Galvanic Corrosion and Dissimilar Metals

Galvanic Corrosion and Dissimilar Metals

Emmanual Pimentel

One of the challenges in designing steel structures or any metallic article is the problem of galvanic corrosion. Basically, this is the risk of dissimilar metals being in physical contact and bridged by an electrolyte in a corrosive environment.

The design of structures utilising dissimilar metals and other materials is becoming more common. This can be commonly seen in architectural applications where the different aesthetic and physical features of varied materials add to the overall visual appeal. Also, many industrial and infrastructure applications seek to make use of the different physical properties of various materials.

It is not always the case that galvanic corrosion from the use of dissimilar metals is problematic. This includes inland rural areas and other environments of low corrosivity, distant from the coast or industrial pollution. Unfortunately, the seeming “success” of such applications leads to design practices and material selection that are not appropriate for more corrosive locations. An example of this can be seen in the selection and use of fasteners. Inland rural locations are forgiving of designs with little or no thought of the different materials that are used and such designs often perform satisfactorily.

While it is well known that dissimilar metals in contact can cause corrosion issues, it is worth discussing why this occurs and how to mitigate galvanic corrosion in the design process. Also, consideration must be given to the fact that galvanic corrosion in not always an undesirable phenomenon. In fact, cathodic protection and the corrosion protection properties of various engineered coating systems are based on the principle of galvanic corrosion.