MIL-HDBK-1004/10
Graphite Anodes. Graphite anodes are the most commonly used
6.6.1
material for impressed current anodes in underground applications. They are
made by fusing coke or carbon at high temperatures and are sealed from
moisture penetration by being impregnated with a synthetic resin, wax, or
linseed oil to reduce porosity and increase oxidation resistance. An
insulated copper cable is attached to the anode internally for electrical
connection to the rectifier. This connection must be well sealed to prevent
moisture penetration into the connection and must be strong to withstand
handling. The most important single improvement in high silicon cast iron and
graphite anodes is placing the lead wire connection in the center of the anode
instead of the end. This eliminates end-effect, where ends of the anode are
consumed 1-1/2 times faster than the center. Although more expensive, the
anode life is nearly doubled (tubular anodes will be 95 percent consumed,
whereas end connected anodes will be only 50 percent consumed before the
anode-to-lead wire connection is lost). This also allows for a more effective
seal of the lead wire connection.
Nearly all anode sizes are available in
tubular form where the lead wire connection is located in the center. Typical
anodes, connections, and seals are shown in Figures 43 and 44.
Specifications. The following are typical specifications for
6.6.1.1
commercially available graphite anodes.
Impregnant (Linseed Oil Synthetic Resin or Wax)
6.5 wt % max
Ash
1.5 wt % max
Moisture & Volatile Matter
0.5 wt % max
Water Soluble Matter
1.0 wt % max
Graphite
Remainder
Physical Properties
Density
99.84 lb/cu ft max
0.0011 ohm-cm max
Mechanical Requirements
Lead wire connection strength
525 lb minimum
Graphite anodes are commercially available in two
6.6.1.2
Available Sizes.
sizes:
Weight (lb) Diameter (in.)
Length (in.)
Surface area (ft)
27
3
60
4.0
68
4
80
7.1
The weights given are for the graphite only and do not include the weight of
the lead wire or connection.
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