Comparison of 304, 316/L, and Duplex 2205 Stainless Steels

In stainless steel selection, engineers often need to choose between 304, 316/L, and Duplex 2205. These three stainless steels differ in chemical composition, mechanical properties, corrosion resistance, machinability, weldability, and applications. If the differences are not well understood, it may lead to overdesign, premature failure, or cost imbalance. The following structured comparison uses a quick reference table y practical engineering case studies to illustrate their performance in various environments.

Quick Comparison Table (Key Points Summary)

Note: Values are typical/representative and may vary with standards and product specifications.

Dimensión	304	316/L	Duplex 2205 (S32205)
Tipo	Austenítico	Austenitic (with Mo), L = Low Carbon	Duplex (≈50%γ + 50%α)
Marine Conditions	Not recommended, prone to tea-staining/pitting	Usable (still risky in splash zone)	Best – resistant to pitting/crevice/SCC
Typical Composition (wt%)	18Cr-8Ni	17Cr-10/12Ni-2/2.5Mo	22Cr-5/6Ni-3Mo-0.15/0.20N
PREN (Pitting Resistance)	~18–20	~24–26	~35–37
0.2% Yield Strength	~205 MPa	~205 MPa	≥450 MPa
Maquinabilidad	Easy	Slightly harder than 304	Significantly harder, tool wear high
Soldabilidad	Excelente	Excellent (L grade better)	Good but requires strict heat input control
Aplicaciones típicas	Indoor hardware, dry environments	Marine, swimming pool, coastal use	Offshore, desalination, chemical, severe coastal railings
Cost (relative)	★	★★	★★★ (higher strength allows thickness reduction)

What type of stainless steel?

304: General-purpose austenitic stainless steel, good formability and polishability, essentially non-magnetic.
316/L: Austenitic stainless steel with added Mo for better chloride corrosion resistance; “L” means low carbon, improving resistance to intergranular corrosion after welding.
Dúplex 2205: Duplex (γ+α), combines austenitic toughness with ferritic strength and SCC resistance; exhibits partial magnetism.

Case A (Storage Tanks and Pipelines)

Chemical plant process water tank: 304 is sufficient and cost-effective.

Brine or weak acid storage: 304 failed from pitting within 1 year → replaced with 316L, lifespan extended 3–5×.

Offshore platform injection water lines: 316L failed from chloride SCC in 1–2 years → upgraded to 2205, safe service >10 years.

How good is it in marine conditions?

In seawater, salt spray, or high-chloride environments, pitting resistance and SCC resistance are critical. The differences among these steels are significant in marine service.

Case B (Offshore Oil & Gas Production)

304: acceptable for indoor fittings in living quarters, but not for seawater or chloride-bearing fluids.
316L: reliable in compressed air systems with dry gas, but prone to pitting if condensation and salt are present.
2205: widely used in subsea manifolds and seawater-cooled heat exchangers, resisting pitting and SCC effectively; >15 years service without failures.

What does it contain? (Chemical Composition)

304: ~18% Cr, 8% Ni.
316/L: ~17% Cr, 10–12% Ni, 2–2.5% Mo (Mo improves pitting resistance).
2205: ~22% Cr, 5–6% Ni, 3% Mo, 0.15–0.20% N (N stabilizes austenite, increases strength and corrosion resistance).

PREN: 304 ≈ 18–20; 316/L ≈ 24–26; 2205 ≈ 35–37 (higher = stronger pitting resistance).

Case C (Desalination Systems)

304: reliable for freshwater transport but fails severely on the brine side of RO systems.
316L: widely used for freshwater piping in desalination plants, but on high-chloride brine side corrodes through within 1–2 years.
2205: used in high-chloride brine discharge lines, normal service life >10 years, far lower maintenance costs than 316L.

What are the mechanical properties?

