316 and 316L Stainless Steel: Properties, Corrosion and Uses

Written by: Emma, Technical Sales Engineer  |  Reviewed by: Ethan, Materials Engineer  |  Updated: August 2026

1. What Is 316 Stainless Steel?

316 is an austenitic chromium-nickel-molybdenum stainless steel — the second most widely used stainless steel grade globally, after 304. Its defining characteristic is the addition of 2–3% molybdenum, which significantly improves resistance to chloride-induced localized corrosion compared to standard Cr-Ni grades.

316 is commonly referred to as "marine grade stainless steel" — not because it is immune to seawater, but because the molybdenum addition provides a meaningful improvement in pitting and crevice corrosion resistance in chloride-containing environments such as coastal atmospheres and marine exposure.

2. Chemical Composition of 316 and 316L

The following composition limits are per ASTM A240, the standard specification for chromium and chromium-nickel stainless steel plate, sheet, and strip.

3. Why Molybdenum Makes 316 More Corrosion Resistant

The central technical question for 316 is: why does 2–3% molybdenum make a measurable difference? The answer lies in how molybdenum interacts with the passive film and with chloride ions at the atomic level.

The Mechanism

Stainless steel resists corrosion through a passive film — a chromium-rich oxide layer a few nanometers thick that forms spontaneously on the surface when exposed to oxygen. This film is electrically insulating and physically separates the metal from the environment.

Chloride ions (Cl⁻) attack this film at weak points — inclusions, grain boundaries, surface defects. Once a chloride ion breaches the passive layer at a single point, an electrochemical cell forms: the exposed metal becomes the anode (dissolving) while the surrounding passive surface becomes the cathode. The pit grows autocatalytically — the interior becomes acidic and chloride-rich, accelerating dissolution.

Molybdenum intervenes at two stages:

• Film stabilization: Mo incorporates into the passive film as molybdate ions (MoO₄²⁻), making it more resistant to chloride attack. The film is physically and chemically more robust — it takes a higher chloride concentration or temperature to initiate a pit
• Repassivation: Once a pit initiates, dissolved molybdenum species adsorb onto the actively dissolving surface inside the pit, slowing dissolution and promoting repassivation. This is why 316 pits more slowly and under narrower conditions than 304 — not because pits never form, but because incipient pits are more likely to repassivate before reaching a critical size

Quantifying the Difference: PREN

The Pitting Resistance Equivalent Number (PREN) translates chemical composition into a comparative index of chloride pitting resistance:

PREN = %Cr + 3.3 × %Mo + 16 × %N

The molybdenum contribution alone accounts for approximately 3.3 × 2.1 = 6.9 PREN points — a roughly 35% increase in pitting resistance index from 304 to 316. While PREN is not a corrosion rate or a service life prediction, it provides a useful comparative framework for understanding why 316 survives chloride exposures that pit 304.

4. 316 Stainless Steel Properties

Corrosion Resistance

316's corrosion resistance is defined by what the molybdenum addition provides — and what it does not:

316 performs well in:

• Coastal and marine atmospheric exposure — the most common reason to specify 316 over 304
• Chemical processing — resistance to phosphoric acid, many organic acids, and dilute sulfuric acid at moderate temperatures
• Food and beverage processing with salt exposure — brine lines, salt-containing sauces, marine products
• Pharmaceutical and hygienic equipment — commonly specified for WFI (Water for Injection) systems and process piping
• Pulp and paper processing — digester and bleaching environments where chlorides are present

316 has clear limits that procurement must respect:

• Warm seawater immersion: 316 will suffer pitting and crevice corrosion in continuous seawater immersion, particularly above ~25°C. This is the single most common misapplication of 316 — assuming "marine grade" means "seawater immune"
• High-chloride process fluids: Chloride concentrations above a few thousand ppm, particularly at elevated temperature, can exceed 316's pitting resistance
• Chloride stress corrosion cracking (Cl-SCC): Like all austenitic grades, 316 is susceptible to Cl-SCC above approximately 60°C when under tensile stress — a failure mode that PREN does not predict
• Strong reducing acids: Hydrochloric acid, hydrofluoric acid, and concentrated sulfuric acid will attack 316 regardless of its molybdenum content

Mechanical Properties (Annealed Condition, ASTM A240)

Fabrication Properties

316 offers excellent weldability by all common processes — TIG, MIG, SMAW, SAW, and resistance welding. Filler metals should match or exceed the base metal molybdenum content (ER316L for TIG/MIG). Formability is good but slightly lower than 304 due to the higher alloy content; deep drawing may require intermediate annealing for complex shapes. Surface finishing capability is equivalent to 304 — from 2B mill finish to No.8 mirror polish — making 316 suitable for both industrial and architectural applications.

