When a metal is exposed to underwater or wet environments, marine grade metals may be necessary to prevent the material from failing under the conditions. To be considered a marine grade, the material must be able to resist corrosive effects that are common in a water environment. To achieve this, special alloying elements are added to these grades in order to defend against corrosion.
Marine Grade Metals include:
- Carbon Steel and Alloy Steel
- Stainless Steel
- Galvanized Steel
Carbon Steel and Alloy Steel
Most carbon steel is not well-suited 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 steels approved by the American Bureau of Shipping. These grades will have slightly more alloying elements such as manganese and chromium compared to their ASTM grade counterparts, which helps achieve higher strength and more corrosion resistance. There are also marine grades of alloy steel as well. Grades MD, ME, MF, MG, and others can provide the strength that normal alloy steel is known for, and have also been approved by the American Bureau of Shipping for use in shipbuilding applications.
Applications: structural shipbuilding and other offshore structural applications
There are several different grades of aluminum that are suitable for marine conditions. Marine grade aluminum, for the most part, is limited to the 5XXX and 6XXX grades. Grade 5052 is an excellent marine grade for when formability is required. If strength is more of a concern, grade 5083 is a good alternative. 6061-T6 is an all-around popular grade of aluminum that is also commonly used in marine applications. It has very good corrosion resistance and is precipitation hardened. These grades, for the most part, have additional chromium and manganese to help protect them from corrosive marine conditions.
Applications: structural shipbuilding, boat hulls, boat lifts, docks, and other offshore structural applications
All grades of stainless steel have some degree of corrosion resistance, however, there are several grades of stainless steel that are far more suitable for use in marine environments than others. Grade 316 is probably the most common grade of stainless steel used in marine applications. It has more molybdenum than other austenitic stainless steels which helps it to 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 desirable choice in chlorine-rich environments.
Applications: marine fittings, marine fasteners, and marine structures
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, which has a similar makeup to alloy C70600, except that it has even more nickel in its chemical composition.
Applications: water lines, desalination equipment, marine fittings, fasteners, valves, and pumps
Silicon bronze alloys like C65500 and aluminum bronze alloys like C95400 are developed to better withstand marine environments than other bronze alloys. Alternatively, the phosphor bronze alloy C51000 is another common grade suitable for marine applications.
Applications: propellers, propeller shafts, pipes, and marine fasteners
Marine brass, or naval brass as it is commonly referred to, comes in a variety of alloys. Alloys C46200 and C46400 have additions of zinc and tin which allow the brass alloy to resist corrosion in wet or even underwater applications. Alloys C48200 and C48500 are similar except that they have a larger amount of lead in their chemical composition.
Applications: pipes, marine fittings, marine fasteners, and pumps
Galvanized steel can be suitable for some marine environments. Zinc coatings typically fare better under cool temperatures in fresh water than warm temperatures in salt water. Salt water contains chlorides which cause zinc to corrode rapidly. A high temperature will enable the corrosion to occur more rapidly.
Applications: marine structures
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