incoloy 800H/800HT pipe
incoloy 800H/800HT pipe
Incoloy 800H and Incoloy 800HT are nickel-iron-chromium alloys.They exhibit outstanding high-temperature strength, creep resistance and corrosion resistance. Applications span the power generation, petrochemical and heat exchanger industries.
The “H” (high carbon) variant offers superior creep strength compared to the base 800 series,while the “HT” (high temperature) variant incorporates controlled aluminum/titanium elements to significantly enhance stress corrosion cracking resistance and fatigue properties,enabling operation in extreme thermal environments.
This series offers oxidation resistance, decarburization resistance, and sulfidation resistance, available in seamless and welded forms (ASTM B407/SB407).
incoloy 800H pipe / incoloy 800HT pipe
Grade | Ni | Cr | Fe | C | Al | Ti | Al + Ti | Cu | |
|---|---|---|---|---|---|---|---|---|---|
Incoloy 800H | 30 – 35 | 19 – 23 | 39.5 Min | 0.05 – 0.1 | 0.15 – 0.6 | 0.15 – 0.6 | 0.3 – 1.2 | 0.75 Max | |
Incoloy 800HT | 30 – 35 | 19 – 23 | 39.5 Min | 0.06 -0.10 | 0.15 – 0.6 | 0.15 – 0.6 | 0.85 – 1.2 | 0.75 Max |
Carbon Content (C):
800HT slightly increases the minimum carbon content to 0.06% (compared to 0.05% for 800H) to ensure higher high-temperature strength.
Aluminum and Titanium Content (Al + Ti):
This is the most significant difference between the two grades.800HT requires the total Al + Ti content to be between 0.85% and 1.20%,while 800H only requires it to be between 0.30% and 1.20%.
Inclusion Relationship:
Since 800HT has stricter composition limits than 800H, materials meeting 800HT specifications necessarily comply with 800H composition requirements, but the reverse is not necessarily true.
Effect of Combined Aluminum (Al) + Titanium (Ti) Content:
Precipitation Hardening Mechanism:
Aluminum and titanium can combine with nickel to form the γ’ phase.The higher Al+Ti lower limit in 800HT ensures sufficient precipitation of the γ’ phase at elevated temperatures.
Performance Results:
At temperatures above 700°C,800HT exhibits significantly higher creep resistance and sustained strength compared to 800H.The composition of 800HT is engineered to ensure the material resists plastic deformation under extreme thermal stress.
Effect of Carbon (C) Content:
Strengthening Mechanism (Carbide Hardening):
Higher carbon content promotes the formation of stable carbides at grain boundaries.These carbides act as “grain boundary pinning” agents,preventing grain boundary slip at elevated temperatures.
Performance Results:
The slightly elevated carbon lower limit (0.06%) in 800HT ensures that tubing achieves coarser grains (ASTM No. 5 or finer) after heat treatment above 1150°C,which is critical for enhancing stress rupture strength.
Performance Parameters | Tensile Strength (Rm) | Yield strength (Rp 0.2%) | Elongation (A5) | Brinell hardness (HB) |
|---|---|---|---|---|
Incoloy 800H | ≥ 450 MPa (65 ksi) | ≥ 170 Mpa (25 ksi) | ≥ 30% | 70 – 90 (Reference value) |
Incoloy 800HT | ≥ 450 MPa (65 ksi) | ≥ 170 Mpa (25 ksi) | ≥ 30% | 70 – 90 (Reference value) |
Temperature (°C) | 800H (MPa) | 800HT (MPa) | Performance Comparison |
|---|---|---|---|
760°C (1400°F) | About 50 MPa | About 65 MPa | 800HT exhibits about 30% higher strength |
870°C (1600°F) | About 22 MPa | About 28 MPa | 800HT delivers superior performance |
980°C (1800°F) | About 8.3 MPa | About 11 MPa | 800HT features enhanced redundancy |
Key Elements | Incoloy 800H Pipe | Incoloy 800HT Pipe |
|---|---|---|
Heat treatment temperature | Minimum 2100°F (1150°C) Solution Annealing | Minimum 2100°F (1150°C) Solution Annealing |
Grain Size | ASTM No. 5 or coarser | ASTM No. 5 or coarser |
Strengthened Mechanism | Solution strengthening + carbide precipitation | Enhanced Precipitation Hardening (Utilizing More Precise Al and Ti) |
Incoloy 800H Pipe and Incoloy 800HT Pipe:How to choose?
Select Incoloy 800H Pipe:
Applications with operating temperatures ranging from 593°C to 982°C (1100°F to 1800°F).
Where slightly lower creep resistance is acceptable for applications such as reformer tubes, superheater/reheater elements, and heat treatment equipment.
Select Incoloy 800HT Pipe:
Applications exceeding 700°C (1292°F).
Suitable for furnace linings, industrial furnace components, petrochemical vessels and aerospace components subjected to extreme thermal stress and cyclic heating/cooling.
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