MIL-HDBK-1004/10
Area in water = 20 x 40 x 7 = 5,600 ft
Area in mud = 20 x 25 x 7 = 3,500 ft
b)
Protective current required:
In water - 5,600 ft x 2 mA/ft = 11.2 A
In mud - 3,500 ft x 1 mA/ft = 3.5 A
Total = 14.7 A
c)
Minimum weight of anodes required for 10-year anode life:
W = YSI
where
W
=
weight of anodes required
Y
=
10 years
S
=
7.6 lbs/A yr (includes efficiency factor)
I
=
14.7 A current required
W
=
10 x 7.6 x 14.7 = 1,117.2 pounds
As there are 10 bents it is desirable for current distribution to have at
least one anode per bent. Thus, 120-pound anodes should be used if the
current output per anode is sufficient.
d)
Current output per anode:
Resistance of a single vertical anode (refer to para. 6.2.1.4)
R
= (P/L)K
V
where
R
= electrolyte-to-anode resistance
V
P = electrolyte resistivity
L = anode length
K = shape function
For A-120 anodes (refer to Table 22)
R
= 22/1(0.008) = 0.176 ohms
V
For A-120-1 anodes (refer to Table 22)
R
= 22/2(0.012) = 0.132 ohms
V
For A-120-2 anodes (refer to Table 22)
R
= 22/4(0.017) = 0.093 ohms
V
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