What Is a Seamless Super Duplex Steel S32750 Tube?
Seamless Super Duplex Steel S32750 Tube — widely known as Super Duplex 2507 — is a 25% chromium, 7% nickel, 4% molybdenum super duplex (ferritic/austenitic) stainless steel tube produced to ASTM A789 from a solid billet with no weld seam, giving uniform structure and reliable pressure integrity.
The high chromium, molybdenum and nitrogen content puts UNS S32750 in the super duplex class, with a PREN of about 40 or higher (Cr + 3.3×Mo + 16×N, calculated from the heat analysis per A789 Table 1 footnote). It withstands hot seawater, brines and acidic chloride media that pit or crack 22Cr duplex and 316L, while its 550 MPa minimum yield strength is roughly double that of austenitic tube — allowing thinner walls, smaller exchangers and higher allowable pressures.
Key Features and Advantages
Seamless UNS S32750 tube combines the corrosion performance of nickel alloys with the strength and economy of a duplex structure, which is why it is specified for the most aggressive chloride service:
Outstanding Pitting and Crevice Resistance: PREN of about 40 or higher (Cr + 3.3×Mo + 16×N, calculated from the heat analysis per ASTM A789 footnote) — designed for seawater, brine and acidic chloride service where 316L and 22Cr duplex fail.
High Yield Strength: 550 MPa minimum yield, roughly twice 316L, permits significant wall-thickness reduction.
Chloride Stress Corrosion Cracking Resistance: the 50/50 duplex structure is inherently resistant to chloride SCC in hot brines.
Excellent General Corrosion Resistance: strong performance in organic acids, inorganic acids and chloride-bearing process streams.
Good Weldability with Established Practice: matched 25Cr fillers and proven procedures; no post-weld heat treatment in most applications.
Product Specifications and Data
To provide a comprehensive overview of this high-performance material, here are the detailed technical specifications and performance data for UNS S32750 seamless tube.
Equivalent Grade
| UNS | Common grade name | EN material number | EN steel name | JIS grade | GB/T grade |
|---|---|---|---|---|---|
| S32750 | 2507 | 1.4410 | X2CrNiMoN25-7-4 | SUS327L1 | 022Cr25Ni7Mo4N |
Grade correspondence does not make ASTM, ASME, EN, JIS and GB delivery requirements interchangeable. Confirm chemistry, heat treatment, mechanical properties, dimensions, testing and certification against the purchase specification. Approximate or unconfirmed correspondences retain their qualification. See the grade designation index.
Chemical Composition
The 25Cr-7Ni-4Mo-N chemistry is what gives UNS S32750 tube its super-duplex performance level.
| Grade | C | Cr | Ni | Mo | Mn | P | S | Si | Cu | N | Others |
|---|---|---|---|---|---|---|---|---|---|---|---|
| S32750 | ≤0.030 | 24.0–26.0 | 6.0–8.0 | 3.0–5.0 | ≤1.20 | ≤0.035 | ≤0.020 | ≤0.80 | ≤0.50 | 0.24–0.32 | – |
Chemical requirements per ASTM A789/A789M-24, Table 1. Single values are maximum content unless a range is indicated. For S32750 the PREN (%Cr + 3.3×%Mo + 16×%N) is calculated from the heat analysis per Table 1, footnote; typical heats are about 40 or higher. State any minimum-PREN requirement in the purchase specification.
Typical Mechanical Properties
UNS S32750 delivers roughly double the yield strength of austenitic 304/316 tube while remaining ductile and tough.
| Grade | Yield Strength, min, ksi (MPa) | Tensile Strength, min, ksi (MPa) | Elongation in 2 in. or 50 mm, min, % | Hardness, max, Brinell / Vickers | Hardness, max, Rockwell |
|---|---|---|---|---|---|
| S32750 | ≥80 (550) | ≥116 (800) | ≥15 | ≤300 HBW / 300 HV | ≤32 HRC |
Tensile and hardness requirements per ASTM A789/A789M-24, Table 4, in the solution-annealed condition (1025 – 1125 °C (1880 – 2060 °F)). Mechanical property requirements do not apply to tubes smaller than 1/8 in. (3.2 mm) OD or with walls thinner than 0.015 in. (0.4 mm).
