Chapter 2 - Corrosion and Protection of Underground and Underwater Structures Attacked by Stray Currents

Abstract

As stray currents are one of the most dangerous factors causing corrosion damage to metals, methods for their detection and control, as well as a means of protection of constructions from their attack, are usually standardized and regulated. Construction areas from which stray currents drain off into the ground (i.e., metal areas attacked by anodic currents) are exposed to corrosion damage. Ions of metal bearing a positive charge are passed into electrolytes, which in the cases considered are ground, water, or concrete. On attack by stray currents of anodic direction, the corrosion rate of carbon steel both in the ground and in seawater is defined by the magnitude of the anodic currents at the areas of their attack. Irrespective of the slope of the polarization curve, at potentials that are more negative than the potential of oxygen evolution, practically all the current which is draining off from the metal into the ground or into the water is spent on metal dissolution. Under the attack of stray currents on metals such as aluminum and lead sheaths of cables, the influence of the structure and properties of the environment become minor, and the corrosion rate, as in the case of steel constructions, is determined by the magnitudes of the currents draining off from the metal into the ground. Electrodrainage protection is the basic method for the protection of underground construction from the corrosion attack by stray currents. It is intended for the elimination of anodic zones from underground constructions by stray current drainage to its source. On the lines of electrified transport, it is carried out by an electric connection of the underground construction with the negative bus of a traction substation or with a section of the rail circuit.