Marine Grade Stainless Steel - Overview
Offshore Oil Rigs frequently utilize 316 stainless (aka marine-grade stainless steel)
As someone who spends a lot of time camping, kayaking, and exploring the outdoors, one of the most satisfying parts of any trip is "Tetrising" each piece of my gear into the truck and double-checking my tie-down knots. It’s a long-standing tradition and joke with my buddies that you aren’t safe to leave until you pat the stack of gear or pluck the rope like a guitar string and say, "Yeah... that ain’t goin’ nowhere."
Those five words almost have a mystical aura about them. They are a seal of approval on a job well done, and you’re trusting them to protect your tent, camp kitchen, kayak, or any other gear from flying out on the highway or bouncing out on a dirt road. Jokes aside, you’ll go through a similar ritual every trip if you’ve ever lost a piece of gear out of a truck bed.
I start with this little anecdote to touch on one key point: trust in your gear is paramount when you are out in the elements. One of our most popular and trusted alloys is 316 Stainless Steel, which is cast for resistance to harsh ocean environments.
In this alloy overview, we’re taking a look at 316 SS, also known as Marine-Grade Stainless Steel. We’ll explore its unique properties, common usage scenarios, and why it is the preferred material for industries that demand durability, corrosion resistance, and longevity in marine environments.
What is Marine-Grade Stainless Steel?
Marine-Grade Stainless Steel is a high-performance, corrosion-resistant alloy that belongs to the austenitic stainless steel family. It is known for its exceptional corrosion resistance, particularly in harsh environments such as exposure to saltwater, chemicals, and extreme temperatures. It is the second most commonly utilized stainless steel worldwide, behind only 304 Stainless Steel.
Marine-Grade Stainless Steel has several names:
SS 316
316 Stainless
AIS 316
S31600
CF8M
316 Stainless Steel: Primary Designations/Types
316 Stainless:
General-purpose 316 stainless steel is used in food processing, marine applications, and medical devices.
316L:
Low-carbon 316 stainless steel is commonly used in high-temperature settings and frequently in medical implants. Because of its lower carbon content, it is also better suited to welding than standard 316.
316F:
Known as the free-machining variant, with less molybdenum present to allow for easier machining. Typically used in marine-grade screws and fasteners or any part with geometry best suited to machining.
316N:
The high-nitrogen grade of 316 stainless steel is used in harsh chemical environments where extra resistance to pitting is critical.
Composition of 316 Stainless Steel
Its primary composition consists of:
Chromium (16-18%): Provides corrosion and oxidation resistance.
Nickel (10-14%): Enhances corrosion resistance and toughness.
Molybdenum (2-3%): Increases resistance to pitting and crevice corrosion, especially in chloride-rich environments.
Manganese (2%): Contributes to strength and workability.
Iron & Other Trace Elements: Including silicon, phosphorus, sulfur, molybdenum (and nitrogen in the case of 316-F).
What Makes 316 Stainless Steel Suited for Saltwater Applications?
The detailed chemistry behind what makes stainless steel special is beyond the scope of this blog, but here are a few basics.
Like all types of stainless steel, SS316 contains chromium, which forms a thin, self-repairing oxide layer on its surface. This doesn’t make 316 impervious to all damage, but, with proper maintenance, it will protect the iron from rusting.
Marine-grade stainless is unique in that it contains molybdenum, which helps it resist high chloride levels found in seawater, de-icing salts, and industrial chemicals. The 2-3% molybdenum in its chemical composition prevents pitting and other corrosion from these chlorides.
Is Marine-Grade Stainless Steel Rust-Proof?
While its chemical composition provides significant protection from the elements, marine-grade stainless still requires care and maintenance to avoid corrosion, rusting, or similar damage. With regular cleaning and inspections, many 316 stainless components can last for decades.
Common Applications for Marine-Grade Stainless Steel
As the name suggests, 316 stainless steel is a mainstay in marine applications. Here are just a few examples:
Boat fittings (e.g., cleats, railings, and propellers)
Underwater hardware
Offshore oil rigs
Desalination plants
Coastal construction (e.g., bridges and piers)
Its resilience also makes it a popular choice in other industries. Here are a few more examples of its uses:
Chemical Processing:
Tanks and Reactors: 316 stainless steel is used in the construction of tanks, reactors, and piping systems that handle corrosive chemicals.
Heat Exchangers: Its resistance to a wide range of chemicals makes it suitable for heat exchangers in chemical plants.
Industrial Equipment:
Pumps and Valves: 316 stainless steel is commonly used in the manufacturing of pumps and valves that handle corrosive fluids.
Fasteners and Bolts: Its strength and corrosion resistance make it suitable for high-stress applications in industrial settings.
Water Treatment:
Piping and Fittings: Used in water treatment plants for their resistance to various water chemistries, including chlorides and other disinfectants.
Tanks and Vessels: Employed in the construction of tanks and vessels that store and treat water.
Aerospace:
Components and Fasteners: 316 stainless steel is used in aerospace applications where high strength and resistance to extreme environments are required.
Automotive:
Exhaust Systems: Its resistance to high temperatures and corrosive gases makes it suitable for automotive exhaust systems.
Trim and Moldings: Used for decorative trim and moldings due to its aesthetic qualities and durability.
304 Stainless vs. 316 Stainless
One of our most frequently asked questions about marine-grade stainless steel is how it differs from 304 Stainless Steel. Today, we’ll focus on three key differences: composition, cost, and application.
Composition:
Both materials are in the 300 series of stainless steel and share many similarities. The most significant difference stems from the inclusion of molybdenum in 316 stainless. The addition of 2-3% molybdenum provides significant protection against chlorides, which are found in harsh chemical environments and seawater.
Cost:
Because of its enhanced resistance, 316 stainless steel is generally more expensive than its 304 counterpart. 304 is the more cost-effective stainless steel option when extreme environments aren’t a concern. However, the additional cost of 316 can be justified when your components are put to the test in chloride-rich environments (e.g., saltwater). The wear and tear that 304 Stainless would experience in these environments could lead to critical failures or require frequent replacement.
Application:
As is often said, you need the right tools for the job. However, some tools can be overkill—you don’t need a lawnmower to trim a bush. In many freshwater applications, 304 stainless can be totally appropriate with proper care and oversight. But for the most demanding applications, you’ll want the resistances that marine-grade stainless provides.
Conclusion
We’ll end today’s blog with another camping gear story. In 2020, I was gifted a cast iron skillet from the 1960s. It had been neglected for years, sitting under a few tarps in a backyard, and was almost completely coated in rust. With the world in lockdown, I had some spare time and decided to restore it. Over a few days, I used a sander, heating cycles, and what felt like a lifetime supply of cleaning oil to bring the pan back to life.
Today, it is a mainstay in my camp kitchen and has cooked meals from the Grand Canyon to Acadia National Park. The right tool, with proper maintenance, has served me well—much like marine-grade stainless steel can for the most demanding applications.
If you’re interested in our stainless steel investment casting services or have questions about any other alloys, contact IPC today!
