Anodes Replacement

Corrosion 

Corrosion is a dangerous and extremely costly problem. The most common kinds of corrosion result from electrochemical reactions. General corrosion occurs when the atoms on the same metal surface are oxidized, damaging the entire surface. Most metals are easily oxidized: they tend to lose electrons to oxygen (and other substances) in water. As oxygen is reduced (gains electrons), it forms an oxide with the metal.

The factors influencing the corrosion of hull are:

1. Chemistry of the water (hardness salts, chlorides, dissolved gases, etc.);
2. Presence of solids in the water;
3. Flow rate;
4. Temperature of the water;
5. Presence of bacteria.

The main ship parts affected is the propeller, the pipes, the copper plates of the heat exchangers, aluminium pieces used in machinery and hull plating.

The most important ways to protect against corrosion used on hull of ships are:

• Anticorrosive/ protective paints.
• Using sacrificial anodes.
• Using ICCP.

Function of Sacrificial Anodes for Corrosion Prevention

Sacrificial anode is a type of cathodic protection system.  The anode is made of a metal alloy with a more negative electrochemical potential, i.e., more active voltage than the metal of the hull it is protecting (the cathode). The difference in potential between the two metals means the sacrificial anode material corrodes in preference to the structure. This effectively stops the oxidation reactions on the hull.

Sacrificial anodes generally come in three metals: magnesium (Mg), aluminium (Al), and zinc (Zn). Zinc and aluminium are generally used in sea water, where the resistivity is generally lower. Typical uses are for the hulls of ships and boats, offshore pipe-lines and production platforms, in some marine engines, on small boat propellers and rudders, and for the internal surface of storage tanks.

Advantages 

The advantage of sacrificial anode systems over others are that they need no external power source, are easy to install, the low voltage and current between the anode and the surface it is protecting infrequently generates stray current, overprotection is unlikely, and inspection and monitoring is simple for trained personnel.

We undertake underwater anode fitting and replacement in the submerged parts of the ship such as rudder, propeller, vertical sides, etc., thereby the smooth operation of the ship is extended and the cost of keeping the ship away from the dry-dock is reduced significantly.

We inspect the area (taking photos and video) which we submit to our Clients and classification society as and if required, in order to determine whether there is a need for anodes replacement. Then our divers remove the depleted anodes and replace new ones.