Dual-action antifouling & anticorrosion anodes
The dual-action anodes releases a low level mix of ions to prevent fouling and supress corrosion in sea chests and seawater piping systems.
Copper based antifouling anodes
For seawater intakes, copper antifouling anodes are usually applied in conjunction with anticorrosion anodes of aluminium or iron.
When impressing current on the anode, the copper ions released will flow through the system, creating an environment, which discourage micro organisms to adhere or settle. Instead, they are carried straight through the system.
You may also read about principles of electrolytic antifouling.
Aluminium or iron based anti-corrosion anodes
Depending on material in the sea water pipes, the anti-corrosion anode should be either aluminium or iron. The released anti-corrosion anode products combines with copper products and are deposited on the structure. The deposit creates a barrier, which discourage marine growth and mitigate corrosion.
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Aluminium MGPS/ICAF anodes
Aluminium anodes are used in conjunction with copper anodes to mitigate corrosion in ferrous pipe works. The dissolved aluminium oxide forms a gelatinous “floc” which is carried by the flow of water throughout the system. The amounts of copper and aluminium released by the anode reactions are very small, but because the action is continuous, the products accumulate, forming a thin protective film throughout the sea water system.
The released aluminium oxide gelatinous floc is claimed to improve distribution of the copper ions along the sea water system.
Iron MGPS/ICAF anodes
Iron anodes are used in conjunction with copper anodes to mitigate corrosion on non-ferrous sea water systems, e.g. copper-nickel, aluminium-brass and nickel-aluminium-bronze alloys. Release of low concentration iron ions is intended to repair and maintain the piping oxide films.
In older sea water systems with majority of ferrous components, corrosion of these components provide a continuous supply of ferrous ions. Experience has shown that this has a positive effect on corrosion of copper based alloys.
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Effect of cathodic protection in pipings
It should be noted that sacrificial and antifouling anodes in sea chest or mud boxes, provide only local cathodic protection nearby the anodes. Galvanic pipeline corrosion caused by poor material quality or incorrect material combinations will not be covered by such an arrangement.
As a rule of thumb, sacrificial spool pieces (also called corrosion pieces) installed in pipes can be assumed to provide cathodic protection aproximately five times the pipe diameter inward the pipe.
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