UNS N09925 Stud Bolt | Alloy 925 High-Strength Fasteners
UNS N09925 stud bolts are high-strength, precipitation-hardened nickel-iron-chromium alloy fasteners designed for corrosive oil and gas, offshore and sour-service applications. The alloy contains nickel, chromium, molybdenum, copper, titanium and aluminum, combining high mechanical strength with resistance to chloride stress-corrosion cracking, pitting, crevice corrosion and many H₂S-containing environments.
We manufacture and supply UNS N09925 stud bolts, threaded studs and matching corrosion-resistant nuts in project-specific diameters, thread forms and lengths, with controlled heat treatment, PMI, hardness testing and EN 10204 3.1 certification.
UNS N09925 Stud Bolt Quick Specification
| Item | Specification |
|---|---|
| Material | UNS N09925 |
| Common Designation | Alloy 925 |
| Material Family | Precipitation-Hardenable Ni-Fe-Cr Alloy |
| Material Standard | ASTM B637 where applicable |
| Stud Standard | ASME B18.31.2 for inch-series flange studs where specified |
| Thread Standard | ASME B1.1 or project-specified thread standard |
| Product Types | Continuous Thread Stud / Flange Stud / Double-End Stud |
| Condition | Solution Treated + Precipitation Hardened |
| Service | Oil & Gas / Offshore / Sour Service / High-Pressure Equipment |
| Certification | EN 10204 3.1 / 3.2 when specified |
What Is UNS N09925?
UNS N09925 is an age-hardenable nickel-iron-chromium alloy containing molybdenum, copper, titanium and aluminum.
The alloy is engineered to combine:
- High tensile and yield strength
- Resistance to chloride stress-corrosion cracking
- Resistance to pitting and crevice corrosion
- Good resistance in many H₂S and CO₂ environments
- Resistance to several reducing chemical environments
- Good mechanical performance for demanding oil and gas equipment
Its high-strength condition is developed through solution treatment followed by precipitation hardening.
This makes N09925 fundamentally different from conventional carbon or low-alloy steel bolting materials.
UNS N09925 Chemical Composition
Typical ASTM B637 composition limits for UNS N09925 include:
| Element | UNS N09925 |
|---|---|
| Nickel, Ni | 42.0–46.0% |
| Chromium, Cr | 19.5–22.5% |
| Iron, Fe | 22.0% min |
| Molybdenum, Mo | 2.5–3.5% |
| Copper, Cu | 1.5–3.0% |
| Titanium, Ti | 1.9–2.4% |
| Aluminum, Al | 0.10–0.50% |
| Niobium, Nb | 0.50% max |
| Carbon, C | 0.03% max |
| Manganese, Mn | 1.00% max |
| Silicon, Si | 0.50% max |
| Phosphorus, P | 0.030% max |
| Sulfur, S | 0.030% max |
The Ni-Cr-Mo-Cu-Ti-Al alloying system provides both corrosion resistance and precipitation-hardening capability.
Actual heat chemistry is reported on the Material Test Certificate.
UNS N09925 Mechanical Properties
UNS N09925 develops high strength after solution treatment and precipitation hardening.
Typical ASTM B637 minimum requirements depend on product size and working condition.
| Condition | Tensile Strength, min. | Yield Strength, min. | Elongation, min. | Reduction of Area, min. | Hardness |
|---|---|---|---|---|---|
| Cold-Worked Range | 965 MPa / 140 ksi | 724 MPa / 105 ksi | 18% | 25% | 38 HRC max |
| Hot-Worked Range | 965 MPa / 140 ksi | 758 MPa / 110 ksi | 18% | 25% | 38 HRC max |
The applicable mechanical requirement depends on the product diameter, working route and ordered material condition.
Actual tensile, yield, elongation, reduction-of-area and hardness results are reported on the supplied MTC.
Heat Treatment of UNS N09925 Stud Bolts
Heat treatment is one of the most important controls for N09925 bolting.
The material is generally processed through:
Solution Treatment → Controlled Cooling → Precipitation / Age Hardening
The precipitation-hardening cycle develops the high strength required for demanding fastening applications.
Correct heat treatment is important because it directly affects:
- Tensile strength
- Yield strength
- Hardness
- Toughness
- Corrosion behavior
- Sour-service performance
For critical oil and gas applications, heat-treatment records and hardness results can be supplied as part of the material documentation.
Stud Bolt and Thread Standards
The material specification and the stud dimensional standard perform different functions.
ASTM B637 covers precipitation-hardenable nickel-alloy bars, forgings and forging stock and can be used as the material basis for N09925 bolting stock where applicable.
For inch-series flange studs, ASME B18.31.2 covers dimensional and general requirements for:
- Continuous-thread studs
- Flange bolting studs
- Double-end studs
Thread geometry can be specified to ASME B1.1 for Unified inch screw threads.
Metric threads or project-specific thread forms can also be manufactured when specified.
A typical stud-bolt purchase description may include:
UNS N09925, Fully Threaded Stud, 1-1/4″-8 UNC, 250 mm Long, Solution Treated + Age Hardened
UNS N09925 Stud Bolts for Sour Service
UNS N09925 is widely used in high-strength oil and gas components exposed to sour environments containing H₂S and CO₂.
Typical applications include:
- Wellhead equipment
- Subsea equipment
- Valves
- Hangers
- Packers
- High-pressure connectors
- Downhole tools
- Offshore fasteners
- Sour-gas systems
- Pressure-control equipment
The alloy combines high strength with resistance to sulfide-related cracking and chloride stress-corrosion cracking under suitable material conditions.
Sour-service suitability is not determined by the UNS designation alone.
