COMPREHENSIVE TECHNICAL ANALYSIS AND DATASHEET OF INCOLOY 925 (UNS N09925) FASTENING SYSTEMS
Incoloy 925 (officially designated as UNS N09925) is an age-hardenable nickel-iron-chromium superalloy. It was engineered to deliver the exceptional, world-class corrosion resistance of Incoloy 825, but with the added capability of reaching immense structural strength through a precipitation-hardening heat treatment. By fortifying the standard 825 chemistry with precise additions of Titanium and Aluminum, metallurgists created an alloy capable of forming microscopic strengthening precipitates (the gamma-prime phase).
This unique metallurgical profile makes Alloy 925 exceptionally resistant to sulfide stress cracking, chloride-induced stress-corrosion cracking, and localized pitting. Consequently, it has become the ultimate fastening standard for the most demanding "sour gas" (hydrogen sulfide) environments in the global offshore oil and gas industry, where high-pressure containment and lethal chemical resistance must coexist.
■ Product Overview & Specifications
Incoloy 925 fasteners are supplied in the solution-annealed and aged condition to guarantee both high yield strength and NACE MR0175 compliance for sour service applications.
| Material Classification | Precipitation-Hardenable Nickel-Iron-Chromium Superalloy |
|---|---|
| UNS Designation | N09925 |
| Microstructure | Austenitic Matrix with Gamma-Prime [Ni3(Ti,Al)] Precipitates |
| Magnetic State | Consistently Non-Magnetic |
| Density | ~8.08 g/cm³ (0.292 lb/in³) |
| Melting Range | 2400°F – 2500°F (1315°C – 1370°C) |
| Size Range | Metric: M6 to M100 | Imperial: 1/4" to 4" Custom subsea valve bolting and wellhead studs available. |
| Thread Types | UNC, UNF, 8UN, Metric Coarse, Metric Fine |
■ Proprietary Datasheet Download (GATED)
Access professional-grade technical data for Incoloy 925, including optimized age-hardening cycles, NACE MR0175 maximum hardness limits, and specific H2S stress cracking thresholds.
Incoloy 925 (N09925) — Complete Technical Datasheet
Contains detailed multi-stage aging parameters, elevated temperature tensile retention curves up to 1000°F, and severe-service torque mapping for API 6A wellhead equipment.
⬇ DOWNLOAD DATASHEET■ MTC Integration Section
To ensure absolute compliance with lethal-service sour gas safety protocols, Ananka Group provides extensive metallurgical certification validating both chemistry and final aged properties.
- EN 10204 Type 3.1: Detailed reporting of actual ladle chemical analysis, specifically verifying Titanium/Aluminum levels for aging, and final mechanical tests (Yield, Tensile, Hardness) proving NACE compliance.
- EN 10204 Type 3.2: Third-party witness testing (e.g., ABS, DNV GL, Lloyd's) heavily utilized for critical offshore platforms and subsea completion hardware.
■ Chemical Composition (UNS N09925)
The foundation is similar to Alloy 825 (high Nickel for chloride resistance, Chromium/Molybdenum for pitting, and Copper for reducing acids). The critical difference is the higher Titanium content, which drives the precipitation-hardening reaction.
| Nickel (Ni) | Chromium (Cr) | Iron (Fe) | Moly (Mo) | Copper (Cu) | Titanium (Ti) | Aluminum (Al) |
|---|---|---|---|---|---|---|
| 38.0 – 46.0 | 19.5 – 22.5 | 22.0 Min | 2.50 – 3.50 | 1.50 – 3.00 | 1.90 – 2.40 | 0.10 – 0.50 |
*Carbon is strictly limited to 0.03% Max to prevent carbide precipitation during aging, ensuring maximum corrosion resistance.
■ Mechanical Properties & Precipitation Hardening
Incoloy 925 relies on a specialized aging process (typically holding at ~1350°F / 732°C for 8 hours, furnace cooling to ~1150°F / 621°C, holding for another 8 hours, then air cooling). This creates a strength profile that rivals high-strength carbon steels while providing superalloy corrosion resistance.
