Zeron 100 and SAF 2507 are the two dominant super duplex stainless steels in offshore, sour-service, and seawater bolting. Both share the 25Cr-7Ni-3.5Mo backbone and both qualify for NORSOK M-650 and NACE MR0175. The compositional differences are small but they shift application preference: Zeron 100 (UNS S32760, ASTM A182 F55) adds tungsten (0.5-1.0%) and copper (0.5-1.0%); SAF 2507 (UNS S32750, F53) does not. This page compares the two grades head to head so a procurement engineer can select the right alloy for a given service envelope.
Composition - PREN - mechanical properties - corrosion envelope - sour-service qualification - application overlap - when to specify F55 over F53
| Element | Zeron 100 (UNS S32760 / F55) | SAF 2507 (UNS S32750 / F53) |
|---|---|---|
| Chromium (Cr) | 24.0 - 26.0 | 24.0 - 26.0 |
| Nickel (Ni) | 6.0 - 8.0 | 6.0 - 8.0 |
| Molybdenum (Mo) | 3.0 - 4.0 | 3.0 - 5.0 |
| Nitrogen (N) | 0.20 - 0.30 | 0.24 - 0.32 |
| Copper (Cu) | 0.50 - 1.00 | 0.50 max (not added intentionally) |
| Tungsten (W) | 0.50 - 1.00 | not added |
| Carbon (C) | 0.030 max | 0.030 max |
| Iron (Fe) | balance | balance |
PREN (Pitting Resistance Equivalent Number) is calculated from Cr + 3.3 Mo + 16 N. By that formula both Zeron 100 and SAF 2507 land at PREN approximately 40-42. Zeron 100 carries an additional metric called PREW, which substitutes 3.3(Mo + 0.5W) and lifts the value to PREW approximately 41-45 due to the tungsten addition. In practical terms, both alloys clear the PREN >= 40 threshold required for super duplex classification. The PREW differential is mostly material-spec marketing; chloride-pitting performance per ASTM G48 Method E (CPT >= 50 degC) is comparable for both grades.
| Property | Zeron 100 / F55 (SA) | SAF 2507 / F53 (SA) | Test |
|---|---|---|---|
| 0.2% Yield (Rp0.2) | ≥ 550 MPa | ≥ 550 MPa | ASTM E8 tensile |
| Ultimate Tensile (Rm) | ≥ 750 MPa | ≥ 795 MPa | ASTM E8 tensile |
| Elongation | ≥ 25% | ≥ 15-25% | ASTM E8, 4D gauge |
| Hardness (sour cap) | ≤ 28 HRC | ≤ 28 HRC | NACE MR0175 |
| Charpy V-notch (RT) | ≥ 45 J avg | ≥ 60 J avg | ASTM E23, 3 specimens |
| Charpy V-notch (-46°C) | ≥ 45 J avg (FLT path) | ≥ 45 J avg | ASTM E23, 3 specimens |
| Ferrite content | 35-55% | 35-55% | ASTM E562 point count |
| CPT | ≥ 50°C | ≥ 50°C | ASTM G48 Method E |
Zeron 100 has documented advantages in two specific environments: (1) chloride pitting at elevated temperatures above 80 degC where the tungsten addition narrows the gap toward 6Mo super-austenitics, (2) mildly reducing acid service (dilute HCl, dilute H2SO4) where the copper addition extends working range by ~5-10 degC vs SAF 2507. For seawater, FPSO topside, subsea manifolds, and standard NORSOK M-650 sour service the two alloys are interchangeable. SAF 2507 has a longer published track record in pulp-and-paper bleach plants and chemical-process valves due to its earlier mill availability (Sandvik introduced SAF 2507 in 1985; Rolled Alloys introduced Zeron 100 in 1990).
| Spec | Zeron 100 | SAF 2507 |
|---|---|---|
| ASTM A182 forging grade | F55 | F53 |
| ASTM A479 bar grade | S32760 | S32750 |
| ASTM A276 bar grade | S32760 | S32750 |
| ASTM A790 / A815 pipe | UNS S32760 | UNS S32750 |
| ASTM A1082 fastener grade | S32760 | S32750 |
| EN designation | 1.4501 (Werkstoff) | 1.4410 (Werkstoff) |
| NORSOK M-650 Edition 4 | qualified (MDS-055) | qualified (MDS-055) |
| NACE MR0175 / ISO 15156-3 | qualified at ≤ 28 HRC | qualified at ≤ 28 HRC |
| API 6A PSL3 | qualified | qualified |
| NORSOK M-630 MDS | MDS-055 | MDS-055 |
| Service | Preferred grade | Reason |
|---|---|---|
| Standard NORSOK / NACE sour-service flange bolting | either (engineer's choice or mill availability) | both qualified; performance equivalent |
| FPSO topside saltwater + sulphide | Zeron 100 (F55) | W + Cu lift pitting margin slightly at elevated T |
| Subsea manifold + jumper flange | either | both qualified; spec usually drives choice |
| API 6A wellhead bonnet + master valve | either | both qualified; track record similar |
| Pulp & paper ClO2 bleach plant valve | SAF 2507 (F53) | longer published track record; user familiarity |
| HCl or dilute H2SO4 process valve | Zeron 100 (F55) | Cu addition extends working range in reducing acids |
| Desalination RO membrane vessel flange | either | both clear CPT ≥ 50°C threshold |
| Geothermal wellhead (H2S + CO2) | either | both qualified per NACE MR0175 |
TorqBolt manufactures both Zeron 100 (F55) and SAF 2507 (F53) fasteners and forgings. Send the spec (grade + component + size + supply state + supplementary requirements + quantity + destination port) to info@torqbolt.com or +91-22-66157017 / WhatsApp. Cross-reference: Zeron 100 FG cornerstone, ASTM A182 F55 spec, Zeron 100 forgings hub, Zeron 100 stud bolts.
