UNS N08811 Incoloy 800HT Pipe Seamless Nickel Iron Chromium Superalloy
Incoloy 800HT represents the highest-performance member of the Incoloy 800 series of nickel-iron-chromium superalloys. Specifically engineered for maximum creep and rupture strength at elevated temperatures, Alloy 800HT features a tightly controlled chemistry with enhanced aluminum and titanium content combined with a precisely regulated carbon range of 0.06-0.10%.
Compared to both standard Alloy 800 and Alloy 800H, this premium grade offers superior high-temperature stability and mechanical performance. The key differentiator lies in its controlled chemistry: 800HT requires a minimum combined aluminum and titanium content of 0.85% (compared to 0.30% for 800H), along with an ASTM grain size of 5 or coarser. These enhancements provide exceptional resistance to oxidation, carburization, and sulfidation in the demanding service temperature range of 593°C to 982°C (1100°F to 1800°F).
Alloy 800HT is commonly supplied to ASTM B409, ASME SB-409, and ASTM B564 specifications, making it the preferred material for critical components requiring the highest possible creep rupture strength, including furnace components, heat exchangers, radiant tubes, thermowells, and piping systems in petrochemical and power generation industries.
Key advantages:
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Maximum Creep & Rupture Strength: Highest performance in the 800 series family
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Enhanced Stabilization: Minimum Al+Ti of 0.85% for superior high-temperature stability
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Controlled Carbon Content: 0.06-0.10% optimizes creep and rupture properties
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Oxidation & Carburization Resistance: Excellent performance up to 982°C (1800°F)
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ASTM Grain Size Control: Minimum grain size of ASTM 5 or coarser ensures stability
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Superior Fabricability: Excellent weldability and formability using standard techniques
| Parameter | Details |
|---|---|
| Product Name | Incoloy 800HT / Alloy 800HT / Incoloy® 800HT |
| UNS Designation | N08811 |
| Werkstoff Numbers | 1.4958, 1.4959 |
| EN Designation | 1.4958 |
| British Standard | BS 3072NA15 (Plate/Sheet), BS 3073NA15 (Strip), BS 3074NA15 (Seamless Tubes), BS 3075NA15 (Wire), BS 3076NA15 (Rod/Bar) |
| Common Trade Names | Nickelvac 800HT, Nickel 800HT, Ferrochronin 800HT, Nicrofer 3220 |
| Product Forms | Plate, Sheet, Strip, Rod, Bar, Wire, Seamless Pipe, Welded Pipe, Seamless Tube, Welded Tube, Forgings, Forging Stock |
| Supply Condition | Solution Heat Treated (SHT), Annealed |
| Available Dimensions | Sheet/Plate: 0.3mm – 50mm thickness; Tube: 6mm – 219mm OD (custom available) |
| Standard Length | 2000mm, 2438mm, 3000mm, 6000mm (or as required) |
| Custom Sizes | Available upon request |
| Surface Finish | Annealed, Pickled, Descaled, Bright Annealed |
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 |
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)
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Tensile Strength: 75 – 100 ksi (515 – 690 MPa)
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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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