What Is a Seamless Incoloy 800HT Pipe?
ASeamless Incoloy 800HT Pipe is a high-performance, nickel-iron-chromium superalloy piping solution engineered for long-term service in extreme thermal environments. Produced from a single solid billet, this seamless pipe eliminates the risk of weld-seam failure, ensuring maximum structural integrity under high-stress conditions.
The“800HT”(UNS N08811) designation represents the most advanced grade in the 800-series family. It is a dual-certified version of Incoloy 800H with precisely controlled levels of carbon, aluminum, and titanium. When combined with a high-temperature solution annealing heat treatment, 800HT delivers significantly higher creep and stress-rupture properties at temperatures above 1100°F(593°C) compared to standard 800 or 800H grades.
Size Range: OD 6–457 mm · WT 0.5–45 mm
Key Features and Advantages
- Superior Creep-Rupture Strength: The strict control of Al + Ti content (0.85% -1.20%) ensures the highest design allowable stresses for long-term high-temperature service.
- Exceptional Oxidation & Carburization Resistance: High chromium content provides a protective oxide scale, while the nickel content maintains stability in carburizing atmospheres.
- Excellent Metallurgical Stability: Designed to resist embrittlement and maintain ductility even after thousands of hours of service in the 1200°Fto
1600°F range.
- Seamless Reliability: Uniform grain structure and wall thickness provide higher safety margins for high-pressure applications in furnaces and power plants.
- Field-Proven Weldability: Easily welded using matching composition filler metals (e.g., Inconel 82 or 617) with excellent resistance to hot cracking.
Product Specifications and Data
To provide a comprehensive overview of this high-performance material, here are the detailed technical specifications and performance data for Incoloy 800HT.
Equivalent Grade
| UNS | Common grade name | EN material number | EN steel name | JIS grade | GB/T grade |
|---|---|---|---|---|---|
| N08811 | Incoloy 800HT | 1.4959 | X8NiCrAlTi32-21 (approx.) | – | NS1104 |
Grade correspondence does not make ASTM, ASME, EN, JIS and GB delivery requirements interchangeable. Confirm chemistry, heat treatment, mechanical properties, dimensions, testing and certification against the purchase specification. See the grade designation index.
Chemical Composition
The composition of Incoloy 800HT is carefully balanced to achieve its superior high-temperature strength and oxidation resistance.
| Grade | Ni | Cu | Fe | Mn | C | Si | S | Cr | Al | Ti | P | Other |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 800 | 30.00-35.00 | ≤0.75 | ≥39.50 | ≤1.50 | ≤0.10 | ≤1.00 | ≤0.015 | 19.00-23.00 | 0.15-0.60 | 0.15-0.60 | ≤0.045 | – |
| 800H | 30.00-35.00 | ≤0.75 | ≥39.5 | ≤1.50 | 0.05-0.10 | ≤1.00 | ≤0.015 | 19.00-23.00 | 0.15-0.60 | 0.15-0.60 | ≤0.045 | – |
| 800HT | 30.00-35.00 | ≤0.75 | ≥39.5 | ≤1.50 | 0.06-0.10 | ≤1.00 | ≤0.015 | 19.00-23.00 | 0.25-0.60 | 0.25-0.60 | ≤0.045 | AL+Ti=0.85-1.20 |
Typical Mechanical Properties
Incoloy 800HT is specifically designed to maintain its strength and shape in high-stress, high-temperature environments.
| Tensile Strength | Yield Strength | Elongation | Hardness |
|---|---|---|---|
| ≥ 450 MPa | ≥ 170 MPa | ≥ 30% | Not an acceptance limit in ASTM B407 |
Per ASTM B407 Table 2 — Annealed.
