Duplex & Super Duplex Fasteners Manufacturer: 2205 and 2507 Bolts, Nuts and Studs
Sour gas, offshore splash zones and high-chloride process streams destroy both carbon steel and standard stainless bolting — the joint needs a duplex microstructure. Yuanpai manufactures duplex and super duplex fasteners — hex bolts, double end studs, nuts and washers in 2205 and 2507 — with the hardness control, impact testing and certification that sour service and offshore projects require.
Yuanpai — Duplex Fasteners Quick Reference:
- Grades: 2205 (UNS S32205 / S31803), 2507 (UNS S32750), Zeron 100-type (UNS S32760)
- Products: hex bolts, double end studs, nuts and washers in ASME B16.5 and metric sizes
- Standards: ASTM A276 / A182 material, ASME B18.2.1 / B18.2.2 dimensions
- Sizes: M8 – M64 (5/16" – 2-1/2"), lengths per project BOM
- Service: sour service (NACE MR0175 / ISO 15156), offshore, high-chloride and high-strength applications
- Certification: EN 10204 3.1, PMI verification, hardness and impact test reports; NORSOK M-650 / API 20E compliance available per project
Based on our supply records to global EPC and OEM projects, duplex fastener acceptance usually hinges on three practical details: correct grade selection, sour-service hardness and microstructure compliance, and complete certification.
Duplex vs Super Duplex: Strength and Corrosion Difference
Both families combine austenite and ferrite in roughly equal proportions, giving higher strength than 316 and better stress corrosion cracking resistance. The practical difference:
- 2205 (UNS S32205) — the standard duplex grade. PREN around 34–36, roughly double the yield strength of 316L, excellent resistance to chloride stress corrosion cracking. The default choice for sour service and offshore bolting where 316 is not enough.
- 2507 (UNS S32750) — the super duplex grade. PREN around 40–42, higher strength and pitting resistance, specified for the most aggressive chloride and sour environments, seawater and high-temperature acid service. Higher cost and tighter processing control; only specified when the service demands it.
The project material specification decides. Where standard stainless is sufficient, our Stainless Steel Fasteners guide covers A2/A4 options.
Sour Service and Hardness Control
For oil & gas bolting, duplex fasteners are commonly specified per API 20E (Level 1/2/3) or API 20F for subsea applications, with ASTM A276 Type 1 (solution annealed) or Type 2 (solution annealed and aged) conditions selected based on strength and toughness requirements.
Duplex fasteners are widely specified for NACE MR0175 / ISO 15156 sour service. The key control points:
- Hardness limits — duplex and super duplex fasteners are supplied within the sour service hardness limits (typically ≤ 32 HRC for 2205 and ≤ 35 HRC for 2507 per the applicable sour service requirements), verified per heat
- Microstructure verification — ferrite/austenite balance (typically 35–65% ferrite) and absence of harmful precipitates (sigma phase, chi phase) verified per lot, especially for larger diameters
- Impact testing — duplex and super duplex grades retain toughness at low temperature; Charpy impact testing per project scope (typical test temperatures: -46°C, -60°C, -101°C) confirms performance
- Material documentation — PMI verification and chemical composition per heat, with EN 10204 3.1 certificates
For the full sour service selection process, see our Custom Fastener Engineering Guide.
Grade Matching: Duplex Bolts and Nuts
| Bolt grade | Matching nut grade | Typical service |
|---|---|---|
| 2205 (S32205) | 2205 nut | Sour service, offshore, high chloride |
| 2507 (S32750) | 2507 nut | Super duplex service, seawater, aggressive sour |
| S32760 | S32760 nut | Zeron-type service, high temperature acid |
The nut grade must match the bolt grade and the hardness requirement. Mixed duplex families in one joint — a 2205 bolt with a 2507 nut, for example — create galvanic and hardness mismatches that fail project review.
Manufacturing and Certification
Duplex fasteners require controlled processing:
- Material control — bar stock from certified mills with heat numbers, PMI verified on receipt
- Heat treatment — solution annealing at the grade-specific temperature range, with hardness, tensile and impact verification per heat
- Machining and threading — turned and threaded to size; thread fit verified with calibrated gauges; galling control on duplex threads
- PMI verification — positive material identification on finished parts per lot
- Traceability — heat number traceability from raw bar to finished batch, supported by EN 10204 3.1 certificates and test reports
For stud bolt configurations in duplex grades, refer to our Stud Bolts page; for hex bolt and nut sets, our Hex Bolts, Nuts & Washers range.
Global Project Supply
Yuanpai supplies duplex and super duplex fasteners to global EPC contractors and OEMs across the Middle East, North Sea, Gulf of Mexico, West Africa and Southeast Asia. Our production line is optimized for sour-service hardness control and microstructure verification, with full documentation support for NORSOK M-650, API 20E and NACE MR0175 / ISO 15156 compliant projects worldwide.
Common Specification Mistakes in Duplex RFQs
Three omissions cause most duplex fastener order delays:
- Grade and UNS not stated — "duplex bolts" alone does not define 2205 versus 2507. State the UNS number (S32205, S32750, S32760) and the ASTM standard.
- Sour service limits not defined — state the NACE MR0175 / ISO 15156 requirement and the hardness limit so heat treatment is set correctly.
- Impact and test scope not defined — state whether Charpy impact testing, PMI and third-party inspection are required, and the acceptance criteria.
Providing these items at RFQ stage reduces clarification cycles during technical review.
FAQ
Q: What is the difference between 2205 and 2507 fasteners?
A: 2205 is the standard duplex grade with roughly double the yield strength of 316L and excellent sour service resistance. 2507 is super duplex with higher strength and pitting resistance, specified for the most aggressive chloride and sour environments.
Q: Are duplex fasteners suitable for sour service?
A: Yes, duplex and super duplex fasteners are widely specified for NACE MR0175 / ISO 15156 sour service, subject to hardness limits and microstructure verification per lot.
Q: What certificates do you provide?
A: EN 10204 3.1 material certificates, PMI reports, hardness, tensile and impact test reports, and dimensional inspection reports per lot. Third-party inspection with witness is available where the project requires.
Q: What is the minimum order quantity?
A: Common sizes start from about 500 pieces depending on grade and size, with project-specific quantities quoted by requirement. Send the BOM and our team will confirm the MOQ and lead time within one working day.
Get your duplex fastener quote within one working day — simply reply with:
- Grade & UNS (e.g. 2507, UNS S32750)
- Size & type (e.g. M24 x 150 double end stud with matching 2507 nuts)
- Quantity & certificate scope (e.g. 1,500 sets with 3.1 + PMI + impact)
Download the duplex fastener specification checklist — grade, sour service limits, test scope and certificate requirements.
Request sample kits — evaluate material identity, thread finish and certificate documentation before ordering.
Direct WhatsApp engineering support: [+1 XXX XXX XXXX] — send the BOM or project inquiry directly to our engineering team.
Related guides: Custom Fastener Manufacturer · Inconel & Nickel Alloy Fasteners · Stainless Steel Fasteners · Stud Bolts