MIL-HDBK-1138
carry over onto the sound, old painted surfaces. The coating
manufacturer or his or her representative can provide
recommendations and guidelines for mixing and applying the
coatings.
8.2.2
Cathodic Protection. Cathodic protection systems
are generally provided for all critical equipment. Often this
equipment includes buried pipelines. Cathodic protection may
also be used on submerged equipment, such as clarifier rake
mechanisms. Cathodic protection provides additional corrosion
protection, supplementing the normal protection offered by
protective coating systems. Refer to MIL-HDBK-1004/10.
Cathodic protection systems generally require a certain
amount of maintenance to ensure that the systems continue to
operate at design levels. O&M personnel need to be aware of any
cathodic protection systems at the WWTP. MIL-HDBK-1136, Cathodic
Protection Operations and Maintenance, provides specific
procedures that must be followed.
8.2.3
Materials of Construction. Much of a typical WWTP
consists of cast-in-place concrete structures. With a few
exceptions, concrete performs well in the environments associated
with WWTPs. Other common construction materials also do well but
require careful selection and maintenance to achieve long-term
service life. The wastewater associated with treatment plants is
usually not extremely aggressive, unless the facility receives
wastewater from certain industrial operations. However, hydrogen
sulfide is everpresent and must be recognized, especially in the
vapor areas above the wastewater surface. The wastewater surface
line in steel tanks is typically one of the first areas to become
susceptible to corrosion. Where the wastewater is agitated or
falls over weirs, hydrogen sulfide is released. Any condensate
formed will be very acidic and therefore aggressive to concrete
and unprotected carbon steel.
Perform regular inspection of the concrete and steel
surfaces in these aggressive areas and take appropriate action
when significant corrosion becomes evident. Corrosion of metal
surfaces usually occurs faster than on concrete surfaces and
corrective action should be performed as soon as possible. In
the case of concrete, the application of protective coatings is
usually required. For metals, use of protective coatings,
application of cathodic protection, or replacement with more
resistant metals may be appropriate.
The following metals are used extensively
8.2.3.1
Metals.
in WWTPs:
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