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ETL 1110-9-10(FR)
5 Jan 91
CATHODIC PROTECTION DESIGN
1-1.
Introduction.
Recently, ceramic coated anodes have been incorporated in
cathodic protection systems. Ceramic or metal-oxide anodes have
been used for cathodic protection since 1971 in Europe and since
1984 in the United States. One of the main advantage of ceramic
anodes are that they are not consumed.
Ceramic anodes consist of various shapes of high purity titanium
substrates with coatings of precious metal oxides tailored to the
environment in which they will be used.
Unlike most other metal oxides (or ceramics), these metal oxides
are conductive. Ceramic anodes are dimensionally stable. The
ceramic coating is already oxidized (corroded).
The current capacity is a function of constituent variables and
is rated by the manufacturers. They have design life
expectancies of up to 20 years at a rated current output. The
life can be extended by a reduction in output current density.
Their life is limited by time and current density. The end of
the ceramic anode life is marked by a chemical change in the
oxide form and a resultant loss in conductivity. Ceramic anodes
are made in a variety of shapes for various applications. Among
these are wire, rods, tubes, strips, discs, and mesh. Ceramic
anodes have excellent ductility, which has eliminated the concern
about mechanical damage during shipment and installation.
Ceramic anodes are also a fraction of the size and weight of
traditional anode materials.
Scratches or other minor physical damages to the coating result
in the formation of an inert and nonconductive oxide of the
substrate (titanium) when operated at less than 60 V in fresh
water and underground applications. If they are installed in
salt or brackish water, the DC design voltage should be limited
to 12 V. The overall function of the anode is not significantly
impaired.
1-2.
Cathodic Protection Design Using Ceramic Anodes.
The following steps are involved in designing a cathodic
protection system using ceramic anodes:
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