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Corrosion Engineering | Electrical Engineering

Cathodic Protection & Isolation Devices

In order for cathodic protection to be an effective means of controlling corrosion on underground metallic structures several factors must be considered during the design phase of a project. Among those factors to be considered is the best application (type) of cathodic protection for the specific structure. The choices, impressed current or galvanic, is often determined by the actual surface area of the structure to be protected.

Many times a new structure which will have a cathodic protection design is physically connected to an existing structure which does not have cathodic protection, such as in the case of a water line expansion project. Typically, the system designer would require a cathodic protection design for the new water line portion. Within the design for cathodic protection there would generally be a notation for, or requirement of an isolation device. The intent of the isolation device is to allow the cathodic protection system design to provide protection to the predefined area of the new structure. Failure to require and later assure installation of the isolation device will result in a reduction in the effectiveness of the cathodic protection design. Once again, designs for cathodic protection systems are often predicated upon the geometry and surface area of the structure to be protected.

When isolation devices are not properly installed the results are either a complete lack of cathodic protection or low levels of cathodic protection that do not provide protection for the original design life, and ultimately fail resulting in no cathodic protection. Although the overall cost of the isolation device is typically a mere fraction of the total system cost it is still a vital component that can impact the overall performance of the cathodic protection system.

Taylor Leon, President