Marine grade stainless steel is a type of alloy specially designed to withstand the harsh, corrosive conditions of marine environments. Its main feature is its excellent resistance to corrosion, making it ideal for use in seawater, salt spray, and humid air. The key elements in marine grade stainless steel are chromium, nickel, and molybdenum, with molybdenum being especially important. It helps to significantly improve the steel’s resistance to corrosion from chlorides found in seawater.
One of the main advantages of marine grade stainless steel is its ability to form a protective chromium oxide layer on its surface. This protective film prevents moisture and oxygen from reaching the metal underneath, which helps to resist corrosion. However, long-term exposure to seawater can sometimes damage this oxide layer, leading to internal corrosion.
Common Types of Marine Grade Stainless Steel
1. 304 Stainless Steel
304 stainless steel is one of the most common types of stainless steel. It has good corrosion resistance but performs less well in marine or highly salty environments compared to 316 stainless steel. It is not ideal for long-term exposure to seawater, as it tends to corrode and rust more easily than 316.
304 stainless steel is typically used in applications where the material is not regularly exposed to seawater or salt spray, such as kitchen equipment, household appliances, and furniture.
2. 304L Stainless Steel (Low Carbon 304)
304L is similar to 304 stainless steel but has a lower carbon content (≤0.03%). This makes 304L less likely to suffer from intergranular corrosion during welding. While it is more corrosion-resistant than regular 304, it still doesn’t perform as well as 316 stainless steel in saltwater environments.
304L is suited for applications that require good corrosion resistance and better welding properties, but not necessarily for marine environments.
316 stainless steel is known for its excellent corrosion resistance, especially in seawater and chloride-rich environments. It’s particularly good at preventing pitting and crevice corrosion caused by seawater. Because it contains molybdenum, 316 stainless steel is the most commonly used material in shipbuilding, marine hardware, offshore equipment, and chemical processing.
316 is used in marine equipment, ship hardware, offshore platform equipment, ladders, portholes, rigging, chemical containers, pharmaceutical equipment, and more.
316L is similar to 316 stainless steel but has an even lower carbon content (≤0.03%). This low carbon content makes 316L less prone to intergranular corrosion, which is especially useful in welded applications that require high corrosion resistance. Its low carbon level also helps it withstand high-temperature environments over long periods.
316L is used in chemical and pharmaceutical industries, medical implants, high-temperature marine equipment, and any application with strict welding requirements.
5. 904L Stainless Steel
904L stainless steel has excellent resistance to corrosion, particularly in highly acidic environments. It is more resistant than 316L, which makes it suitable for extremely harsh marine and chemical environments. Though more expensive, its superior corrosion resistance and strength make it the go-to choice for demanding applications.
904L is used in chemical equipment, offshore platforms, fueling stations, and anywhere there is a need for acid-resistant materials.
6. 2205 Duplex Stainless Steel
2205 duplex stainless steel combines the properties of austenitic and ferritic steels, giving it high strength and outstanding resistance to chloride-induced corrosion. It performs better than 304 and 316 stainless steel at resisting pitting and stress corrosion cracking, making it ideal for marine environments.
2205 is commonly used in marine engineering, chemical processing equipment, oil and gas industries, and offshore platforms.
7. 2507 Super Duplex Stainless Steel
2507 super duplex stainless steel offers exceptional strength and corrosion resistance, making it perfect for extremely harsh marine environments. It resists chloride-induced corrosion and offers excellent mechanical properties and crack resistance. It’s suitable for very demanding marine and chemical applications.
2507 is typically used in deep-sea drilling equipment, offshore platforms, ships, chemical processing, and oil and gas industries.
Key Features of 316 Marine Grade Stainless Steel
Among all the stainless steel materials, 316 marine grade stainless steel stands out for its excellent properties, making it the top choice for marine environments.
1. Outstanding Corrosion Resistance
The biggest advantage of 316 stainless steel is its superb corrosion resistance. It can resist seawater, salt spray, chemicals, and high-salinity environments. Especially in chloride-rich environments (such as seawater), which are particularly corrosive, the molybdenum content (2%-3%) in 316 provides extra protection against pitting or crevice corrosion.
2. High Temperature Resistance
316 stainless steel performs well in high-temperature environments and has excellent oxidation resistance. It can withstand temperatures up to 870°C (1600°F), making it suitable for high-temperature applications such as chemical processing and petrochemical industries.
3. Strong Mechanical Properties
316 stainless steel has high strength and toughness, which helps it resist the mechanical stresses caused by strong winds, waves, and other forces in marine environments. It also has excellent ductility and tensile strength, which makes it ideal for use in critical components like ship hardware, rigging, ladders, and portholes.
4. Exceptional Pollutant Resistance
Thanks to the chromium oxide protective layer on its surface, 316 stainless steel can effectively prevent contaminants from sticking. This feature helps it stay clean and maintain its appearance for longer, even in harsh environmental conditions.
5. Chemical Resistance
316 stainless steel is resistant to a wide range of chemicals, including acids, alkalis, and salt solutions. This makes it an ideal choice for industries like chemicals, pharmaceuticals, and food processing. It’s particularly resistant to acidic liquids and common industrial corrosive substances.
6. Wide Adaptability
Due to its high corrosion resistance, 316 stainless steel is used across various industries, including marine, chemical, food, pharmaceutical, and medical. It’s not only used in shipbuilding but also in surgical instruments, pharmaceutical equipment, chemical containers, and food processing systems.
7. Non-Magnetic Properties
316 stainless steel is nearly non-magnetic when in its annealed state, making it ideal for applications that require non-magnetic materials, such as medical devices and certain industrial uses. This makes it especially important in situations where magnetic interference is not allowed.
