Abstract: 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.

Abstract: A salt bridge reference electrode, immersible in an electrolyte, contains a metal electrode contacting water saturated salt crystals and is configured so both evaporative loss of contained water and diffusion loss of contained salt crystals are minimal. An electrolytically conductive plug, having metallic salt crystals in suspension, within the cell, maintains electrolytic continuity between the water-saturated salt crystals and the surrounding electrolyte while minimizing loss of salt crystals from the saturated water into the surrounding electrolyte by osmosis.