Technical Resources
duplex 2507 DIN1.4410 UNS S32750 Resistance to Corrosion
Applied Forms : Plate & Coil &Pipes
Materials involved : Duplex Steel 2507 DIN1.4410
2507 Duplex Steel is highly resistant to uniform corrosion by organic acids such as formic and acetic acid. It is also highly resistant to inorganic acids, especially if they contain chlorides. Alloy 2507 is highly resistant to carbide-related intergranular corrosion. Due to the ferritic portion of the duplex structure of the alloy it is very resistant to stress corrosion cracking in warm chloride containing environments. Through additions of chromium, molybdenum and nitrogen localized corrosion such as pitting and crevice attack are improved. Alloy 2507 has excellent localized pitting resistance.
The high chromium and molybdenum content of SAF 2507 makes it extremely resistant to uniform corrosion by organic acids like formic acid and acetic acid. SAF 2507 also provides excellent resistance to inorganic acids, especially those containing chlorides.
In dilute sulfuric acid contaminated with chloride ions, SAF 2507 has better corrosion resistance than 904L, which is a highly alloyed austenitic stainless steel pipe grade specially designed to resist pure sulfuric acid.
Stainless steel tube of type 316L (2.5%Mo) cannot be used in hydrochloric acid due to the risk of localized and uniform corrosion. However, SAF 2507 can be used in dilute hydrochloric acid. Pitting need not be a risk in the zone below the borderline in this figure, but crevices must be avoided.
Intergranural Corrosion
SAF 2507’s low carbon content greatly lowers the risk of carbide precipitation at the grain boundaries during heat treatment; therefore, the alloy is highly resistant to carbide-related intergranular corrosion.
Stress Corrosion Cracking
The duplex structure of SAF 2507 provides excellent resistance to chloride stress corrosion cracking (SCC). Because of its higher alloy content, SAF 2507 is superior to 2205 in corrosion resistance and strength. SAF 2507 is especially useful in offshore oil and gas applications and in wells with either naturally high brine levels or where brine has been injected to enhance recovery.
Pitting Corrosion
Different testing methods can be used to establish the pitting resistance of steels in chloride-containing solutions. The data above were measured by an electrochemical technique based on ASTM G 61. The critical pitting temperatures (CPT) of several high-performance steel in a 1M sodium chloride solution were determined. The results illustrate the excellent resistance of SAF 2507 to pitting corrosion. The normal data spread for each grade is indicated by the dark gray portion of the bar.
Crevice Corrosion
The presence of crevices, almost unavoidable in practical constructions and operations, makes stainless steel pipe more susceptable to corrosion in chloride enviroments. SAF 2507 is highly resistant to crevice corrosion. The critical crevice corrosion temperatures of SAF 2507 and several other high-performance stainless steel are shown above.
Duplex stainless steels are a class of stainless steels with a dual-phase microstructure of austenite and ferrite, combining high strength with excellent corrosion resistance. Compared with conventional austenitic grades (such as 304 and 316L), duplex steels perform significantly better in petrochemical, offshore, and desalination industries.
Among them, 2205 (UNS S32205) is the most widely used standard duplex stainless steel, while 2507 (UNS S32750), as a super duplex, demonstrates superior performance in extreme environments.
Comparison: Duplex 2205 vs. Super Duplex 2507
2.1 Chemical Composition (wt%)
| Grade | Cr | Ni | Mo | N | Others |
| 2205 | 21–23% | 4.5–6.5% | 2.5–3.5% | 0.14–0.20% | Mn ≤2% |
| 2507 | 24–26% | 6–8% | 3–5% | 0.24–0.32% | Cu ≤0.5% |
Key Difference: 2507 has higher Cr, Mo, Ni, and N → better corrosion resistance and strength compared to 2205.
2.2 PREN (Pitting Resistance Equivalent Number)
- 2205: ~35–37
- 2507: ~40–45
Conclusion: 2507 is a “super duplex” grade, offering greater reliability in seawater and chloride-rich environments.
2.3 Mechanical Properties
| Property | 2205 | 2507 |
| Yield Strength | ≥450 MPa | ≥550 MPa |
| Tensile Strength | ≥620 MPa | ≥800 MPa |
| Elongation | 25–30% | 15–25% |
Conclusion: 2507 offers higher strength, but slightly lower ductility.
2.4 Corrosion Resistance
- 2205: Good resistance to pitting and crevice corrosion, suitable for medium-to-high chloride environments.
- 2507: Can withstand long-term service in natural seawater (Cl⁻ ~19,000 ppm) with minimal risk of pitting or stress corrosion cracking (SCC).
2.5 Applications
- 2205: Petrochemical equipment, heat exchangers, desalination (freshwater side), chemical tanks, auxiliary piping on offshore platforms, pulp and paper bleaching equipment.
- 2507: Subsea pipelines and wellhead equipment, desalination brine/reject systems, marine heat exchangers and condensers, high-pressure seawater injection systems.
2.6 Cost & Fabrication
- 2205: Lower cost, better workability and weldability.
- 2507: Higher cost, more difficult to fabricate and weld; requires strict heat input control and matching filler metals.
2.7 Overall Comparison
- Strength: 2507 > 2205
- Corrosion Resistance: 2507 > 2205 (especially in seawater/high chloride environments)
- Toughness/Ductility: 2205 > 2507
- Cost & Fabrication: 2205 is more economical and easier to process
- Typical Use:
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2205 → Medium-to-high corrosion environments (refining, pulp & paper, desalination
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Why Develop 2507 (Super Duplex)?
Limitations of 2205:
- PREN ~35–37 → still at risk of pitting in long-term exposure to natural seawater.
- Increased risk of SCC in high-chloride environments at >50 °C.
Advantages of 2507:
- PREN ~40–45 → reliable in natural seawater and high-temperature, high-chloride service.
- Higher strength (yield ≥550 MPa) → suitable for subsea manifolds and high-pressure injection systems.
In other words: 2205 is the general-purpose grade, while 2507 is the safeguard grade for extreme conditions.
The Evolution of the Duplex Stainless Steel Family
Driven by diverse application needs, duplex stainless steels have expanded into different categories:
| Category | Representative Grades | PREN | Features | Applications |
| Lean Duplex | 2304 (UNS S32304) | 22–25 | Low-cost, stronger than 304/316, moderate corrosion resistance | Architecture, freshwater, mild environments |
| Standard Duplex | 2205 (UNS S32205) | 35–37 | Balanced strength & corrosion resistance; most widely used | Chemicals, petrochemicals, desalination freshwater side |
| Super Duplex | 2507 (UNS S32750), Zeron 100 | 40–45 | Excellent seawater resistance, higher strength | Offshore oil & gas, seawater heat exchangers, brine systems |
| Hyper Duplex | S32707, S33207 | 48–52 | Extreme corrosion resistance + ultra-high strength, higher cost | Deepwater (>2000 m) oil & gas, harshest conditions |
Conclusion
- 2205: General-purpose, suitable for most applications requiring both strength and corrosion resistance.
- 2507 / Zeron 100: Preferred choice for extreme seawater and chloride environments.
- 2304: Low-cost option, suitable for mild corrosion.
- Hyper Duplex: Next-generation materials, designed for ultra-harsh deepwater and high-chloride service.
