Introduction
As a manufacturer and global supplier of duplex and super duplex stainless steel pipes, fittings, and flanges, we regularly supply UNS S32750 (Super Duplex Stainless Steel 2507) materials for offshore, oil & gas, chemical processing, and desalination projects.
Due to its exceptional mechanical strength and corrosion resistance, UNS S32750 is widely specified in critical environments where standard austenitic or duplex grades are no longer sufficient.
This article provides a technical overview of UNS S32750, including material properties, corrosion performance, applicable standards, and typical product forms used in pressure piping systems.
What Is UNS S32750?
UNS S32750, commonly known as Super Duplex Stainless Steel 2507, is a high-alloy duplex stainless steel with a balanced austenitic–ferritic microstructure.
Compared with standard duplex grades such as UNS S32205 (2205), S32750 contains higher levels of chromium, molybdenum, and nitrogen, resulting in significantly improved corrosion resistance and mechanical strength.
UNS S32750 is standardized under multiple international specifications, including:
- ASTM / ASME
- EN 1.4410
- ISO and NORSOK standards
Chemical Composition of UNS S32750
Typical chemical composition of UNS S32750 (%):
| Element | Content (%) |
|---|---|
| Carbon (C) | ≤ 0.03 |
| Chromium (Cr) | 24.0 – 26.0 |
| Nickel (Ni) | 6.0 – 8.0 |
| Molybdenum (Mo) | 3.0 – 5.0 |
| Nitrogen (N) | 0.24 – 0.32 |
| Manganese (Mn) | ≤ 1.20 |
| Silicon (Si) | ≤ 0.80 |
| Phosphorus (P) | ≤ 0.035 |
| Sulfur (S) | ≤ 0.020 |
The high Cr–Mo–N alloy system is the key factor behind the excellent corrosion resistance of Super Duplex 2507.
Mechanical Properties
UNS S32750 offers nearly twice the yield strength of conventional austenitic stainless steels.
| Property | Typical Value |
|---|---|
| Yield Strength (0.2% Offset) | ≥ 550 MPa |
| Tensile Strength | ≥ 795 MPa |
| Elongation | ≥ 15% |
| Impact Toughness | Excellent at sub-zero temperatures |
The high strength allows for reduced wall thickness, resulting in weight savings and improved cost efficiency in large piping systems.
Corrosion Resistance & PREN Value
One of the most important performance indicators for duplex stainless steels is the PREN (Pitting Resistance Equivalent Number).
For UNS S32750:
PREN ≥ 40
This high PREN value provides excellent resistance to:
- Pitting corrosion
- Crevice corrosion
- Stress corrosion cracking (SCC)
- Chloride-containing environments
UNS S32750 performs particularly well in seawater, offshore, and desalination systems, where chloride-induced corrosion is a major concern.
Applicable Standards for UNS S32750 Products
Depending on product form, UNS S32750 is supplied under the following standards:
Pipe Fittings
- ASTM A815 UNS S32750
- ASME B16.9 (Elbows, Tees, Reducers)
Pipes & Tubes
- ASTM A790 UNS S32750
- EN 10216-5 / EN 10297-2
Flanges
- ASTM A182 F53
- ASME B16.5 / ASME B16.47
These standards ensure dimensional accuracy, mechanical integrity, and full traceability for pressure applications.
UNS S32750 Product Applications
UNS S32750 is commonly used in the following industries:
- Offshore oil & gas platforms
- Subsea and seawater piping systems
- Desalination and water treatment plants
- Chemical and petrochemical processing
- Heat exchangers and pressure vessels
In many projects, Super Duplex 2507 is selected when UNS S32205 (2205) does not provide sufficient corrosion resistance or strength.
Manufacturing & Quality Control Considerations
From practical manufacturing experience, UNS S32750 requires strict process control, including:
- Solution heat treatment with rapid quenching
- Ferrite content control (typically 40–60%)
- PMI (Positive Material Identification)
- Mechanical and corrosion-related testing
- Full EN 10204 3.1 certification
Improper heat treatment or uncontrolled welding procedures may negatively affect corrosion resistance and mechanical performance.
Selection Tips & Common Mistakes
Based on project experience, the following points should be considered when selecting UNS S32750:
- UNS S32750 is not always necessary; for moderate environments, UNS S32205 may be sufficient
- Welding procedures must be strictly qualified to avoid phase imbalance
- Over-specification may increase project cost without added benefit
Correct material selection should be based on corrosion environment, pressure, temperature, and lifecycle cost, not material grade alone.
UNS S32750 (Super Duplex Stainless Steel 2507) offers an outstanding combination of high mechanical strength, excellent corrosion resistance, and long service life.
When supplied as pipes, fittings, or flanges in accordance with international standards, UNS S32750 is an ideal solution for highly corrosive and demanding pressure applications, particularly in offshore and marine environments.