Duplex Steel Pipes & Tubes
Giriraj Impex stocks, supplies and exports duplex pipes and tubes in duplex 2205 – UNS S31803 and S32205 – to ASTM A790 for pipe, ASTM A789 for tubing and ASTM A928 for electric fusion welded pipe. We supply duplex pipes and tubes from approved mills, seamless and welded, solution annealed and pickled, with mill test certificates giving the composition, PREN and mechanical properties.
Duplex 2205 pipe is chosen where 316L would be at risk from chloride stress corrosion cracking or pitting, and where its higher strength allows thinner walls – seawater and brackish water lines, offshore process piping, desalination, chemical plants, and pulp and paper bleach plants.
Specifications
| Item | Details |
|---|---|
| Standards | ASTM A790 / ASME SA790 (seamless and welded pipe); ASTM A789 / ASME SA789 (seamless and welded tubing); ASTM A928 (EFW pipe) |
| Grades | UNS S31803, S32205; dual certified S31803/S32205 |
| Pipe dimensions | ASME B36.19M and B36.10M; schedules 5S, 10S, 40S, 80S and heavier |
| Tube dimensions | OD and wall in mm, inches or BWG |
| Condition | Solution annealed and rapidly cooled; pickled and passivated |
| Ends | Plain or bevelled to ASME B16.25 |
| Optional tests | Ferrite content, impact test, ASTM A923 (intermetallic phases), ASTM G48 (pitting) |
| Documents | Mill test certificate (MTC) with composition and PREN; third-party inspection on request |
Chemical composition
Duplex pipe is usually dual certified to S31803 and S32205; S32205 has tighter, higher minimums for chromium, molybdenum and nitrogen. The super duplex grades are shown for comparison – see super duplex pipes and tubes.
| UNS | Grade | C | Mn | P | S | Si | Cr | Ni | Mo | N | Other elements |
|---|---|---|---|---|---|---|---|---|---|---|---|
| S31803 | 2205 | 0.030 | 2.00 | 0.030 | 0.020 | 1.00 | 21.0–23.0 | 4.5–6.5 | 2.5–3.5 | 0.08–0.20 | – |
| S32205 | 2205 | 0.030 | 2.00 | 0.030 | 0.020 | 1.00 | 22.0–23.0 | 4.5–6.5 | 3.0–3.5 | 0.14–0.20 | – |
| S32750 | 2507 | 0.030 | 1.20 | 0.035 | 0.020 | 0.80 | 24.0–26.0 | 6.0–8.0 | 3.0–5.0 | 0.24–0.32 | Cu 0.50 |
| S32760 | Zeron 100 type | 0.030 | 1.00 | 0.030 | 0.010 | 1.00 | 24.0–26.0 | 6.0–8.0 | 3.0–4.0 | 0.20–0.30 | Cu 0.50–1.00, W 0.50–1.00 |
S32760 also requires a minimum PREN of 40. Footnotes as given in the standards.
Mechanical properties
Duplex pipe has roughly twice the minimum yield strength of 316L, which is the basis for thinner walls and lighter piping in many designs.
| UNS | Tensile strength, MPa (ksi) | Yield strength, MPa (ksi) | Elongation in 50 mm, % |
|---|---|---|---|
| S31803 | 620 (90) | 450 (65) | 25 |
| S32205 | 655 (95) | 485 (70) | 25 |
| S32750 | 800 (116) | 550 (80) | 15 |
| S32760 | 750 (109) | 550 (80) | 25 |
Hardness limits as given in the standard.
Pipe or tube – A790 or A789?
ASTM A790 covers duplex pipe ordered by nominal size and schedule, for process and utility piping. ASTM A789 covers duplex tubing ordered by outside diameter and wall, for heat exchangers, condensers, hydraulic and instrument lines – a common route for upgrading heat-exchanger bundles that suffer chloride cracking in 316L. ASTM A928 covers electric fusion welded duplex pipe made from plate, used in larger diameters for seawater intake, cooling water and desalination lines.
Quality checks for duplex
The useful properties of duplex depend on a balanced structure of ferrite and austenite and on the absence of brittle intermetallic phases. Mills achieve this through controlled solution annealing and rapid cooling. Buyers in oil and gas, chemical and desalination projects often add tests to the order: ferrite measurement, Charpy impact tests at low temperature, ASTM A923 testing for detrimental intermetallic phases, and ASTM G48 pitting tests at a specified temperature. The PREN is calculated from the actual composition on the mill test certificate. We check each delivery against the certificate and order before dispatch, and third-party inspection is available on request. Pipes can be supplied to NACE MR0175 / ISO 15156 on request.
Fabrication notes
Duplex pipe is welded with procedures that control heat input and interpass temperature, using over-alloyed filler metal (more nickel) to keep the weld metal's phase balance; the welding procedure should be qualified with ferrite and impact testing where the project requires it. Hot bending and other hot work need re-annealing to restore the structure. Like stainless steel, duplex must be kept free of iron contamination and pickled after welding.
Ordering
Please give the standard (A790, A789 or A928), UNS grade, size and schedule or OD and wall, length, seamless or welded, quantity, and any supplementary tests or inspection.
Duplex pipe compared with 316L and super duplex
For many chloride-bearing services, duplex 2205 sits between 316L and super duplex. Compared with 316L it offers a higher PREN, far better resistance to chloride stress corrosion cracking and about twice the yield strength. Compared with super duplex it costs less, is easier to fabricate and is adequate for brackish water, many process streams and moderate seawater duties; for warm seawater and firewater lines, super duplex is the usual step up. The choice is normally made in the project materials selection report, which considers temperature, chloride level, oxygen content and design life.
Applications and related products
Duplex pipes and tubes are used offshore for process and produced water lines, onshore in chemical plants and refineries, in desalination and seawater cooling systems, pulp and paper bleaching, and heat exchangers with chloride-bearing cooling water. They are installed with duplex steel pipe fittings, duplex flanges and duplex fasteners. We also supply duplex sheets and plates and duplex round bars. Grade guidance is on the duplex and super duplex steel page, and other seamless materials on the seamless pipes and tubes page.
Frequently Asked Questions
ASTM A790 (ASME SA790) covers seamless and welded ferritic/austenitic (duplex) stainless steel pipe. Tubing is covered by ASTM A789 and electric fusion welded pipe by ASTM A928.
Both are duplex 2205. S32205 has higher minimum chromium, molybdenum and nitrogen, giving more consistent corrosion resistance and, under A790, a higher minimum yield strength. Pipe is often dual certified.
Duplex resists chloride stress corrosion cracking and pitting much better than 316L and has about twice its yield strength, allowing thinner walls. It is used in seawater, brine and hot chloride service.
Common additions are ferrite content measurement, Charpy impact tests, ASTM A923 testing for intermetallic phases and ASTM G48 pitting tests. These are specified on the order.
Duplex is normally limited to service below about 250–300 °C because prolonged exposure at higher temperature can form brittle phases. The design code gives the exact limit.
Yes. Duplex contains about half ferrite, so it is magnetic. This is expected and is not a sign of incorrect material.
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