Short answer: Duplex stainless steels combine a ferrite and austenite microstructure for high strength and good chloride resistance. Standard duplex 2205 is the workhorse grade; super duplex 2507 extends corrosion resistance further; lean duplex (2304, 2101) targets cost-sensitive structural and piping applications where 304/316 is under-strength or overpriced.
This guide is written for stainless steel buyers, sourcing teams, engineers and product manufacturers. The purpose is not to declare one universal winner, but to turn a broad material question into a specification that a mill or service center can quote, process and inspect consistently.
Quick Comparison
| Option | Key point | Typical use or decision |
|---|---|---|
| Lean duplex 2304 / 2101 | Lower nickel cost, yield ~400–450 MPa | Structural sections, storage tanks, general piping |
| Standard duplex 2205 (S31803 / S32205) | Benchmark combination of strength + chloride resistance | Offshore platforms, heat exchangers, desalination piping |
| Super duplex 2507 (S32750) | Higher PREN (~42), seawater-capable when clean | Subsea components, chloride-rich process vessels |
The table is a starting point. Actual performance depends on the governing standard, delivered condition, dimensions, surface finish, fabrication route and service environment. Commercial names should never replace a complete purchase specification.
What Buyers Should Evaluate
- Confirm whether the supplier delivers S31803 or S32205 when requesting 2205; S32205 has tighter nitrogen and chromium floors.
- Specify weld filler (e.g. 2209) and a post-weld ferrite-austenite balance target where service life depends on it.
- Include PREN (Pitting Resistance Equivalent Number) requirements when chloride content is known.
For production orders, share the end use rather than requesting a grade or finish in isolation. A supplier can then review corrosion exposure, forming severity, welding, visual requirements and packing before material is cut. This early review is usually less expensive than correcting a rejected shipment or unstable production trial.
Common Purchasing Mistakes
- Ordering “duplex” without distinguishing lean, standard or super duplex
- Applying 304/316 welding parameters and then failing impact or corrosion testing
- Ignoring ferrite content requirements for cryogenic or sour service
These mistakes are avoidable when drawings, approved samples, inspection methods and certificate requirements are agreed before production. For visual products, retain a signed master sample. For functional dimensions, define where and how measurements will be taken.
Recommended RFQ Wording
State UNS number or ASTM grade, product form (plate/sheet/bar/tube/piping), dimensions, condition (solution annealed and quenched), corrosion acceptance test (if any), ferrite range, third-party inspection and EN 10204 certificate type. For duplex orders, verify exactly what an EN 10204 3.1 mill test certificate covers before sign-off.
Also include order quantity, acceptable quantity variation, destination, required delivery date and whether partial shipments are allowed. If a requirement is critical, make it measurable and place it on the purchase order rather than only in an email conversation.
How Still Steel Supports the Project
Still Steel supplies stainless steel coil, strip and sheet and provides slitting, cut-to-length, brushing, polishing and protective-film services. We can compare available mill material with your drawing, prepare trial quantities and preserve heat-number traceability through service-center processing.
Send the grade, dimensions, annual volume and application to vip@still-steel.com, or discuss the requirement on WhatsApp.
Frequently Asked Questions
Is 2205 duplex stronger than 316L?
Yes. Annealed 2205 typically has a 0.2% yield strength of 450 MPa, roughly twice that of 316L, allowing thinner, lighter structures at equivalent load.
Can duplex grades replace 316 directly in piping?
Not always. Duplex requires controlled welding and a ferrite-austenite balance check. Discuss joint design and PWHT with a fabricator before switching.
What is a lean duplex?
Lean duplex (e.g. 2304, 2101) reduces nickel content to lower cost while offering yield strength well above 304/316 and moderate chloride resistance.
Technical References
Reference documents support general selection and fabrication principles. The final material decision must follow the applicable contract, standard, regulation and engineering review for the specific product.