UNS S32750 (2507) & UNS S32760 (Zeron 100) stud bolts engineered with PREN ≥ 42 for extreme subsea, sour service, and chemical environments.
Zero-Defect Super Duplex Fasteners with EN 10204 3.1 Traceability
Complete microstructural phase balance (40-60% ferrite) and ASTM G48 pitting corrosion test validation.
Why modern offshore EPCs, subsea equipment operators, and chemical processing facilities choose UNS S32750 and UNS S32760 over standard austenitic and duplex grades.
In high-pressure, high-temperature (HPHT) subsea oilfields, seawater reverse osmosis (SWRO) desalination plants, and aggressive chemical synthesis loops, bolting integrity is non-negotiable. A single fastener failure due to Chloride Stress Corrosion Cracking (CSCC) or localized pitting can lead to catastrophic pressure loss, environmental contamination, and multi-million-dollar operational downtime. As global energy and chemical infrastructure transitions toward deeper waters and more sour production fluids, the Super Duplex Stud Bolt has emerged as the global benchmark for critical mechanical jointing.
Unlike standard austenitic stainless steels (316L, 317L) or conventional duplex alloys (UNS S31803 / 2205), Super Duplex Steels feature a balanced 50/50 dual-phase microstructure of ferrite and austenite, combined with high levels of Chromium (~25%), Molybdenum (~4%), and Nitrogen (~0.28%). This chemical synergy yields a Pitting Resistance Equivalent Number (PREN) equal to or greater than 42, alongside a minimum yield strength of 550 MPa—more than double that of conventional austenitic fasteners.
When procurement managers evaluate fasteners for marine splash zones or hot seawater heat exchangers, the primary ranking metric is the Pitting Resistance Equivalent Number (PREN). For Super Duplex Stud Bolts, PREN is calculated using the established thermodynamic formulas:
The strategic inclusion of Tungsten (W) and Copper (Cu) in UNS S32760 provides extraordinary resistance to hot concentrated sulfuric acid and acidic sour gas environments containing hydrogen sulfide (H₂S). The table below presents a direct engineering comparison between common fastner grades:
| Material Grade | UNS Designation | Nominal Composition (%) | Min. Yield Strength (MPa) | Typical PREN | Critical Pitting Temp (CPT) |
|---|---|---|---|---|---|
| Super Duplex 2507 | UNS S32750 / F53 | 25Cr - 7Ni - 4Mo - 0.28N | 550 MPa | ≥ 42.0 | > 45°C (113°F) |
| Super Duplex Zeron 100 | UNS S32760 / F55 | 25Cr - 7Ni - 3.5Mo - 0.6W - 0.7Cu - 0.28N | 550 MPa | ≥ 42.5 | > 45°C (113°F) |
| Duplex 2205 | UNS S31803 / S32205 | 22Cr - 5Ni - 3Mo - 0.17N | 450 MPa | ~ 34.0 | 25°C - 30°C |
| Austenitic 316L | UNS S31603 / B8M Cl.1 | 17Cr - 12Ni - 2.5Mo | 205 MPa | ~ 25.0 | < 10°C |
Engineered to exact ASME B18.31.2, ASME B16.5, and DIN 976 dimensional tolerances for worldwide project deployment.
Designed for subsea manifolds, christmas trees, and reverse osmosis high-pressure piping. Exceptional resistance to chloride stress corrosion cracking with high yield load capacity.
Request Drawing & RFQ Alloyed with Tungsten and Copper for high resistance to mineral acids and H₂S sour gas. Compliant with NACE MR0175 / ISO 15156 and NORSOK M-650 specifications.
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Super Duplex Stud Bolts coated with premium multi-coat PTFE/Xylan finishes to eliminate thread galling, provide uniform bolt tensioning, and protect topside marine splash zones.
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Fully matching heavy hex nuts (ASME B18.2.2 / ASTM A182 F53/F55) and hardened washers engineered to prevent thread stripping and deliver exact torque retention.
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Custom manufactured studs according to client blueprints. Full-thread studs, double-end studs, and collar studs for high-pressure valve bodies and turbine casings.
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Manufactured strictly from NORSOK M-650 qualified raw material bar stock with qualified heat treatment records, 100% UT, and Charpy impact testing at -40°C.
NORSOK CertifiedMatch your Super Duplex Stud Bolt requirements with certified nuts, bolts, washers, and threaded rods to prevent galvanic mismatch and guarantee joint integrity.
Continuous thread stud bolts manufactured to ASME B18.31.2 for ASME B16.5 & B16.47 pressure flanges.
UNS S32750/S32760 heavy hex nuts engineered to match stud bolt load limits without thread galling.
