 |
Super Duplex Stainless Steel S32750 is a duplex alloy composed of approximately equal proportions of austenite and ferrite phases. This balanced microstructure provides a combination of high mechanical strength and exceptional corrosion resistance.
Because of its high chromium, molybdenum, and nitrogen content, S32750 forms a stable passive oxide layer, which significantly improves resistance to chloride-rich environments.
Therefore, it is widely used in marine, offshore, and chemical processing industries where both strength and corrosion resistance are critical.
The equivalents of S32750 is as follows:
Standard | UNS S32750 | DIN/EN 1.4410 | ASTM A240/SA240M |
Super Duplex Stainless Steel S32750 is a high-performance duplex alloy designed for extreme corrosion and high-strength applications.
UNS Number: S32750.
PREN Value: ≥ 40.
Yield Strength: ≥ 550 MPa.
Tensile Strength: 800–1000 MPa.
Main Advantage: Excellent resistance to chloride stress corrosion cracking (SCC), pitting, and crevice corrosion.
Typical Service Environments: Offshore, seawater, chemical processing, desalination systems.
Grade | C≤ | Mn≤ | P≤ | S≤ | Si≤ | Ni | Cr | Mo | N | Cu≤ |
S32750 | 0.03 | 1.20 | 0.035 | 0.02 | 0.80 | 6.0-8.0 | 24.0-26.0 | 3.0-5.0 | 0.24-0.32 | 0.5 |
S32750 provides significantly higher strength compared to standard austenitic stainless steels.
High yield strength enables thinner and lighter structural designs
Excellent fatigue resistance under cyclic loading
Stable performance in both low and high-temperature environments
Because of its duplex microstructure, it maintains strength without sacrificing corrosion resistance.
Grade | Tensile, min, ksi[MPa] | Yield, min, ksi[MPa] | Elongation, %(min) | Hardness, HB（max） |
S32750 | 116 [795] | 80 [550] | 15 | 310 |
Corrosion resistance: The high chromium and molybdenum content in S32750 makes it have strong overall corrosion resistance to organic acids such as formic acid and acetic acid. Compared with 904L, SAF2507 has stronger corrosion resistance.
Heat treatment ability: S32750 should be solution annealed and quenched after hot or cold forming. The temperature of solution annealing should not be lower than 1052°C, and air or water cooling quenching should be performed immediately afterwards.
Welding performance: S32750 has good weldability and can be welded by the following methods: SMAW, GTAW, PAW, FCW, SAW.
Density (Kg/m3) | 7810 |
Magnetic Permeability (20°C) | 33 |
Young’s Modulus (kN/mm2) | 199 |
Specific Electrical Resistance, 20°C (µΩ.m) | 0.8 |
Mean coefficient of thermal expansion, 20-300°C (m/m/oC) | 11.1 x 10-6 |
Specific Heat, 20°C (J/kg.K) | 475 |
Thermal conductivity, 20°C (W/m.K) | 14.2 |
STANDARD | WERKSTOFF NR. | UNS | EN |
Super Duplex S32750 | 1.4410 | S32750 | X2CrNiMoN25-7-4 |
Product | Standard | Show |
Pipe SMLS & Welded | ASTM A790/A928 |  |
Tube SMLS & Welded | ASTM A789 |  |
Sheet / Plate | ASTM A240 |  |
Bar / Rod | ASTM A276/A479 |  |
Forging / Flange | ASTM A182 |  |
BW Fittings | ASTM A815 |  |
S32750 outperforms 2205 (standard duplex) in every critical corrosion and strength metric: 18% higher PREN, 22% higher yield strength, and significantly better resistance to chloride pitting and stress corrosion cracking. Choose S32750 for severe chloride environments (seawater, desalination, offshore); choose 2205 for milder service where cost is the primary driver.
The comparison between Super Duplex S32750 and Duplex 2205 is one of the most common material selection decisions in the oil and gas, marine, and chemical processing industries. The table below provides a side-by-side analysis across all critical dimensions.
