Stainless steel tubing is vital to modern convenience. It has numerous uses in our home lives, including in appliances; water, heating and plumbing systems; automobiles; and tools. Outside our little spheres, 316 and 316L stainless steel tubing is used in everything from boat fittings to jet engine parts to food preparation equipment.
Some differences exist in 316 vs. 316L stainless steel when it comes to makeup and application. While minor, they can affect the quality of your design and final product.
First, let’s quickly recap the key difference between 316 and 316L stainless steel.
Think of 316L as 316-Low. The 316L grade owns a 0.03% maximum carbon makeup whereas 316 contains up to 0.08%, a mid-range level of carbon. The higher carbon content of 316 makes it a harder material than 316L.
Commercially produced steel, using current methods, is often made as a low-carbon type as a matter of course due to the improved control in modern technology. That means finished steel products are often offered to the market “dual certified” as both grades so they can be used for an expanded number of fabrications.
When you choose 316 stainless steel from the austenitic family, you’re getting a material with molybdenum added to increase corrosion resistance, especially in chloride environments that cause pitting.
Fun Fact: The 316 grade was developed for use in sulfite pulp mills because it resists sulfuric acid compounds. Its use has since been broadened to handle chemicals in process industries.
In fact, both 316 and 316L stainless steel are highly resistant to mild atmospheric, mild freshwater, industrial, marine, and various forms of chemical corrosion. The low-carbon version (remember, 316L stands for “low”) is preferred in corrosive environments, as it’s important to make sure contaminants (i.e. copper and zinc) don’t cause problems at the heat-affected zone of a weld and create cracking.
More specifically, when it comes to tube design, hardness affects bendability. If you’re using a harder material --- in this case, the 316 grade --- you may have to specify slightly larger bend to account for springback. Springback is the tendency of a bent or shaped material to revert to its original form. Remember, a harder tube material will fight the urge to be bent.
Stainless steel bends better than mild steel. It has a higher percentage of elongation, making it easier to bend on tight radii. 316L is slightly more weldable than 316. It’s more extensively used in the oil and gas and chemical industries.
The 316 grade doesn’t have strong forming and welding characteristics, but it can still be folded or rolled. If you need to heavily weld 316 grade, you should specify annealing afterward to achieve the desired corrosion resistance.
As far as ferritic stainless steels go, 316L can be used as a filler metal to improve ductility and toughness. Lack of ductility and sensitization are two of the major difficulties associated with welding ferritic stainless steels.
Applications for 316 and 316L include:
One such use for these metals is tall oil (pulp and paper industry) --- high-rosin-acid streams can be handled by 316L with a minimum molybdenum content of 2.75%. Type 316 can also be used in the more corrosive high-fatty-acid streams at temperatures up to 475 degrees Fahrenheit.
Again, the low-carbon grades may become sensitized at extremely long exposures to temperatures in the sensitization range. Sensitization occurs with heating into the 800-to-1300 F range.
Don’t forget that stainless steel costs more than mild or galvanized steel. While stainless steel, copper, or aluminum may have better properties overall, your application may not require material quality that exceeds that of mild steel.
So let’s say it together one more time: If you're not sure which type of steel is best for your project, remember that if your project requires lots of welding, 316L is a better choice off the bat. However, 316 can be annealed to resist weld decay if you're set on this grade.