UFC 3-570-06
JANUARY 31 2003
anode is in a uniform environment. This is usually the most economical choice when
there are not other utilities in the area, there is sufficient room to locate the anodes
remote from the structure, and there is a rock strata near the surface. Horizontal
placement of the anodes in the earth tends to raise the total resistance to earth of the
system (versus vertical). The distance to remote earth varies according to the resistivity
of the earth, usually 91 to 213 meters (300 to 700 feet).
Soil resistivity testing can be done in the area of a proposed anode bed to
locate an area of low resistance to place the anodes. Care must be taken to ensure
that the low resistance area is not continuous to the protected structure. Poor current
distribution may occur if this condition occurs. In some cases, the best location for an
anode bed may be in higher resistivity earth. The resistance of the anode bed can be
lowered by adding additional anodes, using longer anodes, or by increasing the spacing
of the anodes. The anodes may have individual leads connected to a header cable or
they may be installed on a continuous cable.
Figure 2-27. Horizontal Remote Impressed Current Cathodic Protection System
Special Backfill
Horizontal
Anodes
Anode
Lead
Structure
Typically Over 400 Feet
Lead
PIPELINE (CATHODE)
2-7.3.3
Distributed Impressed Current CP Systems. These systems are
commonly used to protect small structures. This is usually the most economical choice
when the structure is small or the anodes cannot be placed in remote earth. This type
of anode bed is used to protect water tank interiors, ground level tank bottoms,
underground storage tanks, or a short pipeline. Anodes are distributed along the
pipeline, or around the surface of the tank (interior for water tanks, exterior for
underground tanks). The distance from the structure is normally 1.5 to 3 meters (5 to
10 feet), and the distance between anodes is normally double that distance (3 to 6
meters [10 to 20 feet]). In some cases, the anode is continuous, and is placed in a grid
pattern on tanks, or along the side of a pipeline.
2-54
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