Technical note: Anomalous effect of calcareous deposition on cathodic protection

The building of steel structures for oil production often involves siting of parts of the structure in the sea and subsequently adding or connecting further sections. If the immersed structure is cathodically protected from the outset, it will build up a calcareous deposit, which is normally an advantageous feature because it reduces cathodic current demand. However, in certain circumstances the cathodic protection of added sections requires transmission of current directly through mating steel/steel interfaces, unless an electrical bridge has been designed into the system. In the former situation the ability to protect other sections of the structures cathodically may be limited if the calcareous product acts as an insulator.