Stainless Steel 316
Stainless Steel 316 (UNS S31600) is the standard molybdenum-bearing austenitic grade of the 300 series. Its 2-3% molybdenum content gives it much better pitting and crevice corrosion resistance than Grade 304, especially in chloride-containing and reducing acid environments found in chemical and marine industries.
1. Chemical Composition
The table below lists the key alloying elements for Stainless Steel 316. Molybdenum is the defining alloying addition that separates it from 304 and gives it better resistance to localised corrosion.
| GRADE | UNS Designation |
C | Mn | P | S | Si | Cr | Ni | Mo | Ti | Cu | Al | Other |
| TP316 | S31600 | 0.080 | 2.00 | 0.045 | 0.030 | 1.00 | 16.0-18.0 | 10.0-14.0 | 2.0-3.0 | - | - | - | - |
2. Mechanical Properties
The following table gives minimum mechanical properties for Stainless Steel 316 in the annealed condition. These apply to seamless pipe and tube product forms as per ASTM specifications.
| Grade | Condition & Size | Standard | Heat Treating Temp. : min | Tensile Strength Min. MPa |
Yield Strength Min. MPa |
Elongation min. % |
Pipe Hardness | Tube Hardness |
| TP316 | - | A312 | 1040°C | 515 | 205 | 35 | HBW ≤ 217 HRB≤ 95 | HBW ≤ 192 HRB≤ 90 |
3. Equivalent Grade
This table cross-references Stainless Steel 316 designations across global standards for material equivalency, including ASTM, European, Japanese, Chinese, and Russian procurement systems.
| GRADE | UNS | GB | JIS | ISO | DIN/EN | GOST | |
| ISC | NEW | ||||||
| 316 | S31600 | S31608 | 06Cr17Ni12Mo2 | SUS316 | X5CrNiMo17-12-2 | 1.4401 | 08Kh16N11M3 |
4. Key Technical Advantages
- Molybdenum-Based Pitting Resistance: The 2-3% Mo addition raises the pitting resistance equivalent number (PREN = %Cr + 3.3x%Mo + 16x%N) to roughly 24-26. This is well above Grade 304's PREN of about 18-20, and it allows reliable service in moderate chloride environments.
- Resistance to Reducing Acids: Molybdenum improves resistance to reducing acids like dilute sulfuric acid and phosphoric acid, where 304 falls short. Because of this, 316 is a standard choice for chemical process equipment handling these media.
- Better Crevice Corrosion Performance: In stagnant or low-flow chloride environments (flange joints, tube-to-tubesheet gaps, under deposits), 316 maintains its passive film at chloride concentrations that would cause breakdown in 304.
- Elevated-Temperature Creep Allowables: ASME Section II Part D lists slightly higher allowable stresses for 316 compared to 304 in certain elevated-temperature ranges. This is partly because of the solid solution strengthening effect of molybdenum.
Technical Note: Despite its improved pitting resistance, Grade 316 remains susceptible to stress corrosion cracking in hot concentrated chloride solutions above approximately 60°C. For such conditions, duplex grades (e.g., 2205) or super-austenitic grades (e.g., 904L, 6Mo) should be evaluated.
5. Common Manufacturing Standards
Stainless Steel 316 is produced and inspected under the following internationally recognised manufacturing standards:
ASTM A312: Standard Specification for Seamless, Welded, and Heavily Cold Worked Austenitic Stainless Steel Pipes — TP316 designation.
ASTM A213: Standard Specification for Seamless Ferritic and Austenitic Alloy-Steel Boiler, Superheater, and Heat-Exchanger Tubes — TP316 designation.
ASTM A269: Standard Specification for Seamless and Welded Austenitic Stainless Steel Tubing for General Corrosion Resisting and Low- or High-Temperature Service — 316 grade.
DIN EN 10216-5: Seamless steel tubes for pressure purposes — stainless steel (1.4401).
JIS G3459: Stainless Steel Pipes (SUS316).
JIS G3463: Stainless Steel Boiler and Heat Exchanger Tubes (SUS316).
GB/T 14976: Seamless stainless steel tubes for fluid transport (06Cr17Ni12Mo2).
GOST 9941: Seamless cold- and warm-deformed pipes from corrosion-resistant steel.
Standards Comparison Table:
| Standard | ASTM | EN/DIN | JIS | GB/T | GOST |
| Seamless Pipe | A312 (TP316) | EN 10216-5 (1.4401) | G3459 (SUS316) | 14976 | 9941 |
| Welded Pipe | A312 (TP316) | EN 10217-7 (1.4401) | G3459 (SUS316) | 12771 | - |
| Heat Exchanger Tube | A213 (T316) / A249 | EN 10216-5 | G3463 (SUS316) | 13296 | - |
| General Service Tube | A269 | EN 10216-5 | G3463 | 14976 | - |
6. Primary Applications
- Chemical and Petrochemical Piping: Transfer lines, heat exchanger bundles, and reactor piping handling dilute sulfuric acid, phosphoric acid, organic chlorides, and moderately corrosive process fluids.
- Marine and Offshore Equipment: Seawater cooling systems, pump casings, valve bodies, and structural tubing in offshore platforms and shipbuilding, where chloride-induced corrosion is the main design concern.
- Pharmaceutical Manufacturing: Process pipelines, bioreactor vessels, and clean-in-place (CIP) systems that need both corrosion resistance and compliance with hygienic surface finish standards.
- Pulp and Paper Bleaching: Piping and equipment in chlorine dioxide and hypochlorite bleaching circuits, where both chloride and acid attack would quickly degrade 304.
- Desalination Plants: High-pressure brine piping, pressure vessels, and heat exchangers in reverse osmosis and multi-stage flash desalination systems with continuous elevated chloride concentrations.