TM 5-811-7
a.
Design data.
(1) Tank height (from ground to bottom of bowl) is 37 feet.
(2) Tank diameter is 24 feet.
(3) High water level in the tank is 34.5 feet.
(4) Overall tank depth is 34.5 feet.
(5) Vertical shell height is 22.5 feet.
(6) Riser pipe diameter is 4 feet.
(7) The tank has a semicircular bottom.
(8) All inner surfaces are uncoated.
(9) Current required for protection -- bowl, 7.0 amperes, rise, 1.0 ampere.
(10) Electrical power available is 120/240-volt a.c., single phase.
(11) Tank is subject to freezing.
(12) Design for a 15-year life.
(13) Water resistivity is 4000 ohm-centimeters.
(14) Button-type HSCBCI anodes are used for the tank.
(15) Riser anodes are platinized titanium wire.
b.
(1) Find the minimum weight of button anode material required for the tank (eq C-1 from appendix C):
YSI
W'
,
E
where Y = 15 years, S = 1.0 pound per ampere-year, I = 7.0 amperes, and E = 0.50. Thus,
(15 yr)(1.0 lb/A&yr)(7.0 A)
W'
,
0.50
W = 210 lb.
(2) Compute the number of tank anodes needed (button anodes weigh 55 pounds):
210
N'
' 3.82 (use 4 anodes).
55
(3) Find the minimum weight of riser anode material required for the riser (eq C-I from appendix C):
YSI
W'
,
E
where Y = 15 years, S = 1.32 x 10-5 pound per ampere-year, I = 1.0 ampere, and 0 = 0.50. Thus,
(15 yr)(1.32 10&5lb/A&yr)(1.0 A
W'
0.50
W = 3.96 x 10-4 lb.
(4) Find the number of riser anodes needed. Platinized titanium wire, 0.1-inch in diameter, 3 feet long,
with .001-inch-think platinum over titanium will be used for each anode. The weight of platinum on each
anode is 8.8 x 10-5 pound. Thus,
3.96 10&4
N'
' 4.5 (use 5 anodes).
&5
8.8 10
(5) locate anodes as shown in figure D-6.
D-11
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