24 - Distribution of Current and Potential in a Stationary Electric Field

Abstract

This chapter derives important equations for corrosion protection that are relevant to the stationary electric fields present in electrolytically conducting media such as soil or aqueous solutions The equations are also applicable to low frequencies in limited areas, provided no noticeable current displacement is caused by the electromagnetic field.. For the simplest case, the grounding resistance of a spherical anode in surrounding space is derived. The major part of the resistance lies in the soil in the immediate vicinity of the anode. The total grounding resistance of the anode—that is, the resistance between its lead and the infinitely large and distant remote ground, is composed of three terms: (1) the resistance in the lead and the anode itself, which usually is so small that it can be neglected, (2) The transition resistance between the surface of the metal and the electrolyte, and (3) The grounding resistance that is given by the current and potential distribution in the electrolyte. If anode installations for cathodic protection consist of several individual anodes of length, spacing, and grounding resistance, then these are usually spaced far enough from each other so that their mutual interference can be treated by the potential distribution of a spherical anode.