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Impressed Current Cathodic Protection
Systems
Farwest Corrosion Control
Company Impressed Current Cathodic Protection (ICCP) systems are designed to prevent
external corrosion on underwater steel. Applications are suited for ships,
offshore rigs, semi-submersible and other marine structures.
ICCP systems were developed
originally to protect the underwater external hulls of large tankers and
bulk carriers, which could not be adequately protected by sacrificial anode
systems. ICCP systems were so successful that they are in common use on all
ranges of ships.
Each ICCP system fundamentally
comprises of four main parts:
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Titanium anodes designed to
last at least 20 years - either linear surface-mounted or recessed.
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Zinc or silver / silver
chloride reference electrodes - either surface-mounted or recessed.
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Propeller shaft bonding slip
ring and rudder stock cable.
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Automated control panel -
rated from 100A to 800A.
Anodes
ICCP anodes conduct DC
protective current into the seawater to maintain the hull potential at the
correct level to prevent corrosion at areas where the paint has become
damaged. The anodes are constructed of titanium elements coated with either
platinum or mixed metal oxide. The elements are encapsulated in a tough
chlorine-resistant resin carrier. Anodes are available with capacities from
50A to 200A.
Titanium / MMO Linear Anodes: 50A (top) and 200A (bottom)
Systems are sized to suit the
wetted surface area that has to be protected utilizing a current density to
provide enough current to meet any potential coating failure. Systems are
normally mounted in the engine room and the ships forward compartment and
forepeak tank.
Reference
Electrodes
ICCP reference electrodes are designed to
give a stable reference against which the hull to sea potential can be
measured.
Propeller &
Rudder Bonding
To allow the protection for the propeller a
high content silver alloy band is attached around the shaft. Contact between
the shaft and hull is by way of silver graphite brushes. Similarly, the
rudder protection is ensured by the fitting of a bonding cable, which is
attached to the rudderstock and hull.
Power Supply
Units
The ICCP control unit is a
potential controlled computerized power supply. A millivolt signal from the
reference electrode determines the output. A preset signal is fed into the
unit. If the hull signal is outside the set parameters, the unit will put
out DC current to compensate. The power supply element of the control system
is designed to suit the amount of steel to be protected.
The following standard size
rectifiers are available: 50A, 100A, 150A, 200A, 250A, 300A, 400Amp,
450A, 500A.
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