(5) Find the current output to ground for a single 17-pound standard packaged magnesium anode using

equation C-2:

Cfy

i'

,

(eq C-2)

P

where C = 120,000, a constant for well coated structures using magnesium, f = 1.00 (table C-4), y = 1.00

(table C-5), P = 4500 ohm-centimeters. Thus,

120,000 1.00 1.00

i'

4500 ohm&cm

i = 26.7 mA.

Because the structure is well coated, anode spacing will be relatively large.

Size

Anode

factor

weight

Standard anodes

(f)

3

(packaged)

0.53

5

(packaged)

0.60

9

(packaged)

0.71

17

(packaged)

1.00

32

(packaged)

1.06

(packaged-anode dimension 8" dia x 16")a

50

1.09

50

(packaged-anode dimension 5" x 5" x 31"

1.29

Long anodes

9

(2.75" x 2.75" x 26" backfill 6" x 31")

1.01

10

(1.5" x 1.5" x 72" backfill 4" x 78")

1.71

18

(2" x 2" x 72" backfill 5" x 78")

1.81

20

(2.5" x 2.5"x "60" backfill 5" x 66")

1.60

40

(3.75" x 3.75" x 60" backfill 6.5" x 66")

1.72

42

(3" x 3" x 72" backfill 6" x 78")

1.90

Extra-long anodes

(1.6" dia x 10* backfilled to 6" din)

15

2.61

(1.3" x 20* backfilled to 6" din)

20

4.28

(2" dia x 10* backfilled to 8" din)

25

2.81

a

In this table, "denotes inches, ` denotes feet.

Reprinted from DA. Tefankjian, "Application of Cathodic Protection," *Materials Protection and Performance. *Vol 11 (No. 11),

November 1972. Used with permission.

Structure-to-electrolyte

Magnesium

Zinc

potential (volts, relative

structure

structure

to copper-copper sulfate)

factor (y)

factor (y)

-0.70

1.14

1.60

-0.80

1.07

1.20

-0.85

1.00

1.00

-0.90

0.93

0.80

-1.00

0.79

0.40

-1.10

0.64

0.00

-1.20

0.50

0.00

Reprinted from l).A. Tefankjian, "Application of Cathodic Protection.** *Materials Protection and Performance. *Vol 11 (No. 11),

November 1972. Used with permission.