ETL 1110-9-10(FR)

5 Jan 91

b. Computations.

1)

Calculate the external surface area of the pipe (A) to

be protected.

Unit Area*

Pipe diameter

Length

(sq ft/lin ft)

Area (sq ft)

1 1/4 in.

28,000 ft

0.434

12,152

4 in.

1,200 ft

1.178

1,414

6 in.

3,600 ft

1.734

6,242

*from table A-2

Total

19,808

2)

Determine current requirement (I) from equation 1-1:

I = (A)(I')(l.0-CE)

Where:

A

=

19,808 sq ft (Surface area of pipe to

be protected from previous calculation)

I' =

2 mA/sq ft (Current density, from item

4, paragraph 2-5a)

CE =

0.0 (Coating efficiency [bare pipe])

I

=

19,808 sq ft x 2 mA/sq ft x (1.0 - 0.0)

I

=

39,616 mA or 39.6 amp; use 40 amp

3)

Select an anode and calculate the number of anodes

required (N) to meet the design life.

For this

design, tubular anodes have been chosen.

The

groundbed will consist of a series of anodes attached

to a continuous header cable. A typical size tubular

ceramic anode used in deep anode beds, 1-in. diameter

by 39.4 in. long, is selected. The number of anodes

are determined using equation 1-2:

N=

I

IA

Where:

I=

40

amp

(Current requirement

from

previous calculation)

IA =

8.0 amp/anode (Current rating per anode

from table 3-3 [in coke breeze])

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