Regan Brown
Aluminium is commonly used for marine fuel tanks because it is strong, lightweight, and anti-corrosive. However, despite its anti-corrosive properties, aluminium fuel tanks on boats can still corrode and leak. Corrosion can occur due to several factors, including exposure to seawater, contact with copper, fabrication issues, and microbiological factors. This article will explore the causes of corrosion in aluminium fuel tanks and provide insights into preventing and addressing this issue.
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What You'll Learn
Aluminium's anti-corrosive properties
Aluminium is highly resistant to corrosion compared to other metals. This is due to the thin oxide layer that forms when aluminium comes into contact with oxygen. This oxide layer is very hard and difficult to penetrate, protecting the metal from external threats. In dry, stable environments, this oxide layer alone is enough to protect aluminium from corrosion.
However, aluminium is susceptible to corrosion in certain conditions. For example, bases break down aluminium much faster than acids. Wet concrete, which has a high pH, can cause rapid corrosion of aluminium. In marine environments, saltwater can quickly degrade aluminium, although this is less of a problem with marine-grade alloys.
Aluminium alloys offer varying degrees of corrosion protection. The 5XXX series of aluminium alloys, for instance, are known for their good corrosion resistance, even in marine environments. They are commonly used in shipbuilding, transportation, and construction. On the other hand, the 7XXX series of alloys, which use zinc as the primary alloying agent, have the lowest corrosion resistance.
To enhance the anti-corrosive properties of aluminium, it can be treated with protective coatings, such as STEEL-IT®, which further inhibit oxidation and degradation. In marine applications, aluminium is often coated with an anti-corrosive polymer to enhance its performance.
Aluminium fuel tanks on boats can corrode due to various factors, including seawater exposure, fabrication issues, contact with copper, and microbiological induced corrosion. Proper airflow around the tank and keeping moisture-absorbing materials away are crucial to preventing corrosion.
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Seawater exposure
Aluminium is commonly used for marine fuel tanks due to its strength, lightweight nature, and anti-corrosive properties. However, when exposed to seawater, aluminium fuel tanks on boats can be susceptible to corrosion under certain conditions.
Firstly, it is important to understand that aluminium gains corrosion resistance by using oxygen to form a protective surface layer. If this film is damaged or removed through abrasion or prolonged exposure to moisture or chemicals, the aluminium becomes vulnerable to corrosion. Seawater can attack the exterior of an aluminium fuel tank, and if the tank is not properly protected or installed, corrosion can occur.
To prevent corrosion from seawater exposure, it is crucial to ensure proper airflow around the tank. The American Boat and Yacht Council (ABYC) standards specify that there should be a minimum of a quarter-inch of airspace between the tank and the mounting surface to allow for adequate airflow and drainage of any stray seawater. Tank supports should also be made from non-moisture-absorbent materials such as stiff neoprene, Teflon, or high-density plastic.
Additionally, it is important to minimise the entry of seawater into the tank. This can be achieved by ensuring that the deck fill O-ring is in place and in good condition. Regular cleaning and maintenance of the tank are also important to prevent internal corrosion.
Another factor to consider is the use of fittings and adapters. Direct contact between aluminium and certain other metals can lead to galvanic corrosion, especially in the presence of seawater. Bronze or brass fittings should not be attached directly to the tank, and stainless-steel washers or adapters can be used to isolate the fittings and prevent corrosion.
By following these precautions and guidelines, aluminium fuel tanks on boats can resist corrosion from seawater exposure and provide many years of reliable service.
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Copper fittings
Aluminium is commonly used for marine fuel tanks due to its strength and resistance to saltwater corrosion. However, aluminium fuel tanks on boats can still corrode due to fabrication issues, contact with copper, repeated exposure to seawater, internal contamination, and other factors.
To prevent corrosion in aluminium fuel tanks, it is crucial to maintain good airflow around the tank, allowing seawater to drain off and dry. This can be achieved by ensuring a minimum of a quarter-inch of airspace between the tank and the mounting surface, as recommended by the American Boat and Yacht Council (ABYC) standards. Additionally, keep moisture-absorbing materials, such as sound-damping insulation or wood braces, away from the metal.
To protect against internal corrosion, minimise water ingress and keep the tank clean. Ensure the O-ring on the deck fill is in place and in good condition to prevent water from entering the tank. When storing the boat, keep the tanks mostly full to minimise condensation.
It is also important to address any sources of continued exposure to seawater, such as a leaking deck fill or a spraying shaft seal. Properly fabricated and installed tanks, as per ABYC standards, are crucial to maximising tank life.
