Galvanic corrosion or galvanic pair
Galvanic corrosion is one of the biggest problems in industry and metal handling and in which it is essential to consider the application of certain techniques or solutions to prevent this phenomenon.
At Sunenergy System we have prepared this post where we explain everything you need to know about the galvanic couple.
What is galvanic corrosion?
- When a metal is in contact with a different and more noble metal.
- When both metals are half wet or immersed in an electrolyte.
How does galvanic corrosion occur?
Galvanic corrosion occurs when two metals of different electrical potential are in continuous contact in the presence of an electrolyte.
This situation creates an electrochemical process that, by creating an electric current, causes the corrosion of the metal whose compound is less noble (anode), while the other metal (cathode) remains protected.
What factors influence galvanic corrosion?
- The relative size of the metals (anode and cathode): The larger the anode in relation to the cathode, the less corrosion. On the contrary, when the anode is smaller and the cathode is large, it will make the anode more easily damaged.
- Poorly aerated water, such as seawater, can affect stainless steels.
- Due to the degree of electrical contact.
- Due to the range of individual potential difference between the two metals, allowing either of them to act as anode or cathode.
- Biological organisms that coat metals can also affect their exposed areas.
- Humidity and temperature.
Do you have corrosion issues?
How to avoid galvanic corrosion?
Sacrificial anodes
This technique consists of connecting the metal to be protected with another more active metal, which will oxidize while protecting the metal it is in contact with.
The metals that are usually used to apply this technique are magnesium, zinc, and aluminum.
Protection by similar powers
Galvanic corrosion is produced by the difference in potential of the electrode, so that the greater the difference, the faster corrosion will occur.
This solution consists of using metals with similar potentials (usually the same one will be used for the whole piece) to reduce the galvanic current.
Electrically insulate metals
This solution consists of using formulas for the electrical insulation of two metals from each other, so that if they do not maintain electrical contact there cannot be a galvanic cell.
Depending on the type of metal and its use, one insulator or another will be applied. It is very common to make one from plastic as an insulator for metals that are in contact with water or through layers of grease to separate metals such as aluminum and steel.
Dry metals and protected against ionic compounds
In this solution, coatings on metals with paints or epoxy resins are used, where, once dry will create protection.
Electroplating
Electroplating is one of the most effective techniques to prevent galvanic corrosion. It consists of covering one metal over another by means of electricity, where a solution of metallic salts is applied (electrolysis). The objective of electroplating is to modify the surface properties of metals to increase their resistance to corrosion.
The JR2000 coating has excellent behavior in steel and aluminum joints, being an ideal substitute for stainless steel and thus avoiding galvanic corrosion in steel and aluminum.
- Union between S…GD+ZM profile and Cu-Sn braid + Sunenergy System JR2000 coating.
- Union between profile G.C. and hose with Cu-Sn terminal + Sunenergy System JR2000 coating.
Galvanic pair: aluminum and steel
We know that galvanic corrosion occurs when two metals in contact have different electrical potentials, converting the more noble into the cathode and the more active and less noble into the anode.
For the protection of steel and aluminum, the best strategy or solution is to place separators made of inert materials, such as plastic or grease, between the aluminum and other metals such as steel. In this way, at least, we ensure the prolongation and life of metals.
Galvanic corrosion: examples
As we have seen in the illustrations in the previous sections, a very common example of galvanic corrosion appears in the joints of screws and nuts, and whose solution could be the application of a coating on metals such as JR2000.
