316N Stainless Steel (UNS S31651): Composition, Mechanical Properties & Applications
Aug 23, 2023
Get specifications, pricing, and availability from our technical team.
Key Takeaways
• 316N (UNS S31651) is the nitrogen-strengthened variant of 316: a controlled addition of 0.10–0.16% N raises minimum yield strength from 205 MPa to 240 MPa - a gain of approximately 17% - without sacrificing corrosion resistance.
• Chemistry per ASTM A240: Cr 16.0–18.0%, Ni 10.0–14.0%, Mo 2.0–3.0%, N 0.10–0.16%, C ≤ 0.08%.
• Minimum mechanical properties (A240, annealed): tensile strength ≥ 550 MPa, yield strength (0.2% offset) ≥ 240 MPa, elongation ≥ 35% (in 50 mm / 2 in.), hardness ≤ 95 HRB.
• Corrosion resistance equals standard 316 in chloride-bearing and process media, with a modest pitting-resistance boost from nitrogen. PREN ≈ 24–30 (midpoint \~27).
• Best-fit applications: pressure vessels, heat exchangers, and structural components where standard 316's yield strength is marginal but upgrading to duplex or higher-alloy grades is cost-prohibitive.
1. What Is 316N Stainless Steel?
316N (UNS S31651) is an austenitic stainless steel built on the same base chemistry as type 316 - 16–18% Cr, 10–14% Ni, 2–3% Mo - with a deliberate nitrogen addition of 0.10–0.16% by weight. Nitrogen is the most effective solid-solution strengthener available to the austenitic family: it raises both yield and tensile strength significantly while leaving corrosion resistance essentially unchanged. Nitrogen also acts as an austenite stabilizer (reducing the risk of strain-induced martensite) and contributes a measurable improvement to pitting resistance.
Engineers specify 316N when the application demands 316-level corrosion resistance but the design stress would otherwise force a heavier wall thickness. The nitrogen boost allows a thinner, lighter section - reducing material cost and dead weight - without switching to a higher-alloy grade.
Code status: 316N is a recognized material under ASME SA-240 (S31651) for pressure vessel construction and is supplied in plate, sheet, tube, pipe, and bar product forms.
2. Chemical Composition
Standard: ASTM A240/A240M - UNS S31651 (heat analysis, weight %)
| Element | Content (wt%) | Role in 316N |
|---|---|---|
| Carbon (C) | ≤ 0.08 | Strength; kept low to limit carbide precipitation |
| Manganese (Mn) | ≤ 2.00 | Deoxidation; aids nitrogen solubility |
| Phosphorus (P) | ≤ 0.045 | Residual - minimized for weldability |
| Sulfur (S) | ≤ 0.030 | Residual - minimized for corrosion resistance |
| Silicon (Si) | ≤ 0.75 | Deoxidation |
| Chromium (Cr) | 16.0 – 18.0 | Primary element for passivity and corrosion resistance |
| Nickel (Ni) | 10.0 – 14.0 | Austenite stabilizer; ductility and toughness |
| Molybdenum (Mo) | 2.00 – 3.00 | Pitting and crevice corrosion resistance in chlorides |
| Nitrogen (N) | 0.10 – 0.16 | Solid-solution strengthening; pitting resistance; austenite stability |
Mill certificate check: Verify the UNS number (S31651) and nitrogen value on every EN 10204 Type 3.1 certificate. A heat at the lower end of the nitrogen range (0.10%) delivers measurably lower yield strength than a heat at 0.16%. For critical applications, consider specifying an internal nitrogen minimum of 0.12%.
3. Mechanical Properties: 316N vs. 316
Standard: ASTM A240 minimum values - annealed condition at room temperature
| Property | 316N (S31651) | 316 (S31600) | Difference |
|---|---|---|---|
| Tensile strength, min | 550 MPa (80 ksi) | 515 MPa (75 ksi) | +35 MPa (+6.8%) |
| Yield strength, 0.2% offset, min | 240 MPa (35 ksi) | 205 MPa (30 ksi) | +35 MPa (+17.1%) |
| Elongation, min (50 mm / 2 in.) | 35% | 40% | −5 points |
| Hardness, max | 95 HRB / 217 HBW | 95 HRB / 217 HBW | Equivalent |
The yield strength gain of approximately 17% (240 vs. 205 MPa) is the design-relevant difference. It permits thinner wall sections under the same design pressure, or higher allowable stress at the same wall thickness, compared with standard 316. The trade-off is a modest reduction in ductility: elongation drops from 40% minimum (316) to 35% minimum (316N), which is still ample for most forming and fabrication operations.
Design implications (ASME BPVC Section VIII Div. 1): The higher yield strength translates to a higher allowable stress S at temperatures below the creep range. For designs governed by tensile/yield at moderate temperatures, 316N can reduce wall thickness by roughly 8–12% compared with an equivalent 316 section. Always use code-tabulated allowable stresses - never extrapolate from room-temperature tensile data alone.
