Inconel 690

Inconel 690, also known as Alloy 690 or UNS N06690/W. Nr. 2.4642, is a high-chromium nickel alloy that is known for its excellent resistance to many corrosive aqueous media and high temperature atmospheres. It also has superior strength and metallurgical stability, making it ideal for many applications that require these properties. Inconel 690’s corrosion resistance makes it especially useful in industries such as nitric acid production, where tail-gas reheaters are exposed to this type of environment, as well as other areas requiring nitric/hydrofluoric acid solutions such as pickling processes.

Table of Contents

Inconel 690 Chemical Composition

INCONEL® 690 (UNS N06690/W. Nr. 2.4642) is a high chromium nickel alloy that offers excellent corrosion resistance to many corrosive aqueous media and high-temperature atmospheres. It is also known for its strength, metallurgical stability, and favourable fabrication characteristics. The chemical composition of INCONEL alloy 690 includes iron (Fe), chromium (Cr), nickel (Ni), manganese (Mn), molybdenum (Mo), silicon (Si), carbon (C) and other trace elements such as copper (Cu) and cobalt (Co). The most common form for this material consists of approximately 29-33% chromium, 14-17% nickel, 4-7% molybdenum, 0.50% manganese, 0.30% silicon, 1% iron with the balance being carbon and other trace elements in varying amounts.

Its outstanding corrosion resistance makes it the perfect choice for applications exposed to nitric or nitric/hydrofluoric acid solutions such as tail gas reheaters used in nitric acid production and heating coils or tanks used for nitric/hydrofluoric solution pickling. Furthermore, its wide range of mechanical properties allows it to be used in various components like steam generator tubing and nuclear reactor piping systems.

Alloying Elements and their effects

INCONEL® 690 (UNS N06690/W. Nr. 2.4642) contains several alloying elements that contribute to its high-performance characteristics. Chromium is the key element that gives Alloy 690 its corrosion resistance, offering protection from corrosive aqueous media and acidic environments. The chromium content typically ranges from 29-33%, making it one of the most corrosion-resistant alloys available today. Nickel lends strength and stability to the alloy, with 14-17% of it present in Alloy 690’s composition.

Molybdenum offers additional strength and also increases the alloy’s ductility, which can be beneficial for component fabrication and welding processes with molybdenum content usually in the range of 4-7%. Manganese improves hardenability as well as creep resistance at elevated temperatures while Silicon adds further strength and toughness at higher temperatures up to 0.30%. A balance of iron, carbon, and other trace elements ranging from copper to cobalt round out Alloy 690’s composition.

The presence of these elements in Nickel Alloy 690 allows it to perform in an impressive range of temperatures extending from cryogenic levels up to 815°C (1500°F). Its outstanding combination of properties makes INCONEL alloy 690 perfect for demanding applications involving nitric or nitric/hydrofluoric acid solutions such as tail gas reheaters used in nitric acid production or heating coils and tanks for nitric/hydrofluoric solution pickling.

Physical and Mechanical Properties

Alloy 690 has high chromium nickel alloy that offers excellent its corrosion resistance alloy and strength, making it ideal for use in hostile environments.

Density, melting point, and thermal conductivity

INCONEL® 690 (UNS N06690/W. Nr. 2.4642) has a density of 8.2 g/cc, a melting point of 1350°C (2460°F), and a thermal conductivity of 15 W/m-K at 100°C (212°F). Alloy 690 has high thermal conductivity makes it an ideal choice for applications that require efficient heat transfer such as steam generator tubing and nuclear reactor piping systems. Its corrosion resistance alloy also allows it to be used in highly corrosive environments where other alloys would be quickly corroded away.

This makes INCONEL alloy 690 the perfect choice for applications involving nitric or nitric/hydrofluoric acid solutions such as tail gas reheaters used in nitric acid production and heating coils or tanks for nitric/hydrofluoric solution pickling. Furthermore, its wide range of mechanical properties allows it to be used in components like steam generator tubing and nuclear reactor piping systems, making INCONEL alloy 690 one of the most versatile inconel alloys available today.

Mechanical properties (tensile strength, yield strength, elongation)

INCONEL® 690 (UNS N06690/W. Nr. 2.4642) is a high-performance nickel alloy that offers outstanding mechanical properties, including tensile strength, yield strength, and elongation. Its tensile strength ranges from 530 MPa (77 ksi) to 727 MPa (105 ksi) depending on the heat treatment applied and varies with temperature up to 815°C (1500°F). It has a yield strength ranging from 343 MPa (50 ksi) to 586 MPa (85 ksi), again depending on the heat treatment applied. The alloy also exhibits good elongation values of up to 25% in 1 in. gage length at room temperature, making it highly ductile and malleable which can be beneficial for fabrication and welding processes.

