MIL-HDBK-1004/10
9.7.2
a)
Minimum weight of anodes required for tank:
W = YSI/E
where
Y
=
15 years
S
=
8.8 lbs/A yr
I
=
0.7 amp
E
=
0.50 efficiency
W
=
15 x 8.8 x 0.7/0.50
W
=
184.8 pounds
b)
Number of magnesium anodes:
N = 184.8/17 = 10.9 (use 12 anodes for symmetry).
Anodes are placed as shown in Figure 110.
Heating Distribution System. Impressed current cathodic protection
9.8
is designed for a well coated buried heating distribution system as shown in
Figure 111. The distribution system has not yet been installed, so current
requirements, etc., cannot be made. Rectifier size need not be calculated,
because it is sized in the field after installation of anodes.
9.8.1
Design Data
a)
Average soil resistivity, 1,000 ohm-cm.
b)
Design for 80 percent coating efficiency, based on experience.
c)
Design for 4 mA/ft of bare metal heating conduits.
d)
Ground bed resistance must not exceed 1.5 ohms.
e)
Graphite anodes must be installed with carbonaceous backfill.
f)
Design for 15-year life.
g) Insulating joints must be provided on both steam and condensate
lines at the first flange connection inside of all buildings.
h)
All conduit must be metallically bonded together in each
manhole.
i) All conduit is precoated at the factory and at no time is it
holiday-checked.
j) Single-phase electric power is available at 120/240 V ac from
the administration building.
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