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ETL 1110-9-10(FR)
5 Jan 91
2-8.
On-Grade Water Storage Reservoir (Ice Is Expected).
Impressed current cathodic protection is to be designed for the
existing ground level water reservoir shown in figure 2-22.
Coating is in poor condition and expected to deteriorate in the
future.
As the tank is not heated, ice forms in the winter.
Current requirement tests have been made.
a.
Design data.
1)
Tank is cylindrical with a flat bottom.
2)
Water resistivity is 2000 ohm-cm.
3)
Tank dimensions are:
Capacity = 250,000 gal
Diameter of bowl = 46 ft
High water depth = 20 ft.
4)
Design cathodic protection anodes for a 15-year life
since tank will be repainted at that time.
5)
Wire type ceramic anode will be used.
6)
Design current density is 2.5 A per sq ft of tank area
to be protected.
7)
Wetted surfaces are poorly coated.
As coating is
expected to deteriorate, design for bare tank.
8)
Area above high water level will be kept well coated.
9)
Tank is subject to freezing and therefore a hoop type
anode support system will be used.
10) Electrical power available is 120 V AC, single phase.
11) Current requirement at present for adequate cathodic
protection is 9.0 amp.
b.
1)
Find the area of the tank to be protected (A).
A = 2 B r h + B r2
104
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