How Cathodic Protection Works

PART TWO: How Cathodic Protection Works

In a corrosion cell, corrosion occurs where current flows from the anode into the electrolyte (1). Where current flows from the electrolyte onto the cathode, corrosion is halted (2). At its core, cathodic protection aims to manipulate the flow of current within a cell in order to control the location of corrosion.

The discipline of pipeline integrity involves applying these principles at an extremely large scale in order to direct current onto critical infrastructure from the surrounding environment, thereby protecting it from corrosion. 

Because of the scales involved in pipeline integrity and the variability of conditions along a pipeline, we refer to the corrosion cell as a corrosion system –a series of diverse environments connected by a network of pipelines. 

There are two primary methods used in cathodic protection to manipulate the flow of current within a corrosion system. 

1. Galvanic or Sacrificial Anodes

Relatively electronegative material is placed in the earth and connected to the pipeline via a metallic path (aka: a wire).  This material acts as the anode within the corrosion system, gradually breaking down while ensuring that current is directed onto the surface of the pipe. 

2. Impressed Current

An external power source is used to impress current through an anode, actively driving the flow of current out through the electrolyte and onto the surface of the pipeline, thereby halting corrosion.

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