Monitoring and Control- Immersed structures

On an immersed structure, the efficiency of cathodic protection is checked by potential measurements compared to a reference electrode immersed in the vicinity. It can be:

• a reference electrode in free immersion, moved by a diver or moving on a fixed guide,
• a waterproof “gun” which contains at the same time the reference electrode and the millivoltmeter
• a reference electrodes with a fixed system (Ag/AgCl) or with a Zn electrode (the potential of zinc in sea water is rather stable, close to –0,78 V/ENH). The result of measurement is transmitted by cable or acoustic way.

These measurements are done approximately every five years, in a manual way, or more frequently it is done through an automated way.

Measurement " Gun " including the reference electrode (Ref) and the millivoltmeter (E)

The potential measured with the reference electrode (Ref) is transmitted by the transmitter (Em) to the receiver (Tr) associated to an interrogation unit (Interr).

The current can be measured with a "marinized amperometric pliers".