Galvanic corrosion is the damage caused when two different metals are in electrical contact with each other, in the presence of an electrolyte under corrosive conditions, leading to corrosion of the more active metal.
The process of galvanic corrosion is only possible under the following conditions:
- The presence of two different electrochemical metals or alloys.
- The metals must be in electrical contact with each other.
- The metals are exposed to an electrolyte.
The scientific definition refers to the electrode potentials of different metals or alloys or their tendency to become active in the presence of an electrolyte. The more active (less noble) metals form an anode, while the less active (more noble) metals take the cathode position. The electrolyte triggers ion migration, moving metal ions from the anode to the cathode. This reaction causes the anode metal to corrode more quickly while the cathode metal corrodes more slowly, or not at all.
The most common example of galvanic corrosion occurs in corrugated iron, which has a core sheet of iron or steel and a protective coating of zinc. When the zinc coating is damaged, the underlying metal is safe because zinc is less noble and will be corroded first. Only once the zinc layer has been entirely corroded will the core metal be susceptible to attack. With a traditional tin can, the opposite process occurs. Tin is more noble than the underlying steel, so when the tin layer is damaged, the steel beneath is quickly corroded.
Galvanic corrosion is usually avoided, but in some cases, it’s a necessary process. In house-hold batteries, for example, corrosion of the carbon-zinc cells within are an essential part of the battery producing electricity. The cathodic process is also used to preserve buried structures and hot water storage tanks.
Now that we understand what galvanic corrosion is and what causes it, we can determine how to prevent it from damaging the metal components that are essential to our business, particularly the metal fasteners such as bolts, screws, and welds.
The simplest way to protect metal components is to match their electrode potentials by using similar metals for all productions. If it’s impossible to match the surface metal on the fastener with the metal it is fastening to, then coating or electroplating can be employed. Stainless steel studs, (316), for example, can be protected with a zinc coating.
Keeping two different metals apart can be achieved with several insulation techniques. Using non-conductive materials such as glass, rubber or plastic to separate the various electrode potentials is an efficient solution. Greasing or oiling removes the possibility of metal being in contact with an electrolyte and without an electrolyte, galvanic corrosion cannot take place.
Following these simple methods will keep your fasteners and metal components safe from galvanic corrosion. For more information and helpful tips, give the Bearing Centre team a call today!