ETL 1110-9-10(FR)

5 Jan 91

8)

Effective coating resistance at 15 years is estimated

at 2500 ohm-sq ft.

9)

The pipeline is isolated from the pumphouse and tank

with insulating joints.

10) For this example, we have decided that the cathodic

protection system circuit resistance should not exceed

2.5 ohms.

11) Electric power is available at 120/240 V single phase

AC from a nearby overhead distribution system.

12) Current requirement testing indicates that 2.8 amp are

needed for adequate cathodic protection.

b. Computations.

1)

Calculate the external surface area of the pipe.

Pipe diameter

=

6 in.

Pipe length

=

6800 ft

Pipe surface

area per lin ft

=

1.734 sq ft/lin ft (from

table 3-2)

External pipe

surface area

=

6800 lin ft x 1.734 sq

ft/lin ft = 11,791 sq ft

2)

Check the current requirement (I) using equation 1-1:

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

Where:

A

=

11,791 sq ft - External pipe surface

area from previous calculation.

I'

=

2 mA/sq ft - Required current density

from item 5 of paragraph 2-2a.

CE

=

0.90- Coating efficiency expressed in

decimal form from item 7 of paragraph

2-2a.

I

=

11,791 sq ft x 2 mA/sq ft x (1.0 -

0.90)

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