Super Duplex 2507 (UNS S32750) Pipe Fittings & Flanges
Engineered for critical seawater and subsea applications where standard Duplex 2205 fails. NORSOK M-650 Qualified and NACE MR0175 Compliant solutions.
- Guaranteed PREN > 41: Superior pitting resistance via Nitrogen control.
- Phase Balance: 50/50 Austenite/Ferrite ratio for HISC prevention.
- Manufacturing Logic: Welding heat input controlled (0.2-1.5 kJ/mm) to prevent Sigma phase.
1. Strategic Overview: Why Upgrade to 2507?
When standard Duplex 2205 reaches its corrosion limits in aggressive chloride environments—such as hot seawater or acidic brines—Super Duplex 2507 (UNS S32750) provides the necessary safety margin.
With a Chromium content of 25% and Molybdenum of 4%, S32750 offers exceptional resistance to pitting and crevice corrosion. For EPC managers, choosing 2507 is a strategic decision to minimize lifecycle costs (LCC) by eliminating unplanned maintenance in critical offshore and desalination assets.
2. Metallurgy: S32750 vs S32760
While both are "Super Duplex" with PREN > 40, understanding the nuance is key for specific applications.
| Element | UNS S32750 (2507) | UNS S32760 (Zeron 100) | Metallurgical Impact |
|---|---|---|---|
| Chromium (Cr) | 24.0 – 26.0% | 24.0 – 26.0% | Primary passive film former. |
| Molybdenum (Mo) | 3.0 – 5.0% | 3.0 – 4.0% | Critical for pitting resistance. |
| Nitrogen (N) | 0.24 – 0.32% | 0.20 – 0.30% | Stabilizes austenite; increases strength. |
| Copper (Cu) & Tungsten (W) | - | 0.5–1.0% (Each) | Differentiation: Cu improves resistance in acid reducing environments (e.g. Sulfuric Acid). W enhances localized corrosion resistance. |
Sunhy Inventory Strategy: We frequently stock "Dual Certified" material that meets the chemistry and mechanical requirements of both UNS S32750 and S32760, providing maximum flexibility for your project.
3. Mechanical Strength: The Economics of Down-Gauging
Super Duplex 2507 isn't just about corrosion; it's about strength. With a yield strength ≥ 550 MPa, it is roughly twice as strong as 316L.
| Property | Super Duplex 2507 | Duplex 2205 | 316L Stainless |
|---|---|---|---|
| Yield Strength (0.2%) | ≥ 550 MPa | ≥ 450 MPa | ~ 205 MPa |
| Tensile Strength | ≥ 795 MPa | ≥ 655 MPa | ≥ 515 MPa |
| Hardness (HRC) | Max 32 (NACE) | Max 28 | Max 22 |
ROI Impact: High strength allows engineers to reduce wall thickness (down-gauging) in high-pressure piping. This reduces the total weight of the system and welding consumables costs, offsetting the higher material price of 2507.
4. Corrosion Science: PREN & Critical Temperatures
Sunhy guarantees a PREN (Pitting Resistance Equivalent Number) > 41. This is calculated using the formula:
PREN = %Cr + 3.3(%Mo) + 16(%N)
Critical Temperatures (ASTM G48)
- CPT (Critical Pitting Temperature): > 80°C. Compared to ~60°C for 2205, this 20°C gap is crucial for heat exchangers.
- CCT (Critical Crevice Temperature): ~ 50°C. Essential for flanged connections in seawater.
5. Manufacturing: Controlling the Microstructure
The "Achilles' Heel" of Super Duplex is the precipitation of harmful intermetallic phases (Sigma σ, Chi χ) if processing parameters are incorrect.
Sunhy's Process Controls:
- Solution Annealing: 1040-1120°C followed by rapid water quenching to bypass the "Sigma nose".
- Welding Heat Input: Strictly controlled between 0.2 – 1.5 kJ/mm.
- Too Low: Promotes high ferrite content (low toughness).
- Too High: Promotes Sigma phase (embrittlement).
- Ferrite Test: Verified to be 35-55% (ASTM E562) to ensure resistance to stress corrosion cracking.
6. Industry-Specific Solutions
SWRO Desalination
Problem: Crevice corrosion in high-pressure flanges.
Solution: 2507 Flanges with high nitrogen content to stabilize the passive film in stagnant brine.
Subsea Oil & Gas
Problem: HISC (Hydrogen Induced Stress Cracking) from CP systems.
Solution: Fine-grain forgings with optimized phase balance to disrupt hydrogen diffusion.
Chemical Processing
Problem: Aggressive acids (e.g. Hydrochloric).
Solution: S32760 (Zeron 100) option available for enhanced resistance to reducing acids via Copper addition.
7. Authority & QA (The "Trust" Factor)
Our manufacturing process is transparent and verifiable.
- NORSOK M-650: We provide QTRs demonstrating furnace uniformity (+/- 14°C) and qualified heat treatment procedures.
- NACE MR0175: Hardness guaranteed < 32 HRC for S32750 in sour service.
- NDT Matrix:
- Ultrasonic Testing (UT) to ASTM A388.
- Impact Testing at -46°C (> 45J).
- Corrosion Test G48 Method A (50°C, 24h, No Pitting).
8. FAQ: Engineer to Engineer
Yes. Use an over-alloyed filler metal like ER2594. Do not use 316L filler as it will dilute the weld bead, leading to corrosion failure.
Super Duplex is ferromagnetic due to its ferrite phase. This must be considered for mine-sweeping vessels or sensitive electronics, but does not affect corrosion resistance.
Generally, no, if heat input is controlled. However, for heavy wall thicknesses, solution annealing may be required to dissolve intermetallic phases.
9. Talk to a Sunhyings Engineer
Don't compromise on critical path materials. Leverage our 30+ years of manufacturing data.
Technical Resources
- Super Duplex 2507 Datasheet (PDF)
- NORSOK M-650 QTR Sample
- Guide: Preventing HISC in Subsea Flanges