Hull protection

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Sea Water System Protection against Corrosion:

Sea water systems such as ships hull protection may implement several methods for prevention against corrosion. Such systems are:

Sacrificial Anodic Protection

1. Sacrificial anodes work on the principle of electrolysis, and form a galvanic cell
2. When 2 dissimilar metals are in contact with each other in the presence of a corrosive medium (electrolyte), the more active metal in the galvanic series acts as an anode and undergoes corrosion. This means, in a galvanic series of metals, the more active metal acts as anode and undergoes corrosion and the less active metal acts as a cathode and stays protected.
3. an anode and a metallic strip are dipped in electrolytic solution,
4. Anode electron will dissolve and deposit over the metallic strip and make it a cathode.
5. Seawater acts as an electrolyte and transfers the electrons from the anode to the steel plate and making a protecting layer.
6. If the metal is more active, it will be easily oxidized and will protect the metallic compound by making it act as cathode
7. The anode will corrode first sacrificing itself for the other compound and it is thus called sacrificial anode
8. Here Active means more electrochemical potential. (magnesium, aluminium and zinc)

Impressed Current Catholic Protection

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1. Parts to be protected are made cathodic,
2. The anode does not corrode as electron is not generated by it but impressed on it
3. The electric current is supplied from ship supply and converted to low dc voltage
4. Current is impressed on anodes to reduce the potential difference between hull and anode. Hence no chemical reaction
5. Reference cells control the amount of current,
6. If too low, corrosion takes place
7. If too much will damage paint and protective coatings

Hull painting

1. AFS approved anti-fouling paints can be used on ship hull.
2. Anti-fouling paints are used to coat bottom of ship to prevent sea life from attaching themselves to hull, which may slow down the ship increasing the fuel consumption
3. Anti-fouling system is coating, paint, surface treatment, device used on ship to prevent fouling
4. In the past anti-fouling paint contain TBT, caused harm to marine life,
5. Todays technology of anti-fouling paint, do not contain TBT(tributyltin), It provides slippery surface preventing fouling and making easier to clean.