Figure 31

Equavalent Cathodic Protection Circuit

Calculation of Anode-to-Electrolyte Resistance. Anode-to-

6.2.1.2

electrolyte resistance can be computed from data on anode type, size, shape,

and configuration of multiple anode arrays plus the soil resistivity. First,

the type, size, and shape of the anode to be used is chosen. Then, the

resistance of a single anode to be used is calculated. Then the effect of the

use of multiple anodes is determined. However, as the actual environmental

resistivity may not be uniform, or may undergo seasonal variations, the

calculation of anode-to-electrolyte resistivity should only be considered to

be an approximation of the actual resistance to be encountered. This can

result in the actual driving potential required being somewhat different than

the potential calculated using the approximate anode bed resistance. Thus,

after installation, the driving potential must be adjusted to give the

required current output. As the other potentials and resistances in the

cathodic protection circuit vary, the system will also require periodic

adjustments.

Basic Eauations. The formulae developed by H. B. Dwight for a

6.2.1.3

single cylindrical anode can be used to determine the anode-to-electrolyte

resistance. The formula for a vertically oriented anode is:

EQUATION:

54

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