What is the galvanic series and how is it used in material selection?

• A. A chart of coating thickness requirements.
• B. A log of maintenance records.
• C. A list of metals ordered by electrode potential; used to predict galvanic corrosion when metals are in contact in an electrolyte.
• D. A rating of corrosion rates in seawater.

Answer: (C)

The galvanic series is a ranking of metals and alloys by their electrode potentials in a given electrolyte. When two metals with different potentials are in electrical contact in an electrolyte, electrons flow from the more active (anodic) metal to the more noble (cathodic) metal. The anodic metal tends to corrode, while the cathodic metal is protected. This concept is used in material selection to minimize galvanic corrosion: choose metals that are close together in the series to reduce the driving force for corrosion, or separate dissimilar metals with barriers, coatings, or insulating spacers. In some designs, a more active metal may be used intentionally as a sacrificial anode to protect a more noble structure. Remember that the exact ordering can depend on the environment (type of electrolyte, temperature, surface films), so the galvanic series is most reliable when matched to the actual service conditions.