8. Good Workability
While 316 stainless steel is harder than other types, such as 304, it still has good workability. However, due to its high corrosion resistance, processing requires specialized tools and equipment to prevent damage to the protective oxide layer on its surface.
9. Long Service Life
316 stainless steel’s resistance to corrosion and wear makes it incredibly durable, especially in tough marine environments. Compared to other stainless steels, it is less likely to rust or corrode, reducing the frequency of repairs or replacements. This makes it a highly cost-effective material in the long run.
Differences Between 304 and 316 Marine Grade Stainless Steel
304 and 316 are two of the most commonly used marine-grade stainless steels. While both offer some degree of corrosion resistance, 316 stainless steel outperforms 304, particularly in marine environments.
304 stainless steel contains 18% chromium and 8% nickel. It has good corrosion resistance in general environments, but it’s not suitable for exposure to saltwater or highly corrosive conditions, as it tends to rust and corrode more easily than 316.
In contrast, 316 stainless steel performs much better in seawater over long periods, thanks to the addition of molybdenum, which makes it highly resistant to chloride-induced corrosion. Although 316 stainless steel is more expensive than 304, its durability allows shipowners to use 316 hardware for longer periods, reducing maintenance costs and extending the lifespan of the equipment.
Marine Grade Stainless Steel in Ships
Marine grade stainless steel is crucial for ships because it helps them resist the corrosion caused by seawater, salt spray, UV rays, and other harsh marine conditions. Ships spend long periods in the water, so choosing the right materials is essential for ensuring the durability, safety, and performance of the vessel.
Here are some of the main applications of marine-grade stainless steel in ships:
External Ship Structures and Equipment
Hull Structure: Marine-grade stainless steel is often used for parts of the hull, such as the deck, portholes, ladders, anchor chains, and masts. These parts are directly exposed to seawater, so they need excellent corrosion resistance.
Outer Shell: Stainless steel is used for the outer shell of ships to effectively resist corrosion from seawater, especially for parts below the waterline, reducing hull damage and extending the ship’s lifespan.
Deck and Hatch Equipment
Deck Accessories: Components like deck fixtures, portholes, bolts, and cables are often made from 316 or 304L stainless steel. Deck areas exposed to seawater for long periods require 316 stainless steel to resist corrosion effectively.
Hatch Equipment: Stainless steel is used for hatch frames, covers, and sealing devices to maintain durability and sealing properties even in wet, salty environments.
Rigging and Ship Hardware
Rigging: Marine-grade stainless steel is a common material for ship rigging and cables. These components, such as ropes, chains, and bolts, are exposed to seawater and are prone to corrosion. 316 stainless steel is widely used here for its ability to resist salt corrosion.
Mooring and Docking Gear: Ship mooring lines and docking posts also come into frequent contact with seawater. 316 stainless steel helps prevent corrosion from chlorides in the water and prolongs the life of these crucial parts.
Ship Power Systems and Piping
Power Equipment: Engines, pumps, fans, cooling systems, and seawater pipes are often made from marine-grade stainless steel. Thanks to 316’s strength and corrosion resistance, ship power systems remain stable and effective over time.
Cooling Pipes: Cooling systems on ships often use seawater for heat dissipation, so the pipes and other cooling components are usually made from 316 stainless steel or even more corrosion-resistant materials.
Portholes and Doors
The frames and parts of ship portholes and cabin doors are often made from 316 stainless steel. Since these components are exposed to seawater, they must offer exceptional resistance to corrosion to keep the ship’s interior safe from water damage.
Electrical Equipment Enclosures
Shipboard electrical equipment (such as control panels and switchboxes) often uses stainless steel to protect against corrosion and environmental factors. 316 stainless steel is commonly used to prevent the deterioration of these systems in marine conditions.
Ship Living Facilities
Kitchen Equipment and Bathrooms: Ships use a lot of stainless steel in kitchens, dining rooms, and bathrooms. Countertops, sinks, stoves, and other equipment often use 304 or 316 stainless steel for their corrosion resistance and ease of cleaning.
Bathroom Fixtures: Stainless steel is also used in toilets, showers, and other bathroom fixtures, where its durability and resistance to rust are key.
Ship Parts and Maintenance Tools
Fasteners and Screws: Fasteners like bolts, nuts, washers, etc., on ships are often made from 316 stainless steel to endure the harsh marine conditions and prevent corrosion from affecting the ship’s structure.
Maintenance Tools and Parts: Ship repair tools and spare parts are also made from marine-grade stainless steel to avoid rust and corrosion during long-term use on the high seas.
9. Long Service Life
316 stainless steel’s resistance to corrosion and wear makes it incredibly durable, especially in tough marine environments. Compared to other stainless steels, it is less likely to rust or corrode, reducing the frequency of repairs or replacements. This makes it a highly cost-effective material in the long run.
How Can Manek Help
At Manek, we offer our clients a series of customized marine hardware services , including investment casting, sand casting, die casting, CNC machining, sheet metal fabrication as well as various surface treatments.
We also provide a variety of other manufacturing capabilities. You can get quotations for free, such as 3D printing, plastic injection molding and powder coating.
Thanks to its exceptional corrosion resistance, strength, and durability, marine-grade stainless steel (especially 316) is widely used across various parts of ships to ensure reliable and long-lasting performance. From the hull structure to electrical systems, kitchen fixtures, and maintenance tools, stainless steel protects ships from the damaging effects of seawater, UV rays, and oxidation, making it an invaluable material for maritime operations.
