Cathode

A cathode is the location where reduction reactions occur. In cathodic protection, the protected structure is forced to behave more cathodically to reduce corrosion.

Quick Definition

A cathode is an electrode or metal surface where reduction occurs and protective current enters the metal from the electrolyte.

Why This Term Matters

Cathodic protection is named for the cathode. The goal is to make the protected metal surface behave as a cathode rather than as an anode where metal loss occurs.

A learner who does not understand the cathode cannot correctly understand CP current flow, polarization, corrosion cells, or why anodes are required.

Core Concept

Cathode in corrosion

In a corrosion cell, cathodic areas support reduction reactions. These areas do not lose metal in the same way as anodic areas.

Cathode in CP

In cathodic protection, the protected structure receives current from the electrolyte and is polarized in the cathodic direction.

Current entry

Protective current enters the protected structure at exposed metal surfaces such as coating holidays, bare areas, or other electrolyte-contacting metal.

Common Mistakes

  1. Thinking the cathode is where metal loss occurs.
    Why it is wrong: Metal loss occurs at the anode.
  2. Assuming the entire structure is always uniformly cathodic.
    Why it is wrong: Current distribution, shielding, coating condition, and electrolyte conditions vary by location.
  3. Ignoring current entry points.
    Why it is wrong: CP current must reach exposed metal surfaces to provide protection.

Field Example

A coated pipeline has small coating defects. CP current discharges from anodes, travels through the soil, and enters the exposed steel at those coating defects. The exposed steel is being forced in the cathodic direction.

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