Side-by-side comparison of Incoloy 925 (UNS N09925) and Incoloy 825 (UNS N08825). Both are Special Metals nickel-iron-chromium alloys with nearly identical chromium / molybdenum / copper packages and identical sour-service envelope qualifications. The single difference is strengthening mechanism: Incoloy 925 is age-hardenable (1.9–2.4% Ti + 0.1–0.5% Al precipitate as Ni₃(Al, Ti) gamma-prime during the 1365°F age cycle, lifting yield strength from ~50 ksi to a guaranteed 110 ksi minimum); Incoloy 825 is solid-solution only (no Ti package, ships at ~45 ksi yield). Incoloy 925 was developed in the 1980s as the high-strength sour-service derivative of 825 specifically to satisfy API 6A wellhead bolting strength requirements that 825 could not meet.
Trying to choose between 825 and 925? Email info@torqbolt.com with the design strength target, service H₂S partial pressure and temperature; we'll size both alloys with full MTC. WhatsApp +91-22-66157017.
Chemistry Side-by-Side
| Element | Incoloy 925 (N09925) | Incoloy 825 (N08825) |
|---|---|---|
| Ni | 42–46% | 38–46% |
| Cr | 19.5–22.5% | 19.5–23.5% |
| Fe | 22% min (bal) | 22% min (bal) |
| Mo | 2.5–3.5% | 2.5–3.5% |
| Cu | 1.5–3.0% | 1.5–3.0% |
| Ti | 1.9–2.4% (primary strengthener) | 0.6–1.2% (residual, not strengthener) |
| Al | 0.1–0.5% (primary strengthener) | 0.20 max (residual) |
| C | 0.03 max | 0.05 max |
Identical Ni / Cr / Fe / Mo / Cu envelope means identical corrosion behaviour. The titanium and aluminium content is the only meaningful difference, and the Ti + Al sum determines whether the alloy can age-harden. Incoloy 925's Ti + Al ≈ 2.5%; Incoloy 825's Ti + Al ≈ 1%, below the threshold for effective gamma-prime precipitation.
Mechanical Properties Compared
| Property | Incoloy 925 (Aged, ASTM B805 min) | Incoloy 825 (Annealed, ASTM B423 typ) |
|---|---|---|
| Tensile Strength | 165 ksi (1140 MPa) | 85 ksi (586 MPa) |
| 0.2% Yield Strength | 110 ksi (760 MPa) | 35 ksi (240 MPa) |
| Elongation | 18% min | 30% min |
| Hardness max (sour) | 35 HRC | 30 HRC |
| Strengthening | Gamma-prime Ni₃(Al, Ti) | Solid solution only |
Incoloy 925 delivers ~3× the yield strength of 825 in the as-supplied condition. For applications where strength matters, API 6A wellhead bolting, high-pressure flanged joints, structural fasteners, only 925 qualifies. For applications where strength is secondary, sour-service piping, heat exchangers, vessel cladding, 825 is the cost-effective choice.
Sour-Service Envelope
| Limit | Incoloy 925 (Table A.10) | Incoloy 825 (Table A.7) |
|---|---|---|
| H₂S Partial Pressure max | 1000 psi (6.9 MPa) | 15 psi (0.1 MPa) without restrictions; up to 200 psi with derating |
| Temperature max | 400°F (204°C) | 400°F (204°C) |
| Hardness cap | 35 HRC (CW + aged) | 30 HRC (annealed) |
| Cl⁻ | Saturation | Saturation |
Incoloy 925 is qualified to higher H₂S partial pressure than 825 in NACE MR0175. For high-H₂S sour wells, 925 is the qualified choice; 825 is restricted to low-H₂S production tubing and surface piping.
Cost Comparison
Approximate relative pricing for finished bolting:
- Incoloy 825: ~0.65× baseline, lower titanium content, no age cycle, simpler manufacturing
- Incoloy 925: 1.0× baseline, reflects Ti content + 18-hour age cycle + tighter NDE
- Inconel 718: ~3.0×, reflects high Nb content + aerospace-grade pricing
For a typical sour-service order, the 35% premium for Incoloy 925 over Incoloy 825 buys 3× the yield strength + qualification to higher H₂S envelope. The premium is justified for any bolted joint, rarely justified for thin-wall piping where strength is set by wall thickness rather than alloy yield.
When to Pick Each Alloy
| Application | Recommended Alloy |
|---|---|
| API 6A wellhead / Christmas tree bolting (sour) | Incoloy 925, only 925 meets 110 ksi YS spec |
| Sour-service production tubing (low strength) | Incoloy 825, cost-effective for thin-wall |
| Pressure-vessel cladding (corrosion + strength from carbon-steel substrate) | Incoloy 825 sheet |
| Reducing acid service (sulfuric, phosphoric) | Either, pick on strength + cost |
| Heat exchanger tubing (sour, low pressure) | Incoloy 825 |
| Compact-flange bolting (high preload, sour) | Incoloy 925 |
Frequently Asked Questions
Can Incoloy 825 be age-hardened? No. The Ti content (0.6–1.2%) is too low and the Al content (0.20 max) is essentially zero, so the Ti + Al sum is below the threshold for effective gamma-prime precipitation. Heating Incoloy 825 in the 740°C window has no useful strengthening effect, the alloy was designed for solid-solution behaviour only.
Can Incoloy 925 be supplied in solution-annealed-only condition (matching 825 strength)? Yes, in the SA condition, 925 has ~50 ksi YS (similar to 825). It's an unusual order because the Ti package adds cost without delivering its strengthening benefit; specify "925 SA only" only if there's a downstream age cycle planned by the customer.
Why was Incoloy 925 developed? 925 was developed in the 1980s by Inco (now Special Metals) specifically to bridge the strength gap between Incoloy 825 (sour-service corrosion at low strength) and Inconel 718 (high strength but H₂S-restricted). The deliberate addition of Ti + Al to the 825 chemistry produced an age-hardenable alloy with 825's corrosion envelope and the strength needed for API 6A wellhead bolting.
Are 925 and 825 welded with the same filler? Yes, INCONEL Filler Metal 625 works for both alloys and for dissimilar 925-to-825 joints. INCO-WELD 725NDUR matches Incoloy 925 strength after PWHT but is not commonly used for 825 joints because the higher-strength weld is wasted on a solid-solution base. See welding page for filler selection.
Compare Incoloy 925 to Other Alloys
- Inconel vs Incoloy, What's the difference?
- Incoloy 925 vs Inconel 718, gamma-prime vs gamma double-prime
- Incoloy 925 vs Incoloy 926, oilfield CRA vs super-austenitic
- Incoloy 925 vs Monel K-500, nickel-Fe-Cr vs nickel-Cu
- Incoloy 925 vs Duplex 2205, nickel CRA vs duplex stainless
Request a Quote
For Incoloy 925 with full MTC, or for Incoloy 825 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, hex bolts, pipe, plate), size range, quantity, applicable standards (ASTM B805, ASTM B423 / B424 for 825, API 6A, NACE MR0175), required strength target, and service H₂S partial pressure / temperature for alloy-fit verification.
References: ASTM B805 (UNS N09925); ASTM B423 / B424 / B564 (UNS N08825). Special Metals Corporation: INCOLOY® alloy 925 + INCOLOY® alloy 825 Technical Bulletins. NACE MR0175 / ISO 15156-3 Tables A.7 and A.10. INCOLOY® is a registered trademark of Special Metals Corporation.
