Surface Treatments
Certifications
- ISO 9001:2015
- NORSOK M-650
- NACE MR0175
- ISO 15156-3
- PED 2014/68/EC
- EN 10204 type 3.2
- AD 2000 W2/W7/W10
Ferralium 255 (UNS S32550) Super Duplex Stainless Steel
Ferralium 255 (UNS S32550, EN 1.4507, X2CrNiMoCuN25-6-3) is a copper-bearing super duplex stainless steel originally developed by Langley Alloys (UK). The closely related grade Ferralium 255-SD50 (UNS S39274) is a super-duplex variant with higher Mo (~3.5%) and added W (~2%); this site covers the standard S32550 grade unless noted otherwise. Nominal composition is 25 Cr – 5 Ni – 3 Mo – 2 Cu – 0.2 N, with the 2% copper distinguishing Ferralium 255 from other super duplex grades and providing improved resistance to reducing acids (HCl, H2SO4, brines). The alloy has a balanced austenite-ferrite microstructure (35–55% ferrite per NORSOK M-630), PREN ≥ 40, and is supplied solution-annealed (no precipitation hardening). Critical Pitting Temperature (CPT) ≥ 35 °C per ASTM G48 method A. Used in seawater service, oil & gas downhole, subsea, desalination and chemical processing. Ferralium 255 is covered by ASTM A479 / A789 / A790 / A815 / A182 / A276 and NORSOK M-630 material data sheet MDS D55. TorqBolt is a NORSOK M-650 capable manufacturer with Qualification Test Records (QTR) available on request, and supplies Ferralium 255 to NACE MR0175 / ISO 15156-3 sour-service compliance per heat (hardness ≤ 32 HRC, ferrite 35–55%).
TorqBolt manufactures Ferralium 255 components and fasteners (hex bolts, stud bolts, hex nuts, flat washers, threaded rod, socket-head cap screws) and product forms (round / hex / square / flat / forged / cold-finished / hollow bar; plate; sheet; seamless and welded pipe and tube; wrought fittings; forged flanges; open-die and closed-die forgings) at our Mumbai and Rajkot, India facilities. All product is supplied with per-heat Mill Test Certificates (EN 10204 type 3.2) documenting chemistry, mechanical properties, ferrite content and CPT per ASTM G48; NORSOK M-650 QTR and NACE MR0175 compliance documentation are available on request.
Ferralium is a registered trademark of Langley Alloys.
Ferralium 255 in the Super Duplex Stainless Steel Family
Super duplex stainless steel is the family of duplex stainless steel grades with PREN ≥ 40, where PREN (Pitting Resistance Equivalent Number) = %Cr + 3.3·%Mo + 16·%N. The commercially significant super duplex stainless steel grades in current industrial specification are Ferralium 255 (UNS S32550, Cu-bearing), Super Duplex 2507 (UNS S32750, no Cu, marginally higher Cr/Mo), and Zeron 100 (UNS S32760, W-bearing). All three have PREN nominally ≥ 40. The duplex and super duplex stainless steel category as a whole, including standard duplex grades like Duplex 2205 (UNS S31803/S32205, PREN ~35) below the super duplex threshold, is widely used in oil & gas, marine, chemical processing and desalination service.
| Grade | UNS | EN | Distinctive element | Nominal PREN | Class |
|---|---|---|---|---|---|
| Ferralium 255 | S32550 | 1.4507 | Cu (~2%) | ~40 | Super duplex |
| Super Duplex 2507 | S32750 | 1.4410 | none (no Cu, no W) | ~42 | Super duplex |
| Zeron 100 | S32760 | 1.4501 | W (~0.7%) | ~41 | Super duplex |
| Duplex 2205 | S31803 / S32205 | 1.4462 | none (lower Mo/N) | ~35 | Standard duplex |
Ferralium 255 vs Duplex 2205, Chemical Composition
Ferralium 255 chemistry sits one tier above Duplex 2205 in the duplex / super duplex stainless steel family. The key Duplex 2205 chemical composition differences vs Ferralium 255 are higher chromium, higher molybdenum, higher nitrogen, plus a 2% copper addition that Duplex 2205 lacks, pushing PREN from ~35 to ~40+. Both grades are supplied solution-annealed.
