Understanding Corrosion in Water Pipelines: A Guide for Pipeline Designers


Mixed Potential

Last updated: June 11, 2017

What Does Mixed Potential Mean?

Mixed potential is the effective potential of the metal surface in contact with an electrolyte that is driving electrochemical corrosion. Mixed potential theory explains metal corrosion as a reaction of two or more electrodes working simulatneously at the interface of the given metal surface and electrolyte.

The study of mixed potential is important because:

  • It helps explain cathodic protection, which is an effective method of protecting burried pipelines, storage tanks, structures and marine equipment
  • It is useful for fine tuning and calibration of measuring as well as monitoring devices used for corrosion protection systems, and useful for different environmental conditions
  • It is useful in the design of corrosion protection systems and the selection of required components


Corrosionpedia Explains Mixed Potential

Corrosion involves two partial reactions: oxidation and reduction. It occurs only when the total rate of oxidation equals the total rate of reduction.

Mixed potential is based on mixed potential theory, which considers a metal surface dipped in electrolyte as being made up of two or more electrodes.

Electrochemical corrosion is caused by these mixed electrodes formed on the metal surface, with oxidation directly coupled to the reduction reaction of the depolarizer. The resulting potential of the electrodes is the mixed potential, driving corrosion that needs to be controlled for the elimination of the corrosive reaction. By cathodically polarizing the cathode, the corrosion current density can be reduced to reduce and eliminate corrosion.

The value of mixed-potential, being a result of both anodic as well as the cathodic polarization on the metal surface, is affected by ambient temperature, the electrolyte’s concentration and anode-to-cathode surface area ratio.


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