Today, the most common metals used in the construction of yachts, marine structures and fittings are stainless steel and aluminum. Although aluminum is light, it has limited corrosion resistance in seawater and requires extensive maintenance. Stainless steel, on the other hand, is recognized as a superior material for marine applications because of its excellent corrosion resistance, luster, strength and stiffness.
For many boating applications, Grade 304 (UNS S30400 / S30403) stainless steel fittings have proven to be adequate. However, the current industry standard is Grade 316 (UNS S31600 / S31603 - commonly referred to as "marine grade" stainless steel), which provides solutions for approximately 90% of marine applications. 304 and 316 grades are austenitic (300 series) stainless steels, which is attributed to their metallurgical structure (austenitic), giving them excellent ductility. ), which gives it excellent ductility, good strength, non-magnetic properties, weldability and very good corrosion resistance.
The following general rules apply:
304 may be used for fully exposed components, frequently washed with fresh water;
316 may be used for all hull and deck fitting applications above the water line;
S31803 offers higher strength and, therefore, lighter weight components for the same applications as 316 and can additionally be used up to 60çC in wet exhaust systems and in fully submersed applications; andS32750 offers even higher strength and weight savings, and can handle all marine applications with no risk of corrosion even in tropical waters and hot, wet exhaust applications.
While stainless steel grades 304, 316 and duplex steels can all be used in marine applications, they do provide varying degrees of corrosion resistance and durability. The key to their successful application is, therefore, being aware of the strengths and limitations of each grade and how they can be used to their optimum potential.