| Element | Ferralium 255 (S32550) | Duplex 2205 (S31803 / S32205) |
|---|---|---|
| Carbon (C), max. | 0.04 | 0.030 |
| Chromium (Cr) | 24.0 – 27.0 | 21.0 – 23.0 |
| Nickel (Ni) | 4.5 – 6.5 | 4.5 – 6.5 |
| Molybdenum (Mo) | 2.9 – 3.9 | 2.5 – 3.5 |
| Copper (Cu) | 1.5 – 2.5 | none (not specified) |
| Nitrogen (N) | 0.10 – 0.25 | 0.08 – 0.20 |
| Manganese (Mn), max. | 1.5 | 2.0 |
| Silicon (Si), max. | 1.0 | 1.0 |
| Phosphorus (P), max. | 0.04 | 0.03 |
| Sulphur (S), max. | 0.03 | 0.02 |
Source standards: ASTM A479 (UNS S32550, S31803, S32205); EN 10088-3 (1.4507, 1.4462). TorqBolt also supplies Duplex 2205, see Ferralium 255 vs Duplex 2205 upgrade guide for selection criteria.
PREN of Ferralium 255, Why It Qualifies as Super Duplex
PREN, Pitting Resistance Equivalent Number, is the standard scalar predictor of pitting and crevice corrosion resistance for stainless steels. The widely used formula is:
PREN = %Cr + 3.3 · %Mo + 16 · %N
For Ferralium 255 nominal composition (25 %Cr, 3 %Mo, 0.2 %N): PREN = 25 + (3.3 × 3) + (16 × 0.2) = 25 + 9.9 + 3.2 = 38.1 minimum; typical per-heat values are 40–42. PREN ≥ 40 is the threshold defining super duplex stainless steel, the higher PREN value reflects substantially greater resistance to pitting in chloride-bearing environments (seawater, brines, sour gas) than standard duplex (Duplex 2205, PREN ~35) or austenitic stainless steels (316L, PREN ~25). PREN is verified per heat by certified composition; TorqBolt's per-heat MTC documents the calculated value alongside the measured chemistry.
Ferralium 255 Mechanical Properties, Yield, Tensile, Hardness
Ferralium 255 mechanical properties at room temperature, supplied solution-annealed per ASTM A479. Hardness is capped at 32 HRC for NACE MR0175 sour-service compliance; Charpy impact is reported at −46 °C for NORSOK M-630 offshore qualification. See also full Ferralium 255 mechanical properties page.
| Property | Minimum value (Ferralium 255 / S32550) | Test standard |
|---|---|---|
| 0.2% Yield strength (Rp0.2) | 550 MPa (80 ksi) | ASTM E8 |
| Ultimate tensile strength (Rm) | 760 MPa (110 ksi) | ASTM E8 |
| Elongation at fracture (A5) | 15% | ASTM E8 |
| Hardness | ≤ 32 HRC (NACE MR0175 sour-service limit) | ASTM E18 |
| Charpy V-notch impact at −46 °C | ≥ 45 J (NORSOK M-630 offshore) | ASTM E23 / ISO 148-1 |
| Density | 7.81 g/cm³ | none |
Ferralium 255 Spec Compliance, Super Duplex ASTM Grades, NORSOK M-650, NACE MR0175
Ferralium 255 (UNS S32550) is supplied to the following super duplex stainless steel ASTM grades and EN equivalents across product forms. Per-heat Mill Test Certificates (EN 10204 type 3.2) document chemistry, mechanical properties, ferrite content, and corrosion test results (Critical Pitting Temperature per ASTM G48 method A).
