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Proper selection of fasteners for a corrosive
environment in which they are to be used, is
a key parameter affecting the safety of the
structure. There are many types of corrosion.
Fasteners for attaching a light housing compo-
nents for walls and roofs, are particularly vul-
nerable to two types of corrosion: atmospheric
corrosion and galvanic one.
Selection of fasteners for a corrosive envi-
ronment due to the aggressiveness of the
atmosphere, can be done based on the EN-
-IS 12944-2 standard. A description of each
corrosive environment has been presented in
Table 1.
When selecting the fasteners you must also
remember about galvanic corrosion. Galvanic
corrosion occurs when in a corrosive environ-
ment there are at least two different metals,
which are in electrical contact. This creates a
galvanic cell in which one metal is the anode,
and the other - the cathode. Corrosion failure
of a joint depends on several factors:
• position of the two metals in a voltage
series (potential difference)
• metal surfaces in contact,
• the presence of a corrosive solution (e.g.
seawater)
In the fastener selection process it is necessary
to create a situation when the area of cathode
is small and anode area is large.
This is called cathodic protection. In practice
this means that the fasteners should always be
made of a material more noble than the fixed
structural components. Table 2 shows adverse
or indifferent pairs with comments.
CORROSION AND PROTECTIVE COATING
Table 1 Corrosivity categories according to EN-ISO-12944.2
corrosivity
category
Coating thickness weight loss
(after 1 year of exposure)
examples of typical environments in a temperate climate
carbon steel
zinc coating
outdoors
indoors
g/m
2
µm g/m
2
µm
C1
very low
< 10
< 1,3
< 0,7
< 0,1 Not present.
Heated buildings with a clean atmosphe-
re, e.g. offices, shops, schools, hotels.
C2
lov
10 ÷ 200 1,3 ÷ 25 0,7 ÷ 5 0,4 ÷ 0,7 Atmosphere of a small amount of
impurities, mostly in rural areas
Unheated buildings where condensation
may occur, such as warehouses, sport halls.
C3
avarage
200 ÷ 400 25 ÷ 50 5 ÷ 15 0,7 ÷ 2,1
Urban and industrial atmosphere
with an average amount of pollution
with sulphur and carbon dioxide.
Coasteel areas with low salinity.
Production halls of high humidity level
and low contamination of air, e.g. food
production companies, breweries laun-
dries, dairy milk plants
C4
high
400 ÷ 650 50 ÷ 80 15 ÷ 30 2,1 ÷ 4,2 Industrial and waterfront areas with
medium salinity.
Chemical plants, swimming pools,
shipyards and ports.
C5-I
(Industrial)
very high
650 ÷ 1500 80 ÷ 200 30 ÷ 60 4,2 ÷ 8,4 Industrial areas with high humidity
and aggressive atmosphere.
Buildings and other facilities with almost
uninterrupted condensation and
considerable air pollution.
C5-M
(sea)
very high
650 ÷ 1500 80 ÷ 200 30 ÷ 60 4,2 ÷ 8,4 Coasteel areas and islands of high
salinity.
Buildings and other facilities with almost
uninterrupted condensation and
considerable air pollution.