Side-by-side comparison of Incoloy 925 (UNS N09925) and Duplex 2205 (UNS S32205, formerly S31803). The two materials sit at opposite ends of the corrosion-resistant alloy cost-performance ladder. Incoloy 925 is an age-hardenable nickel-iron-chromium alloy with 44% nickel and a deliberate Mo + Cu corrosion package; it costs 3–4× what Duplex 2205 costs but is qualified for severe-sour service up to 1000 psi H₂S. Duplex 2205 is a dual-phase ferritic-austenitic stainless steel with only ~5% nickel; it is the volume CRA for general chemical, marine and mild-sour service where its 65 ksi minimum yield + good chloride pitting resistance + low cost combine attractively. The two alloys overlap in some service windows (mild sour at moderate pressure) and not in others (high-strength bolting, severe-sour service). This page covers when each wins.
Sour-service alloy selection? Email info@torqbolt.com with the service H₂S partial pressure, chloride concentration, design strength and temperature; we'll compare both alloys with full MTC. WhatsApp +91-22-66157017.
Chemistry Side-by-Side
| Element | Incoloy 925 (N09925) | Duplex 2205 (S32205) |
|---|---|---|
| Ni | 42–46% (high) | 4.5–6.5% (low) |
| Cr | 19.5–22.5% | 22–23% |
| Fe | 22% min (bal) | 60+ (bal) |
| Mo | 2.5–3.5% | 3.0–3.5% |
| Cu | 1.5–3.0% | not specified |
| N | not specified | 0.14–0.20% (signature austenite stabiliser) |
| Ti | 1.9–2.4% (gamma-prime) | not specified |
| Al | 0.1–0.5% (gamma-prime) | not specified |
| C | 0.03 max | 0.030 max |
| PREN (Cr+3.3Mo+16N) | ~32 | ~35 |
Duplex 2205 has a slightly higher PREN than Incoloy 925 (~35 vs ~32) due to its nitrogen content. The Cr / Mo / Ni envelopes are similar in chromium and molybdenum, but the nickel content differs by ~10×. The age-hardening Ti + Al package is unique to Incoloy 925.
Microstructure, Single Phase vs Dual Phase
Incoloy 925 is fully austenitic (FCC) with gamma-prime Ni₃(Al, Ti) precipitates after the age cycle. Single-phase microstructure means consistent properties in all directions, no transformation behaviour with temperature, no ferrite-related embrittlement above 600°F.
Duplex 2205 is roughly 50% austenite + 50% ferrite at room temperature (the "duplex" microstructure). The dual phase gives high yield strength via ferrite contribution + good toughness via austenite contribution. But the ferrite phase brings two issues: (1) magnetism (Duplex 2205 is strongly magnetic; Incoloy 925 is not), (2) the 475°C embrittlement window (sustained service above 575°F transforms ferrite to brittle alpha-prime). Duplex 2205 is therefore restricted to ~600°F maximum continuous service; Incoloy 925 is good to 1100°F.
Mechanical Properties Compared
| Property | Incoloy 925 (Aged) | Duplex 2205 (Annealed) |
|---|---|---|
| Tensile Strength min | 165 ksi (1140 MPa) | 90 ksi (621 MPa) |
| 0.2% Yield Strength min | 110 ksi (760 MPa) | 65 ksi (448 MPa) |
| Elongation min | 18% | 25% |
| Hardness max (sour) | 35 HRC | 28 HRC |
| Modulus, GPa | 190 | 200 |
| Magnetic permeability | ~1.005 (non-magnetic) | 30–100 (strongly magnetic) |
| Max continuous service temp | 1100°F (593°C) | ~600°F (315°C) |
Incoloy 925 has ~70% higher yield strength than Duplex 2205. For applications requiring high preload (bolting), 925 wins by a wide margin. For low-pressure piping where strength is set by wall thickness, 2205 is sufficient and far cheaper.
Sour-Service Envelope
| Limit | Incoloy 925 (Table A.10) | Duplex 2205 (Table A.21) |
|---|---|---|
| H₂S Partial Pressure max | 1000 psi (6.9 MPa) | 1.5 psi (10 kPa) at 65°C max; restricted further at higher T |
| Cl⁻ max | Saturation | 50,000 ppm at 65°C, lower at higher T |
| Hardness cap | 35 HRC | 28 HRC (320 HV) |
| Temperature max | 400°F (204°C) | ~250°F (121°C) for sour service |
Sour-service envelope is dramatically different. Duplex 2205 is qualified only up to 1.5 psi H₂S at 65°C in NACE MR0175 Table A.21 with combined chloride + temperature derating. For high-H₂S service or high-chloride brine, 2205 is NOT qualified and a nickel CRA like Incoloy 925 is required. For mild-sour service in moderate brine at low temperature, 2205 is qualified and cost-effective, this is the volume application.
