Hyper Duplex Steel S32707
S32707 (UNS S32707) is a hyper duplex stainless steel. The alloy has a dual-phase microstructure, which means roughly equal parts austenite and ferrite. This gives it both high strength and strong resistance to stress corrosion cracking. The defining characteristic is a PREN (Pitting Resistance Equivalent Number) above 49, which is higher than any standard commercial duplex or super duplex grade. S32707 is used specifically in high-chloride, high-temperature environments such as deep-sea subsea systems, offshore chemical injection lines, and aggressive seawater handling equipment. These S32707 seamless pipes are supplied in accordance with ASTM A790 for demanding applications across oil and gas, petrochemical, and offshore sectors.
1. Chemical Composition
S32707 Seamless Pipe chemical composition, including its proportion, is listed in the table given below.
| Grade | Carbon (C) |
Manganese (Mn) |
Phosphorus (P) |
Sulphur (S) |
Silicon (Si) |
Chromium (Cr) |
Nickel (Ni) |
Molybdenum (Mo) |
Nitrogen (N) |
Copper (Cu) |
| Hyper Duplex S32707 |
0.030 max | 1.50 max | 0.035 max | 0.010 max | 0.50 max | 26.0 – 29.0 | 6.0 – 8.0 | 4.0 – 5.0 | 0.30 – 0.50 | 1.00 max |
2. Mechanical Properties
Typical mechanical properties for S32707 seamless pipe in the solution-annealed and water-quenched condition per ASTM A790.
| Property | Condition | Tensile Strength Min | Yield Strength (0.2% Proof) Min | Elongation Min | Hardness Max | PREN |
| Value | Solution annealed / Water quenched | 1000 MPa (145 ksi) | 690 MPa (100 ksi) | 15% | 310 HBW | ≥ 49 |
3. Equivalent Grade
The international designation equivalent to S32707 seamless pipe is listed in the table below.
| Grade | UNS | GB | JIS | DIN/EN (W.Nr.) | GOST | Trade Name |
| S32707 | S32707 | -- | -- | 1.4658 | -- | SAF 2707 HD (Sandvik) |
S32707 / 1.4658 is the same alloy. SAF 2707 HD is Sandvik's proprietary trade designation. No current JIS, GB, or GOST equivalent exists for this grade.
3. Key Technical Advantages
S32707 has several specific performance characteristics that set it apart from lower duplex grades.
- PREN Above 49, Higher Than Any Standard Duplex Grade: PREN (Cr + 3.3Mo + 16N) measures pitting resistance. S32707 (PREN ≥49) outperforms S32750 (≈42–43), resisting seawater pitting above 60°C due to higher nitrogen and molybdenum levels.
- Yield Strength Close to 700 MPa, Roughly Twice That of 316L: With a 690 MPa proof strength, S32707 pipes can use thinner walls at the same pressure, cutting subsea pipeline weight and material cost per metre without reducing structural safety.
- Resistance to Stress Corrosion Cracking (SCC) in Hot Chloride Environments: Austenitic grades such as 316L are susceptible to SCC at temperatures above approx 60°C in chloride containing media. The duplex microstructure of S32707 reduces this risk considerably and the high nitrogen content stabilises the austenite phase, maintaining this property up to 250°C.
- Improved Crevice Corrosion Resistance Versus Super Duplex: In stagnant seawater and tight gaps, crevice corrosion often damages S32750. S32707 better resists this by having a higher CCT, making it reliable for clamps, flanges, and heat exchangers with unavoidable crevices.
- Retained Toughness at Low Temperatures Down to -50°C: S32707 retains toughness down to -50°C, making it a reliable choice for most LNG and subsea pipelines in cold deepwater or Arctic-type offshore fields where avoidance of low temperature embrittlement is a critical requirement.
4. Common Manufacturing Standards
S32707 seamless pipes are produced and tested against the following standards.
- ASTM A790: Seamless/welded ferritic-austenitic SS pipe; main S32707 product spec
- ASME SA-790: ASME BPVC equivalent of A790; pressure vessel & piping use
- ASTM A999: General requirements for alloy/SS pipe; tolerances, finish, tests
- ASTM A923: Test methods for intermetallic phases in duplex SS; anneal verification
- EN 10216-5: European spec for seamless pressure tubes; covers duplex grade 1.4658
- NACE MR0175 / ISO 15156: Materials for H₂S oil & gas service; hardness & heat treatment limits
- DNV-ST-F101: Offshore subsea pipeline standard; subsea line pipe qualification
5. Primary Applications
S32707 seamless pipe is selected when service conditions exceed the capability of standard super duplex grades.
- Offshore oil & gas: High-pressure methanol and inhibitor injection lines in deep-water fields where cold seawater and high chlorides rule out standard super duplex grades.
- Seawater Handling Systems: Offshore platforms and FPSO vessels in which untreated seawater is circulated at high temperatures in piping systems with inevitable crevice geometries.
- Petrochemical Processing: Heat exchanger tubes and process pipelines handling hot concentrated chloride streams, such as in chlor-alkali, bleach production, or hydrochloric acid recovery units.
- Desalination Plants: Reverse osmosis and multi-stage flash desalination units operating with high-salinity concentrated brine streams, particularly in high-temperature regions where seawater temperatures exceed 35°C.
- LNG and Gas Processing: Pipes used in very cold parts of LNG and gas plants, where the metal must stay strong in low temperatures and resist chloride damage.