Environmental Engineering Reference
In-Depth Information
nance, the expected type of corrosion, and the risk of product contamination by
corrosion products. When the design involves contact of two dissimilar metals,
their compatibility must be checked to avoid the incidence of galvanic corrosion.
The geometrical shape of the components is of the utmost importance. A faulty
geometrical design may be the cause of failure of a component by corrosion even
if the design satisfies all of the mechanical requirements. Some important rules
relating to geometrical design to minimize corrosion are discussed below.
4.6.1
Some Design Rules
1.
Provide corrosion allowance
. The simplest way to ensure the expected full
life of a component like pipe, tank, or a civil engineering structure is to
provide corrosion allowance to the wall thickness. This is simply an added
thickness over the mechanical design that will be corroded out over the
expected lifetime and is calculated from the rate of corrosion multiplied by
the number of years of life. However, with reliable corrosion protection
and monitoring, this additional material cost may be avoided.
2.
Avoid galvanic contact
. Whenever possible, the same or similar material
should be used throughout the entire structure. Otherwise, compatibility
must be checked when two dissimilar metals in contact are used. Providing
an insulation between two dissimilar metals is advisable, provided the insu-
lation does not produce crevice conditions. Lastly, if galvanic corrosion is
Figure 4.16
Crevices arising from design and assembly.
