Galvanic corrosion (also known as bimetallic corrosion) occurs when two dissimilar metals are in electrical contact in the presence of an electrolyte such as water or saltwater. This engineering guide explains how galvanic corrosion works, provides a detailed corrosion chart for common metals, and shows how to prevent material failure in practical applications.
This type of corrosion is common in marine, piping and structural applications where different metals are used together.
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:
Galvanic corrosion is a major cause of unexpected material failure in engineering systems. It commonly occurs in marine structures, pipelines, fasteners, and mixed-metal assemblies. Understanding how different metals interact helps engineers select compatible materials, reduce maintenance costs, and improve safety and reliability.
Galvanic corrosion occurs when two metals with different electrochemical potentials are connected in an electrolyte. An electrical current flows between the metals, causing the more reactive metal (anode) to corrode.
The table below shows the risk of galvanic corrosion between common engineering metals. An X indicates a potential corrosion risk when the two metals are in electrical contact in the presence of an electrolyte.
The table below shows compatibility between common engineering metals. An X indicates a risk of galvanic corrosion when the metals are in contact.
| Contact Metal | Magnesium Alloys | Zinc Alloys | Aluminium Alloys | Cadmium | Steel (Carbon) | Cast Iron | Stainless Steel | Lead | Tin | Nickel Alloys | Brass / Nickel Silver | Copper | Bronze / Cu-Ni | Nickel-Cr-Mo Alloys | Titanium | Graphite / Gold / Platinum |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Magnesium Alloys | - | X | X | X | X | X | X | X | X | X | X | X | X | X | X | X |
| Zinc Alloys | - | X | X | X | X | X | X | X | X | X | X | X | X | X | X | |
| Aluminium Alloys | - | X | X | X | X | X | X | X | X | X | X | X | X | X | ||
| Cadmium | - | X | X | X | X | X | X | X | X | X | X | X | X | |||
| Steel (Carbon) | - | X | X | X | X | X | X | X | X | X | X | X | ||||
| Cast Iron | - | X | X | X | X | X | X | X | X | X | X | |||||
| Stainless Steel | - | X | X | X | X | X | X | X | X | X | ||||||
| Lead | - | X | X | X | X | X | X | X | X | |||||||
| Tin | - | X | X | X | X | X | X | X | ||||||||
| Nickel Alloys | - | X | X | X | X | X | X | |||||||||
| Brass / Nickel Silver | - | X | X | X | X | X | ||||||||||
| Copper | - | X | X | X | X | |||||||||||
| Bronze / Cu-Ni | - | X | X | X | ||||||||||||
| Nickel-Cr-Mo Alloys | - | X | X | |||||||||||||
| Titanium | - | X | ||||||||||||||
| Graphite / Gold / Platinum | - |
Some metal combinations are particularly prone to galvanic corrosion in engineering applications:
Galvanic corrosion is most severe when a small anodic metal is connected to a large cathodic metal. In this situation, the corrosion current is concentrated on a small area, causing rapid material loss.
X = Galvanic Corrosion Risk
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;
| Distilled Water | 0.5-2 μS/cm |
| Stored Distilled Water | 2-4 μS/cm |
| Supply Water | 50-1500 μS/cm |
| Sea Water | 50,000 μS/cm |
| Sat. Sodium Chloride | 250,000 μS/cm |
| Sulphuric Acid | up to 800,000 μS/cm |
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.
The galvanic series ranks metals according to their electrochemical potential. Metals far apart in the series are more likely to experience galvanic corrosion when in contact.
The rate of galvanic corrosion is strongly influenced by the conductivity and pH of the electrolyte. Higher conductivity allows greater current flow between metals, increasing corrosion rates.
In low conductivity environments such as pure or distilled water, galvanic corrosion is minimal. However, in highly conductive environments such as seawater or acidic solutions, corrosion can occur rapidly.
Galvanic corrosion is caused by electrical contact between dissimilar metals in the presence of an electrolyte.
The more reactive (anodic) metal corrodes, while the more noble (cathodic) metal is protected.
No, an electrolyte such as moisture or water is required for galvanic corrosion to occur.
It can be prevented by insulating metals, using similar materials, applying coatings, or controlling the environment.
Seawater has high conductivity, which allows greater galvanic current flow and accelerates corrosion.
Summary: Galvanic corrosion occurs when dissimilar metals are electrically connected in an electrolyte, causing the more reactive metal to corrode. It can be controlled through material selection, insulation and protective coatings.