Graphite anodes have been commercially available since 1940. In manufacturing, carbonaceous fillers (calcined petroleum coke) are bonded with carbon-yielding binders (coal tar pitch), extruded into rods and baked to 1000°C to carbonize the pitch binder. After allowing to cool in a reducing atmosphere, the anode is placed in an electric graphite furnace and reheated to over 250°C, which completes the graphitization process. The material then has crystalline properties with improved electrical and thermal conductivity. Graphitizing at elevated temperatures makes the anode more porous.
The pores allow water to penetrate, resulting in corrosion and premature failure of the metallic lead wire to anode connector. The wear rate could increase further because the pores allow oxidation of the anode material in contact with water inside porous areas.
Carbon industry companies have developed several treatments to improve the performance of the graphite anode. The treatments consist of filling the pores with a high quality nonconducting material. Scientifically boiled linseed oil, microcrystalline wax and special resins are used in this process. Treated anodes perform much better in wet and in hostile environments than non-treated anodes and the resin treat strengthens the anodes. Resin treat anodes are recommended for deep anode ground beds and for "free suspension" applications in water tanks and at docks and piers where the anode is suspended by its lead wire.
BK Corrosion offers a complete line of high quality graphite anodes for impressed current cathodic protection systems. The graphite anodes are stocked in two standard sizes: 3 x 60 inches and 4 x 80 inches. Custom shapes and sizes available upon request. Graphite anodes are available untreated, or impregnated with microcrystalline wax, with double boiled, high purity linseed oil, or resin.
Graphite is particularly suited to cathodic protection because of its chemical inertness, affordable cost and good electrical conductivity. In many applications, especially on underground pipelines, cathodic protection has become a routine and cost effective method of corrosion control.