Precision forged Super Duplex hex bolts for structural offshore and marine pump casing assemblies.
Plain, heavy-duty, and spring washers in UNS S32750 to distribute bolt clamp loads evenly.
Full length 1-meter to 3-meter Super Duplex tie rods cut and chamfered to project specification.
High-strength Super Duplex socket head cap screws for compact subsea actuators and valves.
Strategic insights for procurement directors navigating supply chains, decarbonization mandates, and deep-water developments.
Major international oil companies (IOCs) and global EPC contractors are increasingly integrating environmental sustainability criteria into critical fastener procurement. The production of raw Super Duplex bar stock requires high-purity alloying additions (Chromium, Molybdenum, Nickel, Nitrogen). Modern procurement trends mandate that mills utilize electric arc furnace (EAF) technology powered by renewable energy, combined with high-grade recycled scrap inputs. At Stud Bolt India, we align with green procurement standards by sourcing low-carbon footprint billet certified under ISO 14064 GHG verification.
With subsea assets operating at depths exceeding 2,000 meters, material traceability is migrating from paper-based EN 10204 3.1 certificates to digital product passports embedded with unique heat-lot identifiers. Future procurement protocols for Super Duplex Stud Bolts demand end-to-end digital verification from the melting furnace, solution annealing furnace temperature logs, to final CNC thread rolling and ultrasonic inspection. This digital footprint eliminates counterfeit fasteners and ensures compliance with asset management platforms.
The primary metallurgical challenge in Super Duplex Stud Bolt manufacturing is avoiding the precipitation of embrittling intermetallic phases—specifically Sigma (σ) phase and Chi (χ) phase—which can form rapidly between 600°C and 1000°C during improper cooling. Advanced hot forging processes now employ precise induction heating with digital optical pyrometers, followed by rapid water quenching from solution anneal temperatures of 1050°C - 1120°C. This ensures a pristine ferrite-austenite phase balance (40% to 60%) and zero intermetallic precipitation, passing ASTM A923 Method C ferric chloride corrosion and impact tests.
When Super Duplex Stud Bolts are deployed on subsea structures protected by Cathodic Protection (CP) systems (zinc/aluminum anodes), atomic hydrogen can absorb into the metal structure. Under high tensile stresses, this introduces the risk of Hydrogen Induced Stress Cracking (HISC). Emerging engineering guidelines (such as DNVGL-RP-F112) require controlled cold-work levels, strict hardness caps (≤ 28 HRC or 310 HV), coarse grain size regulation, and specialized thread root radii design to minimize stress concentration factors in subsea environments.
From our state-of-the-art facility in Mumbai, India, Stud Bolt India manufactures and exports high-integrity Super Duplex Stud Bolts to operators across 24+ countries. Our dedicated metallurgy laboratory verifies every heat lot to ensure strict adherence to global engineering standards.
Every single stud is verified with XRF handheld analyzers before shipment.
EBS / Microstructural analysis guarantees 40-60% ferrite range.
Full mechanical, chemical, impact, and ASTM G48 corrosion reports.
Seaworthy export packaging with express dispatch to Middle East & Western ports.
Engineering cross-reference table for procurement specification compliance.
| Parameter | UNS S32750 Specification | UNS S32760 Specification |
|---|---|---|
| Standard Material Specs | ASTM A1082 / A1082M, ASTM A479, ASTM A182 Grade F53 | ASTM A1082 / A1082M, ASTM A479, ASTM A182 Grade F55 |
| Dimensional Standards | ASME B18.31.2, ASME B18.2.1, DIN 976, ISO 4014/4017 | ASME B18.31.2, ASME B18.2.1, DIN 976, ISO 4014/4017 |
| Thread Configurations | UNC, UN8, UNF Class 2A / 3A, Metric Coarse & Fine Pitch | UNC, UN8, UNF Class 2A / 3A, Metric Coarse & Fine Pitch |
| Size Range | M6 to M100 | 1/4" to 4" Diameter (Custom lengths up to 3 meters) | M6 to M100 | 1/4" to 4" Diameter (Custom lengths up to 3 meters) |
| Tensile Strength (Min) | 750 - 1000 MPa (109 - 145 ksi) | 750 - 1000 MPa (109 - 145 ksi) |
| Yield Strength 0.2% (Min) | 550 MPa (80 ksi) | 550 MPa (80 ksi) |
| Elongation in 2" (Min) | 15% to 25% (Depending on strain hardening class) | 15% to 25% (Depending on strain hardening class) |
| Impact Energy (Charpy V-Notch) | ≥ 80 Joules at -40°C (-40°F) | ≥ 80 Joules at -40°C (-40°F) |
| Pitting Corrosion Test | ASTM G48 Method A (24 hrs at 40°C or 50°C without pitting) | ASTM G48 Method A (24 hrs at 40°C or 50°C without pitting) |
| Recommended Nuts & Washers | UNS S32750 Heavy Hex Nuts (ASME B18.2.2) + Hardened Washers | UNS S32760 Heavy Hex Nuts (ASME B18.2.2) + Hardened Washers |
* Special thread pitches, custom studs with unthreaded shank proportions, and tailored anti-galling coatings are supplied to project drawings.
