Surface Treatments
Certifications
- ISO 9001 - 2015 Certified
- PED 2014/68/EC
- NACE MR0175 / ISO 15156-2
- NORSOK M-650 Qualified
- API 6A Certified
- DFAR
- MERKBLATT AD 2000 W2/W7/W10
Super Duplex 2507 vs Zeron 100, S32750 vs S32760
Super Duplex 2507 (UNS S32750) and Zeron 100 (UNS S32760) are both nominally 25Cr-7Ni-3.5Mo super duplex grades with PREN above 41. They look interchangeable on a one-line summary, but the chemistry differs in two intentional ways. Zeron 100 carries 0.5 to 1.0 percent copper and 0.5 to 1.0 percent tungsten, both alloyed on purpose. Super Duplex 2507 carries copper at 0.50 percent maximum (residual, not intentional) and contains no intentional tungsten. The result is two alloys that pass the same NORSOK M-630 acceptance criteria but are not freely substitutable when the project specification names a forging grade. F53 means S32750. F55 means S32760. A purchase order written for one cannot be filled with the other unless the customer formally permits it in writing.
Side-by-Side Comparison
| Property | Super Duplex 2507 (S32750) | Zeron 100 (S32760) |
|---|---|---|
| UNS designation | S32750 | S32760 |
| Werkstoff (EN) | 1.4410 (X2CrNiMoN25-7-4) | 1.4501 (X2CrNiMoCuWN25-7-4) |
| Forging spec (ASTM A182) | F53 | F55 |
| Chromium | 24.0 to 26.0 | 24.0 to 26.0 |
| Nickel | 6.0 to 8.0 | 6.0 to 8.0 |
| Molybdenum | 3.0 to 5.0 | 3.0 to 4.0 |
| Nitrogen | 0.24 to 0.32 | 0.20 to 0.30 |
| Copper | 0.50 max (residual, not intentional) | 0.5 to 1.0 percent intentional |
| Tungsten | (none specified, residual only) | 0.5 to 1.0 percent intentional |
| PREN (Cr + 3.3 Mo + 16 N) | 41 to 43 | 41 to 43 |
| PREW (Cr + 3.3 [Mo + 0.5 W] + 16 N) | (not applicable, no W) | 41 to 45 |
| Yield strength minimum | 550 MPa | 550 MPa |
| Tensile strength minimum | 795 MPa | 750 MPa |
| Elongation minimum | 15 percent | 25 percent |
| Sour service hardness limit | 28 HRC max | 28 HRC max |
| Cost index (S32750 = 1.00) | 1.00 | 1.05 to 1.15 |
| Typical service envelope | Seawater to 50 deg C, sour to NACE MR0175 | Seawater to 50 deg C, sour to NACE MR0175, mild reducing acids |
Read the formula reference at PREN explained. The W coefficient for tungsten-bearing super duplex is 0.5, which is why Zeron 100 reports a slightly higher PREW than its PREN.
When to Choose Super Duplex 2507 (S32750)
- Project specification names F53 on the bill of materials, datasheet, or piping class. F55 is a different grade and substitution requires written permission.
- NORSOK M-630 MDS D45 / D47 lines that do not invoke the W bearing variant.
- Standard offshore seawater piping, splash zone bolting, FGD scrubber internals where chloride is the dominant pitting driver.
- API 6A / 17D wellhead and subsea hardware where the order references S32750 explicitly.
- Cost-sensitive scope where the modest premium for tungsten alloying offers no measurable corrosion benefit.
- Heat treatment is straightforward: solution anneal 1040 to 1100 deg C, water quench. Same window as Zeron 100, but without the W content the carbide and intermetallic precipitation kinetics are slightly slower in the 700 to 950 deg C danger band.
When to Choose Zeron 100 (S32760)
- Project specification names F55. This is non-negotiable. F53 cannot fill an F55 PO.
- NORSOK M-630 MDS D55 / D57 which call out tungsten-bearing super duplex.
- Mildly reducing service. The intentional copper improves resistance to dilute sulfuric and phosphoric acid streams that occasionally appear in upstream produced-water and hydrocracker auxiliaries. Effect is real but moderate (one or two CPT degrees Celsius).
- Higher CPT margin in service close to the alloy's chloride limit. The W contribution to PREW gives a small (typically 1 to 2 deg C) edge in critical pitting temperature.
- End-user technical specifications (Shell DEP, Total GS, Equinor TR) that explicitly require tungsten-bearing super duplex for traceability and weldability consistency on a fleet of platforms already standardized on F55.
