Galvanic corrosion is identifiable by visual examination and is caused when two metal pieces, with differing electrochemical potentials, are in electrical contact with
each other. The metal part with the lowest electrochemical potential (i.e. the more active metal or metal area) will corrode. The more noble metal part, with the more positive electrochemical potential, will be cathodically protected from corrosion.
One way to halt or stop this corrosion is to break the electrical contact between the
dissimilar metals.
Key Properties of Galvanic Corrosion
- Is caused by anodic/cathodic reaction between dissimilar metals in contact with one another in the presence of an electrolyte (liquid that conducts electrical current)
- The less noble metal becomes the anode, corrodes, and metallic elements go into ionic solution, resulting in the protection of the cathodic area.
- The greater the anodic area compared to cathodic area the lower the corrosion rate. However the opposite is also true and this can result in very rapid corrosion rates.
- A table of the electrochemical potentials of metals, called a galvanic series, can be used to predict possible galvanic corrosion problems.
Where does it occur?
- Flanged connections
- Heat exchangers
- Fasteners and bolted joints
- Marine structures
How to Control Galvanic Corrosion?
Galvanic corrosion may be controlled in a variety of ways, including::
- Use metals close to each other in the galvanic series
- Avoid small anode to large cathode areas
- Insulate dissimilar materials
- Apply coatings
- Add inhibitors
- Use a sacrificial third metal anodic to both metals
Source: Chesterton ARC Manuals
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