Galvanic Cathodic Protection (Galvanic CP)

Definition - What does Galvanic Cathodic Protection (Galvanic CP) mean?

Galvanic cathodic protection (CP) is a cathodic protection technique to control the corrosion of metal when using a galvanic anode as a sacrificial metal in an electrochemical cell. This is achieved by placing the metal to be protected in contact with another, more easily corroded metal to act as the anode of the electrochemical cell.

A galvanic cathodic protection system may be used on reinforced concrete structures and metallic structures exposed to aggressive agents. Common applications are:

  • Steel pipelines and storage tanks
  • Ship hulls
  • Offshore oil platforms and onshore oil well casings
  • Metal reinforcement bars in concrete
  • Galvanized steel

Cathodic protection is feasible when the surfaces to be protected are buried or submerged. The anodes in sacrificial anode cathodic protection systems must be periodically inspected and replaced when consumed.

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Corrosionpedia explains Galvanic Cathodic Protection (Galvanic CP)

Normally cathodic protection (CP) can be applied by a sacrificial anode or impressed current system. Galvanic CP can be applied by galvanic or sacrificial system when limited amounts of current are needed, soil resistivity is low (normally less than 5,000 ohm/cm) and electric power is limited or not available.

Galvanic or sacrificial anodes are made in various shapes using alloys of zinc, magnesium and aluminum. The electrochemical potential, current capacity and consumption rate of these alloys are superior for CP of iron. Polyaniline may also be effective in improving the efficiency of these materials or can be used alone.

Galvanic cathodic protection can be accomplished by coupling a given structure, such as iron, with a more active metal, such as zinc or magnesium. This produces a galvanic cell in which the active metal works as an anode and provides a flux of electrons to the structure, which then becomes the cathode. The cathode is protected while the anode is progressively destroyed, and is hence, known as a sacrificial anode. Sacrificial anode systems depend on the differences in corrosion potential that are established by the corrosion reactions that occur on different metals or alloys.

Advantages of galvanic cathodic protection systems include:

  • Guaranteeing protection of reinforcement rods against corrosion
  • Preventing corrosion on older structures with no signs of deterioration
  • Increasing durability of new structures
  • Minimal maintenance required
  • Protecting metal elements and structures already in place against corrosion instead of using zinc coating/plating
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