Stainless Steel 316LN
Stainless Steel 316LN (UNS S31653) adds controlled nitrogen (0.10-0.16%) to the 316L low-carbon molybdenum base. The nitrogen makes up for the yield strength reduction that comes with low-carbon grades, while keeping the sensitization-free weldability intact. It is the preferred grade where ASME nuclear code or cryogenic pressure design governs wall thickness.
1. Chemical Composition
The table below shows the elemental ranges for Stainless Steel 316LN. The nitrogen addition, low carbon ceiling, and molybdenum content together determine its combined strength and corrosion performance.
| Grade | C | Mn | P | S | Si | Cr | Ni | Mo | Other |
| TP316LN | ≤ 0.030 | ≤ 2.00 | ≤ 0.045 | ≤ 0.030 | ≤ 0.75 | 16.00–18.00 | 10.00–14.00 | 2.00–3.00 | N: 0.10–0.16 |
2. Mechanical Properties
The following table lists minimum mechanical properties for Stainless Steel 316LN in the annealed condition. Nitrogen raises the minimum yield strength above the 316L baseline while maintaining equivalent ductility and toughness.
| Grade | Condition | Tensile Strength Min, MPa (ksi) | Yield Strength Min, MPa (ksi) | Elongation Min, % | Heat Treatment Temp |
| TP316LN | Annealed | ≥ 515 (≥ 75) | ≥ 205 (≥ 30) | ≥ 35 | 1040°C (1900°F) min |
3. Equivalent Grade
This table maps Stainless Steel 316LN to its international standard equivalents. EN and ISO designations are the most common references outside the ASTM system for this nitrogen-modified grade.
| GRADE | UNS | GB | JIS | ISO | DIN/EN | GOST | |
| ISC | NEW | ||||||
| 316LN | S31653 | S31653 | 022Cr17Ni12Mo2N | SUS316LN | X2CrNiMo17-12-2 | 1.4429 / X2CrNiMoN17-13-3 | - |
3. Key Technical Advantages
- Nitrogen-Restored Yield Strength: Controlled nitrogen at 0.10-0.16% raises the minimum yield strength of 316LN to 205 MPa, matching standard 316, while carbon stays at or below 0.030%. ASME code designers can therefore use 316LN at 316-equivalent wall thicknesses without giving up as-welded corrosion resistance.
- Nuclear Code Classification: 316LN is specifically listed in ASME Section III (Nuclear Components) Division 1 as a preferred material for safety-class pressure boundary components. Both low carbon (for sensitization control) and adequate design strength are required at the same time in these applications.
- Improved Pitting Resistance via PREN: The nitrogen addition directly increases the pitting resistance equivalent number (PREN), giving 316LN somewhat better pitting resistance than Mo-equivalent 316L in borderline chloride environments.
- Cryogenic Toughness: The austenitic structure combined with no sensitization-inducing carbon makes 316LN well suited for cryogenic pressure vessel and piping service. It produces fully compliant Charpy impact values at temperatures as low as -196°C.
Technical Note: The nitrogen content must be verified by mill certification, as nitrogen additions require controlled melting practice (AOD or VOD). Substituting standard 316L for 316LN in nuclear or cryogenic code-designed systems requires engineering review of design allowable stresses.
4. Common Manufacturing Standards
- ASTM A312: Standard Specification for Seamless, Welded, and Heavily Cold Worked Austenitic Stainless Steel Pipes — TP316LN designation.
- ASTM A213: Standard Specification for Seamless Austenitic Alloy-Steel Boiler, Superheater, and Heat-Exchanger Tubes — T316LN designation.
- ASTM A269: Standard Specification for Seamless and Welded Austenitic Stainless Steel Tubing for General Service.
- ASTM A249: Standard Specification for Welded Austenitic Steel Boiler, Superheater, Heat-Exchanger, and Condenser Tubes.
- ASME Section III: Rules for Construction of Nuclear Facility Components — 316LN listed for Class 1, 2, and 3 pressure boundary applications.
- DIN EN 10216-5: Seamless steel tubes for pressure purposes — stainless steel (1.4429).
- DIN EN 10217-7: Welded steel tubes for pressure purposes — stainless steel (1.4429).
- GB/T 14976: Seamless stainless steel tubes for fluid transport (022Cr17Ni12Mo2N).
Manufacturing Standards Comparison Table:
| Standard | ASTM | EN/DIN | JIS | GB/T | GOST |
| Seamless Pipe | A312 (TP316LN) | EN 10216-5 (1.4429) | - | 14976 | - |
| Welded Pipe | A312 (TP316LN) | EN 10217-7 (1.4429) | - | - | - |
| Heat Exchanger Tube | A213 (T316LN) / A249 | EN 10216-5 | - | 13296 | - |
| General Service Tube | A269 | EN 10216-5 | - | - | - |
5. Primary Applications
- Nuclear Power Plant Piping: Safety-class coolant boundary piping, pressurizer nozzles, and reactor auxiliary systems in light-water reactors. ASME Section III requires the combination of low carbon and verified nitrogen for primary circuit components.
- Cryogenic Pressure Vessels: Storage vessels and transfer piping for liquefied natural gas (LNG), liquid nitrogen, and liquid oxygen. Wall thickness in these systems is governed by design codes that require 316-equivalent yield strength along with cryogenic toughness.
- Subsea and Deepwater Equipment: Manifold piping, Christmas tree components, and umbilical systems where both deep-sea chloride exposure and pressure design load drive material selection.
- Spent Nuclear Fuel Storage: Canister and storage rack fabrications that need long-term structural integrity under combined irradiation and humid storage conditions.
- High-Pressure Chemical Reactors: Thick-wall reactor vessels and nozzles where low-carbon weldability and full design-allowable yield strength must both be demonstrated without post-weld heat treatment.