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


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.

Steel equipment used in petroleum industry such as pipelines storage tanks heat exchangers distillation towers, etc. suffer from severe corrosion owing to the presence of same water containing electrolytes such as NaCl, CaCl2 and MgCl2 in crude oil [1-9]. The rate of corrosion of steel in crude oil is accelerated by the presence of H2Sin the crude [10]. The present work deals with the problem of steel crude oil storage tank corrosion. Although corrosion and protection ofthe outer surface of the storage tank has received a great attention, little has been done on the internal corrosion of crude oil storage tanks. The most studying vulnerable area to corrosion in crude oil storage tank is the bottom of the tank where an aqueous layer of electrolyte resides at the bottom, besides an insoluble porous sludge (e.g., sand and clay)settles on the tank bottom leading to corrosion by differential aeration cells

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Industrial Chemistry