What is marine grade metal?
Metals are used in all kinds of environments, including applications with high exposure to water. In wet or underwater environments, marine grade metals may be necessary to prevent the material from failing under the conditions. Marine grade metals are uniquely able to defend against the corrosive effects of water. To achieve this, special alloying elements are added to these grades in order to defend against corrosion.
MARINE GRADE METALS INCLUDE THE FOLLOWING:
Carbon Steel
Most carbon steels are not suitable for marine environments because iron is inherently vulnerable to oxidation and rust. However, there are several marine grade carbon steels like AH36, DH36, EH36 that are commonly available and are approved by the American Bureau of Shipping. These grades have slightly more alloying elements such as manganese and chromium compared to their ASTM grade counterparts, which helps them to have higher strength and corrosion resistance. Applications for carbon steel includes structural shipbuilding and other offshore structural applications.
Alloy Steel
Marine Grade metals include alloy steels with grades MD, ME, MF and MG which provide the strength that normal alloy steel is known for along with enough corrosion resistance and have also been approved by the American Bureau of Shipping. Applications for alloy steel include structural shipbuilding and other offshore structural applications.
Stainless Steel
Stainless steel is a mainstay in corrosion resistance for its high content of chromium. While all grades of stainless steel have some corrosion resistance, there are a few that are more appropriate for marine environments. The most common is grade 316 which has more molybdenum than other austenitic stainless steels which helps it to resist pitting and pitting and other corrosive effects caused by saltwater. Grade 304 is another marine grade stainless steel but has less molybdenum than grade 316 making it a less suitable for environments with high chlorine content.
Galvanized Steel
Galvanized steel can be used in marine environments under specific conditions. Because of its zinc coating, galvanized steel is typically recommended only for cool freshwater temperatures. Galvanized steel fares poorly in warm temperature saltwater as the chlorides of the saltwater will rapidly corrode the zinc and the higher temperature will speed up the corrosion. Typical applications for galvanized steel in marine environments include freshwater marine structures.
Aluminum
There are several grades of aluminum that are suitable for marine conditions due to its high strength, durability and lower weight compared to steel. Some of the most popular marine grade of aluminum are 5052, 5083 and 6061-T6 due to their formability, strength and good corrosion resistance. Much like carbon and alloy steels, these aluminum grades benefit in their corrosion resistance from the addition of chromium and manganese. Applications for these aluminum grades include structural shipbuilding and offshore structural applications.
Copper
There are several copper-nickel alloys that are appropriate for marine environments. Examples include C70600 which contains nickel and manganese to help resist corrosion with durability. C71500 is also able to withstand marine conditions, which has a similar makeup to alloy C70600, except that it has even more nickel in its chemical composition. Major advantage of copper is that its alloys have high biofouling resistance. Applications for marine grade copper include marine fittings, fasteners, valves, and pumps, in addition to water lines and desalination equipment.
Bronze
Among bronze alloys, those alloyed with silicon and aluminum are most suited to resist the corrosive effects of marine environments and are specifically created for marine use. Another grade that is suitable for marine application is C51000, which is alloyed with phosphor. Like copper, bronze alloys also fight off algae, mussels and other disruptive organisms. Applications for marine grade bronze include propellers, propeller shafts, fasteners and pipes.
Brass
Marine brass is also known as naval brass because of its prevalent use in the military. Brass is often blended with tin and zinc to improve its corrosion resistance in water and leads to improved maneuverability. Most common marine grade brass alloys are C46200 and C46400. The addition of zinc and tin helps the brass alloys resist corrosion in wet and underwater environments. Applications for marine grade brass include fasteners, pumps, pipes and fittings.