Laboratory studies are presented in which a method was devised for determining cathodic current requirements for the protection of storage tank bottoms. This method involves the determination of current distribution efficiencies on tank bottoms from four terminal resistivity measurements. For the purpose of this report the efficiency of current distribution may be defined as the ratio of the current density at the tank bottom center to the average current density. This method offers the corrosion engineer a possible method for estimating the resistance and effectiveness of various tank bottom coatings and pads. Its use offers possibilities for determining the current required to protect either a coated or uncoated tank bottom.
Initial tests of the method were made on three storage tanks near Houston, Texas. Since measurements were made on empty storage tanks in which the release of load had produced warping of the bottom, there was some inconsistency between test data and calculated values. This investigation also revealed that current-potential curves were not reliable in fixing adequate cathodic current values for tank bottom protection. Due to limited number of field tests made, this method should not be considered completely proved at this time.