| Specification | Scope / Form | Notes |
|---|---|---|
| ASTM A479 | Bar, billet, shapes (UNS S32550) | Primary bar spec |
| ASTM A789 | Seamless and welded ferritic/austenitic tube | Tube spec |
| ASTM A790 | Seamless and welded ferritic/austenitic pipe | Pipe spec |
| ASTM A815 | Wrought fittings, ferritic/austenitic stainless | Fittings spec |
| ASTM A182 | Forged or rolled flanges, fittings, valves | Forgings/flanges spec |
| ASTM A276 | Bars and shapes | Alternative to A479 |
| NORSOK M-650 | Manufacturer Qualification Test Records (QTR) | Offshore service qualification |
| NORSOK M-630 | Material data sheet MDS D55 | Ferralium 255-equivalent SDSS |
| NACE MR0175 / ISO 15156-3 | Sour-service compliance | Hardness ≤ 32 HRC, ferrite 35–55% |
| EN 10088-3 | Flat and long products (1.4507) | European bar/plate |
| EN 10222-5 | Forgings (1.4507) | European forgings |
| EN 10272 | Bars for pressure purposes | Pressure-rated bar |
Ferralium 255 Forms and Fasteners, TorqBolt Manufactures
TorqBolt manufactures Ferralium 255 in the following product forms across our Mumbai and Rajkot, India facilities. All product forms are supplied with per-heat MTC (EN 10204 type 3.2) and, on request, NORSOK M-650 QTR and NACE MR0175 compliance certification.
Ferralium 255 Bar & Forms
- Ferralium 255 round bar (ASTM A479)
- Ferralium 255 hex bar
- Ferralium 255 square bar
- Ferralium 255 flat bar
- Ferralium 255 forged bar
- Ferralium 255 cold-finished bar (peeled / turned / centreless-ground)
- Ferralium 255 hollow bar
- Ferralium 255 plate
- Ferralium 255 sheet
- Ferralium 255 pipe (ASTM A790)
- Ferralium 255 tube (ASTM A789)
- Ferralium 255 fittings (ASTM A815)
- Ferralium 255 flanges (ASTM A182)
- Ferralium 255 forgings
Fasteners
- Ferralium 255 hex bolts, ASME B18.2.1 (UNC inch / metric M)
- Ferralium 255 heavy hex bolts, ASME B18.2.1
- Ferralium 255 stud bolts for B16.5 flanges, ASTM A193 S6 / ASME B18.31.2
- Ferralium 255 threaded rod / all-thread
- Ferralium 255 hex nuts, ASTM A479 material per ASME B18.2.2
- Ferralium 255 heavy hex nuts, ASME B18.2.2
- Ferralium 255 lock nuts (prevailing-torque)
- Ferralium 255 flat washers, ASTM A479 material per ASME B18.22.1
- Ferralium 255 lock washers, ASME B18.21.1
- Ferralium 255 socket-head cap screws, DIN 912 dimensional
- Ferralium 255 eye bolts (ASME B18.15)
- Ferralium 255 U-bolts
Ferralium 255 vs Zeron 100 vs Super Duplex 2507 vs Duplex 2205
Ferralium 255 is selected over alternative super duplex grades when service involves reducing acids (the 2% Cu advantage), or when a Cu-bearing super duplex is specifically required by project specification. For environments dominated by chloride pitting alone, Super Duplex 2507 and Zeron 100 perform comparably. Below the super duplex threshold, Duplex 2205 is the standard choice. Detailed side-by-side comparisons:
- Ferralium 255 vs Zeron 100, Cu-bearing vs W-bearing super duplex (Zeron 100 (UNS S32760) manufacturer-reference)
- Ferralium 255 vs Super Duplex 2507, Cu vs no-Cu, PREN comparison (Super Duplex 2507 (UNS S32750) manufacturer-reference)
- Ferralium 255 vs Duplex 2205, when to upgrade from standard duplex to super duplex
- Ferralium 255 vs Inconel 625, super duplex vs nickel alloy
Ferralium 255 Supplier in India, TorqBolt Mumbai & Rajkot
TorqBolt Pvt Ltd manufactures Ferralium 255 components and fasteners at our facilities in Mumbai and Rajkot, India. The Indian super duplex market is the second-largest in the world by search volume after the United States, driven by domestic oil & gas EPC contractors, refining and petrochemical projects, and export work for Middle East, Southeast Asia and African end-users. Our quality system is ISO 9001 certified. Per-heat Mill Test Certificates to EN 10204 type 3.2, NORSOK M-650 QTR and NACE MR0175 compliance documentation are available on request. See Ferralium 255 supplier in India for full sourcing and delivery information, or Ferralium 255 stockist in Mumbai for ready-stock and cut-to-size services.
Ferralium 255 Frequently Asked Questions
What is Ferralium 255?
