Duplex & Super Duplex Fasteners – The Complete Guide to 2205 and 2507 Stainless Steel Bolts, Nuts & Studs
When 316L stainless steel reaches its limits in chloride-rich or high-stress environments, Duplex and Super Duplex fasteners step in with twice the yield strength and superior localized corrosion resistance. RAYCHIN LIMITED is a recognized expert in duplex stainless steel fasteners, supplying the complete range of Duplex 2205 (UNS S31803/S32205) and Super Duplex 2507 (UNS S32750/S32760) bolts, nuts, screws, washers, stud bolts, and threaded rods[reference:15]. This guide provides the technical depth needed to specify the correct duplex grade for your application.
Product Range
Duplex 2205 Bolts
Hex bolts per DIN 931/933 and ASME B18.2.1. Yield strength ~450 MPa minimum. Sizes M6–M64 and 1/4″–2″.
Super Duplex 2507 Bolts
Yield strength ≥550 MPa. PREN ≥40. For the most aggressive seawater and acid environments[reference:16].
Duplex Stud Bolts
Double-end and fully threaded studs per ASME B16.5. Ideal for flange connections in offshore piping.
Duplex Nuts & Washers
Proof-load matched to corresponding bolts. All-metal lock nuts available.
Duplex Threaded Rod
Continuous-thread studding in 2205 and 2507. Diameters 1/4″–2-1/2″ and M6–M64.
Custom Duplex Parts
Special threads, non-standard heads, and precision-machined components per drawing.
Material Grades & Standards
Duplex 2205 vs Super Duplex 2507
Applications
- Offshore & Marine: Seawater piping, riser clamps, subsea manifolds, and deck hardware.
- Oil & Gas: Wellhead studs, flowline fasteners, and sour service bolting (NACE MR0175).
- Chemical Processing: Reactor bolts, heat exchanger fasteners, and piping systems handling chlorides and acids.
- Desalination: High-pressure pump fasteners and membrane housing bolts.
- Pulp & Paper: Bleaching equipment and digester fasteners.
- Flue Gas Desulfurization: Scrubber bolting and ductwork fasteners.
Quality Assurance
- EN 10204 3.1 / 3.2 Material Test Certificates
- Positive Material Identification (PMI) reports
- Mechanical testing: tensile, yield, elongation, hardness
- Ferrite content verification (typically 40–60%)
- NACE MR0175 / ISO 15156 compliance documentation
- Third-party inspection upon request
Frequently Asked Questions
What is the difference between Duplex 2205 and Super Duplex 2507?
Duplex 2205 offers yield strength ~450 MPa and PREN ~35. Super Duplex 2507 contains higher Cr, Mo, and N, achieving PREN ≥40 and yield strength ≥550 MPa, for more aggressive environments[reference:17].
Which standards cover duplex fasteners?
ASTM A1082 (bolting), ASTM A479 (bar), ASTM A276 (bar), and NACE MR0175 for sour service[reference:18].
What is the maximum service temperature?
Duplex grades are generally limited to below 300°C (570°F) due to 475°C embrittlement risk.
Can duplex fasteners be used in seawater?
Yes, both 2205 and 2507 excel in seawater. Super Duplex 2507 is preferred for the most aggressive chloride environments.
Does RAYCHIN provide material certificates?
Yes, EN 10204 3.1 / 3.2, PMI reports, and NACE MR0175 documentation are provided as required.
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