S32750 vs 2205: Complete Comparison Table
Dimension | S32750 (Super Duplex) | S32205 / 2205 (Duplex) | Winner |
UNS Designation | S32750 | S32205 | — |
DIN Number | 1.4410 | 1.4462 | — |
Chromium (Cr) | 24.0–26.0% | 21.0–23.0% | S32750 |
Molybdenum (Mo) | 3.0–5.0% | 2.5–3.5% | S32750 |
Nitrogen (N) | 0.24–0.32% | 0.08–0.20% | S32750 |
Nickel (Ni) | 6.0–8.0% | 4.5–6.5% | S32750 |
PREN Value | ≥ 40 (typically 42) | 34–38 (typically 35) | S32750 |
Yield Strength (MPa) | ≥ 550 | ≥ 450 | S32750 |
Tensile Strength (MPa) | ≥ 795 | ≥ 620 | S32750 |
Elongation (%) | ≥ 15 | ≥ 25 | 2205 |
CPT (Critical Pitting Temp) | ~90°C | ~55°C | S32750 |
CSCC Resistance | Excellent | Good | S32750 |
Seawater Service | Excellent (long-term) | Moderate (risk above 25°C) | S32750 |
Weldability | Good (controlled) | Good (easier) | 2205 |
Relative Cost | 1.0 (baseline) | ~0.65–0.75 | 2205 |
Typical Use Case | Severe chloride, subsea, RO desalination | Mild chemical, topside, utility water | — |
When Should You Choose S32750 Over 2205?
Select S32750 when any of the following conditions apply:
1.Service temperature exceeds 25°C in chloride-containing environments
2.Exposure to seawater or brine with chloride concentration above 15,000 ppm
3.Critical components where failure has safety or environmental consequences (subsea pipelines, risers)
4.High-pressure systems (>60 bar) such as reverse osmosis desalination
5.Design life exceeds 20 years in corrosive service
When Is 2205 Sufficient?
Select 2205 when the following conditions apply:
6.Chloride concentration is low or service temperature is below 25°C
7.Component is non-critical (utility water, structural supports, storage tanks)
8.Cost is a primary driver and the corrosion margin is adequate
9.Welding complexity is a concern (2205 is more forgiving for field welding)
S32750 is the preferred material for high-pressure reverse osmosis desalination systems, brine concentrate piping, and heat exchanger tubes. Its PREN value above 40 and 550 MPa yield strength allow it to withstand high-salinity seawater at operating pressures of 60–80 bar without pitting or crevice corrosion failure.
Seawater desalination is one of the fastest-growing applications for super duplex stainless steel. There are two main desalination technologies, and S32750 plays a critical role in both:
1. Reverse Osmosis (RO) Desalination
In RO plants, seawater is forced through semi-permeable membranes at pressures of 60–80 bar to separate fresh water from salt. The high-pressure environment, combined with chloride concentrations of 35,000–40,000 ppm, creates an extremely aggressive corrosion environment. S32750 is used for:
• High-pressure feed pipes: Carrying pressurized seawater to the RO membrane racks. S32750's 550 MPa yield strength handles the pressure; its PREN > 40 resists pitting.
• RO pressure vessel internals: Permeate tubes and concentrate headers that are continuously exposed to concentrated brine.
• Pump casings and impellers: High-pressure booster pumps that circulate seawater through the RO system.
• Energy recovery device components: Isobaric energy recovery systems that handle alternating high-pressure brine and feed water.
2. Multi-Stage Flash (MSF) and Multi-Effect Distillation (MED)
In thermal desalination plants, seawater is heated to 70–110°C and flashed across multiple stages to produce distilled water. At these temperatures, chloride corrosion rates increase dramatically. S32750 is used for:
• Heat exchanger tubes: Where hot seawater vapor condenses on one side and cooler feed water flows on the other. S32750 resists both chloride pitting and stress corrosion cracking at elevated temperatures.
• Flash chamber bracing and cladding: Structural components exposed to hot brine and vapor.
• Ejector and vacuum system piping: Where corrosive gases (CO₂, H₂S) and hot brine coexist.
Desalination Application Summary
Component | Operating Condition | Why S32750? |
RO high-pressure feed pipes | 60–80 bar, 35,000 ppm Cl⁻, ambient temp | PREN > 40 prevents pitting; high yield strength handles pressure |
RO brine discharge pipes | 80 bar, 65,000 ppm Cl⁻, 35°C | Superior crevice corrosion resistance in concentrated brine |
Heat exchanger tubes (MSF/MED) | 70–110°C, seawater + vapor | Resists SCC and pitting at elevated temperature |
Pump casings | High-pressure, abrasive seawater | 550 MPa yield strength + erosion resistance |
Energy recovery device | Alternating pressure, high Cl⁻ | Fatigue resistance + corrosion resistance |
S32750 is used extensively in deep-sea platforms for subsea pipelines, risers, manifolds, and fire-fighting systems. Its combination of PREN > 40, 550 MPa yield strength, and excellent fatigue resistance makes it ideal for components exposed to deep-ocean seawater at depths of 1,000–3,000 meters, where maintenance is extremely costly and failure is not an option.
