COMPREHENSIVE TECHNICAL ANALYSIS AND DATASHEET OF INCOLOY 800HT (UNS N08811) FASTENING SYSTEMS
Incoloy 800HT (officially designated as UNS N08811) represents the peak of the 800-series nickel-iron-chromium alloys. While sharing the same base chemistry as 800 and 800H, the "HT" variant is characterized by further restricted levels of Aluminum and Titanium (combined 0.85–1.20%). This precise chemistry, combined with a mandatory high-temperature solution anneal, creates a microstructure optimized for maximum creep and stress-rupture resistance.
Alloy 800HT is engineered for long-term reliability in the most severe thermal environments, particularly where temperatures exceed 1300°F (704°C). It provides significantly higher allowable design stresses than its predecessors, making it the definitive choice for critical power generation components, chemical processing retorts, and high-performance industrial furnace hardware.
■ Product Overview & Specifications
Incoloy 800HT fasteners are supplied in a specialized high-temperature solution-annealed state to ensure a coarse grain structure (ASTM No. 5 or coarser), which is 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 800HT, including Larson-Miller Creep parameters, ASME Section II allowable stress curves, and prolonged thermal stability charts.
Incoloy 800HT (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 "HT" 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 800HT mirrors 800H, but with even tighter controls. The minimum Carbon is set to 0.06%, and the Aluminum + Titanium sum must be at least 0.85% to ensure the highest possible creep strength.
| 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
800HT 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 800HT®, Alloy 800HT |
| ASTM Fastener Specs | ASTM B408 (Bar), ASTM B409 (Plate) |
| European Equivalent | W.Nr. 1.4959 / X8NiCrAlTi32-21 |
■ Applications & Industries
Alloy 800HT 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 800HT components should always be paired with matching nuts and washers.
| External Threads (Incoloy 800HT) | Recommended Mating Component (Nuts) |
|---|---|
| Incoloy 800HT Stud Bolts | Incoloy 800HT Heavy Hex Nuts |
| Incoloy 800HT Hex Bolts | Incoloy 800HT Standard / Heavy Hex Nuts |
■ Torque & Installation Guidelines
At the service temperatures typical for 800HT, 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 800HT 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. What makes 800HT better than 800H?
While both have a coarse grain size, 800HT has higher minimum requirements for Aluminum, Titanium, and Carbon. These tighter controls result in significantly higher allowable design stresses and improved long-term creep-rupture performance at temperatures above 1300°F.
2. Can I use 800HT fasteners in a vacuum furnace?
Yes. Alloy 800HT is highly stable in vacuum environments. However, ensure that any lubricants used during installation are compatible with vacuum levels to prevent outgassing and contamination.
3. Does 800HT become magnetic?
No. Incoloy 800HT is a fully austenitic nickel-iron-chromium alloy and remains non-magnetic throughout its entire operating temperature range.
4. What is the maximum service temperature for 800HT?
For oxidation resistance, Alloy 800HT can be used up to approximately 1900°F (1038°C). However, for structural load-bearing applications, the practical limit is usually defined by creep-rupture life at around 1700°F (927°C).