GALVANIC CORROSION

Galvanic corrosion is the corrosion that results when two dissimilar metals with different potentials are placed in electrical contact in an electrolyte.
A difference in electrical potential exists between the different metals and serves as the driving force for electrical current flow through the corrodant or electrolyte. This current results in corrosion of one of the metals. The larger the potential difference, the greater the probability of galvanic corrosion.

Galvanic corrosion only causes deterioration of one of the metals. The less resistant, active metal becomes the anodic corrosion site. The stronger, more noble metal is cathodic and protected.

Galvanic corrosion potential is a measure of how dissimilar metals will corrode when placed against each other in an assembly. Metals close to one another on the chart generally do not have a strong effect on one another, but the farther apart any two metals are separated, the stronger the corroding effect on the one higher in the table.

This table lists the potential differences for various metals in water. The order of the series can change for different electrolytes (for example, different pH, ions in solution).

I have omitted Stainless steel alloys from this table as they can significantly change their potential and become much more active if exposed to stagnant or poorly aerated water.

Electrode Potential at 77 F (25 C)

Anodic end (this is where the corrosion occurs)


Element Standard Electrode Potential (Volts)

Lithium -3.045

Potassium -2.920

Sodium -2.712

Magnesium -2.340

Beryllium -1.700

Aluminum -1.670

Manganese -1.050

Zinc -0.762

Chromium -0.744

Iron; Mild Steel -0.440

Cadmium -0.402

Yellow Brass -0.350

50-50 Tin-Lead Solder -0.325

Cobalt -0.277

Nickel -0.250

Tin -0.136

Lead -0.126

Hydrogen reference electrode 0.000

Titanium +0.055

Copper +0.340

Mercury +0.789

Silver +0.799

Carbon +0.810

Platinum +1.200

Gold +1.420

Graphite +2.250

Cathodic end, passive - (no corrosion here)