Cathodic protection apparatus for well coated metal vessels having a gross bare area

Cathodic protection apparatus employs a grid-type or rod-type anode secured within an electrically insulating tube disposed within an inlet-outlet pipe entering the vessel, the pipe comprising the gross bare area. The vessel is well coated but yet contains minute flaws or bare areas to expose underlying metal, typically steel, to the corroding electrolyte, typically water, contained within the vessel. By maintaining a negative vessel-to-water potential between 0.85 and 1.10 volts as measured between the well coated vessel surface and a saturated copper-copper sulfate reference electrode placed in the water adjacent the coated vessel surface, good corrosion control at the minute flaws is readily effected.