Graphite anodes are used because they are reliable and relatively cost-effective. In the process of cathodic protection, current density or rate of transfer isn’t a necessary factor of the process. It is important that the current keep flowing, but it does not need to achieve a certain rate or level. Therefore, even though graphite is a resistive material, it is highly ideal in these situations.
The anodes are usually constructed from a combination of petroleum coke and coal tar pitch and are relatively easy to machine as finish or appearance is also not a determining factor in effectiveness. Used conjunctively with carbon graphite or other anode backfill, graphite anodes provide a long lasting solution and are one of the most commonly recycled graphite products as they contain few additives.
Custom specifications are often used to produce graphite anodes as they are typically application specific. Common approximate sizes are between 60 and 150mm in diameter and from 1200 to 1500mm long. The extruded graphite rods are baked in an oven and sintered to improve the density of graphite. They are typically extruded around a thin brass pin which is then connected to a cable in order to form the electrochemical cell necessary for the process of cathodic protection.
Over time however, despite its durability and corrosion resistance, graphite will begin to break down, especially when used in the purpose of cathodic protection. However, some graphite anodes are treated with a non-porous quality non-conducting material such as oils, microcrystalline waxes or resins. The treatment of graphite anodes will ensure a higher level of performance, especially in wetter environments when exposure to moisture is prolonged or constant.
The wax, resin or oil seals the porosity of the anode and protects it against water absorption as well as improving the stability and wear rate by reducing the electrochemical reactions within the anode. Applications such as dock-side uses and water tanks, as well as deep underground installations are recommended to pre-treat the anodes to ensure optimal performance.
Graphite Anodes Informational Video