Anode

Anode

Anode

Package

weight

dimensions

surface

area

L/d

K

L/d

K

(lb)

(in.)

size (in.)

(sq ft)

5

0.0140

20

0.0213

6

0.0150

25

0.0224

12

1 x 60

1.4

10 x 84

7

0.0158

30

0.0234

44

2 x 60

2.6

10 x 84

8

0.0165

35

0.0242

60

2 x 60

2.8

10 x 84

9

0.0171

40

0.0249

110

3 x 60

4.0

10 x 84

10

0.0177

45

0.0255

12

0.0186

.50

0.0261

Reproduced from Harco Corporation, *Catalog of Cathodic Protection*

14

0.0194

55

0.0266

16

0.0201

60

0.0270

(4) Calculate number of anodes needed to

28

0.0207

satisfy manufactuere's current density limitations.

Impressed current anodes are supplied with a

Reproduced from W.T. Bryan, *Designing Impressed Current*

recommended maximum current density. Higher

Company, 1970. Used with permission.

current densities will reduce anode life. To deter-

mine the number of anodes needed to meet the

current density limitations, use equation 2-9:

I

N'

,

(eq 2-9)

N

P

N

P

(A1 (I1)

where N is number of anodes required, I is total

2

0.00261

14

0.00168

protection current in milliamperes, A1 is anode sur-

3

0.00289

16

0.00155

4

0.00283

18

0.00145

face area in square feet per anode, and I1 is recom-

5

0.00268

20

0.00135

mended maximum current density output in milli-

6

0.00252

22

0.00128

amperes.

7

0.00237

24

0.00121

(5) Calculate number of anodes needed to

8

0.00224

26

0.00114

meet design life requirement. Equation 2-10 is used

9

0.00212

28

0.00109

to find the number of anodes:

10

0.00201

30

0.00104

12

0.00182

(L) (I)

N'

,

(eq 2-10)

(1000) (W).

Reproduced from W.T. Bryan, *Designing Impressed Current*

where N is number of anodes, L is life in years, and

Company, 1970. Used with permission.

W is weight of one anode in pounds.

(7) Select number of anodes to be used. The

(6) Calculate number of anodes needed to

highest number calculated by equation 2-9,2-10, or

meet maximum anode groundbed resistance re-

2-11 will be the number of anodes used.

quirements. Equation 2-11 is used to calculate the

(8) Select area for placement of anode bed.

number of anodes required:

The area with the lowest soil resistivity will be

DK

DP

chosen to minimize anode-to-electrolyte resistance.

Ra '

'

,

(eq 2-11)

(9) Determine total circuit resistance. The

NL

S

total circuit resistance will be used to calculate the

rectifier size needed.

(a) Calculate

anode

groundbed

tivity in ohm-centimeters, K is the anode shape

resistance. Use equation 2-11.

factor from table 2-5, N is the number of anodes, L

(b) Calculate groundbed header cable

is length of the anode backfill column in feet, P is

resistance. The cable is typically supplied with a

the paralleling factor from table 2-6, and S is the

specified resistance in ohms per 100 feet. The wire

center-to-center spacing between anode backfill

resistance then is calculated from equation 2-12:

columns in feet.

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