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MARCH 2012 / Issue #01
Definition of Terms (as per AWWA Manual M42):
Common Cathodic Protection types:
Corrosion is a normal occurrence common to all metals not in their natural state. The process itself is electrochemical in nature, very similar to a battery, where electrons flow between anodic and cathodic sites on metals. For corrosion to occur four elements are required:
It is defined as the reduction or elimination of the corrosion process, by making the corroding metal a cathode via an impressed direct current, or by connecting it to a sacrificial or galvanic anode.
A sacrificial or galvanic anode system uses a more reactive metal (anode) such as aluminum, zinc or magnesium, to create a current flow. Direct current is generated by the potential between the anode and the reinforcing steel that it is connected to. The sacrificial anode will corrode during the process and is consumed.
Once the CP system is installed it is necessary to provide routine operation and maintenance. This involves visual inspection of the system and periodic checks. Electrically continuity is checked periodically with a multi-meter and the corresponding voltage is recorded. If no voltage is recorded, the CP is no longer operating and the sacrificial anodes must be replaced.
Cathodic Protection Systems can save a tank from total corrosion and replacement that can occur in as little as five to seven years. By providing considerable technical and economic benefits over traditional, remedial approaches CP will have paid for itself by preventing future repairs or total replacement of storage tanks.