MIL-HDBK-1004/10
where
W
=
weight of anodes required
Y
=
15 years
S
=
7.6 lbs/A yr (in this case includes efficiency factor)
I
=
62.16 A
W
=
15 x 7.6 x 62.16 = 7086
Each anode weighs 365 pounds, thus for the desired system life, the required
number of anodes is:
7086/365
=
19.4 (say 20)
There is an option to either select anodes with less output per pound of
material or use 20 anodes. Conservative design using 20 anodes was selected.
f)
Output from 32-pound magnesium anodes on shore side:
i = Cfy/p
where
i = current output in mA
C = 120,000 constant for well coated structures using
magnesium
f = 1.06 anode size factor (refer to Table 3)
y = 1.0 structural potential factor (refer to Table 4)
p = 1,000 ohm-cm, soil resistivity
i = (120,000 x 1.06 x 1.00)/1,000
i = 127.2 mA
g)
Number of anodes required for current output:
N = I/i
where
N
=
number of anodes required
I
=
current requirement (A)
i
=
output per anode (A)
N
=
8.3/0.127
N
=
65.35 (say 66 anodes)
h)
Minimum weight of anodes required for 15-year life.
W = YSI/E
202
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