What Is Cathodic Protection?

Or everything you wanted to know about anode bags but were afraid to ask.

What Causes Underground Tanks to Corrode?

In a word... soil. When soil meets the steel of an underground tank an electrochemical reaction occurs. This reaction is DC current flowing between the tank and the soil. When the current is flowing from the tank to the soil corrosion occurs. When the current flows in the opposite direction, from the soil to the tank, corrosion doesn't take place. So how do we keep the current flowing from the soil to the tank, so the steel doesn't completely break down leaking precious propane into the ground? I'm glad you asked. Here's how.

How To Avoid Underground Tank Corrosion

There are two ways to protect the steel of an underground tank from corroding. The first way is through an external coating using an epoxy powder paint. This paint will protect over 99% of the tank. The second way to protect the steel of an underground tank is... wait for it... cathodic protection. Both of these methods should be used as a combined shield against corrosion because no coat of paint is perfect. Paint can be damaged by construction, or soil can create tiny defects in the paint.

How Does Cathodic Protection Work?

Easy. By creating a galvanic connection between two different metals. Ok, let's explain that. A galvanic connection is when there is an actual electrical contact with the ground. This is done by connecting an anode bag to the underground tank. Anode bags are usually made of magnesium because magnesium has a really low electrode potential. In other words, magnesium is a metal that will corrode before most other metals, and because it will corrode faster than steel it will create a DC current that will flow away from the underground tank which as we learned in the first paragraph is the direction we want to current to flow to keep the underground tank from corroding.

Do you think your anode bag might be failing? Here are six steps to testing the bag for failure.