COMPREHENSIVE TECHNICAL ANALYSIS AND DATASHEET OF INCOLOY 800AT (UNS N08811) FASTENING SYSTEMS
Incoloy 800AT (often colloquially referred to as Inconel 800AT) is a specialized variant of the 800-series nickel-iron-chromium alloys. Officially falling under the UNS N08811 designation alongside Incoloy 800HT, the "AT" nomenclature specifically highlights the strict control and optimization of Aluminum (A) and Titanium (T). This precise chemistry, combined with a mandatory high-temperature solution anneal, creates a coarse-grained microstructure optimized for maximum creep and stress-rupture resistance.
Engineered for long-term reliability in the most severe thermal environments, Alloy 800AT excels where temperatures exceed 1300°F (704°C). It provides significantly higher allowable design stresses than standard Alloy 800 or 800H, making it the definitive choice for critical power generation components, hydrocarbon cracking tubes, and high-performance industrial furnace hardware where structural elongation (creep) is the primary mode of failure.
■ Product Overview & Specifications
Incoloy 800AT fasteners are supplied in a specialized high-temperature solution-annealed state to ensure a coarse grain structure (ASTM No. 5 or coarser), which is absolutely essential for surviving high-temperature creep loads.
| Material Classification | Super-Creep-Resistant Nickel-Iron-Chromium Alloy |
|---|---|
| UNS Designation | N08811 |
| Microstructure | Austenitic (Coarse Grain Size mandatory) |
| Magnetic State | Non-Magnetic |
| Density | ~7.94 g/cm³ (0.287 lb/in³) |
| Size Range | Metric: M6 to M100 | Imperial: 1/4" to 4" Custom high-stress turbine bolts and furnace hangers available. |
| Thread Types | UNC, UNF, 8UN, Metric Coarse, Metric Fine |
| Strengthening Method | Solid Solution + Grain Boundary Stabilization |
■ Proprietary Datasheet Download (GATED)
Access professional-grade technical data for Incoloy 800AT, including Larson-Miller Creep parameters, ASME Section II allowable stress curves, and prolonged thermal stability charts.
Incoloy 800AT (N08811) — Complete Technical Datasheet
Contains detailed stress-to-rupture thresholds for 10,000 and 100,000 hours, Al+Ti combination mapping, and specific dry/lubricated installation values for high-heat flanges.
⬇ DOWNLOAD DATASHEET■ MTC Integration Section
For high-pressure thermal infrastructure, Ananka Group provides 100% heat lot traceability and certified testing that strictly validates the "AT" chemistry and grain size requirements.
- EN 10204 Type 3.1: Mandatory reporting of restricted Carbon (0.06–0.10%), Al+Ti sum (0.85–1.20%), and Grain Size (ASTM No. 5 or coarser), alongside certified solution anneal temperature.
- EN 10204 Type 3.2: Third-party witness testing facilitated for critical boiler systems or petrochemical reactor headers.
■ Chemical Composition (UNS N08811)
The core chemistry of 800AT is defined by its tight controls. The minimum Carbon is set to 0.06%, and the Aluminum + Titanium sum must fall exactly between 0.85% and 1.20% to ensure the highest possible creep strength without inducing embrittlement.
| Nickel (Ni) | Chromium (Cr) | Aluminum (Al) | Titanium (Ti) | Al + Ti | Carbon (C) | Iron (Fe) |
|---|---|---|---|---|---|---|
| 30.0 – 35.0 | 19.0 – 23.0 | 0.25 – 0.60 | 0.25 – 0.60 | 0.85 – 1.20 | 0.06 – 0.10 | 39.5 Min |
*Manganese (1.50 Max) and Silicon (1.00 Max) are strictly controlled to maintain structural integrity under prolonged thermal cycling.
