Galvanic Corrosion, Bimetallic Corrosion or Dissimilar
Metal Corrosion
What causes galvanic corrosion? Different metals and alloys
have different electrochemical potentials (or corrosion
potentials) in the same electrolyte. When the corrosion
potentials of various metals and alloys are measured in a
common electrolyte (e.g. natural seawater) and are listed in
an orderly manner (descending or ascending) in a tabular
form, a Galvanic Series is created. It should be emphasized
that the corrosion potentials must be measured for all
metals and alloys in the same electrolyte under the same
environmental conditions (temperature, pH, flow rate etc.),
otherwise, the potentials are not comparable. The potential
difference (i.e., the voltage) between two dissimilar metals
is the driving force for the destructive attack on the
active metal (anode). Current flows through the electrolyte
to the more noble metal (cathode) and the less noble (anode)
metal will corrode. The conductivity of electrolyte will
also affect the degree of attack. The cathode to anode area
ratio is directly proportional to the acceleration factor.
