COMPREHENSIVE TECHNICAL ANALYSIS AND DATASHEET OF INCONEL 690 / ALLOY 690 (UNS N06690) FASTENING SYSTEMS
Inconel 690 (officially designated as UNS N06690) is a high-chromium nickel alloy engineered specifically to address the vulnerabilities of earlier nickel alloys (such as Alloy 600) in nuclear environments. By increasing the Chromium content to approximately 30%, metallurgists significantly enhanced the alloy's resistance to oxidizing chemicals, sulfidation, and—most critically—primary water stress corrosion cracking (PWSCC).
This metallurgical refinement makes Alloy 690 the global standard for modern Pressurized Water Reactors (PWRs). It exhibits near-immunity to chloride-induced stress corrosion cracking and maintains excellent structural stability at elevated temperatures. Beyond nuclear applications, its robust chromium base makes it a premier fastening material for coal gasification, vitrification of radioactive waste, and high-temperature petrochemical processing involving aggressive oxidizing media.
■ Product Overview & Specifications
Alloy 690 fasteners are typically supplied in the thermally treated (annealed) condition to ensure optimal carbide distribution along grain boundaries, which is crucial for maximizing resistance to intergranular stress corrosion cracking.
| Material Classification | Nickel-Chromium-Iron Superalloy |
|---|---|
| UNS Designation | N06690 (Alloy 690) |
| Microstructure | Face-Centered Cubic (FCC) Austenitic |
| Magnetic State | Non-Magnetic |
| Density | ~8.19 g/cm³ (0.296 lb/in³) |
| Melting Range | 2450°F – 2510°F (1343°C – 1377°C) |
| Size Range | Metric: M6 to M100 | Imperial: 1/4" to 4" Custom nuclear-grade heavy hex bolting available. |
| Thread Types | UNC, UNF, 8UN, Metric Coarse, Metric Fine (Rolled threads recommended) |
■ Proprietary Datasheet Download (GATED)
Access professional-grade technical data for Inconel / Alloy 690, including Primary Water Stress Corrosion Cracking (PWSCC) test data, thermal expansion coefficients for nuclear steam generators, and high-temperature oxidation thresholds.
Alloy 690 / Inconel 690 (N06690) — Complete Technical Datasheet
Contains detailed ASME Section III (Nuclear Facility Components) design stress intensity values, specialized thermal treatment parameters, and welding compatibility charts.
⬇ DOWNLOAD DATASHEET■ MTC Integration Section
Because Alloy 690 is a critical safety component in nuclear power generation, Ananka Group provides absolute metallurgical verification mapping back to the original melt.
- EN 10204 Type 3.1: Mandatory reporting of actual chemical analysis (verifying the critical 30% Chromium level), mechanical property verification, and thermal treatment certification.
- EN 10204 Type 3.2: Third-party witness testing facilitated for nuclear steam generator bolting and critical high-level waste vitrification systems.
■ Chemical Composition (UNS N06690)
The alloy features a high Nickel base for resistance to chloride stress-corrosion cracking and a massive ~30% Chromium content for exceptional resistance to oxidizing media and high-temperature sulfidation.
| Nickel (Ni) | Chromium (Cr) | Iron (Fe) | Carbon (C) | Manganese (Mn) | Silicon (Si) | Copper (Cu) |
|---|---|---|---|---|---|---|
| 58.0 Min | 27.0 – 31.0 | 7.0 – 11.0 | 0.05 Max | 0.50 Max | 0.50 Max | 0.50 Max |
*Sulfur (0.015 Max) is tightly controlled. Cobalt is often restricted for nuclear applications to minimize the formation of radioactive Co-60 isotopes under neutron irradiation.
■ Mechanical Properties
Alloy 690 provides moderate to high strength at room temperature and maintains significant structural integrity at elevated temperatures, making it highly reliable for pressurized thermal systems.
| Property | Annealed / Thermally Treated Condition |
|---|---|
| Tensile Strength (Min) | 85 ksi (586 MPa) |
| Yield Strength (0.2% Offset, Min) | 35 ksi (241 MPa) |
| Elongation in 2" (Min) | 30% |
| Hardness (Typical) | ~85 HRB |
■ Equivalent Grades & Designations
| Standard / System | Designation |
|---|---|
| UNS Designation | N06690 |
| Common Trade Name | Inconel 690®, Alloy 690 |
| ASTM Specifications | ASTM B166 (Bar/Rod), ASTM B168 (Plate/Sheet/Strip) |
| European Equivalent | W.Nr. 2.4642 / NiCr29Fe |
■ Corrosion Resistance Profile
Alloy 690 was specifically engineered to solve the corrosion challenges faced by earlier alloys in specific environments:
- Primary Water Stress Corrosion Cracking (PWSCC): Demonstrates near-total immunity to PWSCC in the high-temperature pure water environments of Pressurized Water Reactors (PWRs).