4. Corrosion Resistance
4.1 Pitting and Crevice Corrosion
316N offers corrosion resistance equivalent to standard 316, with a modest improvement in pitting performance attributable to nitrogen. The widely used Pitting Resistance Equivalent Number (PREN) quantifies this:
PREN = %Cr + 3.3 × %Mo + 16 × %N
| Grade | PREN Range (spec limits) | PREN (midpoint) |
|---|---|---|
| 304 / 304L | 18.0 – 20.8 | ~19 |
| 316 / 316L | 22.6 – 28.5 | ~25 |
| 316N | 24.2 – 30.5 | ~27 |
| 317L | 27.9 – 33.2 | ~30 |
| Duplex 2205 (S32205) | 30.8 – 38.1 | ~35 |
| Super duplex 2507 | > 40 | ~42 |
What PREN means in practice: the 2–3% Mo provides the bulk of chloride pitting resistance; the nitrogen contribution (16 × 0.10 = 1.6 PREN points minimum) moves 316N noticeably ahead of 316 at the low end of the nitrogen range.
4.2 Environmental Performance
• Atmospheric and mildly corrosive service: equivalent to 316. Suitable for coastal and industrial atmospheres.
• Dilute sulfuric and phosphoric acids, organic acids, neutral chloride salts: resistance comparable to 316. Not recommended for concentrated hot acids - consider 317L or duplex grades.
• Seawater and brine: suitable for intermittent exposure and flowing seawater at ambient temperatures, but not recommended for stagnant or warm seawater where crevice corrosion can initiate. For continuous seawater duty, specify duplex 2205 (PREN \~35) or super-austenitic grades (PREN ≥ 40).
4.3 Sensitization Risk
316N is a non-stabilized grade. Prolonged exposure in the 450–850 °C (840–1560 °F) sensitization range can precipitate chromium carbides at grain boundaries, depleting the adjacent matrix of chromium and increasing susceptibility to intergranular corrosion. For heavy welded sections or service in the sensitization range, specify the low-carbon nitrogen variant 316LN (UNS S31653), which limits carbon to ≤ 0.03% while retaining the nitrogen strengthening.
5. High-Temperature Behavior
Like other austenitic stainless steels, 316N retains useful strength well past the temperature limits of ferritic grades. It is commonly specified for heat exchangers and furnace components up to approximately 800 °C (1470 °F) in continuous oxidizing service. The nitrogen content maintains a strength advantage over 316 at elevated temperatures because nitrogen slows diffusion-controlled creep mechanisms.
Key elevated-temperature data points (ASME BPVC Section II Part D, typical values for S31651):
| Temperature | Min. Yield Strength (MPa) | Min. Tensile Strength (MPa) | ASME Allowable Stress S (MPa) |
|---|---|---|---|
| 20 °C (68 °F) | 240 | 550 | 138 |
| 200 °C (392 °F) | 168 | 484 | 120 |
| 400 °C (752 °F) | 136 | 435 | 111 |
| 600 °C (1112 °F) | 118 | 390 | 100 |
Design note: Creep, not tensile strength, governs design above roughly 500 °C. Consult the applicable construction code (ASME Section VIII Div. 1, B31.3, or EN 13445) for time-dependent allowable stresses specific to your product form and service life.
6. Welding 316N
316N is readily weldable by all standard arc processes: TIG (GTAW), MIG (GMAW), SMAW, and SAW. The nitrogen in the base metal helps maintain weld-metal austenite stability, reducing the risk of hot cracking and promoting a balanced ferrite content.
Key Welding Controls
• Heat input: keep heat input moderate (typically 1.0–2.5 kJ/mm for GTAW). Excessive heat promotes chromium-carbide precipitation in the heat-affected zone.
• Interpass temperature: maintain below 150 °C (300 °F). Extended dwell at elevated temperature can cause nitrogen loss from the weld pool and accelerate sigma-phase formation.
• Filler metal selection: for matching corrosion resistance, use ER316L / E316L consumables. For matching-strength welds where the design code requires it, specify nitrogen-bearing filler metal ER316LN / E316LN to compensate for nitrogen lost during welding.
• Post-weld treatment: solution annealing at 1,010–1,120 °C (1,850–2,050 °F) followed by rapid water quenching restores full corrosion resistance and dissolves any chromium carbides formed during welding. Not always required for thin sections; mandatory for heavy sections and code-governed construction.
7. Applications
316N is specified where the corrosion resistance of 316 is required but higher strength permits a weight or cost advantage:
• Pressure vessels and heat exchangers in chemical, petrochemical, and refinery service - particularly where design pressure pushes 316 beyond its economic wall thickness.
• Desalination and marine equipment: brine heaters, evaporator bodies, and seawater piping (flowing, ambient-temperature service only).
• Pulp and paper: bleach-plant internals, digester components, and stock-handling equipment.
• Food and beverage processing: tanks, piping, and heat-exchange surfaces requiring 316-level corrosion resistance with reduced wall thickness.
• Architectural and structural components: where higher strength reduces section size and dead load in exposed stainless structures.
• Cryogenic service: 316N retains excellent toughness at LNG temperatures (−162 °C), thanks to nitrogen-stabilized austenite.
