Boat Metal Fabrication

What are Common Marine Grade Metals?

When metal is exposed to water or moisture, marine-grade metal may be needed to prevent the material from failing under the conditions. To be considered marine grade, the material must be able to resist the corrosive effects commonly found in water environments. To achieve this, special alloying elements are added to these grades to prevent corrosion.

Marine grade metals include:

Carbon and alloy steel

Aluminum

Stainless steel

Copper

Bronze

Brass

Galvanized steel

Carbon and alloy steel

Most carbon steel is not suitable for marine environments, however, there are several marine-grade carbon steels available. AH36, DH36, and EH36 are all examples of commonly used marine-grade carbon steel approved by the Bureau of Shipping. Compared to ASTM grades, these grades will have slightly more alloying elements such as manganese and chromium, which helps achieve greater strength and greater corrosion resistance. Alloy steel also comes in marine grades. Grades such as MD, ME, MF, MG provide the strength that common alloy steels are known for and are approved by the Bureau of Shipping for shipbuilding applications.

Applications: Structural shipbuilding and other offshore structural applications

Aluminum

There are several different grades of aluminum suitable for marine conditions. Marine grade aluminum, in most cases, is limited to grades 5XXX and 6XXX. Grade 5052 is an excellent marine grade when formability is required. If strength is more of a concern, level 5083 is a good choice. 6061-T6 is an all-around popular aluminum grade also commonly used in marine applications. It has very good corrosion resistance and is precipitation hardened. In most cases, these grades have additional chromium and manganese to help protect them from corrosive marine conditions.

Applications: Structural shipbuilding, hulls, boat lifts, docks and other offshore structural applications

Stainless steel

All grades of stainless steel have some degree of corrosion resistance, however, several grades are more suitable than others for use in marine environments. Grade 316 is probably the most commonly used grade of stainless steel in marine applications. It contains more molybdenum than other austenitic stainless steels, which helps resist pitting and other corrosive effects of salt water. Grade 304 is another marine grade stainless steel, although it has less molybdenum than grade 316, making it a less ideal choice in chlorine-rich environments.

Applications: Marine accessories, marine fasteners and marine structures

Copper

There are several copper-nickel alloys suitable for marine applications. Examples include C70600, which contains nickel and manganese to help resist corrosion. C71500 is also able to withstand marine conditions and is similar in composition to the C70600 alloy, except that it contains more nickel in its chemical composition.