Back to basics: What is cathodic protection?
Over the years I’ve been amused with the variety of responses I’ve received when I’ve asked, “What is cathodic protection?” If I’m talking to a corrosion engineer I get one answer, if I’m conversing with an operations person I get something different. I thought, ‘Here’s a challenge - let’s describe cathodic protection in a way a layperson would understand.’
Cathodic protection (CP) is a technique used to control the corrosion of a metal substance in various applications. Some common areas which apply this science are: fuel tanks, pier pilings, ships, offshore oil platforms and casings, metal reinforcement bars for concrete structures, as well as pipelines.
To simplify cathodic protection – assume you have a metal pipeline and you need to protect it against corrosion. Pipelines are generally supplemented with CP after being protected with an anticorrosion system (coating or wrap) as the primary form of corrosion protection. Otherwise the cathodic protection required to combat corrosion for an uncoated pipeline is excessive.
The first step in cathodic protection is to take the metal you are trying to protect (pipeline) and turn it into a cathode. A pipeline is normally anodic, it contains positively charged electrons. By supplying an electric current the 
pipeline becomes passive or cathodic. The science reveals that as long as the electron current is arriving at the cathode (pipeline) faster than oxygen is, then corrosion will be prevented or significantly slowed.
Pipelines commonly use Impressed Current Cathodic Protection (ICCP) which uses a rectifier along with anodes buried in the ground. The rectifier (a DC power source) supplies electrons to the system stopping corrosion of the pipeline and since the anodes don’t surrender many electrons they don’t corrode much either.
Sometimes it’s more economical to use a galvanic anode system in which the anodes (Magnesium, Zinc or Aluminum) are the electron source and are sacrificed and corrode over the steel pipeline.
The video below offers a simple representation of ICCP.
I hope you enjoyed this back to basics session on “What is cathodic protection?”
Photo: http://140.194.76.129/publications/eng-manuals/em1110-1-4008/c-12.pdf
Tags: CP, ICCP, damage prevention, cathodic protection, corrosion control
