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When a project specifies Incoloy 800 for service above 593°C (1100°F) under creep-governed pressure design, the real question is not "800 vs. 825" but Incoloy 800H (UNS N08810) vs. Incoloy 800HT (UNS N08811). Both are upgrades of Incoloy 800 (N08800) with controlled carbon and coarse-grain annealing, but only 800HT has the tightened Al+Ti minimum (≥0.85%) that enables γ′ (Ni₃(Al,Ti)) precipitation strengthening during high-temperature exposure. Below is a clear, engineering-based comparison to help you specify the correct grade and avoid costly under-selection or unnecessary over-specification.
Key Metallurgical Differences Between 800H and 800HT
|
Parameter |
Incoloy 800H (N08810) |
Incoloy 800HT (N08811) |
|---|---|---|
|
UNS Number |
N08810 |
N08811 |
|
Carbon (C) |
0.05 – 0.10% (min. 0.05%) |
0.06 – 0.10% (min. 0.06%) |
|
Aluminum (Al) |
0.15 – 0.60% |
0.25 – 0.60% (raised min.) |
|
Titanium (Ti) |
0.15 – 0.60% |
0.25 – 0.60% (raised min.) |
|
Al + Ti Total |
0.30 – 1.20% |
0.85 – 1.20% (mandatory min. 0.85%) |
|
Solution Anneal Temp. |
≥ 1121°C (2050°F) |
≥ 1149°C (2100°F) |
|
Grain Size (ASTM) |
≥ 5 (coarse) |
≥ 5 (coarse) |
|
γ′ Precipitation (Ni₃(Al,Ti)) |
Possible over long exposure, not guaranteed |
Guaranteed by Al+Ti ≥0.85% — designed for dispersion strengthening |
Both grades share the same base chemistry (Ni 30–35%, Cr 19–23%, Fe bal.) and room-temperature tensile minima (Rm ≥ 450 MPa, Rp0.2 ≥ 170 MPa, A ≥ 30%).
Creep-Rupture Strength Comparison (Where the Choice Matters)
The practical difference appears only above ~650–700°C under sustained stress:
|
Temp. |
100,000 h Creep-Rupture Strength (Typical) |
Interpretation |
|---|---|---|
|
704°C (1300°F) |
800H: ~105–115 MPa |
800HT ~10–15% stronger |
|
760°C (1400°F) |
800H: ~72–82 MPa |
800HT ~15–20% stronger |
|
815°C (1500°F) |
800H: ~45–55 MPa |
Margin widens; 800HT preferred for >760°C creep design |
ASME Section I permits both 800H and 800HT to 982°C (1800°F); Section VIII Div.1 lists allowable stresses to ~899°C. However, 800HT has higher allowable stress values in the upper temperature range (especially >760°C) and is the grade called out in most ethylene cracker and SMR (steam methane reformer) tube specifications.
When to Specify 800H vs. 800HT — Decision Guide
✅ Choose Incoloy 800H (N08810) when:
Design temperature is 593–760°C (1100–1400°F) and creep is a governing factor, but not extreme.
You are replacing 800 (N08800) in a pressure vessel/pipe that failed design-by-ruleat >538°C — 800H satisfies code with lower cost than 800HT.
Project specs accept N08810 and do notexplicitly require Al+Ti ≥0.85% or N08811.
Typical applications: refinery reformer outlet pigtails (moderate temp), high-temp process piping ≤760°C.
✅ Choose Incoloy 800HT (N08811) when:
Design / operating temperature is >760°C (1400°F) up to 982°C (1800°F) in creep-governed pressure service.
Application is ethylene pyrolysis (cracker) radiant tubes, SMR catalyst tubes, or secondary reformer transition pieces — industry standard is 800HT.
Specification calls for UNS N08811, Al+Ti ≥0.85%, or "800H/800HT dual certified."
You want the best available creep-rupture margin within the 800 family.
???? Practical Procurement Tip: Many qualified mills supply Dual Certified 800H/800HT material — meets N08810 carbon range + N08811 Al+Ti ≥0.85% + coarse grain anneal ≥1149°C. For any new project >650°C creep design, specifying dual cert.future-proofs your purchase and avoids grade-confusion between EPC, fabricator, and QA/QC.
What Happens if You Use the Wrong One?
800HT where 800H is specified: Usually acceptable (stronger), but may be unnecessarily expensive if 800H truly meets design margins.
800H where 800HT is required (>760°C creep design, e.g., cracker tubes): Potential under-design → lower calculated life / higher stress than code-allowable for 800HT → rejected by third-party inspector or insurer. Rework/replace = major cost.
Shanghai COCESS Special Alloys Co., Ltd. stocks Incoloy 800H (N08810), 800HT (N08811), and dual-certified 800H/800HT material in plate, round bar, forged block, and seamless pipe. All shipments include EN 10204 3.1 MTC stating C, Al, Ti, heat number, grain size (≥ ASTM 5), and solution anneal temperature. UT, PMI, and third-party inspection (SGS / TÜV / BV / DNV) available per project specification.
Send us your UNS grade requirement, dimensions, quantity, and certification level — we typically respond with stock status and formal quotation within one working day.
Website: https://en.cocessalloys.com
Email: sales@cocessalloys.com
