Marine corrosion, especially seawater corrosion, is one of the most important factors affecting the
service life of ships. At present, most of ships use metal shell. In the marine environment, the
corrosion degree is very serious due to the influence of seawater temperature, seawater salinity,
oceanic atmosphere temperature, oceanic atmosphere humidity and marine microorganism. Corrosion not
only reduces the strength of steel structure, but also shortens the service life of the ship. At
the same time it will increases the sailing resistance, speed reduction, affecting the use of
performance. More seriously, once the perforation or cracking, they will lead to a marine accident,
resulting in staggering losses.This has aroused great concern to corrosion experts, and they
actively explore the metal corrosion to develop a variety of protective technology methods and
measures.For ships parts contact directly with the sea water, adding a electrical connection with
metals or alloys which have lower electrode potential that hull steel so that those metals or
alloys become cathode. Or adding the DC that opposed to the corrosion current of the steel hull it
will also become a cathode and be polarized, finally it will enable the steel hull from corrosion,
that is, be protected. Protection methods like these are called marine cathodic protection. There
are mainly two kinds of ways for protecting marine from corrosion, sacrificial anode protection and
impressed current protection.
Sacrificial anode cathodic protection technology is to protect the hull steel plate as the cathode
the hull. Sacrificial anode cathodic protection is one of the most effective and widely used
methods for the immersing parts of ship. The electrochemical performance of anode materials is the
key to the level of anode cathodic protection.
sacrificial anode protection with an auxiliary anode which only conduct electricity and does not
dissolve. DC power is supplied between the anode and the steel plate, and a circuit is formed
through seawater. The power supply protects the steel plate by inputting a protective current to
the steel plate and making the steel plate a cathode.
The external current protection system consists of a transformer rectifier, an external power
supply, a reference electrode and an insoluble auxiliary anode. The whole system keeps the hull
potential in the protection potential range. The application of current protection technology is
more and more applied to corrosion protection of ship shell. The advantage of this method is that
it has long protection life, strong potential and current regulation, but there are still
shortcomings in reliability and economy. The development trend is to improve the reliability of
the external current system and reduce the cost, and further extend the protection period by
improving the reliability of the transformer rectifier, the discharge of the auxiliary anode and
the long-term stability of the reference electrode.
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