While copper fittings are not advised, bronze or brass fittings can be used but should not attach directly to the aluminium tank. A stainless fitting attached to the tank can accommodate a bronze fitting, reducing the risk of galvanic corrosion.
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Internal corrosion
Aluminium is commonly used for marine fuel tanks because of its strength and resistance to corrosion from saltwater. However, despite its anti-corrosive properties, aluminium fuel tanks on boats can still corrode, especially from the inside.
Microbiologically induced corrosion is another cause of internal corrosion. Diesel fuel is not sterile, and microorganisms can live in the fuel, feeding off the fuel and sulfur. These microorganisms produce acidic by-products that get trapped between the fuel and the tank, causing corrosion and pinhole leaks.
To protect against internal corrosion, it is important to minimise the amount of water that enters the tank and to use a biocide to control the growth of microorganisms. Keeping the tank clean and ensuring the O-ring on the deck fill is in place and in good condition will also help prevent internal corrosion.
Applying a protective polymer coating to the aluminium can also help inhibit oxidation, tarnishing, and staining, further protecting against internal corrosion.
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Protective coatings
Aluminium is commonly used in marine fuel tanks due to its strength and resistance to saltwater corrosion. However, aluminium fuel tanks on boats can still corrode, especially when in contact with copper or seawater.
Types of Protective Coatings
- Epoxy coatings: Epoxy coatings are commonly recommended for aluminium fuel tanks due to their airtight and waterproof properties. They can withstand exposure to fuel and provide effective protection against corrosion. It is important to properly prepare the surface of the aluminium before applying an epoxy coating to ensure optimal adhesion.
- Coal tar epoxy: Coal tar epoxy is a specific type of epoxy coating that is commonly used in the marine industry to protect aluminium fuel tanks. It provides a durable barrier against saltwater and fuel.
- Barrier coats: Barrier coats, such as Interlux Interprotect, are designed to protect aluminium surfaces from saltwater exposure. They can be effective for boats that are not routinely exposed to large amounts of saltwater.
- Polymer coatings: Aluminium can be treated with a protective polymer coating to enhance its performance and further inhibit oxidation, tarnishing, and staining.
- Anti-corrosive coatings: Anti-corrosive coatings are specifically designed to prevent corrosion on aluminium surfaces. They are often applied to marine fuel tanks to protect them from the harsh marine environment.
- Zinc chromate: Zinc chromate is a popular coating for aluminium fuel tanks. It provides protection against corrosion and can be applied through acid etching or priming.
- Powder coating: Powder coating is a type of dry coating process where a dry powder is applied to the aluminium surface and then cured, forming a protective layer.
- Paint: Painting an aluminium fuel tank can protect it from corrosion, especially when shielded from saltwater. However, it is important to properly prepare the surface and use the appropriate type of paint, such as polyurethane topside paint.
Best Practices for Coating Application
- Surface preparation: Proper surface preparation is critical for the successful application of protective coatings. The aluminium surface should be cleaned, stripped, and treated to ensure optimal adhesion of the coating.
- Coating selection: It is important to select a coating that is specifically designed for aluminium fuel tanks and can provide effective protection against corrosion.
- Application method: The application method, such as rolling, brushing, or spraying, should be chosen based on the type of coating and the specific requirements of the application.
- Multiple coats: Applying multiple coats of paint or primer can enhance the protection and durability of the coating.
- Drying time: Allowing adequate drying time between coats is essential for the proper curing of the coating.
By following these guidelines and selecting the appropriate protective coating, boat owners can effectively prevent corrosion and extend the life of their aluminium fuel tanks.
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Frequently asked questions
Aluminium is commonly used in marine fuel tanks because it is lightweight, strong, and anti-corrosive. However, aluminium fuel tanks on boats can corrode under certain circumstances, such as exposure to seawater or contact with copper fittings.
Corrosion in aluminium fuel tanks can occur due to several factors, including microbiological factors, exposure to seawater, condensation, and contact with copper fittings. Microbiological factors include microorganisms living in the fuel and feeding on the sulfur, producing acidic byproducts that corrode the tank and cause pinhole leaks.
To prevent corrosion in aluminium fuel tanks, it is important to follow certain guidelines. Ensure good airflow around the tank to allow seawater to drain off and keep any moisture-absorbing materials away from the metal. Keep the tank clean and minimise water entry. When storing your boat, keep the tanks mostly full to minimise condensation. Additionally, avoid using copper fittings directly attached to the tank, as copper will damage aluminium.
