What are the common types of corrosion on ship hulls and their causes?
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What are the common types of corrosion on ship hulls and their causes? The common types of rust on ship hulls include seven types: layered dead rust, thick hard rust, nail rust, prickly rust, thin frothy rust, oxidative rust, and cottony rust. Its characteristics are as follows: 1. Layered rust, which mostly appears on both sides of the deck and above the sewage drains, is primarily caused by the alternating effects of moisture and exposure to sunlight. It has a large area and a layered structure, with three to four layers in total; the outer layers are crisp while the inner layers are harder and more difficult to remove. 2. Full-hard rust appears mostly on the bottom of ships; it results from corrosion caused by contact with seawater and marine organisms. It is hard in texture and difficult to remove. 3. Nail rust, commonly known as “pimple rust,” appears in needle-like form. It occurs mostly at the bow of the ship; the area affected is small, but the corrosion is severe, and in serious cases it can cause holes in the steel plate. It is difficult to remove. 4. Heat rash rust: On the surface of steel plates and paint coats, there are small spots of rust scattered densely, with a shape similar to that of heat rash. It is caused by the rust on the steel plate not being removed thoroughly before painting. If not dealt with promptly, it will develop into nail rust. 5. Thin foam rust appears mostly on new steel plates and resembles orange peel in shape. It is caused by the steel plates being stored outdoors for too long, resulting in the weathering of the oxide scale on their surface. 6. Oxidized rust is commonly referred to as scale. Although oxidation rust provides protection for the steel plate, over time, once this rust falls off, the steel plate is exposed and becomes susceptible to corrosion. 7. Cotton rust: It has properties similar to cotton, attaching softly to the surface of steel plates. It mostly occurs in coal holds, due to the high humidity, poor ventilation, and lack of sunlight there.
The common types of corrosion on ship hulls include flaky rust, dense rust, nail rust, prickly rust, thin film rust, oxidative rust, and cottony rust. The causes of these rust formations are mainly related to environmental conditions, inadequate material protection measures, and the way in which the ship’s hull is used and maintained. For example: 1. Surface rust: Occurs due to the alternating effects of humidity and exposure to sunlight, mainly appearing on both sides of the deck and above the sewage channels. 2. Full-hard rust: Caused by the erosion of seawater and marine organisms, it is commonly found on the bottom of ships. 3. Nail rust: Common at the sharp ends of the hull; it occurs due to insufficient coating protection, allowing moisture to penetrate and cause rust deep within the steel plates. 4. Rust spots: Tiny rust dots beneath the paint layer, caused by inadequate cleaning of the steel sheet before painting. 5. Thin rust film: New steel plates oxidize due to being left exposed to the elements for an extended period of time. 6. Oxidation rust: Although it provides protection at first, over time its removal exposes the steel sheet to further corrosion. 7. Cotton rust: Occurs frequently in coal holds that are humid, poorly ventilated, and lack sunlight. The occurrence of these types of corrosion highlights the importance of hull maintenance, particularly in terms of coating protection, regular inspections, and proper treatment of the steel plates. .