High Temperature Creep Resistant Incoloy 800HT Tube UNS N08811 Nickel Iron Chromium Alloy
UNS N08811 is a nickel-iron-chromium alloy specifically designed for high-temperature service with exceptional creep and rupture strength. It is a controlled chemistry version of UNS N08800 (Alloy 800), with tighter limits on carbon (0.06-0.10%), aluminum (0.15-0.60%), and titanium (0.15-0.60%) to optimize high-temperature performance.
The alloy maintains an austenitic structure and offers excellent oxidation and carburization resistance, as well as good corrosion resistance in high-temperature environments. UNS N08811 is particularly valued for its high creep-rupture strength at temperatures above 650°C (1200°F), making it the preferred choice for petrochemical furnaces, ethylene cracking tubes, and power generation equipment.
| Parameter | Details |
|---|---|
| Standard | ASTM B407 (Seamless Tube), ASTM B408 (Bar), ASTM B409 (Plate/Sheet), ASME SB407 |
| Grade / UNS | UNS N08811 |
| Type | Seamless tube / Welded tube (ERW / EFW) |
| Outer Diameter | 6.0 mm – 610 mm (1/8″ – 24″) |
| Wall Thickness | 0.5 mm – 50 mm (SCH 5S – XXS) |
| Length | 6 m / 9 m / 12 m, or random lengths |
| Process | Cold drawn / Cold rolled (seamless); Plate rolled (welded) |
| Finish | Annealed & pickled / Bright annealed / Solution annealed |
| Ends | Plain end / Beveled end / Threaded |
| Packaging | Hexagonal bundles + plastic end caps + seaworthy wooden crates or pallets |
The chemical composition of Incoloy 800HT complies with ASTM B408, B409, and B407 standards. Compared to Alloy 800 and 800H, Alloy 800HT features tighter ranges and higher minimums for aluminum and titanium.
| Element | Content (%) | Notes |
|---|---|---|
| Nickel (Ni) | 30.0 – 35.0 | Provides austenitic stability and corrosion resistance |
| Chromium (Cr) | 19.0 – 23.0 | Enhances oxidation and carburization resistance |
| Iron (Fe) | ≥ 39.5 (balance) | Base element, balances cost and properties |
| Carbon (C) | 0.06 – 0.10 | Tightly controlled range for maximum creep strength |
| Manganese (Mn) | ≤ 1.50 | Aids in hot workability |
| Silicon (Si) | ≤ 1.00 | Improves oxidation resistance |
| Phosphorus (P) | ≤ 0.045 | Minimized to maintain ductility |
| Sulfur (S) | ≤ 0.015 | Controlled for hot workability |
| Aluminum (Al) | 0.25 – 0.60 | Higher minimum than 800H for stability |
| Titanium (Ti) | 0.25 – 0.60 | Higher minimum than 800H for stability |
| Aluminum + Titanium | 0.85 – 1.20 | Key differentiator – enhanced stabilization |
| Copper (Cu) | ≤ 0.75 | Residual element |
| ASTM Grain Size | 5 or coarser | Ensures high-temperature stability |
We have the actual mill test certificates (EN 10204 3.1) available per batch.
Comparison of 800 Series Grades:
| Element | 800 (N08800) | 800H (N08810) | 800HT (N08811) |
|---|---|---|---|
| Carbon (C) | ≤ 0.10% | 0.05 – 0.10% | 0.06 – 0.10% |
| Aluminum (Al) | 0.15 – 0.60% | 0.15 – 0.60% | 0.25 – 0.60% ↑ |
| Titanium (Ti) | 0.15 – 0.60% | 0.15 – 0.60% | 0.25 – 0.60% ↑ |
| Al + Ti | 0.30 – 1.20% | 0.30 – 1.20% | 0.85 – 1.20% ↑↑ |
| Grain Size | Not specified | 5 or coarser | 5 or coarser |
| Creep Strength | Standard | Enhanced | Highest |
Room Temperature Properties (Solution Heat Treated / Annealed)
| Property | Metric (MPa) | Imperial (ksi) |
|---|---|---|
| Tensile Strength (Rm) | 550 – 750 | 80 – 109 |
| Yield Strength 0.2% Proof (Rp0.2) | 240 – 310 | 35 – 45 |
| Elongation (A) | ≥ 45% | ≥ 45% |
| Hardness (HB) | 140 – 190 | 140 – 190 |
| Density | 7.94 g/cm³ | 0.287 lb/in³ |
| Melting Point | 1350 – 1400°C | 2460 – 2550°F |
| Modulus of Elasticity | 196 GPa | 28.4 x 10³ ksi |
Operating Temperature Ranges:
| Grade | Temperature Range | Notes |
|---|---|---|
| Incoloy 800 | Up to ~816°C (1500°F) | Standard grade |
| Incoloy 800H | 593°C – 982°C (1100°F – 1800°F) | Enhanced creep resistance |
| Incoloy 800HT | 593°C – 982°C (1100°F – 1800°F) | Highest creep rupture strength |
Typical Rod & Bar Properties:
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0.2% Yield Strength: 30 – 60 ksi (205 – 415 MPa)
-
Tensile Strength: 75 – 100 ksi (515 – 690 MPa)
-
Elongation: 60 – 30%
| Product Form | ASTM | ASME | BS | EN/DIN |
|---|---|---|---|---|
| Rod & Bar | B408 | SB408 | BS 3076NA15 | DIN 17460, EN 10095 |
| Wire | — | — | BS 3075NA15 | — |
| Plate & Sheet | B409, B906 | SB409, SB906 | BS 3072NA15 | DIN 17460, EN 10028-7, EN 10095 |
| Strip | — | — | BS 3073NA15 | — |
| Seamless Tube | B163, B407 | SB163, SB407 | BS 3074NA15 | DIN 17459 |
| Welded Tube | B515 | SB515 | — | — |
| Seamless Pipe | B407, B829 | SB407, SB829 | — | — |
| Welded Pipe | B514, B775 | SB514, SB775 | — | — |
| Forgings | B564 | SB564 | — | — |
| Fittings | B366 | SB366 | — | — |
ASME Code Cases: Case 1325 (All Product Forms), Case 1983 (Seamless Pipe & Tubes)
Incoloy 800HT is widely used in the following high-temperature applications:
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Petrochemical Industry: Ammonia reformers, ethylene pyrolysis tubes, cracking furnace components, heat exchangers
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Industrial Heating: Radiant tubes, furnace muffles, carburizing fixtures, retorts, thermowells
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Power Generation: Superheater components, steam generator parts, nuclear reactor components
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Aerospace: Gas turbine engine components, combustion chamber parts, exhaust systems
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Oil & Gas: Downhole tubing, high-temperature wellhead equipment, gas turbine components
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Other Applications: Pressure vessels, thermal processing equipment, high-temperature springs, and fasteners
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