Carbon Backfill of MMO Anode in Impressed Current Cathodic Protection

Mar 29, 2021

Carbon Backfill of MMO Anode in Impressed Current Cathodic Protection

For nearly all underground installations, a special carbon backfill, referred to in the industry as coke breeze, is provided in the anode hole or well.

This special backfill can lower anode ground bed resistance, and resulting in lower rectifier design voltages and reduced probability of stray current interference. It also improves current distribution along the anode since the backfill will provide a generally uniform environment to avoid premature anode failure.  

The service life of the MMO anode is prolonged because of the carbon backfill’s consumption. This carbon backfill provides a permeable medium for the migration of gases, thereby avoiding a premature increase in anode bed resistance. It helps maintain the stability of the anode hole or well.

Calcined petroleum coke, or coke that has been heated to remove high resistivity petroleum by-products, should be specified. The calcined petroleum coke has a lower total bulk resistivity and its more spherical particles aids in the compaction of the backfill. Also, specify a backfill that has a carbon content greater than 92%, preferably greater than 99%, for greater anode system life. Calcined petroleum coke with small spherical grains is suitable for deep well applications as it enables gas to escape and with a surfactant addition, it can be mixed with water to create a slurry which can then be pumped into the borehole. With a high bulk density, the petroleum coke sinks to the bottom of the hole.

Coke breeze is porous and provides a large volume to weight ratio, decreasing the resistance to earth and delivering a large volume for a long life groundbed. Coke Breeze can be supplied with a slaked lime addition to reduce moisture loss.