Understanding Corrosion in Water Pipelines: A Guide for Pipeline Designers


Polarization Admittance

Last updated: March 28, 2019

What Does Polarization Admittance Mean?

Polarization admittance is the reciprocal of polarization resistance. Polarization admittance methods are applied to determine a material's corrosion rate.

In electrical engineering, admittance is a measure of how easily a circuit or device will allow a current to flow.

Admittance is not only a measure of the ease with which a steady current can flow, but also the dynamic effects of the material's susceptance to polarization:

  • Y = G + jB


  • Y = Admittance, measured in siemens
    G = Conductance, measured in siemens
    B = Susceptance, measured in siemens
    j2 = -1

Polarization admittance is used to study lithium corrosion in propylene carbonate solutions.


Corrosionpedia Explains Polarization Admittance

Corrosion current has a relationship with polarization resistance or polarization admittance as follows:

  • Icorr = B / Rp = BAp


  • Icorr = Corrosion current
    B = Empirical polarization resistance constant that can be related to the anodic and cathodic Tafel slopes
    Rp = Polarization resistance
    Ap = Polarization admittance

Thus, Icorr can be calculated by measuring the linear polarization resistance or the admittance. From the above equation, the corrosion rate at the corrosion potential can be estimated from the Tafel slope and linear polarization admittance.

When Tafel slopes are difficult to estimate, the polarization admittance can often be used to represent the corrosion rate for screening purposes. The inherent assumption is that the Tafel slopes do not change as a function of conditions.

Although the polarization admittance accounts for a substantial part of the total effect, it can be regarded as a constant, which, since it is in series with the electrolyte admittance, reduces the total admittance to a value below that of the electrolyte admittance alone.

High polarization admittance of a metal implies low corrosion resistance and low polarization admittance implies high corrosion resistance. Polarization admittance can be calculated by taking the slope of the current potential curve at open circuit or corrosion potential. Monitoring the relationship between electrochemical potential and current generated between electrically charged electrodes in a process stream allows the calculation of the corrosion rate.


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