0026im.jpg)
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)
24
Previous Page
