(1) Tank diameter is 12 feet.

(2) Tank length is 40 feet.

(3) Design for 80 percent coating efficiency, based on experience.

(4) Design for 15-year life.

(5) Current requirement is 0.7 ampere.

(6) Packaged 17-pound standard magnesium anodes must be used.

(7) The tank is insulated well enough from foreign structures.

(1) Find the minimum weight of anodes required for the tank using equation C-I:

YSI

W'

,

(eq C-1)

E

where Y = 15 years, S = 8.8 pounds per ampere-year, I = 0.7 ampere, and E = 0.50 efficiency. Thus,

(15 yr)(8.8 lb/A&yr)(0.7 A)

W'

,

0.50

W= 184.8 lb.

(2) Find the number of magnesium anodes (17 pounds each) required:

184.8

N'

' 10.9 (use 12 anodes for symmetry).

17

Galvanic cathodic protection is designed for a gas distribution system in a housing area as shown in figure

C-3.

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