Technical knowledge
Duplex 2205 vs super duplex 2507: choosing the right duplex grade
Composition, PREN, strength and cost comparison of duplex 2205 against super duplex 2507, with decision guidance for subsea, desalination, seawater injection and chemical duty.
Chemistry and resulting microstructure
Both alloys contain roughly equal austenite and ferrite, giving strength above that of either phase alone plus immunity to chloride stress corrosion cracking. The difference is alloy level: 2205 has 22 % chromium, 3 % molybdenum and about 0.17 % nitrogen, while 2507 has 25 % chromium, 4 % molybdenum and about 0.27 % nitrogen. That higher alloy content is what drives both the strength and the pitting resistance - and also the risk of sigma phase if heat treatment is wrong.
Side by side data
| Property | Duplex 2205 (S32205) | Super duplex 2507 (S32750) |
|---|---|---|
| UNS | S32205 | S32750 |
| Chromium | 22 - 23 % | 24 - 26 % |
| Molybdenum | 3.0 - 3.5 % | 3.0 - 4.0 % |
| Nitrogen | 0.14 - 0.20 % | 0.24 - 0.32 % |
| Typical PREN | 35 - 38 | Above 40 |
| Tensile strength min | 620 MPa | 800 MPa |
| Yield strength min | 450 MPa | 550 MPa |
| Max hardness | 293 HB / 31 HRC | 310 HB / 32 HRC |
| Continuous temperature limit | About 300 °C | About 300 °C |
| Typical cost index | 1.0 | 1.3 - 1.5 |
When super duplex earns its premium
- Subsea flowlines, manifolds and risers where inspection and repair costs are extreme.
- Seawater injection and produced water systems with high chloride and elevated temperature.
- Reverse osmosis high pressure piping where 800 MPa tensile allows thinner, lighter pipe.
- High velocity lines with erosion corrosion risk, because the higher strength and PREN act together.
- Sour service where NACE MR0175 listing at a controlled maximum hardness of 32 HRC is required.
When duplex 2205 remains the smarter buy
There is no benefit to boosting PREN if the environment does not need it. For ambient seawater, structural applications, storage tanks, chemical tankers, most pulp and paper duties and general process piping, 2205 delivers the same doubling of yield strength over 316L and better chloride SCC resistance at lower cost and with easier fabrication.
Fabrication caution that applies to both grades
Warning Sigma phase precipitation between roughly 550 °C and 1000 °C destroys toughness in duplex alloys. Always specify solution annealed and water quenched material, control interpass temperature below 150 °C during welding, and never slow cool through that range.
Use the correct over-alloyed filler - ER2209 for 2205 and ER2594 for 2507 - to restore the phase balance and pitting resistance of the weld metal, and verify with ferrite measurement plus hardness testing recorded on the certificate.
Questions about this topic
Is duplex stainless steel magnetic?
Yes. The ferritic phase makes both grades magnetically responsive, unlike fully austenitic stainless steel. This is normal and not an indicator of poor quality.
What is the maximum continuous service temperature?
About 300 °C for both grades, because long-term exposure above that promotes embrittling phases and because codes restrict high temperature use of duplex materials.
Can I weld 2507 using 2209 filler?
No. Using the lower alloyed filler drops the weld metal PREN below that of the parent 2507, so the weld becomes the weakest link. Always use ER2594 or an equivalent over-alloyed rod.
How do I check that duplex material is free of sigma phase?
Request solution annealing with water quench plus a ferrite count, impact testing at the design minimum temperature and hardness verification. Charpy impact testing is the most sensitive practical indicator of embrittlement.
Are these grades acceptable under NACE MR0175?
Yes, both are listed under defined conditions of hardness and heat treatment. S32205 has restrictions relating to temperature and chloride content, while S32750 typically has a 32 HRC maximum in the solution annealed condition.
Questions about our products
What products does Hangbo Alloy supply?