5. 316L Stainless Steel Properties

316L — the low-carbon variant — is identical to 316 in chromium, nickel, and molybdenum content. It provides the same corrosion resistance in the unwelded condition. The single metallurgical difference is carbon: ≤ 0.03% for 316L versus ≤ 0.08% for 316.

Why this matters — and what it doesn't change:

Typical 316L applications are heavily weighted toward welded fabrication in corrosive service: pharmaceutical storage and process tanks, chemical reactor vessels, hygienic piping systems (orbital TIG welded), heat exchanger shells and tube sheets, and ASME-coded pressure equipment. In all cases, the low-carbon specification is selected for the weld zone, not because the base metal is inherently more corrosion resistant.

6. Understanding the 316/316L Distinction

The 316 versus 316L question is one of the most frequently discussed — and frequently misunderstood — topics in stainless steel procurement. The reality is more nuanced than a simple "which is better" comparison.

The metallurgical reality:

• 316 and 316L share the same chromium, nickel, and molybdenum ranges — their base corrosion resistance is identical
• The only intentional difference is carbon content: ≤ 0.08% (316) versus ≤ 0.03% (316L)
• During welding, the HAZ reaches 425–870°C — the sensitization range where carbon and chromium combine to form Cr₂₃C₆ at grain boundaries, depleting chromium and creating sites for intergranular corrosion
• 316L's low carbon prevents this — there is simply not enough carbon to form a continuous carbide network
• As a result, 316L welded fabrications do not require post-weld solution annealing to restore HAZ corrosion resistance

The commercial reality: In practice, a large proportion of 316-series flat products are supplied as 316/316L dual certified. Modern AOD (Argon Oxygen Decarburization) refining naturally achieves carbon well below 0.03% while nitrogen additions maintain strength. A dual-certified MTC confirms that one heat of material meets both S31600 and S31603 requirements simultaneously — carbon ≤ 0.03% (L-grade) and strength meeting the higher 316 minimums. For the buyer, dual-certified material effectively resolves the 316-vs-316L question: it satisfies both specification types from a single inventory item.

One material, two specifications — three scenarios:

• A project calling for "316" (S31600) can accept dual-certified 316/316L — the L-grade carbon automatically satisfies the ≤ 0.08% limit
• A project calling for "316L" (S31603) can accept dual-certified 316/316L — carbon is verified ≤ 0.03%
• A project calling for "316 only — no L-grade carbon" is unusual and should trigger a technical discussion. Why is low carbon being specifically rejected? Is this a high-temperature application that requires 316H instead?

7. Typical Applications of 316 and 316L

8. Limitations of 316 Stainless Steel

316 is corrosion resistant, not corrosion proof. Understanding its boundaries is essential — the difference between a successful specification and a costly failure often comes down to whether the buyer recognized a limitation that the grade cannot overcome.

