Incoloy 800, 800H, and 800HT: A Detailed Comparison

Incoloy alloys are a family of nickel-iron-chromium alloys designed for high-temperature strength and resistance to oxidation, carburization, and other forms of high-temperature corrosion. Among the Incoloy alloys, Incoloy 800, 800H, and 800HT are widely used in industries that require high performance in extreme conditions. This post will explore the differences and applications of these three alloys, helping you choose the right material for your specific needs.

Introduction to Incoloy Alloys

Incoloy alloys are known for their excellent resistance to high-temperature oxidation and carburization, making them ideal for applications in petrochemical, nuclear, and heat treatment industries. The 800 series, particularly Incoloy 800, 800H, and 800HT, is noted for its stability and strength at elevated temperatures, with each variant offering slightly different properties suited to specific conditions.

Incoloy 800: Composition, Properties, and Applications

Chemical Composition:

Nickel (Ni): 30.0-35.0%
Chromium (Cr): 19.0-23.0%
Iron (Fe): 39.5% minimum
Carbon (C): 0.10% maximum
Aluminum (Al): 0.15-0.60%
Titanium (Ti): 0.15-0.60%

Key Properties:

High-Temperature Strength: Incoloy 800 is designed for high-temperature service, with good strength and resistance to oxidation and carburization at temperatures up to 815°C (1500°F).
Corrosion Resistance: The alloy offers excellent resistance to both oxidizing and reducing environments, as well as to stress-corrosion cracking in many aqueous environments.
Stability: Incoloy 800 maintains its structure and does not become brittle at elevated temperatures, which is crucial for long-term applications.

Applications:

Heat Exchangers: Incoloy 800 is commonly used in heat exchangers and other components in chemical and petrochemical processing that require high-temperature corrosion resistance.
Furnace Components: The alloy is used in furnace components such as retorts, muffles, and radiant tubes, where resistance to oxidation and carburization is essential.
Nuclear Power Plants: Incoloy 800 is also employed in nuclear power plants for steam generator tubing and other high-temperature components.

Incoloy 800H: Composition, Properties, and Applications

Chemical Composition: (Similar to Incoloy 800, with controlled carbon content)

Nickel (Ni): 30.0-35.0%
Chromium (Cr): 19.0-23.0%
Iron (Fe): 39.5% minimum
Carbon (C): 0.05-0.10%
Aluminum (Al): 0.15-0.60%
Titanium (Ti): 0.15-0.60%

Key Properties:

Enhanced High-Temperature Strength: Incoloy 800H is designed for improved high-temperature strength compared to Incoloy 800, with controlled carbon content (0.05-0.10%) that enhances creep and rupture properties at temperatures above 600°C (1110°F).
Thermal Stability: The alloy maintains its stability and resists thermal embrittlement, making it suitable for prolonged exposure to high temperatures.
Resistance to Oxidation: Incoloy 800H offers excellent resistance to oxidation, making it ideal for use in environments where high-temperature oxidation is a concern.

Applications:

Petrochemical Processing: Incoloy 800H is widely used in ethylene pyrolysis furnaces, hydrocarbon cracking, and other high-temperature processes in the petrochemical industry.
Industrial Furnaces: The alloy is employed in industrial furnaces for components such as radiant tubes, retorts, and other parts that require high-temperature strength and stability.
Pressure Vessels: Incoloy 800H is also used in pressure vessels and heat exchangers that operate at high temperatures, particularly in the chemical and petrochemical industries.

Incoloy 800HT: Composition, Properties, and Applications

Chemical Composition: (Similar to Incoloy 800H, with additional control over titanium and aluminum content)

Nickel (Ni): 30.0-35.0%
Chromium (Cr): 19.0-23.0%
Iron (Fe): 39.5% minimum
Carbon (C): 0.06-0.10%
Aluminum (Al): 0.25-0.60%
Titanium (Ti): 0.25-0.60%

Key Properties:

Optimized High-Temperature Strength: Incoloy 800HT offers even greater high-temperature strength than Incoloy 800H, with more tightly controlled aluminum and titanium content, enhancing its creep and rupture strength at temperatures above 600°C (1110°F).
Long-Term Thermal Stability: The alloy is optimized for long-term exposure to high temperatures, with excellent resistance to both oxidation and carburization.
Enhanced Creep Resistance: Incoloy 800HT is specifically designed for superior creep resistance, making it the preferred choice for applications requiring long-term strength at elevated temperatures.

Applications:

Heat Treatment Equipment: Incoloy 800HT is used in heat treatment equipment such as furnace components, retorts, and radiant tubes, where it provides long-term stability and resistance to thermal fatigue.
Chemical and Petrochemical Processing: The alloy is employed in the chemical and petrochemical industries for reactors, heat exchangers, and other components that operate at high temperatures.
Nuclear Power: Incoloy 800HT is also used in nuclear power plants, where its high-temperature strength and stability are critical for safe and reliable operation.

Key Differences Between Incoloy 800, 800H, and 800HT

Temperature Capability: While all three alloys are designed for high-temperature applications, Incoloy 800 is typically used for temperatures up to 815°C, while Incoloy 800H and 800HT are optimized for use at even higher temperatures, particularly above 600°C.
Mechanical Strength: Incoloy 800H and 800HT offer improved mechanical strength and creep resistance compared to Incoloy 800, making them more suitable for long-term high-temperature applications.
Carbon Content: Incoloy 800H and 800HT have controlled carbon content (0.05-0.10% for 800H and 0.06-0.10% for 800HT) that enhances their high-temperature strength and stability, whereas Incoloy 800 has a broader carbon content range.
Aluminum and Titanium Control: Incoloy 800HT has more tightly controlled aluminum and titanium content compared to Incoloy 800H, providing superior creep and rupture strength at elevated temperatures.

Choosing the Right Alloy for Your Application

When selecting between Incoloy 800, 800H, and 800HT, consider the following factors:

Temperature Requirements: If your application involves extremely high temperatures, particularly above 600°C, Incoloy 800H or 800HT may be the better choice due to their enhanced high-temperature strength.
Creep Resistance: For applications requiring long-term strength and stability at elevated temperatures, Incoloy 800HT offers superior creep resistance and should be considered.
General High-Temperature Corrosion Resistance: If your application requires good corrosion resistance at high temperatures but does not involve prolonged exposure to extreme conditions, Incoloy 800 may be sufficient.

Conclusion

Incoloy 800, 800H, and 800HT are all exceptional materials designed for high-temperature applications, each offering unique properties that make them suitable for specific environments and conditions. Understanding the differences between these alloys will help you select the right material for your project, ensuring optimal performance and longevity.

Whether you are working in chemical processing, petrochemical industries, or any other field requiring high-temperature materials, the choice between Incoloy 800, 800H, and 800HT should be based on a careful assessment of your application’s requirements. If you need further assistance in selecting the right alloy, our team of experts is here to help.