Galvanic corrosion is widely used as a productive way to create electricity, i.e. batteries. However, galvanic corrosion can be very destructive when it is not anticipated. When two dissimilar metals are in contact with each other in an electrolyte, galvanic corrosion can initiate and corrode the less noble metal. For example, a copper pipe bolted to an aluminum header with water flowing through them will generate galvanic current. In water, copper has a potential of +0.340V and aluminum has a potential of -1.670V. The difference between the two metals is 2.010V, which is a large potential difference. The aluminum header (the less noble metal) will start to corrode in the vicinity of the joint. The copper pipe will be protected by the aluminum; however, a leak will eventually occur and the joint will fail. This is a simple example of a galvanic corrosion cell.

A galvanic cell is created by electrically connecting two metals together in a solution that can pass electrons. The flow of electrons, i.e. current, will flow from the less noble metal to the more noble metal. Thus, noble metals [gold and platinum] will not easily corrode in many environments while less noble metals [aluminum, zinc, and magnesium] are extremely reactive and will easily corrode. The less noble metal is typically named the anode and the more noble metal is the cathode.

ASTM G71 - Standard Guide for Conducting and Evaluating Galvanic Corrosion Tests in Electrolytes
This is the standard test recommended used by industry to determine if galvanic corrosion will be problematic in a systems that contains dissimilar metals.