Operation. Platinized anodes can be operated at very high current
densities (100 A/ft are typical). The primary limitation of platinized
anodes is that the oxide film on the substrate can break down if excessive
anode-to-electrolyte voltages are encountered. The practical limit for
platinized titanium is 12 V. Platinized niobium can be used at potentials as
high as 100 V. Since these anodes are small in size, their resistance-
to-electrolyte is high and therefore, higher voltages are required to obtain
Alloyed Lead. Lead alloyed with silver, antimony, or tin have been
used as anodes for impressed current cathodic protection systems in seawater.
The chief advantage of lead anodes is their low cost. The consumption rate
for silverized lead is 2- to 3-lbs/A yr initially but drops off to
approximately 0.2 lbs/A yr after 2 years. The current density from silverized
lead anodes is typically 10 A/ft. Alloyed lead anodes have been unreliable
in many specific applications either because they failed to passivate and
their consumption rate remained in the 2-to 3-lbs/A yr range and they were
completely consumed, or they became so highly passivated that the
anode-to-electrolyte resistance increased substantially.
Other System Components. In addition to the source of power for
cathodic protection and the anodes used, cathodic protection systems contain
other important components. The entire system must be reliable in order to
provide effective protection.
Connecting Cables. The connecting cables used between the various
components of cathodic protection systems are vital to the proper performance
of the system. Any break in the primary circuit will result in failure of the
system and will require repair to restore the flow of protective current.
Breaks in the auxiliary connections such as those used to test the system will
also result in difficulties in proper adjustment and inspection of the system.
Proper selection of cable size, type of insulation, and routing is necessary
for proper and reliable system operation. Only insulated copper cables should
be used in any cathodic protection installation. High connection resistances
and difficulty in making welded connections associated with the use of
aluminum wires precludes their use in cathodic protection installations.
Factors to be Considered. Connecting cables should be selected
based upon consideration of the following factors:
Current carrying capacity
Economics (first cost versus power costs)
Dielectric strength of insulation
Durability (abrasion & cut resistance) of insulation
Standard wire sizes, weights, and breaking strengths are given in Table 10.