Four product families, all available in nickel-based alloys, titanium, duplex and special stainless steel: flanges, butt weld pipe fittings, elbows, and seamless tube and pipe. Flanges cover weld neck, long weld neck, slip-on, blind, socket weld, threaded and lap joint patterns. Fittings and elbows cover concentric and eccentric reducers, equal and reducing tees, caps, stub ends, and 45°, 90° and 180° returns in both long and short radius, plus 3D and 5D bends for piggable lines. Seamless tube and pipe is supplied cold drawn or hot finished from 6 mm to 630 mm outside diameter.
Which alloy grades are available for these products?
More than 90 grades are published in our grade library. The most requested are Inconel 625, 718, 600 and X-750, Hastelloy C-276, C-22 and B-2, Monel 400 and K-500, Incoloy 800H, 825 and 925, duplex 2205 and super duplex 2507, 316L, 904L and 254SMO stainless steel, and titanium Grade 2 and Grade 5. Nickel-based grades can also be supplied with VIM plus ESR double melting where cleanliness or fatigue life is critical.
What sizes, wall thicknesses and pressure classes can you supply?
Flanges run from NPS ½ to NPS 24 to ASME B16.5 and from NPS 26 to NPS 60 to ASME B16.47 Series A or B, in pressure classes 150 through 2500. Butt weld fittings and elbows run from NPS ½ to NPS 48 (DN 15 to DN 1200) in wall thickness Schedule 5S through XXS. Seamless tube and pipe covers 6 mm to 630 mm outside diameter, in random lengths of about 5 to 7 metres or fixed lengths up to 12 metres. Non-standard and intermediate sizes are quoted on request.
Which material and dimensional standards do you work to?
Forged flanges to ASTM B564, B381 and A182 with dimensions to ASME B16.5 and ASME B16.47. Butt weld fittings and elbows to ASTM B366 and A403 with dimensions to ASME B16.9 and MSS SP-43. Seamless tube and pipe to ASTM B444, B423, B622, B163, B167, B861, A312, A213 and A790. Marking follows MSS SP-25 and the applicable product standard. If your project is governed by EN, DIN, JIS or a company specification, send the document and we will confirm equivalence before quoting.
Is there a minimum order quantity?
There is no minimum for standard sizes and grades held in stock, and prototypes, spares and small trial batches are accepted. Made-to-order melts and special forgings carry a minimum weight that depends on the alloy and the route, typically from about 500 kg for special grades.
What inspection and certification is issued with the goods?
Every shipment carries an EN 10204 3.1 mill test certificate quoting the actual chemical and mechanical results for the specific heat lot, together with dimensional records and heat treatment data where applicable. Testing is carried out in house by optical emission spectrometry, tensile, impact and hardness testing, plus ultrasonic and eddy current examination, with hydrostatic pressure and intergranular corrosion testing to ASTM G28 or A262 Practice E where the specification requires it. Third party inspection by SGS or another recognised agency can be arranged, and their report is issued alongside the shipment.
What are typical lead times?
Standard stock items ship within days. Common production grades such as Inconel 625 or duplex 2205 are typically a few weeks. Special chemistries, larger forgings and items that require third party inspection take longer and are quoted individually against the requirement.
How are the products packed for export?
Flanges and fittings receive a rust preventive coating, are individually wrapped and are packed in plywood cases secured with steel banding. Tube ends are capped and bundles are strapped. Packing lists quote heat numbers so every case can be cross-checked against the mill certificate on arrival. We quote EXW, FOB, CFR, CIF and DAP, and mixed-alloy orders can be consolidated into one shipment with a single documentation package.
How do I request a quotation or a sample?
Send the grade or UNS number, the dimensions including schedule or wall thickness, the governing material and dimensional standards, quantity, any heat treatment or NDT scope and the certificate type you need; a drawing is ideal for special flanges and fittings. Email demi@nickel-alloy.com or message us on WhatsApp +86 15618279078 and we normally issue a formal quotation within 24 hours on working days. Samples and previous test reports can be arranged before the first order.
Talk to an engineer
Share your duty conditions and we will shortlist candidate alloys within one working day.