The first known appearance of iron or steel as an anode were installations of iron “wastage plates” in the early 1900’s in condensers and boilers. Although unintentional, steel acted as an anode on some early DC traction systems. Many of the corrosion failures experienced on these systems were due to DC current discharge from the rails. Probably the first planned use of steel as an anode was in the 1930’s. Scrap steel was commonly used, either in the form of old railroad rails or used pipe.
Steel anodes can take many forms. Scrap materials include buried structures which have been abandoned in place; such as pipelines or well casings. Scrap pipe, tubing, or railroad rails are commonly used. Any shape is capable of use; however, massive shapes are more conducive to practical use.
A major problem in the use of steel as an anode is maintaining electrical connections. Multiple connections are typically used. Methods of protecting the connections and maintaining electrical continuity includes coating the structure in the vicinity of connection and continuous coating strips along the length of the anode. The consumption rate of steel is approximately 20 pounds per ampere year. Complete consumption of anode material is not typically achieved because of non-uniform corrosion and the difficulty of maintaining electrical connection. There is no established maximum recommended current density.
Steel can be used in horizontal, vertical, or deep groundbeds, with or without carbonaceous backfill. With proper application, steel will perform well as an anode material. The major disadvantages of steel as an anode material are:
- Anodic corrosion product films may build up on anode surface, increasing the resistance to earth. This effect may be partially overcome by installation in carbonaceous backfills.
- Preferential corrosion may occur in the area of the connection.
- Maintaining electrical connections.
- Large mass requirements.
Although most people would consider the use of steel as an anode as outmoded; there are operators who currently use steel in groundbeds with successful results.