8. Equivalent Designations
| Standard / Region | Designation | Notes |
|---|---|---|
| UNS (USA) | S31651 | Definitive UNS number for 316N |
| AISI (USA) | 316N | Common trade designation |
| ASTM | A240 TP316N, A312 TP316N, A276 316N | Product-form-specific grades |
| ASME | SA-240 S31651 | Pressure vessel code designation |
| EN 10088 (Europe) | ~1.4406 / X2CrNiMoN17-11-2 | Closest EN grade; technically the low-carbon variant (316LN). Verify N range on certificate. |
| ISO 15510 | X6CrNiMoN17-12-3 (~1.4495) | ISO designation; closer in carbon but differs in Ni range |
| GB/T 1220 (China) | 06Cr17Ni12Mo2N | Chinese national standard; ISC S31658 |
| JIS (Japan) | SUS 316N | Japanese Industrial Standard |
Important: EN 1.4406 (X2CrNiMoN17-11-2) is the closest European grade, but it limits C to ≤ 0.03% and specifies N at 0.12–0.22% - wider than the ASTM range for 316N. Grades 1.4436, 1.4429, and 1.4439 are different alloys with higher Ni and/or Mo contents. Always confirm exact chemistry and UNS number on the mill certificate; do not assume EN/GB/JIS interchangeability without verification.
9. Frequently Asked Questions
Q1: What is the difference between 316 and 316N?
The sole intentional difference is nitrogen content: 316N contains 0.10–0.16% N (vs. ≤ 0.10% for standard 316). This raises the minimum yield strength from 205 MPa to 240 MPa - a 17% gain - while corrosion resistance stays essentially the same. The trade-off is a small reduction in ductility: minimum elongation drops from 40% to 35%.
Q2: Is 316N available as seamless pipe?
Yes. 316N is supplied as seamless and welded pipe per ASTM A312 TP316N, tube per ASTM A249/A213, plate per ASTM A240, and bar per ASTM A276. Availability varies by mill and product form - confirm lead times and minimum order quantities with your supplier.
Q3: Can 316N be used in seawater?
316N performs similarly to 316 in mildly chloride-bearing marine environments and is suitable for intermittent seawater exposure or flowing seawater at ambient temperatures. However, it is not recommended for stagnant or warm seawater where crevice corrosion can initiate. For continuous seawater immersion, upgrade to:
• 317L (PREN \~30) - moderate improvement
• Duplex 2205 (PREN \~35) - good seawater resistance with higher strength
• Super-austenitic 6Mo grades (PREN ≥ 40) - severe seawater and high-chloride service
Q4: What mill certificates are supplied with 316N?
Standard delivery includes an EN 10204 Type 3.1 mill test certificate with heat analysis (including the nitrogen value), room-temperature tensile results, and corrosion test data where specified. Positive Material Identification (PMI) verification is available on request. Type 3.2 certificates (with third-party inspection) can be specified at the time of order for code-governed fabrication.
Q5: 316N or 316LN - which should I specify?
The decision turns on welding and corrosion requirements:
• 316N (S31651): standard carbon (≤ 0.08%). Suitable for most applications without heavy welding. Lower cost and broader availability.
• 316LN (S31653): low carbon (≤ 0.03%) plus nitrogen. Eliminates sensitization risk in heavy welded sections and service in the 450–850 °C range. Slightly lower strength minimum (yield 205 MPa) but typically higher nitrogen (0.10–0.16% in ASTM, 0.12–0.22% in EN 1.4406).
For welded pressure vessels and heat exchangers operating in corrosive service, 316LN is usually the safer choice despite the higher cost.
10. References
1. ASTM A240/A240M-24a - Standard Specification for Chromium and Chromium-Nickel Stainless Steel Plate, Sheet, and Strip for Pressure Vessels and for General Applications. ASTM International, 2024. DOI: [10.1520/A0240\_A0240M-24A]
2. ASTM A312/A312M-24 - Standard Specification for Seamless, Welded, and Heavily Cold Worked Austenitic Stainless Steel Pipes. ASTM International, 2024.
3. ASME BPVC Section II Part D - Properties (Metric), 2023 Edition. The American Society of Mechanical Engineers.
4. ASME BPVC Section VIII Division 1 - Rules for Construction of Pressure Vessels, 2023 Edition.
5. EN 10088-1:2014 - Stainless steels - Part 1: List of stainless steels. European Committee for Standardization (CEN).
6. GB/T 1220-2007 - Stainless Steel Bars (grade 06Cr17Ni12Mo2N). Standardization Administration of China.
7. ISO 15510:2014 - Stainless steels - Chemical composition. International Organization for Standardization.
8. Sedriks, A.J. - Corrosion of Stainless Steels, 2nd ed., John Wiley & Sons, 1996. (PREN methodology and chloride pitting fundamentals.)
9. NORSOK M-001:2014 - Materials Selection. Standards Norway. (PREN-based material selection for offshore service.)
10. EN 10204:2004 - Metallic products - Types of inspection documents. CEN.
Disclaimer: This article provides general technical guidance. Always consult the applicable construction code and material specification in the edition mandated by your contract. Verify all material properties against the mill test certificate for the specific heat in question.
