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Utilitiesman (Advanced) - Manual for electric, plumbing, water and other utilities | Next
Chapter 8 Fire Protection Systems |
moved along a pipe that is covered by a
coating or wrapping, a completed circuit
between it and the pipe reveals a holiday and
causes a bell to ring or a bulb to light or a
buzzer to sound.
MAINTENANCE OF ANODE SYSTEMS
The anode system of cathodic protection
requires little maintenance since there is no
power source.
Magnesium and zinc anodes used in the
anode system sometimes suffer local or
self-corrosion that reduces their efficiency.
Replace the anode when the efficiency drops
to a minimum. Anode life varies from 5 to
30 years, depending upon the type of anode
used. It is conservative to figure that about
17 pounds of magnesium or 25 pounds of
zinc are wasted away by electrolysis from an
anode per ampere year. To detect the
effectiveness of cathodic protection, you
should install test stations in anode systems.
MAINTENANCE OF IMPRESSED
CURRENT SYSTEMS
The impressed system of cathodic
protection requires considerably more
maintenance than the anode system. This is because
an electrical current is used for the operation of the
system. The current may come from any alternating
current source. When alternating current is not
available, you can use other generating sources to
furnish the alternating current. The transformer-
rectifier used in the system requires much less
maintenance and servicing than other sources of
current. However, systematic maintenance
procedures must be used to keep these units in
operating condition.
The transformer-rectifier set consists of two
units, a transformer and a rectifier. The transformer
steps the voltage down to a value of 12 to 40 volts.
The rectifier changes the alternating current to
direct current. Remember to keep all of the
connections on this unit airtight.
The materials most often used for anodes with
impressed current are aluminum, high-silicon cast
iron, and graphite. Scrap iron and steel may be used
for anodes since they waste away at a rate of 20
pounds per ampere year. Replace anodes when they
are wasted away. Insulated wire that resists
electrolytic action must be used to make the
connections between the anodes and the structures
to be protected. The insulation on existing
current-carrying lines should be checked. Replace
the wires if they are deteriorating. Ensure that
overhead wiring is fastened securely to the poles
and that all connections are tight.
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