Underwater Anodes Replacement
When a metal or an alloy is released in the atmosphere it has the propensity to degrade its energy, the tendency to convert to oxide or other compound (to return to its natural state) , and simultaneously heat removal occurs. This automatic activity of metals is the cause of corrosion. From discussions within the International Commission for Maritime Corrosion and fouling Structures the following definition was revealed :
“Corrosion is called every spontaneous, even forced, chemical, electrochemical, physical, mechanical, biological deterioration process of the surface (external and internal) of material leading to loss of material.”
Corrosion is the worst enemy of a ship. It is an unavoidable aspect of the life of the ship, due to the constant contact with water and the presence of moisture. The moisture greatly accelerates the rate of corrosion. All metals of the ship, whose composition is not homogeneous, are victims of the negative impact of erosion. The main ship parts affected is the area of the propeller, the piping, the copper plates of the heat exchangers, aluminum pieces used in machinery and hull plating.
The method of the sacrificial anodes is mainly used on the steel plates of the ship which are permanently in contact with the water. The anodes are plates of anodic metal (for steel commonly used magnesium [Mg], zinc [Zn], aluminum [Al]) welded onto the plates. The anodic metals spontaneously acquire a negative potential relative to the corrosive environment. The same negatively charged are also the steel plates. These metals are more prone to corrosion compared to steel, therefore more negatively charged. Thereby, creating a galvanic cell with a negative pole and the positive metal into steel, which is oxidized, i.e. namely sacrificed to protect the plates. Decisive role in the life of the ship plays, early underwater replacement anodes (u/w replacement anodes) before the old are completely consumed and begin to erode the plate.
The most important ways to protect against corrosion used on ships are:
- With painting over the metal surfaces with anticorrosive paints or other blocking substances.
- By using sacrificial anodes.
- With the method ICCP.
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