9. How to Specify 316/316L When Purchasing

10. How Shangyou Supports 316/316L Stainless Steel Supply

• ASTM Compliance Verification: Every 316/316L order is confirmed against the applicable ASTM product standard — A240 for plate/sheet, A312 for pipe, A276 for bar. Compliance is verified, not assumed
• Molybdenum Content Confirmation: The defining element of 316 is molybdenum. We verify Mo content (2.0–3.0%) on every MTC — a heat that falls below 2.0% is not 316 and does not ship
• Carbon Content Verification: For 316L and 316/316L dual-certified orders, carbon ≤ 0.03% is confirmed from the MTC heat analysis. This is the single most important data point for welded fabrication — it is checked on every order
• UNS Grade Verification: Every MTC is cross-checked against the specified UNS designation — S31600 for 316, S31603 for 316L — to eliminate any cross-standard grade ambiguity
• MTC 3.1 Documentation: Full chemical composition and mechanical properties traceable to heat number, provided with every shipment. No "typical" or "nominal" values — only actual heat analysis data
• PMI Testing Coordination: Positive Material Identification using XRF confirms Cr, Ni, and Mo content — screening for grade mix-ups and providing independent verification of the defining alloy elements
• Third-Party Inspection: Pre-shipment inspection with SGS, Bureau Veritas, TÜV, or Intertek — MTC review, PMI, dimensional check, and surface condition verification against your purchase order
• Surface Inspection: Visual inspection for surface defects and finish conformity before dispatch — surface condition directly affects pitting initiation in chloride service
• Technical Grade Recommendation: Our engineering team reviews your chloride concentration, temperature, and service conditions to confirm that 316/316L is appropriate — or recommend an alternative if it is not

11. Frequently Asked Questions

Q1: What is 316 stainless steel?
316 is an austenitic chromium-nickel-molybdenum stainless steel — UNS S31600, EN 1.4401. Its nominal composition is approximately 17% chromium, 11% nickel, and 2.1% molybdenum. The molybdenum addition distinguishes it from 304 and provides measurably improved resistance to chloride-induced pitting and crevice corrosion. 316 is non-magnetic in the annealed condition, cannot be hardened by heat treatment, and is the most commonly specified grade where chlorides are present at levels that would cause 304 to pit.

Q2: What makes 316 stainless steel more corrosion resistant than 304?
The 2–3% molybdenum addition in 316. Mo improves chloride pitting resistance through two mechanisms: (1) it incorporates into the passive film as molybdate ions, making the film more resistant to chloride attack; (2) if a pit does initiate, dissolved Mo species adsorb onto the actively dissolving surface inside the pit, slowing dissolution and promoting repassivation. Quantitatively, 316's PREN is approximately 23–28 compared to 304's 18–20 — a roughly 30–40% higher pitting resistance index, driven almost entirely by the 3.3 × %Mo coefficient in the PREN formula.

Q3: What is the difference between 316 and 316L stainless steel?
The only intentional difference is carbon content: 316 allows ≤ 0.08% C; 316L limits to ≤ 0.03% C. Chromium, nickel, and molybdenum ranges are identical — their base corrosion resistance is the same. The lower carbon in 316L prevents sensitization (chromium carbide precipitation at grain boundaries) during welding, maintaining intergranular corrosion resistance in the HAZ without requiring post-weld solution annealing. This makes 316L the standard choice for welded fabrication in corrosive service. In the unwelded condition, 316 and 316L perform equivalently.

Q4: Is 316 stainless steel magnetic?
In the fully annealed condition, 316 is non-magnetic — its austenitic (FCC) crystal structure is paramagnetic. However, cold working (bending, forming, drawing, machining) transforms some austenite to strain-induced martensite, which is ferromagnetic. A cold-worked 316 component — such as a deep-drawn vessel, a threaded fastener, or a heavily formed pipe bend — may be slightly magnetic. This is normal and does not indicate a material defect. If non-magnetic behavior is required after fabrication, specify solution annealing after all forming operations.

Q5: Can 316 stainless steel rust?
Yes. 316 is corrosion resistant, not corrosion proof. Under conditions that exceed its corrosion resistance — high chloride concentration, elevated temperature, stagnant seawater, or exposure to strong reducing acids — 316 will corrode. The most common corrosion modes for 316 are pitting corrosion, crevice corrosion (particularly under gaskets, deposits, or in stagnant zones), and chloride stress corrosion cracking (above ~60°C under tensile stress). The molybdenum addition raises the threshold at which corrosion initiates compared to 304 — it does not eliminate the threshold entirely.

Q6: Is 316 stainless steel suitable for seawater?
It depends on the form of seawater exposure. 316 is generally suitable for coastal atmospheric exposure and intermittent splash/spray, provided surfaces are regularly washed by rain or cleaned. 316 is not recommended for continuous seawater immersion, particularly in warm (>25°C) or stagnant conditions, where pitting and crevice corrosion are likely. For seawater immersion, duplex 2205 (PREN 33–36) is the minimum practical starting point; super duplex 2507 (PREN >40) or 6Mo super austenitics are the standard for reliable immersed service. Do not assume "marine grade" covers all seawater scenarios.

