Principle: A metal in sea water corrodes by anodic dissolution; corrosion is prevented by making the whole underwater structure cathodic (i.e. supplying electrons to it) so that no anodic areas exist. In ICCP this is done by impressing a controlled direct current through the sea water from anode(s) to the hull, using an external DC source and a reference electrode to maintain the hull at a chosen protective potential (typically about -850 mV vs Ag/AgCl reference) where steel is protected and further wastage is stopped.

Key components and their functions

• Transformer-rectifier (power source): converts AC to DC and is the controlled supply; it receives the control signal and supplies the impressed current.
• Impressed current anodes (e.g. platinised titanium, mixed-metal-oxide or lead silver anodes, mounted in the underwater hull): the current leaves via these anodes into the sea water. They are made of a near-inert/consumeable material that conducts the protection current without being rapidly consumed.
• Reference electrodes (e.g. Ag/AgCl or zinc reference half cells, mounted at hull): sensing the hull potential; they give the control signal to the rectifier.
• Controlling/feedback unit: adjusts the rectifier output current to hold the hull at the set protective potential, compensating for changes in water resistivity, coatings, temperature and current demand.
• Anode/insulated fittings, cabling and hull electrical bonding/grounding to give low-resistance return paths.

The system safeguards the metal structure by maintaining the hull and components below the corrosion (free-corrosion) potential, so that no anodic dissolution occurs, protecting hull, rudder, propeller areas and fittings while the (usually) paint coating and sacrificial close-out perform the rest.

• Use of permanent, low-consumption anodes (platinum-coated titanium and mixed-metal-oxide) replacing old lead/silver anodes, giving longer life, lower maintenance and steadier output.
• Solid-state electronic controllers and digital potential-control/reference electrodes with automatic current adjustment, giving precise hull potential control, lower power and reduced over-protection.
• Remote monitoring and data logging (computerised control, data acquisition and telemetry) allowing shore- or bridge-side optimisation and early warning, reducing surveys and wastage.
• Integration with condition monitoring of the hull, coatings and fouling, improving fuel efficiency (less fouling) and reducing emissions.
• Improved reference electrodes and current sharing across zones so the system protects complex geometries evenly, reducing over/under-protection and hence resource use.

These contribute to more efficient and sustainable corrosion protection by: lower electrical consumption, longer anode service life, less maintenance and dry-dock intervention, reduced hull fouling/drag (fuel economy and lower emissions), and protection that is renewable and controllable without the environmental cost of frequent sacrificial-anode renewal.