Ferralium 255 (UNS S32550, EN 1.4507, X2CrNiMoCuN25-6-3) is a Cu-bearing super duplex stainless steel with nominal composition 25Cr-5Ni-3Mo-2Cu-0.2N. PREN ≥ 40, balanced austenite-ferrite microstructure (35-55% ferrite per NORSOK M-630), supplied solution-annealed (no precipitation hardening). Critical Pitting Temperature ≥ 35 °C per ASTM G48 method A. Used in seawater service, oil & gas downhole, subsea, desalination and chemical processing. Ferralium is a registered trademark of Langley Alloys.
How does Ferralium 255 chemical composition differ from Duplex 2205 chemical composition?
Ferralium 255 (UNS S32550) chemistry: Cr 24-27%, Ni 4.5-6.5%, Mo 2.9-3.9%, Cu 1.5-2.5%, N 0.10-0.25%, balance Fe. Duplex 2205 (UNS S31803/S32205) chemistry: Cr 21-23%, Ni 4.5-6.5%, Mo 2.5-3.5%, N 0.08-0.20%, no Cu. Ferralium 255 has higher Cr, higher Mo, higher N, plus 2% Cu, pushing PREN from ~35 (Duplex 2205) to ~40+ (super duplex threshold).
What is PREN and why is Ferralium 255 super duplex?
PREN (Pitting Resistance Equivalent Number) = %Cr + 3.3 · %Mo + 16 · %N. With nominal 25 Cr, 3 Mo, 0.2 N, Ferralium 255 PREN = 25 + 9.9 + 3.2 = 38.1 minimum, typically 40-42 per heat. PREN ≥ 40 is the threshold defining super duplex stainless steel grades, distinguishing Ferralium 255 from standard duplex grades like Duplex 2205 (PREN ~35).
What super duplex stainless steel grades exist alongside Ferralium 255?
The commercially significant super duplex stainless steel grades are: Ferralium 255 (UNS S32550, Cu-bearing, EN 1.4507), Super Duplex 2507 (UNS S32750, no Cu, EN 1.4410, slightly higher Cr/Mo), and Zeron 100 (UNS S32760, W-bearing, EN 1.4501). All have PREN ≥ 40. Standard duplex grades like Duplex 2205 (UNS S31803/S32205, EN 1.4462, PREN ~35) sit below the super duplex threshold.
Which super duplex stainless steel ASTM grades cover Ferralium 255?
ASTM A479 (bar/billet/shapes), ASTM A789 (seamless/welded tube), ASTM A790 (seamless/welded pipe), ASTM A815 (wrought fittings), ASTM A182 (forged flanges/fittings/valves), ASTM A276 (bars/shapes alternative). All under UNS S32550 designation. EN equivalents: EN 10088-3, EN 10222-5, EN 10272.
Is Ferralium 255 NORSOK M-650 qualified?
Ferralium 255 can be supplied with NORSOK M-650 Qualification Test Records (QTR) demonstrating manufacturer qualification per NORSOK M-630 material data sheet MDS D55. The QTR documents heat treatment, ferrite content (35-55% base, 35-65% weld), Charpy ≥ 45 J at −46 °C, Critical Pitting Temperature per ASTM G48 method A, and microstructural verification. Required for North Sea, Norway and high-criticality offshore projects.
Is Ferralium 255 NACE MR0175 / ISO 15156 compliant for sour service?
Yes. Ferralium 255 is qualified under NACE MR0175 / ISO 15156-3 for sour service when supplied solution-annealed with hardness ≤ 32 HRC and ferrite content 35–55% per NORSOK M-630. TorqBolt provides per-heat MTC (EN 10204 type 3.2) certifying NACE MR0175 compliance for downhole, wellhead and sour-gas applications.
Where can I buy Ferralium 255 in India?
TorqBolt Pvt Ltd manufactures Ferralium 255 at facilities in Mumbai and Rajkot, India. Bar, plate, sheet, pipe, tube, fittings, flanges, forgings, hex bolts, stud bolts, hex nuts and threaded rod available with per-heat MTC (EN 10204 type 3.2) and optional NORSOK M-650 QTR + NACE MR0175 documentation. Contact info@torqbolt.com or +91-22-66157017.
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