Corrosion Control of Above Ground Storage Tank Bottom Steel Plates Using Aluminum Mesh Anode with Newly Developed Backfill

Tank bottom plates of above-ground storage tanks may be protected from corrosion by oil sand, asphalt sand or ICCP. The protection by oil or asphalt sand takes advantage of the dielectric, non-electrolytic property of the oil and asphalt. Recently, however, the effectiveness of this approach has been questioned due to corrosion failure. ICCP systems generally use inert anodes which are embedded in sand or soil with a rectifier to generate CP current. The CP current travels to the tank bottom through the sand or soil electrolyte.  So long as the tank plate contacts the sand, the ICCP is effective. However, when the product inside the tank becomes depleted or emptied, the tank plate rises from the sand, resulting in development of air gaps in some areas. If this occurs, the CP current cannot reach the tank steel surface located over the air gaps because the air cannot transfer the CP current. As a result, the effectiveness of the corrosion protection using ICCP is lost, and those areas are subject to corrosion. To overcome these problems, a new sacrificial anode CP system was developed with a special backfill material. This paper will discuss the new sacrificial anode CP system.