How does 316 compare with super duplex stainless steels?
Super duplex stainless steel gives three to four times the yield strength of Alloy 316 and about twice its pitting resistance, for less than double the cost. Choose super duplex for seawater immersion, chemical processing or other aggressive duties; 316 remains the better choice for hygiene-led environments and for cryogenic-to-870°C service.
316 vs Ferralium® 255: the numbers
| Property | Alloy 316 | Ferralium® 255 |
|---|---|---|
| PREN | ~25 | >40 |
| Chromium | ~18% | 24.5-26.5% |
| Molybdenum | - | 3.10-3.80% |
| Nickel | ~8% | 5.50-6.50% |
| Nitrogen | - | 0.20-0.25% |
| 0.2% proof strength | - | 586 N/mm² (85 ksi) |
| Tensile strength | - | 790 N/mm² (114.5 ksi) |
| General corrosion resistance | Good; suited to milder, hygiene-led environments | Very good; suited to aggressive industrial environments |
| Pitting / CPT resistance | Moderate (PREN ~25) | About twice that of 316 (PREN >40) |
| Typical applications | Food, dairy and brewing; heat exchangers; chemical processing; marine parts | Seawater immersion; chemical processing; oil and gas; mining; power generation; water treatment |
Calculate PREN for your own composition with our PREN calculator.
What Alloy 316 is
Alloy 316 is the most widely known and specified grade of stainless steel. Sometimes called 18/8 for its 18% chromium and 8% nickel, it is an austenitic stainless steel: good corrosion resistance, excellent impact toughness down to very low temperatures, non-magnetic, and relatively easy to fabricate. We stock the low-carbon Alloy 316L variant, which resists intergranular corrosion after welding.
Where 316 is used
316 is widely used in domestic applications where its appearance and function are appreciated, and in less aggressive industrial conditions where cleanliness matters as much as corrosion - food production, dairy and brewing.
It is also common in exhaust manifolds, furnace parts, heat exchangers, valve and pump parts, chemical processing equipment, pharmaceutical and photographic equipment, tanks and evaporators, textile, pulp and paper equipment, and parts exposed to marine environments. It is also specified for process-industry containers and transport units, marine and shipbuilding piping and fittings, oil and gas piping and pumps, and woven screens for the mining industry.
Where super duplex takes over
Their greater corrosion resistance makes super duplex stainless steels the choice for long-term immersion in seawater and for aggressive industrial solutions - chemical processing, oil and gas, mining, power generation and water treatment.
We are a leading supplier of super duplex stainless steels, including Ferralium® 255, S32750 and S32760, in solid bar up to 16" diameter and plate up to 3" thickness, plus pipes and fittings.
Where super duplex is chosen, applications include sugar cane processing, mixers and centrifuges, all well served by Ferralium® 255. In water treatment - sewage treatment, desalination and swimming pools - super duplex resists corrosion from seawater and from contaminated or brackish solutions.
Where 316 still has the edge
Super duplex has real limits. It loses much of its impact toughness below -50°C, whereas 316 retains impact toughness down to cryogenic temperatures. Super duplex is also limited to continuous service below 250°C, whereas 316 can be used up to 870°C, provided it is the low-carbon 316L or titanium-stabilised 316Ti variant to avoid intergranular corrosion.
Super duplex is also harder to machine given its much higher strength, and is perceived as more difficult to weld - though it can be readily fabricated with the right equipment and procedures.
Which should you choose?
316 remains the right choice for cryogenic through to high-temperature service, for lighter fabrication and machining, and for hygiene-led duties like food, dairy and brewing where its appearance and cleanability matter. Move to super duplex once the environment turns aggressive: long-term seawater immersion, chemical processing, oil and gas, mining, power generation and water treatment all call for its higher strength and pitting resistance. Keep 316 for anything below -50°C or above 250°C, where super duplex loses toughness or risks degrading.