| Property | Solution Annealed (Base) | Solution Annealed & Aged (Typical) |
|---|---|---|
| Tensile Strength (Min) | 90 ksi (620 MPa) | 165 - 170 ksi (1140 - 1170 MPa) |
| Yield Strength (0.2% Offset, Min) | 40 ksi (275 MPa) | 115 - 120 ksi (790 - 825 MPa) |
| Elongation in 2" (Min) | 40% | 20% |
| Hardness | ~85 HRB | 32 to 43 HRC (Max 38 HRC for NACE) |
■ Equivalent Grades & Designations
| Standard / System | Designation |
|---|---|
| UNS Designation | N09925 |
| Common Trade Name | Incoloy 925®, Alloy 925 |
| Industry Standards | API 6A, NACE MR0175 / ISO 15156 |
| ASTM Fastener Specs | ASTM B805 (Bar) |
■ Applications & Industries
Alloy 925 is specifically mandated in high-pressure environments where the combination of deadly H2S gas, chlorides, and immense physical stress would destroy lesser alloys.
- Offshore Oil & Gas: Subsea wellheads, surface blow-out preventers (BOP), hangers, and downhole tool joints exposed to sour gas.
- Valve Manufacturing: High-pressure stems, seats, and severe-service fastening assemblies for chemical and petro-valves.
- Marine & Subsea: High-strength shafting and high-load structural fasteners exposed continuously to stagnant seawater.
- Refining: High-strength bolting for separators and heat exchangers handling aggressive acidic crudes.
■ Compatible Fastener Assemblies
To avoid galvanic corrosion in conductive electrolytes (like seawater or sour brine) and to ensure uniform strength, 925 components are almost always mated with identical grades.
| External Threads (Incoloy 925) | Recommended Mating Component (Nuts) |
|---|---|
| Incoloy 925 Stud Bolts (Aged) | Incoloy 925 Heavy Hex Nuts (Aged) |
| Incoloy 925 Stud Bolts (Aged) | Inconel 718 Nuts (Acceptable high-strength alternative) |
■ Torque & Installation Guidelines
Because Alloy 925 provides extremely high yield strength, it can sustain massive clamping forces. However, it remains highly susceptible to thread galling. High-pressure, extreme-duty anti-seize lubricants (such as MoS2 or Nickel-based compounds) are strictly mandatory.
| Nominal Diameter | Threads Per Inch (UNC) | Target Torque (Aged Condition) — Lubricated (ft-lbs) |
|---|---|---|
| 1/2" | 13 | 65 - 80 |
| 5/8" | 11 | 130 - 150 |
| 3/4" | 10 | 230 - 270 |
| 1" | 8 | 550 - 620 |
■ Why Choose Ananka Group?
Ananka Group delivers flawless execution of complex precipitation-hardening cycles to provide the global energy sector with infallible sour-service bolting.
- In-House Thermal Processing: Complete control over the multi-stage aging cycle, ensuring the exact precipitation of the gamma-prime phase for optimal strength.
- NACE MR0175 Compliance: We rigorously test and certify that all Alloy 925 fasteners remain below the 38 HRC maximum hardness limit required to prevent sulfide stress cracking.
- Machining Before Aging: To guarantee perfect thread profiles, we can machine components in the softer, solution-annealed state before performing the final age-hardening treatment, reducing tool wear and thread tearing.
- 100% Traceability: Heat numbers permanently stamped on every fastener, mapped directly back to premium superalloy mill certificates.
■ Frequently Asked Questions
1. What is the fundamental difference between Incoloy 825 and 925?
They share a nearly identical base chemistry, giving them the same world-class corrosion resistance against reducing acids and sour gas. However, Alloy 825 cannot be hardened by heat treatment and has a relatively low yield strength (~35 ksi). Alloy 925 adds Titanium and Aluminum, allowing it to be age-hardened to a massive yield strength of over 115 ksi, making it suitable for high-pressure structural loads.
2. Is Incoloy 925 approved for Sour Gas (H2S) environments?
Yes. Alloy 925 is heavily utilized in sour service and is fully approved under NACE MR0175 / ISO 15156, provided the final aged hardness is carefully controlled to remain at or below 38 HRC (353 HBW).
3. Can Incoloy 925 be welded?
Welding Alloy 925 is possible but challenging, as it is a precipitation-hardenable alloy. It should generally be welded in the solution-annealed condition and then subjected to the full age-hardening process post-weld to restore its mechanical strength across the joint.
4. Does the aging process cause dimensional distortion?
The precipitation-hardening process for Alloy 925 causes a very slight contraction (shrinkage) in the material. For highly precise tolerance components, this minimal dimensional change is usually accounted for during the CNC machining phase prior to aging.