Q7: Why is 316L preferred for welded applications?
During welding, the heat-affected zone adjacent to the weld reaches 425–870°C — the sensitization range where carbon and chromium combine to form chromium carbides (Cr₂₃C₆) at grain boundaries. These precipitates deplete the surrounding metal of chromium, destroying local corrosion resistance and creating sites for intergranular corrosion (IGC). 316L's ≤ 0.03% carbon limit ensures there is insufficient carbon available to form a damaging network of carbides during typical welding thermal cycles. The result: 316L weld joints retain their corrosion resistance without requiring post-weld solution annealing — an expensive, energy-intensive process that is often physically impossible for large fabrications.

Q8: What is the PREN value of 316 stainless steel?
316 typically has a PREN (Pitting Resistance Equivalent Number) of 23–28, calculated as %Cr + 3.3 × %Mo + 16 × %N from its nominal composition (~17% Cr, ~2.1% Mo, ~0.05% N). This compares to 304's PREN of ~18–20. The difference of ~5–8 points is driven almost entirely by the molybdenum coefficient. For comparison: duplex 2205 has PREN ~33–36, and super duplex 2507 exceeds PREN 40. The actual PREN for a specific heat should be calculated from the MTC's reported chemistry, not the grade's nominal midpoint — a heat at 2.0% Mo has measurably lower pitting resistance than one at 2.8% Mo.

Q9: What industries use 316 stainless steel?
Major industries include: marine and coastal (deck hardware, architectural cladding, fittings), pharmaceutical (WFI tanks, process piping, cleanroom equipment), chemical processing (storage tanks, reactor vessels, heat exchangers), food and beverage (brine and salt-containing product equipment, dairy processing), oil and gas (topsides piping, instrument tubing, valve components), pulp and paper (digesters, bleaching equipment), and architectural (coastal building facades, street furniture). The common thread: all involve chlorides or corrosive process fluids where 304 would be at risk of localized corrosion.

Q10: What documents should I request when purchasing 316/316L stainless steel?
Request as a minimum: (1) EN 10204 3.1 MTC with full chemical composition — verify Mo content (2.0–3.0%) and carbon (≤ 0.03% for 316L/dual certified); (2) Product standard compliance statement (e.g., ASTM A240 for plate/sheet); (3) UNS number confirmation — S31600 or S31603; (4) For welded fabrication — IGC testing per ASTM A262 Practice E if sensitization resistance must be demonstrated; (5) For critical chloride service — ASTM G48 CPT/CCT testing data; (6) PMI report if supplementary grade verification is required. Review all documents before the material ships — grade errors identified after delivery are exponentially more expensive to correct.

Related Reading

• [What Is Stainless Steel? Types, Properties, Manufacturing and Uses]
• [304 and 304L Stainless Steel: Properties, Composition and Uses]
• [304 vs 316 Stainless Steel: Differences and Applications]
• [Does Stainless Steel Rust? Causes, Corrosion Types and Prevention]
• [L, H and Dual-Certified Stainless Steel Grades Explained]
• [PREN Explained: Formula, Grade Comparison and Selection Limits]
• [Stainless Steel Grades Chart: AISI, UNS, EN and JIS Cross-Reference Guide]

Technical References

• ASTM A240 — Standard Specification for Chromium and Chromium-Nickel Stainless Steel Plate, Sheet, and Strip
• ASTM A312 — Standard Specification for Seamless and Welded Austenitic Stainless Steel Pipe
• ASTM A276 — Standard Specification for Stainless Steel Bars and Shapes
• ASTM A262 — Standard Practices for Detecting Susceptibility to Intergranular Attack
• ASTM G48 — Standard Test Methods for Pitting and Crevice Corrosion Resistance
• Outokumpu Stainless Steel Handbook — Grade 316/316L datasheets and corrosion curves
• Nickel Institute — Stainless Steel for Corrosion Engineers: Pitting and Crevice Corrosion
• British Stainless Steel Association (BSSA) — Grade 316/316L Selection and Application Guide