Corrosion driven by connecting two different metals through both a metallic path and a common electrolyte. The more active metal in the galvanic series becomes the anode and corrodes faster, while the more noble metal is protected. Severity depends on the potential difference, the electrolyte's conductivity and especially the area ratio: a small anode tied to a large cathode, like steel rivets in copper sheet, fails fast. Sacrificial anodes use the same effect on purpose.
Somebody put carbon steel bolts in the stainless flanges, classic galvanic corrosion, the bolts are half gone.
Watch the area ratio, not just the metals. A big anode with a small cathode is often tolerable; the reverse eats the small part quickly.
Also heard as
- bimetallic corrosion
- dissimilar metal corrosion
Related terms
Galvanic series
Ranking of real metals and alloys by their measured potential in a given electrolyte, usually seawater.
Sacrificial anode
Block of a more active metal such as magnesium, zinc or aluminum that corrodes to protect connected steel.
Insulating joint
Fitting that electrically isolates one pipe section from another so CP current stays where it belongs.
Anode
Electrode where oxidation happens and metal dissolves; in CP, the hardware installed to discharge current.