Sacrificial anodes in zinc or aluminium designed for preventing corrosion on underwater hull and in tanks.
The number and size of the anodes required are generally determined by the coating quality/condition and the area being protected from corrosion.
Sacrificial anodes for hull
Anodes can be customised to any design or compostion to suit most application and requirements. See the full product range of sacrificial anodes.
Below illustrations show the most common anode models applied on external submerged zones of vessel’s hull.
Several factors determine the size and type of anodes that should be fitted. Firstly the coating condition of the area being protected, secondly the type of construction (hull, rudder, azimuth, sea chest, thruster tunnel, etc.) and finally the length of time that the vessel is likely to be afloat before the next maintenance docking.
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Factors that affect the durability of the anodes are the grade and the composition of the anodes, whether the vessel is equipped with an ICCP system, an if so, how the ICCP system is configured.
The only way of preventing corrosion in ballast tanks, when coatings become damaged or ultimately break down, is to apply sacrificial anodes.
Aluminium anodes are generally preferred over zinc anodes, as a result of their technical and economical advantages. There are, however, concerns using aluminium alloyed anodes in certain tanks due to the risk of sparking if the anodes fall off.
In cases where residual ballast water is expected to be left in the bottom of the tank, a low location of the bottom anodes should be provided, for example pitguard anodes mounted on the webs of bottom longitudinals. Provisions should then be made for higher (more continuous) anode consumption than initially expected.
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In oil and chemical cargo tanks, where there is a risk of a saline water layer settling in the bottom section of the tank, local corrosion attacks may occur. These attacks can be particularly severe in the presence of more noble metals in the water phase, like heating coils and pump units. Such components will make structural steel become anodic, and bare steel spots in the coating can experience rapid, galvanic corrosion. Read about forms for corrosion.
Pitguard anodes are easily clamped to bottom longitudinals to provide protection against corrosion during cargo voyages, when residual water settles in the tank bottom.
High temperature conditions
Conventional anodes tend to collaps at high temperatures. Therefore, the special HT-Anode, designed for elevated temperature conditions, should be used in tanks intended for the carriage of liquid cargo at elevated temperatures.
The HT-Anode is composed with the objective of obtaining consistent behaviour at ambient temperatures up to 90 °C.