Q: Are galvanic corrosion and galling the same?

A: Galvanic corrosion and galling are actually very different. One causes accelerated corrosion while the other cause the threads to seize.

Galvanic corrosion is when two dissimilar metals are brought in contact with a solution or moisture – most commonly, salt water. In these conditions, these two metals will create an electric current which will accelerate corrosion. This chart can help you avoid galvanic corrosion as it compares how different metals will react with one another.  For galvanic corrosion to occur, all three elements all must be in play:

1. Two different metals
2. Direct metal-to-metal electrical contact
3. A conductive electrolyte solution, most commonly water or even moisture.

Galling occurs not because of dissimilar metals, but from the process of fastening the bolt. Here the friction and pressure put on the bolt when torquing, causes the threads to seize or “cold weld” together. When galling occurs, you can only remove the fastener by cutting it or breaking the nut. To avoid galling you can:

1. Use a bolt with a coating – like silver plating or dry film lubricants
2. Apply a lubricant
3. Be careful not to over-torque the bolt
4. Use dissimilar materials (but be careful about galvanic corrosion!!)

Q: I want to use Duplex bolts to bolt down a Monel plate. Will these materials be compatible?
A: When you mean compatible, I’m assuming you are referring to galvanic corrosion. Galvanic corrosion is when two dissimilar metals create an electrochemical reaction and corrosion occurs. Duplex and Monel can experience this but for galvanic corrosion to occur the parts involved must be wet with a solution. Galvanic corrosion cannot occur when the metals in question are completely dry however humidity might be enough to create that galvanic coupling.