Glossary

Definition : The electrode through which direct current enters an electrolyte and at which oxidation or corrosion of some component occurs (opposite of cathode).

Definition : Material placed in a drilled hole to fill space around anode and buried components of a cathodic protection system. Generally improves the performance and efficiency of anodes.

Definition : A piece of metal conductor, either solid or flexible, usually of copper, connecting two points on the same or on different structures, to prevent any appreciable change in the potential of the one point with respect to the other.

Definition : The electrode through which direct current leaves an electrolyte. Opposite of anode.

Definition : A technique used to minimise the rate of corrosion of a structure. Cathodic protection does not eliminate corrosion, it transfers corrosion from the structure under protection to a known location where anodes are placed and could be replaced easily. The cathodic protection principle is based on the electrochemical nature of the corrosion phenomena; the anodic area corrodes (current is discharged) and the cathodic area does not corrode (current is received). Cathodic protection overrides the naturally occurring anodic areas of a structure, thus turning the structure under protection completely cathodic, which means it receives current from the surrounding electrolyte (for example, soils, water) and does not corrode. Cathodic protection is achieved by passing enough direct current electricity from an external source (a more powerful anode), which could be a galvanic anode or an impressed current anode.

Definition : A complete electrolytic system comprising of a cathode and an anode in electrical contact with an intervening electrolyte.

Definition : A substance (mainly a metal or carbon) in which electric current flows by the movement of electrons.

Definition : A bond designed and installed specifically to ensure the electrical continuity of a structure.

Definition : A reference electrode consisting of copper in a saturated copper sulphate solution.

Definition : The chemical or electrochemical reaction of a metal with its environment, resulting in its progressive degradation or destruction.

Definition : The current per unit geometrical area of the protected structure in contact with the electrolyte.

Definition : One or more anodes installed vertically at a nominal depth of 15m or more below the earth’s surface in a drilled hole for the purpose of supplying cathodic protection for an underground or submerged metallic structure. See also groundbed.

Definition : A decrease in the polarisation of an electrode; the elimination or reduction of polarisation by physical or chemical means; depolarisation results in increased corrosion.

Definition : A conductor of the metallic class (including carbon) by means of which current passes to or from an electrolyte.

Definition : A liquid, or the liquid component in a composite material such as soil, in which the electric current flows by movement of ions.

Definition : The state of a metallic electrode when its potential is negative with respect to another metallic electrode in the system.

Definition : The state of a metallic electrode when its potential is positive with respect to another metallic electrode in the system.

Definition : Any metallic structure that is not intended as part of a cathodic protection system of interest.

Definition : Pertaining to the current resulting from the coupling of dissimilar electrodes in an electrolyte.

Definition : A metal which because of its relative position in the galvanic series, provides sacrificial protection to metals that are more noble in the series when coupled in an electrolyte.

Definition : Accelerated corrosion of a metal because of an electrical contact with a more noble metal or non-metallic conductor in a corrosive electrolyte.

Definition : A system of buried or submerged electrodes (anodes) connected to the positive terminal of an independent source of direct current, in order to lead to earth the current used for the cathodic protection of a buried or immersed metallic structure.

Definition : The current supplied by a rectifier or other direct-current source (specifically excluding a sacrificial anode) to a protected structure in order to attain the necessary protection potential.

Definition : The structure/electrolyte potential measured immediately after the synchronous interruption of all sources of applied cathodic protection current.

Definition : The state of the surface of a metal or alloy susceptible to corrosion where its electrochemical behaviour becomes that of a less reactive metal and its corrosion rate is reduced.

Definition : A logarithmic index for the concentration of hydrogen ions in an electrolyte.

Definition : A non-uniform corrosion of a metal whereby a number of cavities, not in the form of cracks, are formed in the surface. Localised corrosion of a metal surface, confined to a point or small area that takes the form of cavities or pits.

Definition : Change in the potential of an electrode as the result of current flow.

Definition : A device inserted in the earth connection of a structure that drains only a small current from the source used to provide cathodic protection for the structure, but provides a low resistance path to currents from high DC voltages and all AC voltages carried by the structure.

Definition : A buried or immersed structure cathodically protected by a system that may constitute a source of corrosion interaction with another (secondary) structure.

Definition : A structure to which cathodic protection is applied.

Definition : A dielectric material adhering to or bonded to a structure to separate it from its environment in order to prevent corrosion.

Definition : A process of chemical or electrochemical change, particularly taking place at or near an electrode in a cell.

Definition : An electrode the potential of which is accurately reproducible and which serves as a basis of comparison in the measurement of other electrode potentials. Sometimes called a ‘half-cell’.

Definition : Reduction of corrosion of a metal in an electrolyte by galvanically coupling it to a more anodic (or active) metal; a form of cathodic protection.

Definition : A buried or immersed structure that may be subject to corrosion interaction arising from the cathodic protection of another (the primary) structure.

Definition : Current flowing through paths other than the intended circuit. Current flowing in the soil or water environment of a structure and arising mainly from cathodic protection, electric power or traction installations, and which can pass from the environment into the structure and vice versa.

Definition : Stress corrosion cracking (SCC) is the cracking induced from the combined influence of tensile stress and a corrosive environment.

Definition : The difference in potential between a structure and a specified reference electrode in contact with the electrolyte at a point sufficiently close to (but without actually touching) the structure to avoid error due to the voltage drop associated with any current flowing in the electrolyte. Often referred to as Pipe to Soil Potential for buried pipelines.