In the case of cathodic protection by impressed current for fixed structures, the anodes are generally immersed at a significant distance from the structure that need to be protected while trying to minimize the risks of interference to other metal structures (ships in the harbours, etc). For ships’ hulls, the impressed current anodes are installed on the hull, in the centre of a dielectric screen (shield) in order to avoid too high densities of protection current in the immediate vicinity of the anode (risk of over-protection).
The galvanic anodes are mainly made from aluminium alloys (Al-Zn-In), from zinc (with controlled composition) or from magnesium. They are fixed on the structure by a system that facilitates their replacement when they are consumed. For the offshore structures, the calculation relating to the anodes (mass, number) is carried out to cover the design life of the structure.