- Oxidizing Acids: Exceptional resistance to nitric acid and hydrofluoric acid mixtures, crucial for nuclear fuel reprocessing and pickling operations.
- Sulfidation: High chromium content provides superior resistance to high-temperature sulfidation in coal gasification processes.
- Chloride SCC: High nickel content ensures excellent resistance to chloride-ion stress-corrosion cracking.
■ Applications & Industries
Alloy 690 is the material of choice when extreme reliability is required in oxidizing and nuclear environments:
- Nuclear Power: Steam generator tubing, baffles, and critical structural bolting in Pressurized Water Reactors (PWRs).
- Waste Vitrification: Fastening systems and hardware used in the high-temperature vitrification (glassification) of highly radioactive liquid waste.
- Petrochemical & Refining: Heat exchangers and piping systems handling nitric acid and other aggressive oxidizing chemicals.
- Coal Gasification: Structural components exposed to high-temperature sulfidizing atmospheres.
■ Compatible Fastener Assemblies
To avoid galvanic corrosion and ensure uniform thermal expansion across joint assemblies in high-heat systems, mating components must match metallurgically.
| External Threads (Alloy 690) | Recommended Mating Component (Nuts) |
|---|---|
| Alloy 690 Stud Bolts | Alloy 690 Heavy Hex Nuts |
| Alloy 690 Hex Bolts | Alloy 690 Standard / Jam Nuts |
■ Torque & Installation Guidelines
Like all nickel-based alloys, Alloy 690 is susceptible to thread galling. The use of high-quality, high-temperature anti-seize lubrication is non-negotiable for accurate installation and future maintenance.
| Nominal Diameter | Threads Per Inch (UNC) | Target Torque — Lubricated (ft-lbs) |
|---|---|---|
| 1/2" | 13 | 40 - 50 |
| 5/8" | 11 | 80 - 100 |
| 3/4" | 10 | 140 - 170 |
| 1" | 8 | 340 - 390 |
■ Why Choose Ananka Group?
Ananka Group operates at the pinnacle of high-temperature alloy manufacturing, ensuring that your extreme-environment infrastructure remains secure.
- Nuclear-Grade Supply Chain: We can source and process specialized low-cobalt Alloy 690 required for neutron-irradiated zones.
- Precision Thread Rolling: Threads are rolled rather than cut whenever possible, significantly increasing cyclic fatigue resistance.
- Advanced Machining: Expertise in handling tough-to-machine nickel alloys to ensure perfect thread profiles and dimensional accuracy.
- 100% Traceability: Every fastener is heat-lot tracked and mapped directly back to premium steel mill certificates compliant with ASME BPVC codes.
■ Frequently Asked Questions
1. What makes Alloy 690 an upgrade over Alloy 600?
Alloy 600 (~15% Chromium) was widely used in early nuclear reactors but proved susceptible to Primary Water Stress Corrosion Cracking (PWSCC) over decades of service. Alloy 690 doubles the Chromium content (to ~30%), which dramatically improves resistance to PWSCC, making it the modern standard for PWR replacement components.
2. Why is Cobalt restricted in nuclear-grade Alloy 690?
In the reactor core environment, natural Cobalt (Co-59) can absorb a neutron and transmute into Cobalt-60, a highly radioactive isotope with a long half-life. Restricting Cobalt minimizes long-term radiation levels, making maintenance and eventual decommissioning safer.
3. Is Alloy 690 magnetic?
No. Because its base microstructure is fully austenitic, Alloy 690 remains completely non-magnetic under standard operating conditions.
4. Does Alloy 690 require a special "thermal treatment"?
For nuclear steam generator applications, Alloy 690 is often given a specific "Thermal Treatment" (TT) after annealing. This process (typically ~1320°F/715°C for several hours) optimizes the precipitation of carbides along the grain boundaries, further enhancing resistance to intergranular stress corrosion cracking.