Table 3.2 provides the compatibility of carbon steel with selected
corrodents. A more comprehensive list will be found in Reference [1].
Atmospheric corrosion of steel is a function of location. In country air, the
products of corrosion are either oxides or carbonates. In industrial
atmospheres, sulfuric acid is present, and near the ocean some salt is in
the air. Corrosion is more rapid in industrial areas because of the presence of
the acid, and it is higher both near cities and near the ocean because of the
higher electrical conductivity of the rain and the tendency to form soluble
chlorides or sulfates that cause the removal of protective scale.
When steel is exposed to a clean, dry atmosphere, the surface is covered
with a 20–50-A˚ thick oxide film consisting of a layer of Fe2O3. This film
practically prevents further corrosion. If small amounts of water are present,
FeOOH may also form.
In noncontaminated atmospheres, the initiation of corrosion on a clean
metal surface is a very slow process, even if the atmosphere is saturated with
water vapor. Under these conditions, initiation of corrosion may occur at
surface inclusions or MnS, which dissolves when the surface becomes wet.
However, the presence of solid particles on the surface is a more important