0020im.jpg)
ETL 1110-9-10(FR)
5 Jan 91
EXAMPLES OF IMPRESSED CURRENT
CATHODIC PROTECTION DESIGN
2-1.
Purpose.
The following examples show the use of design procedures explained
in the previous section:
2-2
Steel fuel oil lines
2-3
Underground storage tanks
2-4
On-grade tank bottoms
2-5
Gas distribution systems
2-6
Elevated water tanks (ice is expected)
2-7
Elevated water tanks (no icing will occur)
2-8
On-grade water storage reservoir (ice is expected)
2-2.
Steel Fuel Oil Lines.
Impressed current cathodic protection is desired for the 6-in.
welded fuel oil line shown in figures 2-1A and 2-lB. Since this
pipeline is in existence, current requirement tests have already
been made. There are no other underground structures in the area,
so a surface point groundbed is chosen. Figure 2-2 illustrates a
surface point groundbed anode system using prepackaged ceramic rod
anodes. These prepackaged ceramic rod anodes are further detailed
in figures 2-3 and 2-4.
a. Design data.
1)
Soil resistivity in area where groundbed is desired is
2000 ohm-cm.
2)
Pipe has 6-in. diameter
(outside diameter
=
6.625
in.)
3)
Pipe length is 6800 ft.
4)
Design life for cathodic protection anodes is 15 years
since the structure will no longer be needed after that
time.
5)
Design current density is 2-mA per sq ft of bare pipe.
6)
The pipe is coated with hot-applied coal-tar enamel.
7)
90 percent coating efficiency based
on
previous
experience with this type coating.
18
Previous Page
