cathodic protection facts

Cathodic Protection Facts: A Brief Introduction

Corrosion is an electrochemical process and cathodic protection is an electrical process which counteracts the electrical process of corrosion. Thus cathodic protection will, in the proper environment, stop corrsion already in progress.

Myth or Mystery or Science

Two Cathodic Protection Systems

Cathodic protection is an external electrical system which provides small currents which counteract the electrical currents of the corrosion cell.Cathodic protection thereby removes one part of the corrosion cell and corrosion ceases. Cathodic protection treats a fundamental cause of corrosion.

Cathodic protection has successfully been used to protect steel in concrete since about 1973, but has been used to protect steel in many other electrolytes since about 1823. It has been used extensively to protect pipelines, ship hulls, underground tanks, offshore platforms, heat exchangers, etc. Cathodic protection is based in pure physical science. It has been proven theoretically as well as in the laboratory and tens of thousands of field applications.

Cathodic protection is neither mystical nor complicated: it is a straight-forward application of basic laws of electrochemistry.

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A cathodic protection system consists of an external electrical power source which can impose a current sufficient to counteract the existing currents of the corrosion cell. Classification of cathodic protection systems is based on the source of the external electrical power.

An impressed current cathodic protection system is so named because the power is provided by a conventional power source (the local utility company). The current is "impressed" on the corroding structure through the use of relatively inert materials.

A galvanic (or sacrificial) cathodic protection system is so named because the electrical currents are generated by dissimilar metals in a common electrolyte. The same theory that makes a battery work. When dissimilar metals are placed in an electrolyte (and are connected by a metallic return path) a current will flow from the metal with the higher potential, through the electrolyte, to the metal with the lower potential.

For example, zinc has a higher potential than steel, so if they are immersed in an electrolyte a current will flow from the zinc to the steel. In this situation zinc is the anode and steel is the cathode. Corrosion only occurs at the anode.