COMPREHENSIVE TECHNICAL ANALYSIS AND DATASHEET OF INCOLOY 825 (UNS N08825) FASTENING SYSTEMS
Incoloy 825 (officially designated as UNS N08825) is a titanium-stabilized, nickel-iron-chromium superalloy engineered for exceptional resistance to a vast range of severely corrosive environments. With a higher nickel content than the 800-series, Alloy 825 provides superior protection against chloride-induced stress corrosion cracking and is specifically fortified with Copper and Molybdenum.
This unique metallurgical synergy makes Alloy 825 remarkably resistant to reducing acids (such as sulfuric and phosphoric acids) as well as oxidizing acids (like nitric acid and oxidizing salts). It is the definitive fastening choice for offshore oil and gas acid-gas (sour) service, chemical processing plants, and nuclear fuel reprocessing facilities where absolute material reliability is mandatory under aggressive chemical attack.
■ Product Overview & Specifications
Incoloy 825 fasteners are typically supplied in the annealed condition to ensure maximum corrosion resistance and structural ductility for high-pressure industrial service.
| Material Classification | Nickel-Iron-Chromium-Molybdenum-Copper Superalloy |
|---|---|
| UNS Designation | N08825 |
| Microstructure | Austenitic |
| Magnetic State | Non-Magnetic |
| Density | ~8.14 g/cm³ (0.294 lb/in³) |
| Melting Range | 2500°F – 2550°F (1370°C – 1400°C) |
| Size Range | Metric: M6 to M100 | Imperial: 1/4" to 4" Custom U-bolts, heavy hex nuts, and threaded rods available. |
| Thread Types | UNC, UNF, 8UN, Metric Coarse, Metric Fine |
■ Proprietary Datasheet Download (GATED)
Access professional-grade technical data for Incoloy 825, including Iso-corrosion charts for Sulfuric Acid, Critical Pitting Temperature (CPT) charts, and NACE MR0175 compliance logs.
Incoloy 825 (N08825) — Complete Technical Datasheet
Contains detailed PREN calculations, stress-corrosion cracking threshold data, and specific installation torque values for sour-gas flanged connections.
⬇ DOWNLOAD DATASHEET■ MTC Integration Section
For critical infrastructure in offshore and chemical environments, Ananka Group provides 100% heat lot traceability and certified validation of the alloy's specialized chemistry.
- EN 10204 Type 3.1: Detailed reporting of actual chemical analysis (verifying Ni, Cr, Mo, Cu, and Ti levels) and mechanical test results (Tensile, Yield, Elongation) to guarantee ASTM/ASME compliance.
- EN 10204 Type 3.2: Third-party witness testing (e.g., ABS, DNV, TUV) facilitated for offshore oil and gas or nuclear fuel reprocessing hardware.
■ Chemical Composition (UNS N08825)
Alloy 825 features a complex balance of elements: Nickel for SCC resistance, Chromium and Molybdenum for pitting resistance, Copper for sulfuric acid resistance, and Titanium for stabilization against intergranular attack.
| Nickel (Ni) | Chromium (Cr) | Iron (Fe) | Copper (Cu) | Moly (Mo) | Titanium (Ti) | Carbon (C) |
|---|---|---|---|---|---|---|
| 38.0 – 46.0 | 19.5 – 23.5 | 22.0 Min | 1.50 – 3.00 | 2.50 – 3.50 | 0.60 – 1.20 | 0.05 Max |
*Manganese (1.0 Max), Silicon (0.5 Max), and Aluminum (0.2 Max) are tightly controlled to maintain the integrity of the austenitic structure.
