Monitoring cathodic protection

How do we know that we have enough cathodic protection?

Current flow onto any metal shifts its normal potential in the negative direction. To know whether or not the structure is sufficiently protected the potential of the steel (metal/electrolyte potential difference) should be measured versus a standard reference electrode.

The corrosion is stopped if steel receives enough current to shift the potential (polarise) to more negative values than:

  • -800mV versus a silver/silver chloride (Ag/AgCl)
  • +250 mV versus a zinc (Zn)
  • -850 mV versus a Cu/CuSO4

... which are the most common electrodes.

Ag/AgCl and standard Zn reference electrodes are used for sea water measurements, while Cu/CuSO4 electrode is normally used for buried structure measurements.