Written by TW Williams

The phrase ‘cathodic protection’ simply refers to the process of protecting metal from corrosion when exposed to the elements. This is achieved by making the metal of, for example, an underground tank part of an electrochemical cell. Specifically, it becomes the cathode of an electrochemical cell. The anode of the cell is seen as sacrificial as it is usually made of a metal that is more easily corroded than the tank itself. That way the ‘sacrificial’ anode corrodes while the tank does not.

The easiest way to visualize this is to consider the potato powered clock. How could a potato possibly power a clock without a battery? It works on the same corrosive principle. The anode (the nail in the diagram below) gives itself up to the cathode (the copper wire in the diagram below) through corrosion within the moist potato.

potato clock

In the case of the underground tank, the moist soil is the potato. Without a sacrificial metal the electrochemical difference between the metal of the tank and the surrounding soil causes corrosion. This corrosion is a result of small difference in direct current (DC) flow from the tank to the soil. The tank forms a cell with the soil and becomes the anode and as we saw before with the potato, the anode is the ‘sacrificial’ metal and will give itself up to the cathode (the soil). More moisture means more corrosion as water is a terrific conductor. To prevent the tank from becoming an unwilling anode, we instead provide our own anode forcing the tank to be the cathode.

However, before you can protect your underground propane system you need to consider some important factors. These factors include but are not limited to the amount of steel to be protected, soil conditions, external coatings, and type of cathodic protection applied. All bare steel should be protected by use of coatings and wraps according to the manufacturer’s specifications.

Anodes are usually made of Magnesium and when you see the following chart of common metals you’ll see why. When creating an electrochemical cell with two different metals the metal with the lowest potential will corrode. As is made obvious by this chart, Magnesium has the lowest potential.

common_metals_potential

Sizing anodes can be a little confusing. There are some basic rules of thumb that will help but I would recommend contacting your local Tarantin Industries office for help with sizing based on your specific needs.

To test whether you’re tank is properly protected or not do the following. Using a digital volt meter, set to the 2 volt DC range, connect the red lead to the tank test point or structure, and connect the black lead to the copper sulfate reference electrode. Place the porous end of the electrode into the soil at several points above and around the tank or piping system being tested. The meter should read at least -0.850 VDC or more negative. Record all test points on the survey sheet and be sure to reference them as negative or positive DC volts based on your results.

Anode Record Keeping Form Propane

Tarantin Industries offers the highest quality H1 Magnesium anodes, a variety of testing equipment, and some of the best technical support in the industry. We’re here to help you maintain and preserve your investments in the field.

 

Salesman TW Williams

TW Williams

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