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Study of the Rate of Zinc Consumption During Sacrificial Cathodic Protection of the Bottom of Crude Oil Storage Tanks

Khodary MA, Sadik ER, Khalifa SHMN, Mansour MS and Farag HA

The bottom of crude oil storage tank suffers from severe corrosion as a result of the presence of an aqueous layer containing electrolytes MgCl₂, NaCl, CaCl₂ and H₂S beside porous deposits of sand and clay. Sacrificial cathodic protection using Zn anodes can be used to protect the tank bottom from corrosion. To contribute to the economic assessment of sacrificial cathodic protection the rate of Zn consumption under different condition was studied during cathodic protection in the present work. Variables studied were NaCl concentration, porosity of the porous bed overlying the tank bottom, height of the porous bed and the area ratio between Zn and the steel bottom. It was found that the rate of Zn consumption increases with increasing NaCl concentration and increasing porous bed height but decreases with increasing bed porosity. Increasing cathode/anode area ratio was found to increase the rate of Zn consumption.