MIL-HDBK-1005/16
Cabinets
Factory finished, usually
baked epoxy enamel
Buss bars
Tinned copper or aluminum
Connections
Tinned
12.2.4.3 Outdoor Enclosures and Lighting. Use Type 304 stainless
steel, aluminum, or FRP for these pieces of equipment. Interior
process areas with moisture and/or hydrogen sulfide should use
similar material.
12.2.5
Instruments and Control Systems. Specify these systems
to withstand the environment to which they are exposed.
Generally, the specific information listed under par. 12.2.4 will
be applicable to instrument and control equipment. Direct
exposure to process fluids and chemicals, such as sensors,
requires alloys that will resist the exposure. For direct
contact with wastewater, Type 304 or 316 stainless steel is
preferred. For exposures to specific chemicals, the exposed
elements should resist the chemical exposure (see par. 12.2.6).
12.2.6
Chemical Handling Systems. A number of chemicals may
be used in a wastewater treatment plant. Many are very
aggressive to materials and should be carefully evaluated when
specifying storage tanks, piping, valves, and pumps. Chemical
storage facilities are usually required to be within a secondary
containment area that should also be protected against the
specific chemical exposure. Specific coating systems for
chemical containment areas are given in par. 12.3.1. Table 22
lists the preferred materials of construction for most of the
chemicals associated with wastewater treatment plants (the first
material listed is preferred). If linings are required for
chemical storage tanks or wastewater equipment, they should be
fabricated in accordance with National Association of Corrosion
Engineers (NACE) Standard RP0178, Fabrication Details, Surface
Finish Requirements, and Proper Design Considerations for Tanks
and Vessels to be Lined for Immersion Service.
12.2.6.1 Chlorine Gas. Normally, chlorine gas is handled in
carbon steel equipment leading to the vaporizer. Downstream of
the vaporizer (low pressure), the preferred piping is
nonmetallic. Dry chloride (liquid or gaseous) is not corrosive
to carbon steel. However, once moisture is present in the gas,
it is very corrosive to all but the most exotic metals, requiring
the use of nonmetallics.
204
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