2.1.3
Precious Metal Anodes
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NOTE: At installations where icing conditions exist
and the scaling index of water is less than 20,000
(i.e., low hardness water), the designer should
consider using precious metal anodes, such as
platinized niobium, for cathodic protection systems.
The consumption rate of precious metal anodes is
less than that of other relatively non-sacrificial
anodes. However, precious metal anodes are more
vulnerable to damage and loss.
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2.1.3.1
Selection Requirements
Precious metal anodes shall be [solid] [composite] [wire] [rod] [expanded
mesh] [ribbon] in form. Selection of the configuration should be left to
the designer of the system. Long, continuous wire form lengths of precious
metal anodes may have an attenuating effect. This can be overcome by using
parallel feeder cable connected to segmented lengths of precious metal
anodes at intervals. Such assemblies shall be factory assembled with
factory sealed and tested electrical connections to the anode.
2.1.3.2
Anode Life Test
The anode wire material shall sustain current densities of 100 ampere per
square meter 10.764 square feet in an oxygen generating electrolyte for 20
years. The manufacturer shall certify that a representative sample taken
from the same lot used to construct the anode, has been tested and meets
the following criteria. The test cell sustains a current density of 10,000
ampere per square meter 10.764 square feet in a 15 weight percent sulfuric
acid electrolyte at 66 degrees C 150 degrees F without an increase in anode
to cathode potential of more than 1 volt. The cell containing the anode
shall be powered with a constant current power supply for the 30 day test
period. The representative sample shall be 125 mm 5 inch in length taken
from the lot of wire that is to be used for the anode.
2.1.4
Anode Connecting Cables
Anodes, except for mixed metal oxide and precious metal wire anodes, shall
have connecting cables installed at the factory. The Contractor shall
submit a certified test report showing that the connecting method has
passed a 120-day laboratory test without failure at the place of connection
wherein the anode was subjected to maximum recommended current output while
immersed in a 3 percent sodium chloride solution. Aluminum anodes
connected together by a threaded system shall have water-tight seals and be
electrically continuous.
2.2
RECTIFIERS AND ASSOCIATED EQUIPMENT
2.2.1
Rectifier Unit
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NOTE: Air-cooled rectifiers will be used for most
applications. Where highly corrosive atmospheres
exist, the equipment will be oil-immersed in a
tank-type housing. For hazardous area applications,
SECTION 13111A
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