Deep-sea and offshore oil and gas platforms operate in some of the most corrosive and mechanically demanding environments on Earth. Seawater at depth is cold (2–4°C), oxygen-rich, and exerts enormous hydrostatic pressure. The structural and piping materials must resist corrosion for design lives of 20–30 years with minimal intervention.
Deep-Sea Platform Applications of S32750
•Subsea flowlines and pipelines: Transporting hydrocarbons from wellheads to processing facilities. S32750 pipes resist both internal corrosion from sour gas (H₂S-containing) and external corrosion from seawater. Their high strength allows thinner wall thickness, reducing subsea weight and installation cost.
•Risers and riser joints: Vertical pipes connecting the seafloor to the platform, subject to wave-induced fatigue loading. S32750's excellent fatigue resistance under cyclic loading ensures long-term integrity.
•Subsea manifolds and templates: Structural assemblies that distribute and control flow from multiple wells. S32750 forgings (ASTM A182 F53) provide the required combination of strength, toughness, and corrosion resistance.
•Fire-water systems: Seawater-based fire-fighting piping on offshore platforms. The system must remain functional after years of standby exposure to seawater. S32750 does not pit or corrode even in stagnant seawater.
•Umbilical tubing: Small-diameter tubes that carry hydraulic fluid and chemicals to subsea control systems. S32750's high strength allows small wall thickness while maintaining pressure rating.
•Heat exchangers and coolers: Seawater-cooled heat exchangers on platforms where process fluids must be cooled. S32750 tubes resist both internal process fluid corrosion and external seawater corrosion.
Deep-Sea Platform Application Summary
Component | Service Environment | Key S32750 Advantage | Design Life |
Subsea flowlines | Seawater external, sour gas internal, 1,000–3,000 m depth | PREN > 40 + 550 MPa yield | 25–30 years |
Risers and jumper pipes | Dynamic wave loading, seawater, cyclic stress | Excellent fatigue resistance | 20–25 years |
Subsea manifolds (F53 forgings) | Static seawater, high pressure | Strength + SCC resistance | 25–30 years |
Fire-water piping | Stagnant/seawater, intermittent use | No pitting in stagnant seawater | 20–25 years |
Umbilical tubing | High pressure, chemical injection | High strength, small diameter | 15–20 years |
Seawater heat exchangers | Hot process fluid + cold seawater | Dual-side corrosion resistance | 15–20 years |
Why S32750 Outperforms Alternatives in Deep-Sea Service
Material | PREN | Yield (MPa) | Deep-Sea Performance | Cost Index |
316L (austenitic) | ~24 | 205 | Fails: rapid pitting in seawater | 1.0 |
2205 (duplex) | 34–38 | 450 | Marginal: pitting risk above 25°C | 1.3 |
S32750 (super duplex) | ≥ 40 | 550 | Excellent: long-term seawater resistance | 1.8 |
904L (super austenitic) | ~36 | 220 | Good corrosion but low strength | 2.5 |
Inconel 625 (Ni alloy) | ~50 | 415 | Excellent but very expensive | 5.0+ |
S32750 occupies the optimal cost-performance position: it provides 90%+ of the corrosion resistance of nickel alloys at roughly 35% of the cost, and far exceeds the capabilities of 2205 and 316L in critical seawater service.
Oil and Gas Industry Equipment
Super Duplex S32750 is widely used in oil and gas equipment because it provides excellent resistance to chloride stress corrosion cracking (SCC), high mechanical strength, and strong resistance to pitting and crevice corrosion. These properties make it suitable for harsh offshore and sour service environments where high pressure, seawater exposure, and corrosive gases are present.
Chemical Processing Industry and Pipelines
In chemical processing environments, S32750 is used due to its outstanding resistance to a wide range of corrosive media, including acids, chlorides, and oxidizing agents. Its duplex microstructure provides a strong balance of mechanical strength and corrosion resistance, making it suitable for high-pressure chemical pipelines and aggressive processing systems.
Mechanical Parts (High-Strength, Corrosion-Resistant Components)
Super Duplex S32750 is used for mechanical components because it offers a combination of very high yield strength and excellent corrosion resistance. This allows engineers to design lighter yet stronger parts that can operate reliably in aggressive environments without deformation or premature failure.
Energy Industry: FGD Systems, Industrial Washing Systems, and Absorption Towers
In power generation and energy processing systems, S32750 is selected due to its superior resistance to sulfur-containing gases, acidic condensates, and chloride-rich wash solutions. In flue gas desulfurization (FGD) and absorption towers, it prevents corrosion damage while maintaining long-term mechanical stability under continuous wet and acidic operating conditions.
