This occurs when two metal elements having a different electric potential are directly and continuously connected to each other in the presence of an electrolyte (BATTERY).
The electrochemical process thereby generated produces an electric current which causes the corrosion of one of the two electrodes, the one made of the "less noble" metal (that is, the one with higher electronegativity, the anode), while the other, the cathode, is protected.
It should be noted that the more aggressive an environment is, the greater the corrosion will be. Moreover, in the case of small surfaces the process is more marked.
Below is a table which shows the electrochemical series in seawater, that is, under particularly aggressive conditions.
How to protect a structure against galvanic corrosion?
Use materials in contact that are of the same nature or sufficiently close to each other in the galvanic series.
Or else adopt the following solutions: