CATHODIC PROTECTION SYSTEM DESIGN EXAMPLES
Introduction. The following examples illustrate the application of
the design principles outlined in Sections 4, 6, and 7. They are intended to
illustrate the design methods to be used and are not standard designs. In
these examples, interference to or from foreign structures is not considered.
In practice, the design should be based upon field measurements whenever
possible and not on calculated estimates. In some examples, more detailed and
rigorous calculations than actually required are presented for illustrative
purposes. Shorter, more simplified calculations would give equally applicable
estimates, but should only be used once the basic concept of the process is
understood. It must be remembered that all cathodic protection system designs
make many assumptions, such as uniform environmental resistivity, which may or
may not prove to be true. When the system is installed, it will require
adjustment and possible modification in order for effective protection to be
achieved. In congested areas, interference problems are often difficult to
correct and optimum levels of protection may not be practically achieved. In
such cases, cathodic protection will reduce the incidence and degree of
corrosion damage but corrosion may not be entirely eliminated.
Twelve examples are provided:
Elevated steel water tank.
Elevated steel water tank where ice is expected.
Steel gas main.
Natural gas distribution system.
Hot water storage tank.
Underground steel storage tank.
Steam heat distribution system.
Aircraft multiple hydrant refueling system.
Steel sheet piling in seawater (galvanic anodes).
Steel sheet piling in seawater (impressed current).
Steel H piling in seawater (galvanic anodes).
Steel H piling in seawater (impressed current).
Elevated Steel Water Tank. This impressed current design is for a
tank that has not been built; hence, it is not possible to determine current
requirements, etc., by actual measurement. Calculated estimates are used.