High-temperature Properties

INCONEL® 690 (UNS N06690/W. Nr. 2.4642) is a high-performance nickel alloy that offers excellent resistance to corrosion and outstanding mechanical properties at both low and high temperatures making it ideal for applications exposed to extreme conditions.

Heat Treatment of Inconel 690

INCONEL® 690 (UNS N06690/W. Nr. 2.4642) can be heat treated using a variety of methods to achieve the desired mechanical and corrosion properties. The most common is solution annealing, which is followed by rapid cooling to improve dimensional stability and improve the microstructure by removing any impurities or segregation that may have occurred during the forging or welding processes. This also increases the alloy’s strength, ductility, and resistance to stress corrosion cracking.

Ageing heat treatments can then be used to increase the strength of the alloy at higher temperatures up to 815°C (1500°F). Forging heat treatments are also used in specific applications where additional strength is needed, though tempered martensitic structures are best avoided as they tend to reduce creep resistance at higher temperatures. Finally, surface hardening heat treatments can be applied for applications that require increased wear resistance and toughness without sacrificing corrosion resistance or other mechanical properties. All in all, INCONEL® alloy 690 offers excellent malleability and versatility when it comes to heat treatment options for a wide range of applications.

Annealing and Solutionising processes

Solution annealing is a heat treatment process where the metal is heated to a temperature above its recrystallization temperature before being cooled rapidly to room temperature or below. During this process, any impurities or segregation that may have occurred during forging or welding processes are removed while simultaneously improving dimensional stability and increasing strength, ductility, and resistance to stress corrosion cracking. The most suitable temperature range for solution annealing of INCONEL® alloy 690 is between 870-940°C (1600-1720°F) for optimal results, with a cooling rate of around 50 °C (90 °F)/hour typically being used depending on the application.

After solution annealing the material’s hardness should remain relatively low while exhibiting excellent weldability without any risk of cracking or changes in mechanical properties due to over-welding. Additionally, grain growth can be prevented by ensuring that the material has been adequately quenched after heating so that it remains within the desired size range while keeping its surface finish intact. Following these steps will ensure that INCONEL® alloy 690 retains its outstanding combination of mechanical and corrosion-resistant properties even after heat treatment allowing it to perform reliably in hostile environments involving nitric or nitric/hydrofluoric acid solutions.

Precipitation hardening of Inconel 690

Precipitation hardening is a type of heat treatment process used to increase the strength of INCONEL® alloy 690 without significantly affecting its other properties. During this process, the material is first solution annealed and then aged at a temperature between 538-760°C (1000-1400°F) for an extended period. During the ageing process, gamma prime and delta phase particles are precipitated throughout the structure giving it increased strength at higher temperatures up to 815°C (1500°F).

Heat treatment effects on mechanical properties

Further to the heat treatment process of Nickel Alloy 690, it is important to understand the effects that this process has on its mechanical properties. As mentioned before, solution annealing can increase its strength and ductility while also improving its resistance to stress corrosion cracking.

Corrosion Resistance of Alloy 690

INCONEL® 690 (UNS N06690/W. Nr. 2.4642) is well known for its excellent corrosion resistance in a wide variety of corrosive aqueous media and high-temperature atmospheres. Its superior corrosion resistance is due to its high chromium.

Resistance to oxidation and high-temperature environments

INCONEL® 690 (UNS N06690/W. Nr. 2.4642) is designed to provide excellent resistance to a variety of oxidizing agents and high-temperature atmospheres. Its high chromium content helps it resist oxidation at temperatures up to 815°C (1500°F). It also features a high melting point of 1362°C (2485°F) that helps protect it from thermal fatigue due to rapid temperature changes. The alloy will form an oxide layer on its surface when exposed to the atmosphere, which serves as an additional layer of protection against corrosion and chemical attack.

The alloy’s exceptional oxidation resistance makes it suitable for applications in industries such as power generation, petrochemical processing, aerospace, and nuclear engineering where it can be exposed to harsh environments or extreme temperatures with confidence. Additionally, its resistance to sulfidation is particularly beneficial in hot sulfur-containing media such as those encountered in petrochemical plants and refineries, making INCONEL® alloy 690 the perfect choice for components that need superior performance and durability without compromising safety or reliability.

Excellent Resistance to many acids, alkalis, and aqueous solutions

INCONEL® 690 (UNS N06690/W. Nr. 2.4642) shows excellent corrosion resistance in various acids, alkalis, and aqueous solutions due to its high chromium content. It resists corrosion by strong acids such as hydrochloric acid and sulfuric acid even at elevated temperatures and concentrations without any significant loss in strength or other mechanical properties. This makes it the perfect choice for applications involving nitric or nitric/hydrofluoric acid solutions such as tail-gas reheaters used in nitric acid production and heating coils and tanks used in pickling processes.