Cost Comparison
- Duplex 2205: ~0.30× baseline, the volume sour-service CRA at low cost
- Super-duplex 2507 / Zeron 100: ~0.50×, higher PREN, better seawater performance
- Incoloy 925: 1.0× baseline, the high-strength nickel CRA
- Inconel 718: ~3.0×
The 3× cost premium of Incoloy 925 over Duplex 2205 reflects nickel content (44% vs 5%) + the 18-hour age cycle. The premium is justified for high-H₂S service or high-strength bolting; not justified for mild service where 2205 meets the spec.
When to Pick Each Alloy
| Application | Recommended Alloy |
|---|---|
| API 6A wellhead bolting (sour, high strength) | Incoloy 925, only 925 meets 110 ksi YS + high H₂S |
| Mild-sour production tubing (low H₂S, low temp) | Duplex 2205 |
| Severe-sour deep gas well | Incoloy 925 or Inconel 725 |
| Topside piping (saltwater spray, mild sour) | Duplex 2205 |
| Subsea Christmas tree internals | Incoloy 925 |
| FPSO ballast tank piping | Duplex 2205 or Super-duplex 2507 |
| MWD / LWD downhole tool housing (low magnetic permeability) | Incoloy 925 (2205 is magnetic, disqualifies it) |
| Pulp & paper bleaching equipment | Duplex 2205 |
Frequently Asked Questions
Why is Duplex 2205 so much cheaper than Incoloy 925? Nickel content. Nickel is the dominant raw-material cost in stainless and CRA pricing, 925 has 44% Ni vs 5% in 2205. At ~$10/kg nickel, the alloy chemistry alone gives a ~$4–5/kg base-cost difference, and processing complexity (age cycle for 925) widens the gap further. The 3× price ratio is a function of the global nickel market, not a quality difference.
Can Duplex 2205 be used for wellhead bolting? Generally no, 2205's 65 ksi YS minimum is too low for most API 6A bolting specs (typically 75–110 ksi YS required). Cold-worked 2205 can hit ~95 ksi but the cold-work raises hardness above 28 HRC, disqualifying it from sour service. Incoloy 925 is the only practical choice when high-strength + sour-service + bolting all converge.
Is Duplex 2205 magnetic? Yes, strongly magnetic (relative permeability 30–100) due to the ferrite phase. This disqualifies it from MWD / LWD downhole tool housings and any application near sensitive magnetic instruments. Incoloy 925 is essentially non-magnetic (μr ~1.005) and is preferred where low magnetic signature matters.
Can the two alloys be welded together? Yes, with INCONEL Filler Metal 625 (NiCrMo solid-solution filler). The dissimilar joint requires careful heat-input control because Duplex 2205 needs a moderately high heat input (1.5–2.5 kJ/mm) to maintain the 50/50 austenite/ferrite balance, while Incoloy 925 prefers lower heat input (0.5–1.5 kJ/mm) to avoid HAZ over-ageing. The compromise is typically 1.0–1.5 kJ/mm with multi-pass technique. Post-weld solution anneal is impractical because 2205 needs 1900°F + rapid quench while 925 needs 1900°F + age cycle.
What about Super-duplex 2507 vs Incoloy 925? Super-duplex 2507 (UNS S32750) has higher PREN (~42) and better seawater performance than Duplex 2205 but the same sour-service restriction (Table A.21 envelope). For the high-H₂S oilfield bolting application, 2507 still cannot replace Incoloy 925. For severe-chloride seawater service (FPSO, swimming-pool covers), 2507 is the cost-effective choice.
Compare Incoloy 925 to Other Alloys
- Inconel vs Incoloy, What's the difference?
- Incoloy 925 vs Inconel 718
- Incoloy 925 vs Incoloy 825
- Incoloy 925 vs Incoloy 926
- Incoloy 925 vs Monel K-500
Request a Quote
For Incoloy 925 with full MTC, or for Duplex 2205 / Super-duplex 2507 alternatives in the same enquiry:
- Email: info@torqbolt.com
- WhatsApp: +91-22-66157017
- Datasheet PDF + sample MTC available on request
Specify product type (stud bolts, nuts, pipe, plate), size, quantity, applicable standards (ASTM B805, ASTM A276 / A479 for 2205, API 6A, NACE MR0175), service H₂S partial pressure / temperature / chloride concentration, and required mechanical envelope.
References: ASTM B805 (UNS N09925); ASTM A276 / A479 / A240 (UNS S32205). Special Metals Corporation: INCOLOY® alloy 925 Technical Bulletin. Outokumpu / Sandvik Duplex 2205 product literature. NACE MR0175 / ISO 15156-3 Tables A.10 and A.21. INCOLOY® is a registered trademark of Special Metals Corporation.