Substitution Rules
F53 and F55 are NOT interchangeable. The substitution rule is one-directional and requires customer written approval in every case.
- F55 supplied against an F53 PO: often technically acceptable (Zeron 100 meets every property minimum of S32750) but commercial premium and re-stamping is required. Customer approval still mandatory.
- F53 supplied against an F55 PO: not acceptable without rework. F55 owes its specification existence to W and Cu intentional alloying; replacing with F53 deletes both. NORSOK D55 lines reject the substitution.
- Mixing in a single weldment: permissible if WPS qualifies the dissimilar joint per ASME IX with super duplex filler ER2594 or ER2553. Ferrite count and PWHT acceptance criteria apply to the combined weld metal.
- Bolt-flange combinations: common to see F53 stud bolts in F55 flanges or vice versa. Both meet the same NACE hardness ceiling and the same NORSOK M-630 ferrite window. No galvanic concern in the same alloy family.
Welding and Heat Treatment
Both alloys weld with super duplex consumables to AWS A5.9: ER2594 (overmatching, slightly higher PREN) or ER2553 (matching). Heat input window 0.5 to 2.5 kJ per millimetre. Interpass temperature below 150 deg C. GTAW root pass with argon plus 2 to 5 percent nitrogen shielding. Post-weld ferrite count 35 to 65 percent per ASTM E562. Solution anneal at 1040 to 1100 deg C followed by water quench restores the 50:50 austenite-ferrite balance and dissolves any sigma or chi phase that may have formed in the HAZ.
Related References
- UNS S32750 reference
- ASTM A182 F53 forgings
- NORSOK M-630 super duplex
- Super Duplex 2507 seawater applications
- Super Duplex 2507 sour service
- Super Duplex vs Duplex
- Super Duplex 2507 vs Ferralium 255
FAQ
Are F53 and F55 interchangeable on a project?
No. They are different UNS grades (S32750 and S32760 respectively) with different intentional chemistry. A purchase order naming F53 cannot be filled with F55 without the customer's written approval, and the reverse substitution is not normally accepted because F55 specifically calls for tungsten and copper alloying that F53 does not provide.
Which alloy is more expensive, 2507 or Zeron 100?
Zeron 100 typically prices 5 to 15 percent higher than Super Duplex 2507. The premium reflects the tungsten and intentional copper additions and the smaller producer base. Spot pricing varies with the nickel and molybdenum LME indices.
What is the PREN difference between 2507 and Zeron 100?
By the standard PREN formula (Cr + 3.3 Mo + 16 N), both alloys land in the 41 to 43 band with overlap. Zeron 100 also reports a PREW (Cr + 3.3 [Mo + 0.5 W] + 16 N) that picks up the tungsten contribution and lands in the 41 to 45 band. The CPT difference in lab ASTM G48 testing is typically 1 to 2 deg C in favour of Zeron 100, which is within run-to-run scatter.
When does 2507 fail and Zeron 100 survive?
In dilute reducing acid streams (sulfuric or phosphoric in the 5 to 30 percent concentration band, ambient temperature) Zeron 100's intentional copper improves general corrosion resistance compared with 2507. The effect is moderate, not transformational. In pure chloride pitting service at the alloy's CPT limit, the W contribution gives Zeron 100 a small margin. In standard seawater splash-zone applications below 50 deg C both alloys perform identically.
Can I weld F53 to F55 in the same joint?
Yes, with a qualified WPS. Use super duplex filler ER2594 (overmatching) or ER2553 per AWS A5.9. Heat input window 0.5 to 2.5 kJ per millimetre, interpass below 150 deg C, GTAW root with N2-bearing shield gas. Post-weld ferrite count 35 to 65 percent per ASTM E562 applies to the weld metal. NORSOK M-601 acceptance criteria apply.
Does NORSOK M-630 distinguish between 2507 and Zeron 100?
Yes. NORSOK M-630 issues separate Material Data Sheets. D45 / D47 cover the no-tungsten S32750 family. D55 / D57 cover the W-bearing S32760 family. Project material requisitions cite the MDS number, which sets the PO grade unambiguously.
Is Zeron 100 always the better choice if budget allows?
No. Choice is driven by project specification, not by a generic ranking. F53 and F55 are different grades with different acceptance criteria. Defaulting to F55 because it costs more is not a metallurgical decision and creates traceability problems on multi-vendor projects. Match the BOM exactly.
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