- Dissimilar metals
- Metal-to-metal contact
- Both metals immersed in the same electrically conducting solution.
Because stainless steels are more noble than carbon steel, aluminum, and zinc (galvanized steel is a zinc coating on steel), there is often concern about the possibility of galvanic interaction between the stainless and less noble metals. The possibility of galvanic corrosion can be eliminated if the metals are not physically touching, therefore, placing an insulator between them will prevent galvanic corrosion. Even if they are touching, for example carbon steel welded to a stainless steel, galvanic corrosion can occur only if both metals are also simultaneously in the same liquid that has sufficient conductivity to carry an electrical current. Keeping a dissimilar metal couple dry will prevent any possibility of galvanic corrosion.
There is virtually no galvanic potential for corrosion between two different grades of stainless steel when both of the grades are independently passive in the exposure environment. Therefore, there will not be galvanic corrosion between two grades of stainless steel unless the less corrosion resistant of the two grades would have corroded in that environment if exposed by itself.
Because the amount of corrosion on a component in a galvanic couple will be inversely related to the areas of exposure of the two components of the couple, it is possible to use galvanic interactions in a positive way to protect the more critical parts of a structure.