In-plant cathodic protection of buried piping network in congested areas of a complex petrochemical plant has been a critical issue for the CP design engineers. There have been cases where reinforced concrete foundations and plant grounding have either a shielding effect or consumed a major portion of the protective current from the impressed current cathodic protection (ICCP) system. A significant quantity of protective current drain to unintended structures has also been observed, when remote ICCP anode beds are used for congested areas because of the universal electrical continuity within the plant. This paper describes a case history, where a number of deep well anode beds were installed for the protection of a congested underground piping network for a new petrochemical plant. The plant grounding system was also taken in consideration for ICCP design. The system was energized but failed to achieve the required polarization even at system's maximum design output. Two of the NACE criteria (-850 mV ON potential and 100 mV formation/decay) were not achieved during the performance evaluation tests. However, the firewater pipeline outside the congested area of the plant did achieve the protection. Detailed investigations were conducted to determine the effects of the concrete foundations, backfill around grounding rod, plant grounding, and locations of soil access holes for potential measurements and effects of deep well anode bed. Various alternate schemes of ICCP are highlighted with recommendations for the protection of a piping network in congested areas.
Keywords: Deep well anode ground bed, In-fill titanium surface anode, grounding grid, shielding, synthetic liner, bituminous coating