Marine cathodic protection controls the corrosion of submerged steel on ships, vessels, FPSOs and offshore structures. Seawater is corrosive environment, so unprotected steel below the waterline corrodes quickly. Two complementary technologies address the marine environment: sacrificial cathodic protection, which protects the steel itself, and marine growth prevention systems (MGPS), which keep seawater pipework clear of biofouling. This article explains how each works and where it is applied.
Corrpro Europe, formerly Wilson Walton International, has led the field of marine corrosion protection and antifouling for over 45 years and has supplied CP materials, installations and services to more than 1,000 vessels worldwide. Hull and tank anodes are cast at our foundry in Stockton-on-Tees.
Sacrificial Hull Anode Systems
A sacrificial cathodic protection system uses anodes of a more reactive metal bolted or welded to the submerged structure. These anodes corrode in preference to the steel, supplying a protective current that holds the structure at a potential where corrosion is controlled, typically minus 0.80 volts or more negative with respect to a silver and silver chloride seawater reference electrode. As the anodes consume, they are replaced, usually during a scheduled dry-dock or inspection cycle.
Choosing the Anode Material
Three anode materials are used in marine cathodic protection, each selected according to the water chemistry and application. Aluminium alloy anodes offer high current capacity and long life, and are widely used on hulls, ballast tanks, subsea structures and FPSO hulls. Zinc anodes are a robust and well-proven choice for seawater and brackish water, applied to hulls, tanks and fittings where established practice calls for them. Magnesium delivers a high driving voltage but consumes quickly, so its use in open seawater is limited; it is generally reserved for low-conductivity fresh or brackish water and soil applications.
Corrpro Europe supplies Aloline aluminium and Zincoline zinc hull and tank anodes worldwide, cast in-house to the required dimensions and output.
Marine Growth Prevention Systems (MGPS)
Seawater cooling and firewater circuits draw raw seawater through pipework, heat exchangers and pumps. Without treatment, mussels, barnacles and other marine life settle and grow inside these systems, restricting flow and reducing the performance of critical cooling. A marine growth prevention system stops this fouling at source.
Corrpro Europe manufactures the Anfomatic MGPS, which applies a direct current to copper anodes to release a controlled quantity of copper ions into the seawater system. This creates an environment in which the primary forms of marine life do not settle or develop. Current applied to an aluminium anode releases a floc of aluminium hydroxide that reduces corrosion of ferrous components in the system, and iron anodes are used for cupro-nickel pipework. The system is automatic, requires minimal maintenance and allows ships and vessels to continue operating without interruption.
Sacrificial CP and MGPS: How They Differ
The two systems solve different problems and are often fitted together. Sacrificial cathodic protection protects the external submerged steel of the hull, tanks and structures from corrosion. A marine growth prevention system protects the internal seawater pipework from biofouling and helps control corrosion within those circuits. One guards the steel against the sea; the other keeps the seawater systems clear and flowing.
Protecting Vessels, FPSOs and Offshore Structures
Marine cathodic protection and MGPS protect commercial vessels, naval ships, FPSOs and offshore platforms. FPSOs in particular benefit from both technologies, since they remain on station for long periods without dry-docking. Corrpro Europe supports FPSO life extension projects, where anode systems and seawater circuit protection are assessed and upgraded to extend service life.
A common FPSO and platform upgrade is the conversion of obsolete chlorination systems to copper dose. Where older electrochlorination antifouling has reached the end of its life, an Anfomatic copper-dose system offers a proven, lower-maintenance alternative for keeping seawater systems free of marine growth.
A Marine OEM with Over 45 years of Heritage
Through its Wilson Walton heritage, Corrpro Europe is the original equipment manufacturer for long-established marine CP and antifouling systems. Our marine range includes Aloline and Zincoline sacrificial anodes, Aquamatic impressed current cathodic protection for hulls and the Anfomatic marine growth prevention system, supported by worldwide ICCP and antifouling servicing and spares. As OEM, we also support legacy installations with genuine replacement parts and engineering advice.
Frequently Asked Questions
How often should hull anodes be replaced?
Sacrificial hull anodes are sized to last a defined design period, then replaced once consumed. In practice, replacement is aligned with the vessel’s dry-dock or inspection cycle, and the anode mass is calculated so that sufficient material remains until the next planned docking.
What is the difference between sacrificial CP and MGPS?
Sacrificial cathodic protection protects submerged steel from corrosion using anodes that corrode in its place. A marine growth prevention system prevents biofouling inside seawater cooling and firewater pipework by dosing the water with copper ions. They address different problems and are frequently installed together.
Can a chlorination system be converted to copper dose?
Yes. Obsolete electrochlorination antifouling systems can be replaced with a copper-dose marine growth prevention system such as Anfomatic. This is a common upgrade on FPSOs and offshore platforms during life extension work.
What is the difference between zinc and aluminium hull anodes?
Both protect steel in seawater. Aluminium anodes offer higher current capacity and longer life for a given mass, which can reduce the number of anodes required. Zinc anodes are a robust and well-proven option. The choice depends on the application, the water chemistry and the design life.
To discuss hull anode supply, an MGPS installation or an FPSO life extension project, contact our marine department.