Deployed in critical pressure containment systems operating under extreme chemical attack and high static fatigue.
Subsea Christmas trees, wellheads, manifolds, and high-pressure risers subject to marine immersion and sour fluids.
Terephthalic acid (PTA) reactors, organic acid plants, and chlor-alkali synthesis heat exchangers.
High-pressure seawater pumps, energy recovery devices, and reverse osmosis membrane vessels operating with hot brine.
Flange bolting, bonnet studs, and impeller shafts handling corrosive, abrasive slurries and aggressive fluids.
Direct feedback from subsea leads, QA managers, and EPC procurement specialists.
We specified UNS S32750 Super Duplex Stud Bolts for our North Sea offshore manifold package. Stud Bolt India delivered full EN 10204 3.1 certification along with Charpy testing at -40°C. Zero defects during subsea installation.
Finding NORSOK M-650 qualified UNS S32760 stud bolts on tight timelines was a challenge until we partnered with Stud Bolt India. Their PMI testing and Xylan coating quality are exceptional.
For our seawater reverse osmosis expansion in Australia, we ordered over 8,000 sets of Super Duplex studs and nuts. Thread accuracy was 100%, and the batch-wise ASTM G48 pitting corrosion reports passed perfectly.
Expert answers to the most common engineering, metallurgical, and commercial queries raised by global procurement buyers.
Super Duplex Stud Bolts (such as UNS S32750 and UNS S32760) deliver a Pitting Resistance Equivalent Number (PREN) equal to or greater than 42, compared to ~25 for 316L stainless steel and ~34 for standard Duplex 2205. They feature a balanced 50/50 ferrite-austenite microstructural ratio that grants roughly twice the yield strength of austenitic grades (~550 MPa vs ~220 MPa). This high strength allows engineers to downsize bolt diameters and flange weights while gaining immunity to chloride-induced stress corrosion cracking (SCC) in hot marine atmospheres and sour oilfield environments.
PREN is a metallurgical formula measuring localized corrosion resistance in chloride-rich media. For UNS S32750 (2507), the formula is PREN = %Cr + 3.3(%Mo) + 16(%N). For UNS S32760 (Zeron 100), tungsten is incorporated: PREN = %Cr + 3.3(%Mo + 0.5%W) + 16(%N). Global procurement specifications require a guaranteed PREN ≥ 42 to prevent catastrophic pitting breakdown in seawater applications exceeding 40°C.
Every shipment is accompanied by EN 10204 3.1 Material Test Reports (MTRs). Reports include: 1) Chemical analysis with verified Nitrogen levels, 2) Mechanical tensile, yield, and elongation testing, 3) Hardness testing (HRC/HBW), 4) Charpy V-notch impact testing at -40°C, 5) Microstructural phase ratio balance (40-60% ferrite via ASTM E562), 6) ASTM G48 Method A ferric chloride pitting test reports, and 7) Positive Material Identification (PMI) certificates.
HISC prevention relies on strict control during raw material manufacturing and heat treatment. We ensure precise solution annealing between 1050°C and 1120°C followed by immediate water quenching to eliminate sigma and chi phase precipitates. Furthermore, cold work levels are strictly controlled to maintain hardness below 28 HRC (310 HV), conforming with NORSOK M-650 and DNVGL-RP-F112 subsea design specifications.
While Super Duplex stainless steel inherently resists corrosion, bare stainless threads are susceptible to galling under high clamp loads during hydraulic torque makeup. Applying a multi-layer PTFE or Xylan 1424 fluoropolymer coating lowers the torque coefficient (nut factor K ~ 0.12), ensuring smooth, predictable tensioning, reducing breakout torque during maintenance, and adding atmospheric corrosion defense in offshore splash zones.
Yes. UNS S32750 and UNS S32760 Super Duplex Stud Bolts are qualified for sour service under NACE MR0175 / ISO 15156, provided they are in the solution-annealed condition with a maximum hardness of 28 HRC and operating within the specified partial pressures of H₂S and environmental temperature limits outlined in NACE MR0175 Table A.24.
Share your material grade (UNS S32750 / S32760), thread sizes, lengths, quantities, and coating requirements. Our engineering team provides immediate technical quotes and EN 10204 3.1 material compliance support.
