Abstract
Shielding of underground piping network in congested petrochemical plants is one of the major problem when cathodic protection is applied for its protection from the soil side corrosion. Process equipment reinforced concrete foundations and electrical plant grounding are integral part of a plant. Not only a significant amount of protective current is consumed by these elements, but also they restrict the flow of protective current to the intended structures from a remote ground bed. Similarly, large diameter pipes shield small diameter pipes when shallow and closely distributed anodes are installed. Various alternative scheme to overcome these shielding effects have been proposed including installation of DC current decoupling devices in the grounding system that allows the AC current to pass through but stops the DC current flow to the grounding rods and thus eliminating the protective current drainage.
This paper describes, a new approach in providing adequate cathodic protection to the shielded piping network in congested areas of a petrochemical plant using either mixed metal oxide (MMO) coated Ti ribbon or polymeric anodes. These anode systems were placed just beneath the reinforced concrete slab and primarily intended to compensate for all areas that were fully or partially shielded from the protective current of deep well anodes. Initial results have shown that adequate protection was afforded to the shielded piping network using either of these two methods.
