MIL-HDBK-1110
1.3.4.2
Crevices. Crevices should be avoided in structures,
because these oxygen-deficient areas accelerate metal corrosion.
Thus, continuous welds should be used rather than skip welds.
Back-to-back angles should also be avoided for this reason.
1.3.4.3
Rough and Sharp Surfaces. To obtain protection of a
surface, a painter must be able to apply a uniformly thick,
continuous film. Thus, irregular surfaces such as welds and other
projections should be ground smooth to eliminate projections
through the paint film. Weld-spatter, which is loosely-bonded to
the steel, must be removed for two reasons. First, it creates
crevices which lead to crevice corrosion and, second, as the mill
scale becomes disbonded, the barrier film will be broken.
Sharp edges should be rounded (1/8 inch or more radius
is ideal) because a uniformly thick coating cannot be applied
over the edge. This is because wet coatings draw thin on them.
Sharp interior corners should be avoided, since they may receive
an excessive coating thickness.
1.3.4.4
Limited Access to Work. Areas to be protected should
be readily accessible for inspection and maintenance. Difficult-
to-reach areas are not only difficult to prepare and coat, but
reaching them may also constitute a safety hazard.
1.3.4.5
Incompatible Environment. Materials must be compatible
with the environment in which they are located. Thus, aluminum
should not come into direct contact with concrete, because the
alkalinity of the concrete will attack the aluminum.
1.3.4.6
Contact of Dissimilar Metals. Dissimilar metals
probably present the biggest design problem. Because they have
different corrosion potentials, they may corrode rapidly when in
contact with each other. Examples of dissimilar metal (galvanic)
corrosion are:
a)
Steel pipe passing through an aluminum deck
b)
Steel nut on a copper valve
c)
Aluminum stanchion with a bronze lifeline
d) Aluminum plate with steel or different alloy
aluminum rivets
e)
Mild steel attached to stainless steel
Dissimilar surface conditions (e.g., threads,
scratches, etc.) may also cause galvanic corrosion.
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