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Marine Cathodic Protection

Nov 30, 2016

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.

(1). Sacrificial Anode Cathodic Protection

Sacrificial anode cathodic protection technology is to protect the hull steel plate as the cathode 

from corrosion by installing a sacrificial metal block acting as an anode on the outer surface of 

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.

(2).Impressed Current Cathodic Protection

Impressed current cathodic protection technology is to replace the sacrificial anode  in the 

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.

zinc hull anodezinc hull anode

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