Bi-Metallic corrosion is the additional corrosion that occurs when dissimilar metals are in contact in the presence of an electrolyte.   The corrosion of a metal, the anode, results from the positive current flowing from the anode to the less reactive (more noble) metal, the cathode, through the electrolyte.   This process is similar to the conventional corrosion of a single, uncoupled metal but generally proceeds at a higher rate depending on the difference in electrochemical reactivity of the anode and cathode metal.

The requirements for bi-metallic corrosion are as follows:

The degree of bi-metallic corrosion is affected by the electrolyte pH and conductivity. The intensity of the corrosion can increase with the conductivity of the electrolyte. Typical values of conductivity of various fluids are listed below;

Bi-metallic corrosion is seldom a problem when the metals are immersed in pure water.

Where contact between dissimilar metals cannot be avoided the following steps should be considered

Reference -Oxidation -Reduction

Galvanic corrosion is driven by the voltage potential between two electrically connected conductors (  To minimize this form of attack, materials in electrical contact, if required, should be selected so as to minimize their relative potential.

The galvanic series of metals lists common materials in order of their electrical potential relative to a recognized standard.   Materials widely separated on this list will rapidly corrode in the presence of electolyte (e.g. Seawater) when in electrical contact, the anodic material suffering rapid material loss.   Materials close together on this list will suffer less damage due to corrosion.