MIL-HDBK-1011/1
Section 5: METALS
5.1
Scope. This section covers structural steel and metals in a
generic nature and does not deal with specific products.
5.2
General Design Considerations. Since most metals deteriorate as a
result of exposure to the action of oxygen, water vapor, carbon dioxide, salt
and other chemical substances, the use of metals in tropical area construction
requires careful consideration. High humidity and the heavy concentration of
salt in the air, soil and in the water in the tropics provide an ideal
environment for metal corrosion to occur. Protection of all metals from these
conditions is critical.
5.2.1
Corrosion Protection. It is equally important to avoid corrosion
of metals caused by galvanic action between two dissimilar metals. Some means
of separating dissimilar metals must, therefore, always be found. Because of
the combination of both high humidity and salt-laden air, the key to an
acceptable steel structure is understanding that each steel component must be
properly and adequately maintained. Any structural joints that are accessible
to moisture are also be accessible for proper inspection and maintenance.
(Refer to para. 15.4 for a comparison of metals exposed to various potentially
corrosive environments.)
5.2.2
Moisture Intrusion. If the design of the steel structure precludes
adequate maintenance accessibility, then the design also precludes moisture
accessibility to such members and joints. The design of structural members
provides for adequate shedding of rainwater and permits water entrapment.
5.3
Ferrous Metal. Avoid unprotected ferrous metal in exposed
locations wherever possible. It is particularly unsuited for coastal salt-
laden environments. For protected interior locations, hot-dip galvanizing is
acceptable; for exposed exterior locations, it is not recommended. Hot-dip
galvanizing does not provide adequate protection in exposed coastal salt-laden
environments.
If galvanized ferrous metal must be used, it is advised that a
three-layered paint coating of all surfaces be applied, Consider membrane
type paint (not latex), or high solids epoxy for best results. Electroplating
or cadmium plating is not permitted.
5.4
Aluminum. Aluminum is subject to pitting or corrosion in salt-
laden environments. It is recommended that heavy duty anodized coatings be
required. For covering large expansive areas, recognize that even light
shades of dark colors pick up excessive solar radiation. Because of this
potential for heat gain, all designs involving color-anodized aluminum
products need to accommodate expansion caused by heat. Take care to avoid
galvanic action conditions, particularly in salty, wet areas.
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