Types of Impressed Current Anodes

What Are Anode Ground Beds?

Impressed current anodes are working electrodes used to provide cathodic protection for underground structures. Thanks to this electrochemical method of protecting metal from oxidation, various metal objects can be operated underground. The purpose of the ground bed is to ensure current flows into the ground, which is why a highly conductive material is chosen.

How Do Impressed Current Anodes Work?

The simplest cathodic protection scheme looks as follows: a “minus” from a DC power source is applied along the pipeline, and an electrode made from a conductive material is installed next to the pipe. The “plus” is connected to this electrode, turning it into an anode. As a result, the anode gradually dissolves in the soil, taking on the destructive effects of corrosion and diverting them from the cathode—that is, the gas pipeline, other utilities, or tanks. The rate at which the anode dissolves is critical; replacing an old anode or an early failure not only incurs economic costs but may also lead to a catastrophe. Of course, the scheme also includes additional equipment such as reference electrodes, corrosion rate sensors, and so on.

To provide cathodic protection for metal objects, anodes are implemented using shallow horizontal and deep well anodes as well as the flexible ones.

Shallow Horizontal Anodes

This type of anode is installed at the same depth as the protected structure. It is characterized by its compact size and limited radius of action. It consists of an electrode made of magnesium, zinc, or high silicon cast iron alloys, with a cable for connection to the power supply. Modern models are made from polymer materials, which significantly extend the ground bed’s service life, lower the cost without compromising quality, and simplify installation. Devices for such grounding are typically shaped as rods with a round casting and insulated connection sections for the contact cable. Each rod is connected to the main line by thermite welding or clamps.

Deep Well Anodes

These anodes serve the same purpose as their shallow horizontal counterparts but differ in installation and construction. Their installation depth can reach up to 40 meters. Such devices are coated with a coke breeze backfill, which significantly increases their mass. Installation costs are higher due to the need for mechanized drilling. If drilling with self-propelled machines is not feasible, portable drilling rigs are used. Despite the complex installation process, this equipment is very effective: it protects metal structures located at a considerable distance in the soil. This method is especially relevant in urban environments where extensive shallwo gorizontal installations are difficult or impossible.

Deep well anodes allow for reduced electricity costs due to their large radius of action. Their resistance remains unaffected by seasonal changes. Moreover, the electrodes are placed at such depths that soil freezing is not an issue.

Although the cost of such grounding is higher than that of the previous type, their service life is slightly shorter, averaging around 30 years.

Flexible Anodes

Extended electrodes can be classified as the shallow horizontal type, but they differ not only in appearance but also in installation method. These anodes are long cylinders with cable leads at both ends, enclosed in a casing under which an activator for the anode space is located. This type of grounding is typically laid along the pipeline, sometimes in the same trench, and is excellent for dry and rocky soils. Its flexibility makes installation very convenient.

The Best Models Of Anodes

There are many different models of anode ground beds available on the market for shallow horizontal or deep well installation. The effectiveness of the cathodic protection depends on the quality of the devices.

The most in-demand types among modern anodes are classified by material as follows:

• High silicon cast iron
• Polymeric
• Magnetite
• Graphite
• Mixed metal oxide (MMO/Ti)

By installation method:

• Shallow horizontal
• Prepackaged deep well
• Sectional deep well
• Flexible