What is Ship Cathodic Protection?
Sep 20, 2022
Cathodic protection of ships includes external protection of underwater parts including all attachments and openings (such as propeller, rudder, propeller support, sea suction tank, buoyancy tank, water inlet booster), and internal protection of various ship holds (ballast tank, fresh water tank, fuel tank), pipelines (condenser and heat exchanger), and bilge. When ships are exposed to waters with different components, salt concentration and conductivity are particularly important indicators, because they have a great impact on the activity and current distribution of corrosive batteries. In addition, on the ship, it is also necessary to consider the problem of different metals.
Distribution principle of ship anode
Anodes should be evenly distributed on the surface of underwater parts of the ship to achieve good current distribution. When setting, the following basic principles should be followed: about 25% of the total anode mass should be used to protect the stern, and the remaining anode should be distributed in the middle of the bow and hull; They should be installed on the bilge radius, so that they can not be easily pulled off after being attached; At bilge keels, they should be attached alternately on the upper and lower sides; The distance between the anodes on the bilge in the middle of the hull shall not be greater than 6~8cm to ensure that the protection areas overlap each other; In water areas with high protection current density (such as the tropics) and water areas with low resistivity (such as the Baltic Sea), the distance between anodes should be smaller. On such ships, 5m interval is selected. If the ship will talk about serious mechanical damage, such as ships sailing in the ice sea in the Arctic waters, this distance should be smaller.
Service time of ship anode
The design life of the cathodic protection material anode of the ship shall be at least 4, so the time for ballast tanks that are empty or filled with ballast water is 40% of the service time. For the type of cabin containing dirty materials, the ballast time is 25% of the service time, which is equivalent to 146 days and 91 days of ballast in a year. It will take at least 5 days to load water reservoir for each ballast tank voyage.
The surfaces to be protected shall be all surfaces, including inserts, round rods and tubes. The upper 1.5m of the side wall and the cover shall be protected against corrosion with a high-quality anti-corrosion coating of certified quality.
