MIL-HDBK-1004/10
c) Minimum weight of riser anode material required for riser:
W = YSI/E
where
Y
=
15 years
1.32 x 10-5 lbs/A yr
S
=
I
=
1.0 A
E
=
0.50
(15 x 1.32 x 10-5 x 1.0)/0.50
W
=
3.96 x 10-4 pounds
W
=
d) Number of riser anodes. Platinized titanium wire 0.1-inch
diameter, 3 feet long, with 0.001-inch-thick platinum over titanium will be
used for each anode. The weight of platinum on each anode is 8.8 x 10-5
pounds:
N = (3.96 x 10-4)/(8.8 x 10-5) = 4.5 (use 5 anodes)
e)
Location of anodes (see Figure 106):
(1) Button anodes are mounted on the base of the tank at a
distance of 1/4 the tank diameter (6 feet) from the center. They are mounted
on metal angles and plates welded to the tank bottom; polyethylene insulation
is required to separate the anode from the metal mounting. Riser anodes are
suspended in the center of the riser pipe, spliced to a No. 4 AWG cable. The
top anode is placed 1 foot from the tank base. The remaining four anodes are
spaced at 4-foot intervals.
(2) Each button anode has its own No. 8 AWG, 7-strand copper
cable (HMWPE) run in conduit to a resistor box mounted at eye level on a tank
leg. The riser anode's one No. 4, AWG, 7-strand cable is run in conduit to
the resistor box. If required to get proper current output, a resistor must
be installed in the riser anode circuit at the time of rectifier sizing. The
rectifier must be sized once the anodes are installed and must be mounted at
eye level adjacent to the resistor box.
Steel Gas Main. Impressed current cathodic protection is designed
9.4
for the 6-inch welded gas main shown in Figure 107. This pipeline is not
constructed, so measurements may not be made.
177
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