■ Mechanical Properties & Creep Resistance
800AT is utilized where structural failure would occur via creep rupture. Its high allowable stress values in the 1300°F–1700°F range make it superior to almost any other iron-base high-temperature alloy.
| Property | Room Temperature (Annealed) | At 1400°F (760°C) |
|---|---|---|
| Tensile Strength (Min) | 65 ksi (450 MPa) | ~45 ksi (310 MPa) |
| Yield Strength (0.2% Offset, Min) | 25 ksi (170 MPa) | ~18 ksi (125 MPa) |
| Elongation in 2" (Min) | 30% | ~45% |
| 10,000-Hour Rupture Stress | N/A | ~10 ksi (69 MPa) |
■ Equivalent Grades & Designations
| Standard / System | Designation |
|---|---|
| UNS Designation | N08811 |
| Common Trade Name | Incoloy 800AT®, Alloy 800AT |
| ASTM Fastener Specs | ASTM B408 (Bar), ASTM B409 (Plate) |
| European Equivalent | W.Nr. 1.4959 / X8NiCrAlTi32-21 |
■ Applications & Industries
Alloy 800AT is the premium choice for components that must endure decades of stress at extreme temperatures:
- Ethylene Production: Pigtails, headers, and internal bolting for hydrocarbon cracking furnaces.
- Chemical Processing: Retorts, nitric acid cooler-condenser fasteners, and process piping.
- Power Generation: Superheater tubing fasteners and structural steam components in high-efficiency plants.
- Thermal Processing: Heavy-duty radiant tubes, muffle fasteners, and furnace fixtures operating up to 1700°F.
■ Compatible Fastener Assemblies
To ensure uniform thermal expansion and consistent creep life across the joint, Alloy 800AT components should always be paired with matching nuts and washers.
| External Threads (Incoloy 800AT) | Recommended Mating Component (Nuts) |
|---|---|
| Incoloy 800AT Stud Bolts | Incoloy 800AT Heavy Hex Nuts |
| Incoloy 800AT Hex Bolts | Incoloy 800AT Standard / Heavy Hex Nuts |
■ Torque & Installation Guidelines
At the service temperatures typical for 800AT, thread seizure (cold welding) is a high risk. The use of high-purity, metal-free or nickel-based anti-seize is mandatory for installation.
| Nominal Diameter | Threads Per Inch (UNC) | Target Torque — Lubricated (ft-lbs) |
|---|---|---|
| 1/2" | 13 | 35 - 45 |
| 5/8" | 11 | 70 - 90 |
| 3/4" | 10 | 120 - 150 |
| 1" | 8 | 300 - 350 |
■ Why Choose Ananka Group?
Ananka Group specializes in the complex manufacturing of severe-service nickel alloys, ensuring your critical thermal joints remain secure.
- Chemical Precision: We verify that the Al+Ti sum and Carbon levels strictly meet the 800AT standard for maximum creep resistance.
- Coarse Grain Verification: Every batch is tested to ensure a grain size of ASTM No. 5 or coarser, as mandated by code for high-temperature service.
- In-House Manufacturing: Complete production control from raw alloy selection through to precision thread rolling and quality assurance.
- 100% Traceability: Every fastener is marked with a heat number and provided with a comprehensive MTC.
■ Frequently Asked Questions
1. Is it Incoloy 800AT or Inconel 800AT?
Technically, it is Incoloy 800AT. The "Incoloy" prefix is used for nickel-iron-chromium alloys (where iron is a major component, ~40%), while "Inconel" is reserved for predominantly nickel-chromium alloys. However, "Inconel 800AT" is a very common industry misnomer.
2. What is the difference between 800HT and 800AT?
Metallurgically, they are essentially identical and both fall under the UNS N08811 designation. "800HT" is the broader industry standard, while "800AT" was a specific trade designation highlighting the controlled Aluminum and Titanium additions used by certain metal producers.
3. Why is grain size so important for 800AT?
At extreme temperatures, metals deform primarily through "grain boundary sliding." A coarse grain structure (ASTM No. 5 or larger) reduces the total surface area of grain boundaries in the metal, which significantly slows down this deformation, thereby increasing the material's creep and rupture strength.
4. Does 800AT resist carburization?
Yes. The high Nickel (30-35%) and Chromium (~20%) content provide excellent resistance to both oxidation and carburizing atmospheres, making it the premier choice for internal combustion furnace components and ethylene cracking pigtails.