Anode

An anode is the location where oxidation occurs. In corrosion, the anode is where metal loss occurs. In cathodic protection, anodes are used to discharge protective current into the electrolyte.

Quick Definition

An anode is an electrode or metal surface where oxidation occurs and current leaves the metal to enter the electrolyte.

Why This Term Matters

The word anode is used in two closely related ways in cathodic protection. In a corrosion cell, the anode is the area where the structure corrodes. In a CP system, the installed anode is the component intended to corrode sacrificially or discharge impressed current so the protected structure becomes cathodic.

Confusing these two uses leads to bad interpretation. The protected structure should not be the anodic area in the CP circuit. The CP anode is intentionally made the current-discharge point.

Core Concept

Anode in corrosion

In a corrosion cell, the anode is where metal atoms give up electrons and enter the electrolyte as ions. This is the location of metal loss.

Anode in cathodic protection

In a CP system, the anode discharges current into the electrolyte. That current travels through the electrolyte and enters the protected structure at exposed metal surfaces.

Galvanic anode

A galvanic anode is a more active metal, such as magnesium, zinc, or aluminum, that corrodes preferentially to provide protective current.

Impressed current anode

An impressed current anode discharges current supplied by an external DC power source, commonly a rectifier.

Common Mistakes

Thinking corrosion occurs at the cathode.
Why it is wrong: Metal loss occurs at anodic areas.
Assuming all anodes are sacrificial.
Why it is wrong: Galvanic anodes are sacrificial, but impressed current anodes are powered by an external DC source.
Ignoring anode consumption.
Why it is wrong: CP anodes have finite service life and can be depleted, damaged, or disconnected.

Field Example

A magnesium anode connected to a buried steel pipe corrodes preferentially and supplies current to the pipe. In that CP system, the magnesium anode is intentionally consumed so the steel pipe receives protective current.