Corrosion handbook

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The outcome of this approach is an estimated rate of corrosion of zinc or steel in
a given environment. The resulting corrosion rates define the prevalent corrosivity
category (C-class, see table 3).
As stated in the standard, the possible deviation using environmental data and the
dose-response function may be up to 50 %. It must be noted that the results are
only valid for macroclimatic and fully exposed (unsheltered) conditions. Moreover,
factors such as accumulation of corrosive substances or galvanic corrosion,
which can have a significant effect on the corrosion rate, are not taken into
account in this approach. Nevertheless, as long as these other potential sources
of corrosion are not present, the results of this calculation are usually accurate
enough to allow selection of the right material.
Corrosion is a natural process influenced by varying environmental factors which
cannot be foreseen for the entire designed lifetime. A conservative approach is
therefore always advised when it comes to the use of fastening and installation
products.
Corrosivity
category C
Corrosion
level
Typical environments
Indoor Outdoor
C1 Very low Heated spaces with low relative humidity and insignificant
pollution, e.g. offices, schools, museums.
Dry or cold zone, atmospheric environment with very low
pollution and time of wetness, e.g. certain deserts, Central
Arctic / Antarctica.
C2 Low Unheated spaces with varying temperature and humidity.
Low frequency of condensation and low pollution, e.g.
storage, sports halls.
Temperate zone, atmospheric environment with low
pollution (SO
2 < 5 µg/m
3
), e.g. rural areas, small towns.
Dry or cold zone, atmospheric environment with short time
of wetness, e.g. deserts, subarctic area.
C3 Medium Spaces with moderate frequency of condensation and
moderate pollution from production processes, e.g. food-
processing plants, laundries, breweries, dairies.
Temperate zone, atmospheric environment with medium
pollution (SO
2: 5 µg/m
3
to 30 µg/m
3
) or some effect of
chlorides, e.g. urban areas, coastal areas with low
deposition of chlorides.
Subtropical and tropical zone, atmosphere with low
pollution.
C4 High Spaces with high frequency of condensation and high
pollution from production processes, e.g. industrial
processing plants, swimming pools.
Temperate zone, atmospheric environment with high
pollution (SO
2: 30 µg/m
3
to 90 µg/m
3
) or substantial effect
of chlorides, e.g. polluted urban areas, industrial areas,
coastal areas without salt water spray, or exposure to
strong effect of de-icing salts.
Subtropical and tropical zone, atmosphere with medium
pollution.
C5 Very high Spaces with very high frequency of condensation and/or
with high pollution from production processes, e.g. mines,
caverns for industrial purposes, unventilated sheds in
subtropical and tropical zones.
Temperate and subtropical zone, atmospheric
environment with very high pollution (SO
2: 90 µg/m
3
to
250 µg/m
3
) and/or significant effect of chlorides, e.g.
industrial areas, coastal areas, sheltered positions on
coastline.
CX Extreme Spaces with almost permanent condensation or extensive
periods of exposure to extreme humidity effects and/
or with high pollution from production processes,
e.g. unventilated sheds in humid tropical zones with
penetration of outdoor pollution including airborne
chlorides and corrosion-stimulating particulate matter.
Subtropical and tropical zone (very high time of wetness),
atmospheric environment with very high SO
2 pollution
(higher than 250 µg/m
3
) including accompanying and
production factors and/or strong effect of chlorides, e.g.
extreme industrial areas, coastal and offshore areas,
occasional contact with salt spray.
This table gives a description of possible environments with respect to the
corrosion class. Although it can be used to estimate the corrosion class of the
application, one has to keep in mind that strictly following the standard means
that the corrosion class has to be determined by measurement of the corrosion
rate or the most important environmental parameters. Furthermore, the table only
takes typical atmospheric conditions into account.
The corrosion rates for steel, zinc, aluminum and copper with respect to the
corrosivity classes can be found in the ISO 9223 standard.
Table 3: Corrosivity categories and description of typical environments as stated in the ISO 9223 standard