating the effect of a changing pollution situation
over time (trends), where it is appropriate to use the same climate data (e.g. 30-year averages) for the
meteorological data in all maps in this series.
NOTE Data are generally available from national weather services, European agencies or other worldwide
data sources. A list of some common sources for data is given in Annex C.
Data used as input to dose-response functions shall not be outside the intervals for the parameters
upon which the dose-response function was derived. An extrapolation outside the boundaries of the
equation should be clearly marked in the map or map legend.
4.3 Transformation of the environmental data to a common grid system
To combine data by use of the dose-response function, all environmental data shall be transformed to
the same grid system and resolution.
It is recommended to keep the data with highest degree of uncertainty untransformed and transform
all remaining data accordingly.
4.4 Calculation and presentation of corrosion
The unit to be used for expressing uniform corrosion is µm. If the corrosion is localised but needs to be
expressed as an average, the unit g/m shall be used.
2 . 3
NOTE The relationship between these two units for uniform corrosion [g/(m µm) = g/cm ] is equal to the
density of the metal.
For carbon steel, zinc, copper and aluminium intervals corresponding to corrosivity categories C1-
C5 and CX as defined in ISO 9223 shall be used. Intervals for low-alloyed steels, including weathering
steels, shall follow those for carbon steel, zinc alloys and zinc coatings shall follow those for zinc, copper
alloys those for copper, and aluminium alloys those for aluminium.
Corrosivity shall be presented in maps with different colours ranging from lighter, corresponding to
low values of corrosivity, to darker, corresponding to high values of corrosivity.
It is recommended to use a scale which gives a logical representation of corrosivity (lighter – low;
darker – high) when a colour map is printed in black and white.
5 Mapping of lifetime
If the time development is given in the dose-response function, this expression shall be used. Otherwise,
the time expression given in ISO 9224 shall be used.
The corrosion rate, D, is given as a function of time according to ISO 9224:
b
D = r t (1)
corr
where
r is the corrosion rate experienced in the first year, which can be mapped and expressed ac-
corr
cording to the procedures in Clause 4;
t is the exposure time, expressed in years and t < 20 years;
b is the metal-environment-specific time exponent, usually less than 1.
The use of Formula (1) beyond 20 years is probably justified in most cases, especially if the exposure
is not much greater than 20 years. However, ISO 9224 also introduces an alternative linear a
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