Cast iron and steel respectively contain 95% and 99% iron. The latter is naturally exposed to reversion to its ore form due to the iron/oxygen chemical exchange. Backfill materials generate chemical reactions and stray currents; these oxidation reactions liberate electrons: That is what corrosion is!
Cathodic protection is the technique that allows that loss of electrons to be steadily avoided by using sacrificial anodes or impressed current: The work is monitored 365 days a year.
For an investment under €2/ml BT and an annual power consumption lower than 100 W/h (calculated on 30 km ND 1,000), the client benefits from a life insurance on the totality of his work (tubes, connections, valves and fittings and accessories)..