Super Duplex S32750 is selected when standard stainless steels such as 316L or duplex 2205 are no longer sufficient.
Compared with 316L, it offers significantly higher resistance to chloride corrosion
Compared with 2205, it provides improved strength and higher PREN value
Compared with nickel alloys, it offers a more cost-effective solution while maintaining high performance
Therefore, it is widely used in critical engineering systems where failure is not acceptable.
Q1: What is the difference between S32750 and S32205 (2205)?
Answer: S32750 (super duplex) has higher chromium (25% vs 22%), molybdenum (4% vs 3%), and nitrogen (0.28% vs 0.18%) content than S32205 (2205). This gives S32750 a PREN value above 40 compared to 2205's PREN of 34–38, meaning significantly better pitting and crevice corrosion resistance in chloride environments. S32750 also offers higher yield strength (550 MPa vs 450 MPa). The trade-off is that 2205 is approximately 25–35% less expensive and somewhat easier to weld.
Q2: Can Super Duplex S32750 be used in seawater desalination plants?
Answer: Yes. S32750 is widely used in seawater desalination plants for high-pressure reverse osmosis systems, brine piping, and heat exchanger tubes. Its PREN value above 40 provides excellent resistance to chloride pitting in high-salinity seawater (35,000–40,000 ppm Cl⁻), and its high yield strength of 550 MPa allows it to withstand the high operating pressures of 60–80 bar in RO membrane systems. In MSF and MED thermal desalination plants, S32750 heat exchanger tubes resist both chloride pitting and stress corrosion cracking at operating temperatures of 70–110°C.
Q3: What is the PREN value of S32750?
Answer: The PREN (Pitting Resistance Equivalent Number) of S32750 is greater than 40, calculated as PREN = %Cr + 3.3 × %Mo + 16 × %N. This places it in the super duplex category and ensures superior resistance to chloride-induced pitting and crevice corrosion compared to standard duplex 2205 (PREN 34–38) and austenitic 316L (PREN ~24). A PREN above 40 is the generally accepted threshold for reliable long-term performance in full-strength seawater.
Q4: Is S32750 better than 2205 for offshore platforms?
Answer: Yes, for critical offshore components. S32750's higher PREN (>40 vs 34–38) and higher yield strength (550 MPa vs 450 MPa) make it more suitable for subsea pipelines, risers, manifolds, and fire-fighting systems exposed to high-chloride seawater. For deep-sea platforms at depths of 1,000–3,000 meters where maintenance is extremely costly, S32750's superior corrosion resistance ensures design lives of 25–30 years. However, 2205 may suffice for less critical topside components where service temperature is low and cost is a primary concern.
Q5: What welding methods are suitable for S32750?
Answer: S32750 can be welded using SMAW (Shielded Metal Arc Welding), GTAW (Gas Tungsten Arc Welding), PAW (Plasma Arc Welding), FCW (Flux-Cored Wire), and SAW (Submerged Arc Welding). Heat input should be controlled between 0.5–2.5 kJ/mm, and the interpass temperature should not exceed 150°C to maintain the balanced austenite-ferrite microstructure (approximately 50/50). Post-weld solution annealing at 1052°C minimum is recommended for critical applications to restore full corrosion resistance.
Q6: What temperature range is suitable for S32750?
Answer: S32750 performs well from -50°C to 300°C. Below -50°C, the ferrite phase may become brittle, reducing impact toughness. Above 300°C, there is a risk of 475°C embrittlement and sigma phase precipitation, which can reduce corrosion resistance and toughness. For applications outside this range, consult material engineering guidelines and consider alternative grades such as Inconel 625 for high-temperature service.
Q7: What are the equivalents of S32750?
Answer: S32750 is equivalent to DIN/EN 1.4410, ASTM A182 F53, and EN X2CrNiMoN25-7-4. It is governed by standards including ASTM A240 (plate), A276/A479 (bar), A790/A928 (pipe), A789 (tube), A815 (fittings), and A182 (forgings). The JIS equivalent is SUS 329J4L.
Q8: What is the critical pitting temperature (CPT) of S32750?
Answer: The critical pitting temperature of S32750 in standard ASTM G150 testing is approximately 90°C, compared to about 55°C for 2205. This means S32750 can resist pitting corrosion in chloride solutions at temperatures 35°C higher than 2205, making it suitable for hot seawater and brine service where 2205 would fail.