304 / 316L: Yield ~205 MPa, Tensile ~515 MPa, Elongation ~40%.
2205: Yield ≥450 MPa, Tensile ≥620 MPa, Elongation ~25–30%.
Thermal Expansion: lower for 2205 → better dimensional stability in large structures.
Thermal Conductivity: slightly higher for 2205 → beneficial for heat exchangers.

Case D (High-Pressure Vessel)
In a fertilizer plant, a vessel originally designed with 316L (20 mm thick) was redesigned using 2205. Due to ≥450 MPa yield strength, wall thickness was reduced to 12–14 mm, lowering welding volume and weight, making transport and installation more economical.

Differences to machine and cut?

304: Excellent machinability, general tooling parameters suffice.
316/L: Tougher, slightly more prone to tool galling; slower speeds, higher feed, and sufficient coolant improve tool life.
2205: High strength + work hardening → much more difficult to machine; carbide tooling, lower speeds, higher feeds, and abundant coolant required.

Post-cut finishing: For near-sea or poolside use, deburring + pickling/passivation (nitric or citric acid systems) + electropolishing strongly reduces pitting risk.

Case E (Pump and Valve Manufacturing)

304: Pump bodies machined smoothly, high efficiency.
316L: Valve bodies wore tools ~15–20% faster than 304, still acceptable.
2205: High-pressure injection pump housings caused rapid tool wear; required carbide tools and abundant coolant, machining cost +30%. But final parts met severe strength/corrosion demands.

Soldabilidad

304 / 316L: Excellent weldability; 316L (low carbon) better intergranular corrosion resistance; common fillers: ER308L, ER309L, ER316L.
2205: Weldable, but requires strict control of heat input and interpass temperature to avoid σ and χ phases and phase imbalance; filler ER2209 is typically used.

Best practice: medium-low heat input, interpass ≤150 °C, post-weld cleaning + pickling/passivation, and verification of ferrite content in critical welds.

Case F (Refinery Piping)

304 & 316L: familiar to welders, mature procedures.
2205: In refinery hydroprocessing cooling water lines, poor heat input control led to σ phase in HAZ → premature failures. Corrective use of ER2209 filler + low-heat input resolved issue, reliable service achieved.

Costo

Material price: 304 < 316/L < 2205.
Total cost of ownership (TCO): 2205 offsets higher unit cost with reduced wall thickness and much lower maintenance frequency.
Fabrication cost: 2205 is harder to cut/form and weld, requiring more skilled labor and tooling.

Case H (Offshore Platform Piping)

316L piping: lower initial cost, but injection lines failed within 2 years from corrosion → major overhaul required, costly downtime.
2205 piping: initial cost +25–30%, but service life >10 years, greatly reduced shutdowns, overall lifecycle cost much lower.

Limitations of Duplex 2205

Difficult machining: lower cutting speeds, higher tool wear, greater springback in forming.
Narrow welding window: strict heat input and interpass temperature control; matching filler (ER2209) and post-weld treatment required.
Availability: fewer options for stock sizes and fittings compared to 304/316 (longer lead times, higher sensitivity to price).
Mid-temperature embrittlement: long-term exposure at 300–500 °C (esp. ~475 °C) causes embrittlement.
Low-temperature toughness: better than ferritics but not as good as austenitics (caution in cryogenic service).

Case I (Fertilizer Plant Retrofit)
Equipment originally planned to upgrade from 316L to 2205, but local contractors lacked duplex welding expertise → schedule delays. Solution: engage experienced duplex welding team and conduct ferrite content checks on welds, ensuring long-term reliability.

Summary (Chemical & Oil Industry Context)

304 → Suitable for non-critical components, indoor or mild environments.
316L → Widely used in chemical industry, suitable for moderate corrosion environments (weak acids/alkalis, limited seawater cooling).
2205 → Preferred for seawater, chloride, H₂S service; especially in offshore oil & gas, refinery cooling systems, and desalination plants, offering greatly extended life and reduced downtime.