Determining Current Requirements for Cathodic Protection

Before it is possible to design a cathodic protection system for an underground structure, it is frequently necessary to set up a temporary cathodic protection system that simulates the operation of an actual system.  There are two primary types of cathodic protection system.  One of these systems used anodes that are energized by DC power source.  In this case, the anodes are connected to the positive terminal of the DC source and the structure to be protected is connected to the negative terminal.  The second type of system used galvanic anodes which are self energized and which are connected directly to the structure to be protected.  These galvanic anodes are made of a material such as magnesium or zinc, which material is anodic with respect to the structure to be protected.  In systems for underground structures, the first type of system usually is designed to drain relatively large currents at limited number of locations, while the second type of system drains relatively small currents at many locations.

All cathodic protection system pass current through the soil from anodes that are installed in soil to the structure that is to be protected.  When current flows onto a structure from the soil, the structure-to-soil potential is made more negative than the potential that existed before cathodic protection current was applied.  By measuring the change in potential for a given current that is made to flow with a particular type of system the current necessary to provide cathodic protection for the structure can be calculated.

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