Incoloy 800H/800HT Pipe
Incoloy 800H/800HT pipe is a high-performance nickel-iron-chromium alloy pipe specifically designed for extreme high-temperature environments.These grades represent an optimized version of standard Incoloy 800 (Alloy 800) for applications requiring superior resistance to creep (slow deformation under heat) and stress corrosion cracking.
Key Differences and Components
The primary distinction between these variants lies in the controlled content of carbon,aluminum,and titanium,combined with specialized heat treatment to enhance mechanical stability.
- Incoloy 800H (UNS N08810):
A higher-carbon variant of Alloy 800 (0.05–0.10%).It undergoes solution annealing at elevated temperatures to achieve coarser grain sizes (typically ASTM 5 or larger),significantly enhancing its creep strength and fracture toughness. - Incoloy 800HT (UNS N08811):
A finer-grained variant limiting total aluminum and titanium content to 0.85%–1.20% and carbon content to 0.06%–0.10%.This stricter control ensures maximum creep resistance and long-term stability at temperatures up to 925°C (1700°F).
800H/800HT Equivalent Designations
Incoloy 800H
- UNS N08810
- W.Nr. 1.4958
- EN X5NiCrAlTi31-20
- JIS NCF 800H
- BS NA 15(H)
Incoloy 800HT
- UNS N08811
- W.Nr. 1.4959
- EN X8NiCrAlTi32-21
- JIS NCF 800HT
- BS NA 15(HT)
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Chemical Composition of Incoloy 800H/800HT Pipe, wt.%
| Element | Ni | Cr | Fe | C | Al | Ti | Al + Ti | Mn | Si | Cu | S |
|---|---|---|---|---|---|---|---|---|---|---|---|
| Incoloy 800H | 30.0 – 35.0 | 19.0 – 23.0 | Balance | 0.05 – 0.10 | 0.15 – 0.60 | 0.15 – 0.60 | 0.30 – 1.20 | 1.50 Max | 1.00 Max | 0.75 Max | 0.015 Max |
| Incoloy 800HT | 30.0 – 35.0 | 19.0 – 23.0 | Balance | 0.06 – 0.10 | 0.25 – 0.60 | 0.25 – 0.60 | 0.85 – 1.20 | 1.50 Max | 1.00 Max | 0.75 Max | 0.015 Max |
Key Differences in Composition
- Aluminum-Titanium Control:
800HT requires a higher minimum combined aluminum and titanium content (0.85% vs. 0.30%),which improves creep and stress rupture properties at temperatures above 700°C (1292°F). - Minimum Carbon Content:
800HT has a slightly higher minimum carbon content (0.06% vs. 0.05%) to ensure the formation of carbides that pin grain boundaries. - Dual Certification:
Since 800HT’s chemical limits fall entirely within the broader range of 800H,many pipes are dual-certified to meet both specifications.Kaysuns also offers dual-certified pipes.Contact us anytime for a real-time quote and to initiate your order.
Metallurgical Notes
Beyond their chemical composition,both alloys require high-temperature solution annealing (typically at a minimum temperature of 2100°F / 1149°C) to ensure grain sizes reach ASTM No. 5 or larger.Based on Kaysuns’ over a decade of manufacturing experience with pipes and fittings,we have concluded that it is precisely this unique microstructure that enables these pipes to resist deformation under prolonged thermal stress.
Mechanical Properties of UNS N08810 / UNS N08811
At room temperature (20°C),the minimum mechanical property requirements for both materials are identical according to the standard.
| Tensile Strength | Yield Strength (0.2% Offset) | Elongation | Hardness (Max) |
|---|---|---|---|
| ≥ 450 MPa (65,000 psi) | ≥ 170 MPa (25,000 psi) | ≥ 30% | 70 – 90 HRB |
Core Difference: High-Temperature Creep and Fracture Strength
Although both exhibit consistent room-temperature performance,the 800HT (N08811) is an enhanced upgrade of the 800H (N08810),with differences becoming apparent in environments exceeding 593°C (1100°F).
Creep Strength
- UNS N08811 (800HT):
With total aluminum and titanium content strictly controlled between 0.85% and 1.20%,it exhibits superior resistance to creep deformation.Under identical high-temperature loads,800HT deforms at a slower rate than 800H. - UNS N08810 (800H):
With a broader aluminum-titanium content range (0.30%–1.20%),its high-temperature stability is slightly inferior to that of 800HT.
Allowable Stress
In the ASME Boiler and Pressure Vessel Code,the allowable stress for 800HT at extremely high temperatures is typically higher than that for 800H.This means that at the same temperature and pressure,thinner-walled tubes can be designed using 800HT.
Temperature Variation in Heat Treatment
- Incoloy 800H (N08810):
Requires a minimum solution treatment temperature of 1121°C (2050°F). - Incoloy 800HT (N08811):
Requires a higher minimum solution treatment temperature of 1149°C (2100°F) to ensure further grain coarsening.
