Specific Terms Related to Cathodic Protection
Cathodic Protection
Process of reducing or preventing corrosion of metal structures in contact with an electrolyte by the flow of direct current from the electrolyte into the structure surface.
Cathodic Protection Station
Combination of equipment installed to provide cathodic protection to the structure to be protected.
Current Density
Amount of current per unit area of the steel surface, coated or uncoated, in contact with the electrolyte.
Drain Point
Point on the pipeline or structure where the connection of the negative terminal of the cathodic protection voltage source is made to conduct (drain) the returning current from the pipeline to the voltage source.
Electrolyte
Conductive liquid or material such as soil or water in which an electric current can flow.
Foreign structures/pipelines
Metal structures or pipelines other than the structure or pipeline under consideration, in contact with the same electrolyte, and which are or may fall under the influence of the cathodic protection system; they may be owned by the Principal or other companies and may or may not be equipped with cathodic protection.
Groundbed
System of buried or submerged electrodes, to conduct the required current into and through the electrolyte to the steel surface to be protected.
Isolating flange
Set of two flanges assembled with an insulating gasket and insulating sleeves and washers, for the purpose of electrically isolating two metallic pipe sections.
Isolating joint
Factory assembled pipe fitting provided with insulating gaskets and resins, to be welded into a pipeline or piping for the purpose of electrically isolating two metallic pipe sections.
Midpoint
Point on a pipeline between two cathodic protection stations where the influence of the two cathodic protection stations is expected to be equal and the protection levels are usually lowest.
Natural Potential
Pipe-to-soil potential measured when no cathodic protection is applied and polarisation caused by cathodic protection is absent.
“OFF” potential
Pipe-to-soil potential measured immediately after the cathodic protection system is switched off and the applied electrical current stops flowing to the pipeline surface, but before polarisation of the pipeline has decreased.
“ON” potential
pipe-to-soil potential measured while the cathodic protection system is continuously operating.
Pipeline
Pipeline and associated equipment as defined in the scope of the cathodic protection design contract.
Pipe-to-soil potential
Difference in electrochemical potential between a pipeline or foreign structure/pipeline and a specified reference electrode in contact with the electrolyte. Similar terms such as structure-to-soil potential, pipe- to-electrolyte potential and pipe-to-(sea)water potential are sometimes used as applicable in the particular context.
Polarisation
Change of the pipe-to-soil potential caused by the flow of DC current between an electrolyte and a steel surface.
Polarisation cell (Kirkcell)
Device inserted in the earth connection of a structure that isolates for DC in the cathodic protection range.
Reference electrode
Non-polarising electrode of which the electrochemical potential is accurately reproducible and which serves as a reference for pipe-to-soil potential measurements.
Stray currents
Electrical currents running through the electrolyte, originating from a foreign DC source and causing interaction with the corrosion and cathodic protection processes of the structure or pipeline. Stray currents may also originate from the pipeline’s cathodic protection system and act upon foreign structures/pipelines.
Structure
Structure and associated equipment as defined in the scope of the cathodic protection design contract.
ABBREVIATIONS
Ag/AgCl Silver/Silver Chloride as used for the Silver/Silver Chloride type of reference electrode
Cu/CuSO4 Copper/Copper Sulphate as used for the Copper/Copper Sulphate type of reference electrode
AC Alternating Current
DC Direct Current
PVC Poly Vinyl Chloride
ROV Remotely Operating Vehicle (underwater)
SBM Single Buoy Mooring