Duplex Steel Fasteners Supplier in Mumbai, India
Nicorex Alloys is an ISO 9001 and ISO 14001 certified stockist and supplier of Duplex Steel fasteners in Mumbai, India. We stock grades S31803, S32205 (2205), and S32304 (2304) in bolts, nuts, studs, screws, washers, and threaded rods conforming to ASTM A182 (F51, F60), ASTM A479, NACE MR0175/ISO 15156, and NORSOK MDS D43.
Duplex stainless steels are dual-phase alloys with roughly 50% austenite and 50% ferrite, a PREN of 30-38, and about double the yield strength of 316L. All shipments include EN 10204/3.1B mill test certificates.
We stock a wide range of Duplex Steel Fasteners in multiple grades, including:
Duplex Steel Fastener Specifications
The table below covers Duplex Steel fastener specifications like standards, dimensions, sizes, thread forms, finishes, and conditions.
| Standards | ASTM A182 / ASME SA-182 (F51, F60); ASTM A479 |
|---|---|
| Size Range | M6 to M100; larger sizes custom manufactured |
| Thread Forms | UNC, UNF, metric coarse, metric fine, BSW, BSF, 8UN |
| Finishes | Pickled and passivated, PTFE/Xylan coated, waxed |
| Supply Condition | Solution annealed and water quenched |
| Testing | Ferrite 40–60% (ASTM E562), IGC per ASTM A262, max 36 HRC, impact at -46°C |
What are Duplex Steel Fasteners?
Duplex Steel fasteners are bolts, nuts, screws, studs, washers, and threaded rods from austenitic-ferritic stainless steels. The dual-phase structure gives minimum yield of 450 MPa, higher than 316L. A PREN of about 35 means they resist chloride pitting up to 35–40°C, versus 20–25°C for 316L. In bolted joints, the crevice under bolt heads is prone to pitting that destroys 316L in warm seawater. Duplex 2205 resists chloride stress corrosion cracking better than all austenitic grades.
Types and Forms of Duplex Steel Fasteners
Duplex Steel fasteners come in several forms for offshore, chemical, and marine use.
Duplex Steel Hex Bolts
Duplex Steel Stud Bolts (Double-End Studs)
Duplex Steel Socket Head Cap Screws (SHCS)
Duplex Steel Hex Nuts (Heavy Hex, Nylon Lock, Flange Nuts)
Duplex Steel Washers (Flat, Spring, Lock, Belleville)
Duplex Steel Threaded Rods / All-Thread
Duplex Steel U-Bolts
Duplex Steel Set Screws
Duplex Steel Eye Bolts
Duplex Steel Anchor Bolts
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Available Grades of Duplex Steel Fasteners
Nicorex Alloys stocks Duplex Steel fasteners in 3 grades.
Duplex 2205 / S32205 Fasteners
This is the most widely used Duplex fastener grade with PREN of about 35. Yield is minimum 450 MPa, tensile minimum 620 MPa. It resists chloride pitting up to 35-40°C and is NACE MR0175 compliant (36 HRC max).
Duplex S31803 Fasteners
S31803 is the original designation for Duplex 2205 with a wider nitrogen range (0.08–0.20% vs 0.14–0.20%). S32205 is now preferred for consistent pitting resistance.
Duplex 2304 / S32304 Fasteners
Duplex 2304 is a lean Duplex grade with PREN of 25–28 and yield minimum 400 MPa. It is a cost-effective replacement for 316L in mild chloride settings.
Industries and Applications of Duplex Steel Fasteners
Duplex Steel fasteners serve industries where chloride corrosion exceeds austenitic limits.
- Offshore Oil and Gas: Platform flange bolts and structural bolting per NORSOK MDS D43.
- Chemical Processing: Reactor bolting and heat exchanger flange studs.
- Desalination: RO housing bolts and seawater intake bolting.
- Marine: Ballast system bolts and exhaust scrubber fasteners.
- Pulp and Paper: Digester manway bolts and bleaching equipment fasteners.
- Food and Beverage: CIP system fasteners and tank manway bolts.
- Structural: Bridge fasteners and coastal handrail bolts.
Frequently Asked Questions
What is the difference between S32205 and S31803 fasteners?
S32205 has tighter nitrogen range (0.14–0.20%) than S31803 (0.08–0.20%), giving consistent pitting resistance. F60 covers S32205; F51 covers S31803. Both supplied with EN 10204/3.1B mill test certificates.
Why choose Duplex 2205 bolts over 316L?
Duplex 2205 has PREN of about 35 versus 24 for 316L, resisting pitting up to 35–40°C versus 20–25°C. Yield (min 450 MPa) is about 2.5 times that of 316L.
Do Duplex Steel fasteners gall during assembly?
Yes. Apply PTFE-based or nickel-based anti-seize to threads before assembly. PTFE/Xylan-coated fasteners are also available. Use calibrated torque wrenches per ASME PCC-1.
Are Duplex Steel fasteners suitable for sour service?
Yes. Duplex S32205/S31803 in solution annealed condition meet NACE MR0175/ISO 15156 when hardness stays below 36 HRC and ferrite is 40–60%.
When should I choose Duplex over Super Duplex fasteners?
Use Duplex 2205 when conditions are within its corrosion limits: seawater up to about 35-40°C, medium-chloride process fluids, or where 316L has failed but exposure is still not harsh enough to need alloys with PREN above 40. Choose Super Duplex (S32750/S32760) for hot seawater (above 50°C), high-chloride brines, and subsea applications.
What ferrite content is required for Duplex Steel fasteners?
Duplex fasteners should have 40–60% ferrite. Less than 40% means poor heat treatment and lower SCC resistance; more than 60% means risk of embrittlement from sigma phase.
What is the maximum service temperature for Duplex Steel fasteners?
Duplex 2205 fasteners are suitable for continuous service up to about 250°C (482°F) and keep good toughness down to around -50°C.
What size range is available for Duplex Steel fasteners?
Duplex Steel stud bolts are normally available from about M6 up to M64, with larger sizes up to M100 made from bar. Custom sizes, lengths, and thread types can also be supplied with full test certification.