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II. Cathodic Protection Sacrificial Anode Anti-Corrosion Measures

The main reason for the corrosion of ballast tanks is the electrochemical reaction occurring on the submerged steel plate sections. Seawater is a strong electrolyte, and since the ship's steel is not a pure ideal metal but an alloy composed of iron, carbon, and other metallic elements, numerous micro-cell pairs form on the steel surface due to variations in electrode potential at different locations. The micro-anode areas suffer corrosion, while the micro-cathode areas remain unaffected. According to electrochemical corrosion theory, the corrosion of the ship's steel plates in seawater is caused by the action of these micro-cells.

III. The arrangement of sacrificial anodes should follow the following principles:

(1) The sacrificial anodes required for the ship's outer plates should be uniformly and symmetrically arranged along the bilge keel and the flow lines before and after the bilge keel to reduce additional resistance of the hull;

(2) The sacrificial anodes required for the propeller and rudder should be uniformly arranged on the stern shell plate and the rudder. Sacrificial anodes should not be placed on the shell plate within 300 m of the propeller blade tip or in the anode-free zone of single-screw ships;

(3) The sacrificial anodes required for the sea chest and sonar transducer well should be arranged inside the chest and well.

IV. Installation of Sacrificial Anodes

Sacrificial anodes can be installed by welding or bolting. Generally, the welding method is simple, provides high installation strength, and has low contact resistance, while bolting allows for easier replacement without damaging the coating on the surrounding area or the reverse side of the steel plate.

The following points should be noted during the installation of sacrificial anodes:

(1) Before installation, the back of the anode should be coated with an insulating paint. The hull surface at the installation site should also be coated with insulating paint or padded with other insulating materials to prevent detachment due to corrosion on the back of the anode and to ensure the back remains inactive. The usable area of the anode should match the design value;

(2) The anode surface must not be painted or contaminated and should be protected before painting and launching;

(3) During installation, the anode should be welded to the designated position, with the back tightly pressed against the hull surface. The welding points of the iron feet should be repainted.

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