STS316 vs. SUS316 Stainless Steel: Chloride Corrosion Resistance Compared
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What the SUS316 and STS316 Designations Mean
SUS316 and STS316 are the Japanese and Korean names for the same austenitic stainless steel. SUS316 is defined under the Japanese JIS standard system, while STS316 is the Korean KS designation. Both correspond to the internationally recognised Type 316 family covered by ASTM A240 and ASTM A276 for plate, sheet and bar.
The practical consequence is that the two grades can be substituted for one another in international projects without any change to design calculations, welding procedures or corrosion allowances. What the buyer should verify is the certificate, the mill tolerances and the surface condition of the delivered product.
Chemical Composition Compared
The two grades share the same core alloying elements and the same ranges for the elements that control corrosion resistance.
| Element | SUS316 (JIS standard) | STS316 (KS standard) | Function |
|---|---|---|---|
| Carbon (C) | 0.08% max | 0.08% max | Low carbon reduces intergranular corrosion risk, especially in welded components |
| Chromium (Cr) | 16.0-18.0% | 16.0-18.0% | Forms a dense passive chromium oxide film against oxidation and general corrosion |
| Nickel (Ni) | 10.0-14.0% | 10.0-14.0% | Enhances austenitic stability and maintains ductility at low and high temperature |
| Molybdenum (Mo) | 2.0-3.0% | 2.0-3.0% | Strengthens the passive film against chloride-induced pitting and crevice corrosion |
| Silicon (Si) | 1.00% max | 1.00% max | Deoxidation and control of trace residuals |
| Manganese (Mn) | 2.00% max | 2.00% max | Austenite stability and hot workability |
| Nitrogen (N) | 0.10% max | 0.10% max | Modest strength contribution |
Because molybdenum, the element that governs chloride resistance, is specified over exactly the same range in both standards, there is no metallurgical reason for a difference in corrosion performance. Any variation in practice comes from impurity control, mill processing and the completeness of solution annealing.
Chloride Pitting and Crevice Corrosion Behaviour
Type 316 with 2-3% molybdenum resists pitting and crevice corrosion significantly better than Type 304 in chloride-bearing environments such as seawater, salt solutions and bleach. That improvement comes directly from the molybdenum, which reinforces the passive film at points where it is locally broken down by chloride ions.
Applicable service window for both grades:
Chloride concentration up to about 1000 ppm and metal temperature up to about 60°C
No stagnant zones, no tight crevices and no deposits that trap chlorides
Smooth, passivated surfaces with clean welds free of heat tint and spatter
Typical duties inside that window are seawater desalination equipment, chemical pipelines and food processing equipment. Above roughly 3000 ppm chloride, or with seawater at approximately 20000 ppm, a higher-molybdenum grade such as 317L or a duplex grade such as 2205 must be selected instead.
Temperature acts as an accelerator rather than an independent variable. Above about 60°C the breakdown of the passive film by chloride is much faster, so both concentration and temperature must be assessed together for the actual duty rather than as separate limits.
Fabrication, Surface Finish and Weld Quality
Corrosion performance in service is decided as much in the fabrication shop as in the mill. The difference between two components made from identical SUS316 or STS316 material can be an order of magnitude in service life, depending on how they were processed.
Weld with controlled heat input and, for heavily restrained or thick joints, consider a low-carbon 316L grade to avoid sensitisation
Pickle and passivate after welding to restore the passive film on and beside the weld
Avoid carbon steel contamination from brushes, grinding wheels, lifting gear and marking inks
Remove spatter and oxide scale from the weld area; both trap chlorides
Keep surface roughness low where the component will be exposed to salt spray
The key point for specification writers is that the achievable difference between the two designations is negligible, whereas the difference produced by fabrication quality is large. Budget and inspection effort are best spent on procedure qualification and surface treatment.
Interchangeability and Selection Guidance
| Consideration | Practical guidance |
|---|---|
| International projects | Substitute freely, but confirm equivalence on the material certificate |
| Asian supply chain | SUS316 is more common in the Japanese and Chinese markets, STS316 in Korea and parts of Southeast Asia |
| Welded pressure parts | Specify the low-carbon 316L variant where heat treatment is not possible |
| Seawater duty | Move to 317L or 2205 duplex once chloride exceeds about 1000 ppm or temperature exceeds 60°C |
Frequently Asked Questions
Q: Are SUS316 and STS316 exactly the same?
They are equivalent grades from two national standard systems with identical chromium, nickel and molybdenum ranges. For engineering purposes they are interchangeable, and the selection is normally driven by market availability.
Q: Does one grade resist chloride better than the other?
No measurable difference is expected. The difference in service performance depends on fabrication quality, especially solution annealing completeness and surface roughness, rather than on the designation itself.
Q: What chloride level is safe for 316 stainless steel?
Up to roughly 1000 ppm chloride with metal temperatures at or below about 60°C, and only where crevices and stagnant zones are avoided. Higher chloride levels or higher temperatures call for a higher-molybdenum or duplex grade.
Q: Why is molybdenum important for chloride resistance?
Molybdenum strengthens the passive film and helps it repassivate where chloride ions have locally broken it down, which directly raises resistance to pitting and crevice corrosion.
Q: Should 316L be used instead for welded parts?
Yes, where heavy sections are welded or post-weld heat treatment is impractical. The lower maximum carbon of the low-carbon variant reduces sensitisation and therefore intergranular corrosion risk.
Q: What surface treatment gives the best corrosion life?
Pickling followed by passivation, or mechanical polishing to a smooth finish, combined with thorough post-weld cleaning. A clean, smooth passive surface is the single most effective protection in chloride service.
