Why MMO Tubular Anodes are Mostly Used for Groundbed Cathodic Protection?

Why MMO Tubular Anodes are Mostly Used for Groundbed Cathodic Protection?

MMO tubular anode is an efficient choice for many underground cathodic protection applications. The mixed metal oxide (MMO) coated titanium tubular with a center connection was shown to be the most economical for this application. These types of electrodes were used in both surface and deep anode configurations. Since the anodic reactions are anticipated to be both oxygen evolution and chlorine evolution, it is important that the coating be a combination of iridium and tantalum oxides and not the more common (and less expensive) ruthenium oxide that is designed to be used under conditions of chlorine evolution.

The tubular shape is superior to rods or mesh since a low resistant, well-sealed wedge connector can be placed at the center of the anode for connecting the anode lead wires. As demonstrated in a laboratory research project that simulated gas evolution of a deep anode, Halar lead wire insulation is preferable to either HMWPE or Kynar when the anodic reaction is chlorine evolution. Lead wires from individual anodes were extended, without splices, from the anode to a junction box for both surface and deep anodes.

There were four anode configurations selected for cathodic protection of the well casings. Two were deep anodes for either one or two-well clusters, and two were surface anodes for either one or a two-well cluster. In the case of deep anodes, the depth to the top of the active anode column varied by location to account for variations in subsurface geology and depth of water.

Surface anode configurations were used only in stable soils with low resistivities. The anodes in both the deep and surface anode beds were backfilled with calcined petroleum coke.