An investigation has been made for the purpose of determining if buried or submerged steel pipe can be supplied adequate cathodic protection against corrosion by the maintenance of some constant open circuit potential. The experimental work consisted in establishing the open circuit potentials required to prevent corrosion of test pipe specimens exposed under a variety of conditions. Identical groups of six specimens each were exposed in four different environments. Test locations were selected to include as wide a variation in soil conditions as possible and one group of specimens was exposed in water.
Current was applied to five of the six specimens in each test group with the object of maintaining the open circuit potential of each specimen at a designated value. Measurements were made throughout the test of the open circuit potential and the amount of current supplied to each respective specimen. At the conclusion of the four tests, which were run for some 70-80 days, actual corrosion weight losses for all test specimens were determined and then correlated with the current and potential measurements. The results are presented and the data are explained and illustrated by accompanying graphs and tables. These data indicate that in each test environment there was a definite, potential at which corrosion was stopped. This potential was found to vary with the environment, and in all cases, was less than —0.85 volt with reference to the copper-copper sulfate electrode. The test results also indicate that films, or coatings, formed by the applied current are of considerable importance in some soils in reducing current requirements, and that there is a definite advantage in applying sufficient current to form the coating as soon as possible after the cathodic protection installation is completed.
In appraising the test method used in this investigation the conclusion is reached that the method is apparently sound and that it can be used to determine what must be done to the pipe potential in order to prevent corrosion in any environment. The method appears to be capable of more precise results and recognition is made of the fact that further development and refinements are desirable. In this respect certain improvements are suggested for consideration.
