Inaccuracy of corrosion current determination in presence of ohmic drop – Corrosion – Application Note 48

Abstract

Ohmic drop is one of the error factors leading to an inaccuracy in the corrosion rate measurement. This factor, resulting from a low conductivity of a solution, has the effect to decrease the measured corrosion current and so leads to underestimating the true corrosion rate of a material.
In this application note a special dummy cell (Test Box #3-2), built to mimic a linear electrochemical system, was tested in order to study the effect of Ohmic drop on the measured corrosion parameters. The corrosion rate and Tafel parameters were estimated using Ohmic drop compensation with four techniques available in EC-Lab software. A good correlation between the corrosion parameters obtained with the four methods was obtained.

Introduction

The effect of the ohmic drop on the electrochemical measurements was presented in Application note #27 [1]. The ohmic drop RΩ I(t), due to the resistance RΩ of the electrolyte between the working electrode and the reference electrode, is given by (Fig. 1) [1]:

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