What is galvanic or dissimilar metal corrosion?

Dissimilar metal corrosion, often know as galvanic or bimetallic corrosion, is a electrochemical reaction that is caused when different types of metals touch. It can result in rusting and erosion as it literally eats away the weaker metal .

A well known extreme example of this phenomenon was exhibited in the Statue of Liberty. In the 1980s, regular maintenance checks showed that dissimilar metal corrosion had occurred between the outer copper skin and wrought iron structure. Insulation had been installed between the two metals but over time that had degraded, allowing contact between the two metals which caused the rusting of many areas within the iron supports.

Prevention of dissimilar metal corrosion can be achieved by using protective layers such as EPDM foam tape, insulation, plastic, varnish and paint as these create an electrolysis barrier.