Corrosion in Ships: Risks, Causes, and Impacts on Metal Structures

Corrosion in Ships: Any business that deals with metal, including the shipping industry, may have serious corrosion-related problems. The ships are vulnerable to corrosion because of the severe maritime environment and its high salinity and moisture content. If ignored, it may erode the ship’s structure, posing a risk to safety and necessitating costly repairs.

Metals undergo a process called corrosion, in which they shift toward their lowest energy state. This causes a rapid response between the metal and its surroundings, reducing the metal’s quality and lifespan. The word “corrosion” comes from the Latin “corrodes,” which means “gnaw to pieces.”

Because of its affordability, mechanical strength, and ease of manufacturing, mild steel is the most popular metal for building ships in the maritime and shipping industries. But the biggest problem is that when it comes into contact with seawater, it corrodes very quickly. Second, it loses strength quickly without adequate protection, which increases the risk of structural failure.

Repairing the coating while the vessel is offshore is one approach to avoiding this, but it can be 100 times more expensive than the initial coating, and NACE International estimates that the global cost of corrosion in the maritime industry is between 50 and 80 billion dollars a year.

Shipowners may achieve optimal performance and cost efficiency with their vessels, though, if they begin with sufficient preparation and use caution while applying the first coating.

Should inadequate surface preparation be the cause of the degradation, the remedy would be to scrape off the paint and start over.

Types of Corrosion in Ships

Corrosion in Ships
(Credit: Ducorr)

Two types of corrosion are relevant to the shipping industry: bacterial corrosion and pitting corrosion and corrosion caused by bacteria.

As a result, ship owners and builders take numerous precautions to keep their boats from corroding. We’ll talk about a few common techniques in this post for protecting ships from rust.

The ship can be ready to combat corrosion in the following ways:

Improving the Design of Ships

To prolong the lifespan and maintain the security of their vessels, ship designers and operators make every effort to minimize corrosion. During the ship’s active life, a few design elements can help lower the rate of corrosion and maintenance expenses.

To facilitate the removal of water from decks, wells, and bilge regions and to prevent corrosive activity, scuppers and drains must be installed correctly.

  1. Insulation should be installed in locations where various metals are positioned close to one another to prevent galvanic corrosion.
  2. To identify and control corrosion, an impressed current system that tracks corrosive cell activity and delivers a current to protect anodes can also be deployed.
  3. Insulation is necessary in areas where temperature swings occur to prevent thermal fatigue.
  4. Metal fatigue can be reduced by anti-vibration techniques such as installing sliding feet on turbine machinery, and corrosion can be prevented by using sacrificial anodes composed of magnesium, aluminium, or zinc.
  5. Utilizing corrosion-resistant alloy steel or stainless steel can also reduce corrosion. An further way to prolong a ship’s service life is to include rubbing strakes or double plates to withstand additional wear and tear.
  6. Once a vessel is in service, corrosion control can also be facilitated by structurally user-friendly design that facilitates maintenance and coating applications.

By implementing these design elements during the construction phase, maintenance expenses can be greatly decreased and corrosion can be managed.

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Coating the surfaces of a ship is one of the best techniques to prevent corrosion on the vessel. The metal surface and the corrosive environment are separated by these speciality paint coats. This extra layer of protection keeps moisture and salt from getting into contact with the metal surface and lessens the chance of corrosion because the ship’s hull and open deck are constantly in contact with water and the marine atmosphere.

Additionally, hull paint coatings stop marine life from adhering to the hull, which might expose the metal to seawater and accelerate corrosion. This includes mollusks and algae. Additionally, they offer a smooth hull surface that lowers resistance and drag across the hull, improving fuel economy.

The three most popular kinds of coatings are zinc-rich, polyurethane, and epoxy. Epoxy coatings are widely used because of their exceptional adherence to metal surfaces and good resistance to chemicals and water.

Because polyurethane coatings offer a strong, long-lasting surface that is resistant to adverse weather, they are also frequently utilized. Since a large percentage of zinc serves as a sacrificial anode to prevent corrosion on the metal surface, zinc-rich coatings are very useful.

Protective Cathodic

Protective Cathodic

Sacrificial anodes are used in the process of cathodic protection. Sacrificial anodes, as the name implies, are composed of metals that are more anodic than the metal that needs to be shielded. They are sacrificed, or deteriorated, in place of the ship’s metal, preventing corrosion of the metal.

Galvanic and impressed current cathodic protection are the two forms.

Sacrificial anodes attached to the metal under protection are used in galvanic cathodic protection. Electrons are released from the corroding anodes and move to the metal to stop further corrosion.

On the other hand, impressed current cathodic protection makes use of an external power source to supply the electrons required to shield the metal surface.

Either cathodic protection method is capable of effectively protecting ships from corrosion. Larger surface areas are typically covered by impressed current cathodic protection, which may be precisely tailored to the needs of the ship.

In smaller spaces or in equipment that transports or uses saltwater, sacrificial anodes are employed.

Inhibitors of corrosion

These are the chemical substances that have been applied to the metal’s surface. Corrosion inhibitors lessen the rate of corrosion on materials like metal and alloys, but they are not a preventative measure. Because employing corrosion inhibitors can save up to 35% of losses resulting from pollution on ships, it is an affordable method of preventing or controlling corrosion.

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Utilizing less expensive metals in severe environments instead of steel and alloy is the main benefit of corrosion inhibitors. Once treated with chemicals that limit corrosion, they can continue to function over the recommended age. Because it offers extended protection against rust, it also lowers maintenance expenses.

Anodic Defense

This is a further corrosion prevention approach. Nevertheless, because it requires an ongoing electrical supply, which can be difficult to sustain in the event of a blackout, it is not widely employed in the maritime sector.


As a result, there are numerous approaches to stop ship corrosion. One of them is cathodic protection, which consists of two steps: first, coating the ship’s surface, particularly the hull and other areas that are more exposed to seawater and dissolved salts. The other method involves the use of impressed current systems and sacrificial anodes. Maintaining the asset’s long life is mostly dependent on routine maintenance.

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