Typical Physical Properties
These physical properties highlight the material’s ability to perform reliably under a wide range of conditions.
| Density | Melting Point | Thermal Expansion | Thermal Conductivity | Modulus of Elasticity | Electrical Resistivity |
|---|---|---|---|---|---|
| 7.94 g/cm³ | 1357 – 1385 °C approx. | 14.4 µm/m·°C (20-100°C) | 11.5 W/m·K (20°C) | 196 GPa | 0.989 µΩ·m (20°C) |
Size Tolerance Chart (mm)
Cold-Finished Pipe and Tube:
| Specified/Calculated Nominal OD (Inches) | Permissible Variation (Inches) | Specified/Calculated Nominal OD (mm) | Permissible Variation (mm) |
| 0.500 to 5⁄8, excl. | ±0.005 | 12.7 to 15.8, excl. | ±0.127 |
| 5⁄8 to 1 1⁄2, incl. | ±0.0075 | 15.8 to 38.1, incl. | ±0.190 |
| Over 1 1⁄2 to 3 1⁄2, incl. | ±0.010 | Over 38.1 to 88.9, incl. | ±0.254 |
| Over 3 1⁄2 to 4 1⁄2, incl. | ±0.015 | Over 88.9 to 114.3, incl. | ±0.381 |
| Over 4 1⁄2 to 6, incl. | ±0.020 | Over 114.3 to 152.4, incl. | ±0.508 |
| Over 6 to 6 5⁄8, incl. | ±0.025 | Over 152.4 to 168.3, incl. | ±0.635 |
| Specified/Calculated Nominal OD (Inches) | Permissible Variation (Inches) | Specified/Calculated Nominal OD (mm) | Permissible Variation (mm) |
| 2 1⁄2 to 5 1⁄2, excl. | ±0.031 | 63.5 to 139.7, excl. | ±0.787 |
| 5 1⁄2 to 9 1⁄4, incl. | ±0.047 | 139.7 to 234.9, incl. | ±1.19 |
| Condition | Specified/Calculated Nominal OD (Inches) | Permissible Variation (Wall Thickness) |
| Cold-Finished | 0.500 to 5⁄8, excl. | ±15.0% |
| 5⁄8 to 4 1⁄2, incl. | ±10.0% | |
| Over 4 1⁄2 to 6 5⁄8, incl. | ±12.5% | |
| Hot-Finished | 2 1⁄2 to 9 1⁄4, incl. | ±12.5% |
Common Industrial Applications
The exceptional combination of high-temperature strength, creep rupture resistance and oxidation stability makes Incoloy 800HT seamless pipes indispensable in several demanding sectors:
Petrochemical Processing
Ethylene pyrolysis furnace tubes and convection sections.
Power Generation
Superheater and reheater tubing in advanced coal-fired and nuclear power plants.
Thermal Processing
Radiant tubes, retorts, and muffles for industrial heat-treating furnaces.
Hydrocarbon Processing
Components for steam/hydrocarbon reforming and pigtails.
Incoloy Series Comparison Reference:
| Grade | UNS Number | Primary Advantage |
| Incoloy 800 | N08800 | General corrosion and heat resistance. |
| Incoloy 800H | N08810 | Controlled carbon for improved creep strength. |
| Incoloy 800HT | N08811 | Optimized Al+Ti for maximum high-temp performance. |
| Incoloy 825 | N08825 | Superior resistance to sulfuric and phosphoric acids. |
Frequently Asked Questions
What sizes are available for Incoloy 800HT seamless pipe?
Continuous supply covers OD 6–457 mm and WT 0.5–45 mm. Requirements outside this range are reviewed against mill capability on request.
Which specification governs Incoloy 800HT seamless pipe?
ASTM B407 / ASME SB407 is the governing seamless specification for Incoloy 800HT pipe (Grade HT, aluminium + titanium 0.85–1.20%); the edition in force at order time is stated on the quotation and purchase order.
What inspection documents are provided?
Each order is documented with a mill test certificate stating heat chemistry and mechanical test results. EN 10204 3.1 certification, hydrostatic testing, eddy-current or ultrasonic inspection and PMI are performed when specified in the purchase order.
Technical review: page data reviewed by the Xinzhe technical desk on 2026-09-27. Property values are typical reference data compiled from Special Metals Corporation alloy data sheets and the governing ASTM specifications; they are not acceptance guarantees unless stated in the purchase order. “Incoloy” is a trademark of Special Metals Corporation, used here to identify the alloy family only.
Ready to Request a Quotation?
Send the NPS and schedule (or actual OD and wall), quantity, length, end finish and the inspection items you need as acceptance criteria — you will get a written quotation stating the specification and edition, delivery condition, documents included and lead time.