Typical Physical Properties
These physical properties highlight the material’s ability to perform reliably across a range of environments.
| Density | Melting Point | Thermal Expansion | Thermal Conductivity | Modulus of Elasticity | Electrical Resistivity |
|---|---|---|---|---|---|
| 7.8 g/cm³ | 1350 – 1400 °C | 13.0 μm/m.°C (20-100°C) | 14 W/mK (20°C) | 196 GPa | 0.80 x 10-6 Ω·m (20°C) |
Size Tolerance Chart (mm)
Permissible variations for seamless super duplex tube in accordance with ASTM A789/A789M-24, Table 5:
| Outside Diameter, mm | Permissible Variation in OD, mm | Average Wall | Minimum Wall |
|---|---|---|---|
| Up to 12.7, excl | ±0.13 | ±15% | +30% / −0% |
| Over 12.7 to 38.1, excl | ±0.13 | ±10% | +20% / −0% |
| Over 38.1 to 88.9, excl | ±0.25 | ±10% | +20% / −0% |
| Over 88.9 to 139.7, excl | ±0.38 | ±10% | +20% / −0% |
| Over 139.7 to 203.2, incl | ±0.76 | ±10% | +20% / −0% |
Notes (ASTM A789/A789M-24, Table 5): When the ordered wall is 19 mm or over, or the ID is 60% or less of the OD, average wall may vary ±12.5% and minimum wall +25% / −0%. For thin-walled tubes, ovality is limited per 12.2: max and min diameter at any cross section shall deviate no more than twice the OD variation, with the mean diameter still within tolerance.
Length Tolerance
- For tube ordered to a specific cut length: +3 mm / −0 mm (OD 38.1 mm and under) or +5 mm / −0 mm (over 38.1 mm), for cut lengths up to 7.3 m (24 ft).
- For lengths over 7.3 m, the over-tolerance increases by 3 mm for each 10 ft (3 m) or fraction thereof over 24 ft, or 13 mm (1/2 in.), whichever is less.
- Tube is normally supplied in mill lengths or specific cut lengths as agreed in the order.
Disclaimer: Dimensional data above are summarized from ASTM A789/A789M-24, Table 5. The full and most current specification document must always be consulted for official design and procurement purposes.
Common Industrial Applications
The combination of high strength, outstanding chloride stress corrosion cracking resistance and pitting resistance makes UNS S32750 seamless tube a preferred choice for:
Oil and Gas
Subsea umbilicals, downhole and process tubing handling hot, sour, chloride-rich production fluids.
Desalination and Seawater Service
High-pressure brine, evaporator and seawater-cooled exchanger tubing.
Chemical Processing
Heat-exchanger tube for acidic chlorides, fertilizer and petrochemical streams.
Pulp, Paper and Power
Bleach washers, liquor circuits and flue-gas scrubbing where hot chlorides attack 300-series grades.
Frequently Asked Questions
What sizes are available for S32750 (2507) super duplex seamless tube?
The overall range is OD 6–257 mm; WT 0.5–35 mm. Requirements outside this range are reviewed against mill capability on request.
Which specification governs S32750 (2507) super duplex seamless tube?
ASTM A789 / ASME SA789 is the governing specification for S32750 (2507) super duplex seamless tube. The edition in force at order time is stated on the quotation and purchase order; chemistry, mechanical properties, heat treatment, dimensions and testing are reported against the ordered standard and material heat.
What inspection documents are provided?
Each order is documented with a mill test certificate stating heat chemistry and mechanical test results. EN 10204 3.1 certification, hydrostatic testing, eddy-current or ultrasonic inspection and PMI are performed when specified in the purchase order.
Ready to Request a Quotation?
Send the NPS and schedule (or actual OD and wall), quantity, length, end finish and the inspection items you need as acceptance criteria — you will get a written quotation stating the specification and edition, delivery condition, documents included and lead time.