Grain Size
Although both require grain size of ASTM No. 5 or coarser (coarse grains enhance high-temperature strength),800HT typically achieves a more stable coarse-grained structure through higher annealing temperatures.This maintains superior toughness during prolonged high-temperature service and prevents embrittlement.
Incoloy 800H/800HT Pipe Physical & Thermal Properties
Incoloy 800H/800HT pipes are renowned for their physical stability and consistent thermal properties across extreme temperature ranges.Since 800HT (UNS N08811) is a designated variant of 800H (UNS N08810),both exhibit nearly identical physical and thermal constants.
Physical Properties
- Density:7.94 g/cm³ (0.287 lb/in³).
- Melting Point range:1357 – 1385°C (2475 – 2525°F).
- Young’s Modulus:196.5 GPa at 20°C (28.5 x 10⁶ psi).
- Electrical Resistivity:99 μΩ·cm (59.5 μΩ·in) at 20°C.
- Curie Temperature:-115°C (-175°F), meaning the material exhibits no magnetism at standard or elevated operating temperatures.
Thermal Properties
| Property | Temperature | Value |
|---|---|---|
| Specific Heat | 20°C (70°F) | 460 J/kg·K(0.11 BTU/lb·°F) |
| Thermal Conductivity | 20°C (70°F) | 11.5 W/m·K(80 BTU·in/ft²·hr·°F) |
| 427°C (800°F) | 18.3 W/m·K(127 BTU·in/ft²·hr·°F) | |
| Mean Coeff. of Thermal Expansion | 20 – 100°C | 14.4 µm/m·°C(8.0 x 10⁻⁶ in/in·°F) |
| 20 – 538°C (1000°F) | 16.8 µm/m·°C(9.4 x 10⁻⁶ in/in·°F) | |
| 20 – 871°C (1600°F) | 18.0 µm/m·°C(10.2 x 10⁻⁶ in/in·°F) |
Key Design Considerations of Incoloy 800H/800HT Pipe
- Thermal Expansion:
The coefficient of expansion increases significantly with rising temperatures.For example,at 871°C (1200°F), the expansion rate is approximately 25% higher than at room temperature,necessitating careful design of expansion joints in long-distance piping systems. - Stability:
Unlike many stainless steels,these alloys do not form embrittling sigma phases even after prolonged exposure at 649°C (1200°F),maintaining ductility and impact strength throughout years of service. - Operating Range:
While certified for use up to 1100°C (2012°F) in certain environments,our decade-plus experience indicates that 800HT is typically the safer choice for applications exceeding 700°C (1292°F) due to its higher guaranteed stress rupture strength.
Applications of Incoloy 800H/800HT Pipe
- The primary operating range for 800H:593°C (1100°F) to 760°C (1400°F)
Within this medium-to-high temperature range,800H exhibits outstanding mechanical properties.It is commonly used in standard pressure vessels,heat exchanger tubes,and industrial furnace components. - 800HT’s primary operating range:Above 700°C (1292°F)
When operating temperatures consistently exceed 700°C,particularly in extreme environments near 800°C to 950°C,800HT is the preferred choice.Its chemical composition (Al + Ti ≥ 0.85%) ensures microstructural stability at extremely high temperatures,preventing premature creep failure in tubing due to prolonged thermal exposure.
- Ethylene Cracking Tubes
- Steam Methane Reformers
- Pigtails
- Superheater & Reheater Tubing
- Nuclear Steam Generator Tubing
- Radiant Tubes
- Muffles & Retorts
- Heat Treating Baskets & Fixtures
- VCM
- Waste Incinerator Components
FAQs About Incoloy 800H/800HT Pipe
Yes.Common welding processes include GTAW (TIG) and GMAW (MIG).Inconel 82 (ERNiCr-3) or Alloy 617 (ERNiCrCoMo-1) welding wire is recommended to ensure high-temperature strength of the weld.
Since the chemical composition range of 800HT is fully encompassed within that of 800H,many manufacturers produce tubing that meets the chemical and physical requirements of both standards simultaneously.Consequently,it is designated as 800H/HT on the Material Test Report (MTR).
Yes.Containing approximately 33% nickel and 21% chromium,it exhibits excellent resistance to carburization and oxidation in ethylene cracking and steam reforming processes within the petrochemical industry.
- Seamless Pipe:ASTM B407 / ASME SB407
- Welded Pipe: ASTM B514 / ASME SB514
- Forgings/Pipe Fittings: ASTM B564 / B366
This is primarily because the 800HT has an extremely narrow control window for chemical composition (C, Al, Ti),and its heat treatment process (high-temperature solution treatment) is more complex,resulting in higher production costs.
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