Final compliance depends on factors including:
- Heat treatment
- Hardness
- Product form
- Stress level
- H₂S partial pressure
- Chloride concentration
- Temperature
- pH
- Applicable NACE / ISO requirements
- Project material specification
NACE MR0175 / ISO 15156 compliance can therefore be supplied when the specified material condition and application requirements are satisfied.
Available Stud Bolt Types
UNS N09925 bolting can be manufactured in several configurations.
| Product | Description |
|---|---|
| Fully Threaded Stud | Threaded over the full length |
| Flange Stud Bolt | Used with two nuts for flange joints |
| Double-End Stud | Threads provided at both ends |
| Custom Stud | Manufactured to drawing or project specification |
| Hex Bolt | Available when specified by the applicable design |
Available thread options can include:
- UNC
- UNF
- 8UN
- Metric coarse
- Metric fine
- Project-specific threads
Diameter, length, thread pitch and thread class should be stated in the purchase order.
Matching Nuts for N09925 Stud Bolts
N09925 stud bolts should not automatically be paired with conventional carbon-steel nuts.
Matching nuts can be supplied in:
- Project-specified nickel alloy
- Corrosion-resistant alloy
- High-strength CRA material
- Other approved bolting material
Nut selection should consider:
- Required proof strength
- Stud-bolt strength
- Corrosion environment
- Galvanic compatibility
- Flange material
- Operating temperature
- Sour-service requirements
- Applicable project specification
For severe corrosion or sour-service applications, the complete stud + nut assembly should be evaluated as one bolting system.
Corrosion Resistance
UNS N09925 provides a combination of high strength and corrosion resistance that is useful in aggressive oil and gas environments.
Important characteristics include resistance to:
- Chloride stress-corrosion cracking
- Sulfide-containing environments
- Pitting corrosion
- Crevice corrosion
- CO₂-containing production environments
- Seawater
- Several reducing acid environments
Nickel contributes strongly to resistance against chloride stress-corrosion cracking.
Molybdenum improves pitting and crevice-corrosion resistance, while copper contributes to resistance in selected reducing environments.
Chromium improves resistance under oxidizing conditions.
Final material selection should always be based on actual process conditions.
UNS N09925 vs N07725 Bolting
UNS N09925 and UNS N07725 are both precipitation-hardenable corrosion-resistant alloys used in demanding oil and gas applications.
| Item | UNS N09925 | UNS N07725 |
|---|---|---|
| Alloy Type | Ni-Fe-Cr-Mo-Cu-Ti | Ni-Cr-Mo-Nb-Ti |
| Ni Content | ~42–46% | Higher |
| Mo Content | 2.5–3.5% | Higher |
| Cu Addition | 1.5–3.0% | Limited |
| Strength | High | High |
| Sour-Service Use | Common when qualified | Common when qualified |
| Typical Selection | High-strength sour oil & gas components | Severe corrosive oil & gas service |
The appropriate bolting alloy depends on strength requirements, environment, hardness limits, temperature and project specifications.
Inspection & Certification
UNS N09925 stud bolts can be supplied with:
- EN 10204 Type 3.1 MTC
- EN 10204 Type 3.2 when specified
- Heat chemical analysis
- Tensile test results
- Yield-strength results
- Elongation and reduction-of-area results
- Hardness testing
- Heat-treatment records
- PMI
- Dimensional inspection
- Thread inspection
- Visual examination
- UT when specified
- Sour-service documentation when required
- Third-party inspection
- Full heat-number traceability
Thread dimensions can be inspected using the applicable gauges and project acceptance criteria.
Frequently Asked Questions
What is a UNS N09925 stud bolt?
A UNS N09925 stud bolt is a high-strength corrosion-resistant fastener manufactured from precipitation-hardenable nickel-iron-chromium alloy N09925. It is commonly used in demanding oil and gas, offshore and sour-service equipment.
Is UNS N09925 precipitation hardened?
Yes. N09925 is solution treated and precipitation hardened to develop its required high-strength condition. Heat treatment is a critical part of controlling mechanical properties, hardness and sour-service performance.
Is UNS N09925 suitable for H₂S sour service?
UNS N09925 is widely used in sour oil and gas applications, but sour-service suitability depends on the exact heat treatment, hardness, environmental conditions and applicable NACE MR0175 / ISO 15156 or project requirements.
The UNS grade alone does not guarantee compliance for every H₂S environment.
What standard covers UNS N09925 stud bolts?
ASTM B637 can provide the material basis for N09925 bar or forging stock, while stud dimensions and threads are specified separately. ASME B18.31.2 can be used for inch-series flange studs, and ASME B1.1 can be used for Unified inch threads.
What nuts are used with N09925 stud bolts?
Matching nuts should be selected according to the required mechanical strength, corrosion environment, flange material and project specification.
For severe corrosive or sour service, corrosion-resistant nickel-alloy or project-approved CRA nuts are commonly specified rather than automatically using conventional carbon-steel nuts.
N09925 Stud Bolt Hex Nuts
UNS N09925 Stud Bolt Manufacturer
We manufacture and supply UNS N09925 stud bolts, fully threaded studs, double-end studs and matching corrosion-resistant nuts for oil and gas, offshore, subsea, wellhead and sour-service applications.
Available manufacturing and inspection options include:
UNC / UNF / 8UN / Metric Threads, Custom Lengths, Solution Treatment + Age Hardening, PMI, Hardness Testing, Thread Inspection and EN 10204 Certification.
For quotation, please specify:
Material + Product Type + Diameter + Thread + Length + Nut Requirement + Quantity + Material Condition + Inspection / Sour-Service Requirements
Example:
UNS N09925 Stud Bolt, 1-1/4″-8UN, 300 mm Long, Fully Threaded, Solution Treated + Precipitation Hardened, Matching CRA Nuts, EN 10204 3.1
