Technical knowledge
Duplex 2205 flanges to ASTM A182 F51: what the grade actually delivers
Duplex 2205 flanges to ASTM A182 F51 and UNS S32205: composition, strength advantage over 316L, temperature limits, sigma phase risk and what to state on the purchase order.
Why the two phase structure matters
Duplex stainless steel contains roughly equal amounts of ferrite and austenite. The ferrite phase provides strength and chloride stress corrosion cracking resistance, while the austenite phase provides toughness and ductility. This combination is what allows a 2205 flange to be both thinner and more corrosion resistant than its 316L equivalent.
Composition and mechanical properties
| Item | Value | Significance |
|---|---|---|
| UNS number | S31803 or S32205 | S32205 is the tighter, preferred range |
| Chromium | 21.0 - 23.0 % | Passivity, pitting resistance |
| Nickel | 4.5 - 6.5 % | Austenite balance |
| Molybdenum | 2.5 - 3.5 % | Pitting and crevice |
| Nitrogen | 0.08 - 0.20 % | Strength, PREN, weld restoration |
| Yield strength | About 450 MPa | Roughly double 316L |
| Typical PREN | 35 - 38 | Well above 316L |
| Recommended metal temperature | About minus 50 to 300 C | Upper limit set by phase stability |
S31803 or S32205: specify the tighter range
The two UNS numbers cover similar alloys but S32205 has narrower chromium, molybdenum and nitrogen ranges that keep the composition inside the window where pitting resistance is reliable. Most modern project specifications call for S32205 and require the pitting resistance equivalent number to be calculated and reported for each heat.
Heat treatment and inspection requirements
- Solution anneal and quench. Typically around 1020 to 1100 C followed by water quench. Slow cooling through the 600 to 900 C range precipitates sigma phase.
- Ferrite measurement. Where specified, verify the ferrite content of the forging and of the weld metal.
- Impact testing. Often required at minus 46 C for offshore and subsea service.
- Weld procedure. Use a nitrogen bearing over alloyed filler such as ER2209, control interpass temperature, and avoid excessive heat input.
Questions about this topic
Can duplex 2205 replace 316L directly?
Usually yes, and often with a thinner wall because of the higher allowable stress. Confirm the pressure design, the temperature limits and the welding procedure with the piping engineer before substituting.
What is the maximum temperature for duplex 2205?
Most codes limit the use of duplex 2205 to about 300 C metal temperature. Above that range the risk of phase transformation increases and the allowable stresses are no longer established.
Is duplex magnetic?
Yes. The ferrite phase makes duplex strongly magnetic, unlike austenitic stainless steel. This can be a quick sorting check on site but should never be used as the only identification method.
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
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