Abstract
Methods of making duct surveys, surface potential gradient surveys, measurements of cable to reference electrode potentials, sheath current measurements and earth resistivity measurements are described. Examples are given of various types of measurement and their interpretation. It is pointed out that a single measurement of the potential between a cable sheath and a reference electrode in contact with nearby earth may not reveal the existence of a corrosive condition. Emphasis is given to the difference in polarity between self-produced corrosion cells and those resulting from external influences such as stray current or contact with a more noble metal. The importance of employing a variety of measurements in any particular study is shown. References are given to techniques employed by other workers in making underground corrosion tests. 4.5.3
