Incoloy 800, Incoloy 800H, and Incoloy 800HT belong to the same nickel-iron-chromium alloy family, but they are not interchangeable in every engineering application. Their differences become especially important when equipment operates at elevated temperatures for long periods under sustained mechanical stress.
For designers, the key question is not simply “Which alloy is stronger?” It is:
Which material provides the required high-temperature strength, metallurgical stability, corrosion resistance, and code compliance for the intended service?
This guide compares Incoloy 800, UNS N08800; Incoloy 800H, UNS N08810; and Incoloy 800HT, UNS N08811, explaining their differences and how to select the appropriate grade.
What Are Incoloy 800, 800H, and 800HT?
These alloys are nickel-iron-chromium materials developed for high-temperature service. They share a common alloy family but differ in chemistry controls and intended performance characteristics.
The applicable standard should always be checked because the permitted chemistry, heat treatment, grain size, and mechanical requirements may differ by product form and specification.
Main Difference: High-Temperature Metallurgical Design
The principal distinction between these grades is their optimization for elevated-temperature mechanical performance.
Incoloy 800
Incoloy 800 is widely recognized for resistance to oxidation, carburization, nitridation, and other high-temperature corrosion mechanisms in suitable environments.
It is often considered where the material must withstand heat and corrosive gases but where the most demanding creep-strength requirements do not govern the design.
Incoloy 800H
Incoloy 800H is designed for improved high-temperature creep and rupture performance compared with standard 800 in relevant service conditions.
Its chemistry and material requirements are intended to support structural performance during prolonged exposure to elevated temperatures. This makes it particularly relevant to pressure-containing and high-temperature industrial equipment.
Incoloy 800HT
Incoloy 800HT has more tightly controlled composition requirements intended to provide consistent high-temperature mechanical performance.
It is often selected for demanding high-temperature applications where creep and rupture strength are central to the design. The “HT” designation should not be interpreted as meaning that it is automatically the best choice for every high-temperature environment; corrosion chemistry and design code requirements remain essential.
Composition and Why It Matters
The three grades share nickel, iron, and chromium as major alloying elements. Their performance differences are influenced by controls on elements such as carbon, aluminum, and titanium, as well as processing and heat treatment.
Nickel
Nickel supports the austenitic matrix and contributes to high-temperature structural stability and corrosion resistance.
Chromium
Chromium helps provide resistance to oxidation and high-temperature corrosion by supporting protective oxide formation.
Carbon, Aluminum, and Titanium
These elements influence carbide and precipitate formation, grain-boundary behavior, and elevated-temperature mechanical properties. Their permitted ranges and controls are particularly important when comparing 800, 800H, and 800HT.
Important: Exact chemical limits should be taken from the relevant standard or purchase specification. Commercial summaries should not replace the certified heat analysis.
Incoloy 800 vs 800H vs 800HT: Comparison Table
Petrochemical and Chemical Processing
These alloys may be used in process equipment, furnace components, heat-transfer systems, and piping exposed to elevated temperatures and corrosive atmospheres.
The selection depends on whether the controlling issue is oxidation, carburization, nitridation, creep, pressure containment, or a combination of these mechanisms.
Industrial Furnaces and Heat-Treatment Equipment
Incoloy 800-family alloys are relevant to furnace components and high-temperature equipment where dimensional stability and resistance to oxidation are required.
The appropriate product form may include plate, sheet, bar, tube, or fabricated components.
Heat Exchangers and Process Heaters
Tube and pipe applications require careful evaluation of pressure, temperature cycling, thermal expansion, corrosion, and weld performance. A higher-temperature grade is not automatically a better heat-exchanger material if the fluid environment creates a different corrosion risk.
Nuclear and Energy-Related Equipment
Certain 800-family grades are used in high-temperature energy-related systems. For nuclear or safety-critical projects, the exact grade, code edition, heat treatment, testing, and traceability requirements must be specified in advance.
How to Choose the Correct Grade
Choose Incoloy 800 When:
- The application requires high-temperature corrosion resistance.
- The mechanical loading and creep requirements are within the grade’s approved design limits.
- The project specification calls for UNS N08800.
- Fabrication and material availability favor the standard grade.
Choose Incoloy 800H When:
- Long-term elevated-temperature strength is a major design concern.
- Creep and rupture performance must be evaluated explicitly.
- The equipment operates under sustained stress at high temperature.
- The applicable design code or customer specification requires 800H.
Choose Incoloy 800HT When:
- The application requires a controlled high-temperature material condition.
- Creep and rupture performance is central to the design.
- The project specification specifically identifies UNS N08811.
- The engineering team requires the relevant chemistry and heat-treatment controls.
Why Temperature Alone Is Not Enough
A common procurement mistake is to choose a material based only on the maximum operating temperature. A complete selection must also consider:
- Stress level and design life
- Creep and rupture exposure
- Thermal cycling
- Oxidizing, carburizing, or nitriding atmosphere
- Fluid composition and contaminants
- Welding and post-weld requirements
- Product thickness and grain-size requirements
- Applicable pressure-vessel or piping code
- Inspection and certification requirements
Two components operating at the same temperature may require different materials because their stress levels and failure consequences differ.
Purchasing Checklist for Incoloy 800-Series Materials
When requesting a quotation, provide the following information:
- Grade and UNS designation.
- Product type: pipe, tube, sheet, plate, bar, rod, strip, or custom component.
- Applicable ASTM, ASME, or project standard.
- Dimensions and dimensional tolerances.
- Required heat-treatment condition.
- Mechanical-property requirements at room or elevated temperature.
- Surface and finishing requirements.
- Testing requirements, including NDT where applicable.
- Heat number traceability and material certificates.
- Intended operating temperature, pressure, and environment.
For high-temperature pressure equipment, the material should be reviewed against the design code before procurement.
Frequently Asked Questions
Is Incoloy 800H stronger than Incoloy 800?
800H is designed for improved creep and rupture performance in relevant high-temperature service. However, “stronger” must be defined by temperature, test condition, product form, and the property being compared.
Is Incoloy 800HT the same as 800H?
No. They are distinct grades with different UNS designations and chemistry requirements. They should not be substituted without engineering and specification approval.
Can 800, 800H, and 800HT be used for tubes and pipes?
Yes, these grades are available in various product forms depending on the supplier, standard, dimensions, and manufacturing capability. Tube and pipe orders should specify the exact grade and applicable product standard.
Which grade is best for high-temperature equipment?
There is no universal best grade. The correct choice depends on the temperature, stress, creep requirements, corrosion mechanism, design code, and project specification.
Conclusion
Incoloy 800, 800H, and 800HT offer related but distinct solutions for high-temperature engineering. Incoloy 800 is commonly considered for heat-resistant corrosion service, while 800H and 800HT are more closely associated with demanding elevated-temperature mechanical performance.
The most reliable selection process combines alloy designation, service conditions, creep requirements, applicable standards, and certified material documentation.
Need help sourcing Incoloy 800, 800H, or 800HT tubes, pipes, plates, bars, or custom products? Contact Alloysfactory with your grade, dimensions, operating conditions, and technical requirements.
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