The alloy is also highly resistant to oxidation at temperatures up to 815°C (1500°F), making it suitable for use in industries such as power generation, petrochemical processing, aerospace, and nuclear engineering where components may be exposed to harsh environments or extreme temperatures with confidence. Furthermore, its resistance to sulfidation is particularly beneficial in hot sulfur-containing media found in petrochemical plants and refineries, enabling engineers to design reliable parts that can withstand the most aggressive conditions with ease.

In addition to its superior corrosion resistance properties, INCONEL® alloy 690 also offers good machinability despite its high hardness due to its inherent malleability. This means that components made from this material can be worked into complex shapes that offer superior strength without compromising on surface finish or dimensional accuracy. Overall, INCONEL® alloy 690 is an ideal material for applications requiring both excellent corrosion resistance and good machineability characteristics

Applications of Inconel 690

INCONEL® alloy 690 (UNS N06690/W. Nr. 2.4642) is highly sought after in various industries due to its combination of excellent corrosion resistance, high strength, good metallurgical stability, and favourable fabrication characteristics. The material’s ability to withstand nitric or nitric/hydrofluoric acid solutions make it suitable for applications in the chemical processing, energy production, and aerospace industries.

Industrial applications of Inconel 690

INCONEL® alloy 690 (UNS N06690/W. Nr. 2.4642) is a highly sought-after material for many types of industrial applications due to its impressive properties. The material’s superior corrosion resistance, high strength, and favourable fabrication characteristics make it ideal for use in industries such as chemical processing, energy production, and aerospace.

In the chemical processing industry, INCONEL® alloy 690 can be used for components that come into contact with nitric or nitric/hydrofluoric acid solutions such as tail-gas reheaters used in nitric acid production and heating coils and tanks used in pickling processes. Additionally, the material’s resistance to oxidation at temperatures up to 815°C (1500°F) makes it suitable for components that may be exposed to harsh environments or extreme temperatures with confidence.

Nickel 690 is also popularly utilized in energy production applications due to its ability to withstand high temperatures without significant loss in strength or other mechanical properties. This makes it an ideal choice for components of power plants and other energy-related equipment that must operate reliably under hostile conditions where high temperatures are present. Alloy Nickel 690 is also resistant to sulfidation which is beneficial when dealing with hot sulfur-containing media found in petrochemical plants and refineries.

The aerospace industry relies heavily on INCONEL® alloy 690 for its incredible strength and durability under extreme conditions such as those encountered during flight operations or extreme temperature changes experienced during re-entry into Earth’s atmosphere from space. Its excellent oxidation resistance also ensures that aircraft parts made from this material remain safe from corrosion even after prolonged exposure to the elements.

Overall, INCONEL® alloy 690 is an ideal material for various applications requiring both excellent corrosion resistance and good machineability characteristics, making it a versatile solution perfect for industrial uses in numerous industries worldwide.

Welding and Fabrication of Inconel 690

Welding INCONEL® alloy 690 requires the use of special techniques to obtain satisfactory results. It is generally advised that gas tungsten arc welding (GTAW) be used for this material due to its superior penetration and cleanliness when compared with other methods such as shielded metal arc welding (SMAW). Generally speaking, all welds must be kept free from oxidation or contamination by using a shielding gas such as argon-oxygen mixtures during the process.

Fabricating parts out of INCONEL® alloy 690 can be done with relative ease since the material has good machinability despite its hardness. The alloy can be rolled into sheets for forming bends or cut into plates for shaping parts with minimal effort involved in achieving satisfactory results without compromising on surface finish or dimensional accuracy. Additionally, milling operations can also be performed on this material easily since it is resistant to work hardening which could otherwise lead to tool wear or damage if proper precautions are not taken during the process.

Machining and Forming of Inconel 690

Machining of INCONEL® alloy 690 can be done with relative ease due to its inherent malleability which allows components made from the material to be worked into complex shapes without sacrificing strength or surface finish. Additionally, the material’s resistance to work hardening makes it suitable for milling operations where tool wear could otherwise occur if proper precautions are not taken during the process. It is recommended that gas tungsten arc welding (GTAW) be used when welding INCONEL® alloy 690 instead of shielded metal arc welding (SMAW) due to GTAW’s superior penetration and cleanliness.

Forming parts out of INCONEL® alloy 690 can also be done with relative ease since the material has good machinability despite its hardness. The alloy can be rolled into sheets for forming bends or cut into plates for shaping parts with minimal effort involved in achieving satisfactory results without compromising on surface finish or dimensional accuracy. Overall, INCONEL® alloy 690 is an ideal choice for machining and forming applications due to its corrosion resistance properties combined with its good malleability characteristics which enable engineers to craft reliable components that can withstand harsh environments without compromising safety or reliability.

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