MIL-HDBK-1005/16
12.3
Corrosion Control. In addition to the proper selection
of construction materials for the various equipment and systems
associated with a wastewater treatment plant, there are other
methods of controlling corrosion. With the exception of critical
service applications or extremely corrosive environments, carbon
steel and ductile iron are still the primary materials for much
of the equipment provided for a wastewater treatment plant.
While carbon steel and ductile iron (ferrous materials) do have
acceptable corrosion resistance in some environments, they still
require protection against the high moisture and the hydrogen
sulfide that is so prevalent. If not for corrosion resistance,
then some techniques are required just for aesthetic reasons.
The two most common methods to provide additional
protection against corrosion involve the use of protective
coatings and linings on ferrous surfaces. In immersion or buried
applications, the protection provided by the coatings is usually
supplemented by the application of cathodic protection.
12.3.1
Protective Coatings. With the exception of chemical
storage containment areas, the environments found in a wastewater
treatment plant are not excessively aggressive to high-quality
coating systems.
In most nonimmersion, process environments (both
interior and exterior), a coating system based on epoxy primer
with a polyurethane finish coat is preferred. This combination
provides excellent color and gloss retention, good durability,
and minimal maintenance. In interior, nonprocess areas, an alkyd
enamel system will provide good service. For immersion service,
coal-tar epoxy or straight epoxy materials have been used for
many years.
12.3.1.1 Surface Preparation. Critical to long-term performance
of any coating system is the surface preparation. Industrial
standards prepared by the SSPC should be specified and followed
for all coating applications. Table 23 lists the SSPC surface
preparation standards.
For immersion applications, SSPC SP5 is required. For
most process areas, SSPC SP10 is preferred. For less aggressive
environments, SSPC SP6 is acceptable. Hand- and power-tool
cleaning methods should only be used for repair and touch-up.
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