■ Mechanical Properties
Alloy 825 provides impressive mechanical strength that remains stable from cryogenic temperatures up to approximately 1000°F (540°C), above which other 800-series alloys are generally preferred.
| Property | Annealed Condition (Typical Minimums) |
|---|---|
| Tensile Strength (Min) | 85 ksi (585 MPa) |
| Yield Strength (0.2% Offset, Min) | 35 ksi (240 MPa) |
| Elongation in 2" (Min) | 30% |
| Hardness (Typical) | ~135 - 165 HBW (75 - 90 HRB) |
■ Equivalent Grades & Designations
| Standard / System | Designation |
|---|---|
| UNS Designation | N08825 |
| Common Trade Name | Incoloy 825®, Alloy 825 |
| ASTM Specifications | ASTM B425 (Bar), B424 (Plate), B423 (Pipe) |
| European Equivalent | W.Nr. 2.4858 / NiCr21Mo |
■ Corrosion Resistance Profile
Incoloy 825 is specifically chosen for its resistance to both oxidizing and reducing media:
- Sulfuric & Phosphoric Acids: The addition of Copper provides unique resistance to these reducing acids, outperforming most standard stainless steels.
- Chloride Stress-Corrosion Cracking: High nickel content (over 38%) provides near-immunity to SCC in chloride-rich environments.
- Pitting & Crevice Corrosion: Chromium and Molybdenum provide excellent protection against localized attack in saline and sour gas environments.
- Intergranular Corrosion: Titanium stabilization prevents the precipitation of chromium carbides at grain boundaries during welding or high-heat exposure.
■ Applications & Industries
Alloy 825 is a cornerstone material for aggressive chemical environments:
- Oil & Gas: Subsea piping fasteners, sour gas (H2S) service hardware, and offshore platform splash-zone bolting.
- Chemical Processing: Sulfuric acid pickling tanks, heating coils, and process equipment handling phosphoric and nitric acids.
- Pollution Control: Flue gas desulfurization (FGD) systems and wastewater treatment fasteners.
- Nuclear: Nuclear fuel reprocessing equipment and specialized radioactive waste handling hardware.
■ Compatible Fastener Assemblies
To maintain joint integrity in corrosive media, pairing Alloy 825 with matching nuts and washers is critical to avoid galvanic acceleration.
| External Threads (Incoloy 825) | Recommended Mating Component (Nuts) |
|---|---|
| Incoloy 825 Stud Bolts | Incoloy 825 Heavy Hex Nuts |
| Incoloy 825 Hex Bolts | Incoloy 825 Standard / Jam Nuts |
■ Torque & Installation Guidelines
Alloy 825 is a "gummy" alloy that work-hardens rapidly. High-performance, metal-free or nickel-based anti-seize is mandatory for all installations to prevent thread galling and ensure future maintenance accessibility.
| Nominal Diameter | Threads Per Inch (UNC) | Target Torque — Lubricated (ft-lbs) |
|---|---|---|
| 1/2" | 13 | 45 - 55 |
| 5/8" | 11 | 90 - 110 |
| 3/4" | 10 | 160 - 190 |
| 1" | 8 | 380 - 430 |
■ Why Choose Ananka Group?
Ananka Group delivers precision-engineered 825 fastening solutions for the world's most aggressive industrial environments.
- In-House Manufacturing: Total quality control from raw material sourcing to final thread rolling and inspection.
- Sour Service Expertise: We understand the requirements of NACE MR0175/ISO 15156 and ensure our 825 fasteners meet the necessary hardness limits.
- Precision Threading: Advanced machining protocols specifically for high-nickel alloys to ensure perfect thread profiles.
- 100% Traceability: Every fastener is marked with a heat number and provided with a comprehensive MTC.
■ Frequently Asked Questions
1. How is Alloy 825 different from Alloy 800?
Alloy 825 has a higher Nickel content and adds specific amounts of Copper and Molybdenum. While 800 is primarily for high-temperature strength, 825 is optimized for corrosion resistance, specifically against sulfuric acid and chloride pitting.
2. Is Incoloy 825 suitable for sour gas (H2S)?
Yes. Alloy 825 is widely used in sour service. It is listed in NACE MR0175 for use in oil and gas production environments due to its high resistance to sulfide stress cracking.
3. Can 825 fasteners be used in sulfuric acid?
Absolutely. Alloy 825 is one of the premier materials for handling sulfuric acid at various concentrations and temperatures due to its high copper and nickel content.
4. Is Alloy 825 magnetic?
No. Incoloy 825 is a fully austenitic alloy and remains non-magnetic across all standard operating conditions and temperatures.