Inconel 718 Tubing – Ideal for Jet Engines & High-Pressure Systems

Inconel 718 is a high-performance nickel-chromium superalloy designed for use in extreme environments, where high strength, corrosion resistance, and high-temperature stability are required. Composed primarily of nickel (50-55%), chromium (17-21%), and iron, Inconel 718 also includes significant amounts of molybdenum, niobium, and titanium, which provide the alloy with its exceptional properties. Inconel 718 tubing is specifically engineered to meet the rigorous demands of industries such as aerospace, power generation, and chemical processing, where components need to perform reliably under high-pressure and high-temperature conditions.

The alloy’s combination of high tensile strength, excellent fatigue and oxidation resistance, and good weldability make it the ideal choice for critical applications like jet engines and high-pressure systems. Inconel 718 tubing maintains its structural integrity and mechanical properties even in the most challenging operating conditions, including extreme temperatures and intense mechanical stresses.

Applications of Inconel 718 Tubing

Inconel 718 tubing is widely used across a variety of industries due to its ability to withstand harsh conditions. Some of the key applications include:

1. Jet Engines and Aircraft Turbine Engines: One of the most prominent uses of Inconel 718 tubing is in jet engines, particularly in components like fuel lines, cooling systems, and combustion chambers. The tubing's ability to withstand the high temperatures generated in the engine, as well as its resistance to oxidation and corrosion, ensures that it can operate safely and effectively over long periods. Inconel 718 tubing is also used in turbine engines for military and commercial aircraft, where components are subjected to high pressure and thermal cycling.

2. High-Pressure Systems: Inconel 718 tubing is commonly used in high-pressure systems, where components are required to maintain structural integrity under extreme conditions. Applications include pressure vessels, hydraulic systems, and valves that operate in power generation plants, chemical processing facilities, and other industries where maintaining high pressures over long periods is crucial.

3. Rocket Motors: The aerospace industry also relies on Inconel 718 tubing in rocket propulsion systems. Components like cooling lines, nozzle extensions, and combustion chambers need tubing that can handle both the intense heat and pressure of rocket motors. Inconel 718 is particularly valued for its ability to withstand the high-pressure environments and thermal stresses found in rocket engines during launch.

4. Gas Turbines: Inconel 718 tubing is used extensively in the production of gas turbines, particularly in power generation and aerospace applications. The tubing is critical in applications where high pressures and high temperatures must be managed over prolonged periods. Its resistance to thermal creep and fatigue ensures long-term reliability, especially in turbine blades and combustion chamber cooling systems.

5. Chemical Processing: The chemical processing industry uses Inconel 718 tubing for applications that require resistance to corrosion and high temperatures. Chemical reactors, heat exchangers, and other high-temperature systems benefit from the alloy’s ability to maintain integrity in aggressive environments where conventional materials might fail.

6. Marine and Offshore Applications: Inconel 718 tubing is also used in marine environments where components are exposed to both high pressures and corrosive saltwater. Marine turbines, heat exchangers, and oil and gas drilling systems benefit from Inconel 718's resistance to seawater corrosion and its ability to withstand high pressures and temperatures.

Grade & Specifications

Inconel 718 tubing is manufactured according to specific grades and standards to ensure its suitability for high-performance applications. Some of the key grades and specifications include:

1. UNS N07718: The standard designation for Inconel 718, used extensively in high-temperature and high-pressure applications. This grade of Inconel 718 tubing is known for its high strength, resistance to oxidation and corrosion, and excellent mechanical properties under elevated temperatures.

2. AMS 5596: This specification covers Inconel 718 seamless tubing for aerospace applications. It is used for parts in jet engines and rocket motors where high strength, fatigue resistance, and the ability to withstand high temperatures and pressures are critical.

3. AMS 5589: Another aerospace-grade specification for Inconel 718 tubing, primarily used for applications like turbine engine cooling systems. It is designed for parts that experience high temperatures and pressures, ensuring excellent reliability and durability.

4. DIN 2.4668: The European equivalent of UNS N07718, this grade is commonly used for applications in the aerospace and industrial sectors that require materials with high mechanical strength and resistance to heat and corrosion.

Manufacturing Process of Inconel 718 Tubing

The production of Inconel 718 tubing involves a series of highly controlled manufacturing steps to ensure the material’s mechanical properties are maintained and that the tubing meets the stringent demands of aerospace and high-pressure applications:

1. Melting and Alloying: The production process begins with the melting of the raw materials, which is typically done in a vacuum induction furnace or electric arc furnace. This ensures that the material has the proper chemical composition, including nickel, chromium, molybdenum, niobium, and titanium, to achieve the desired properties of high strength, oxidation resistance, and fatigue resistance.

2. Casting: After the alloy is melted, it is cast into billets or ingots. The casting process ensures the uniformity of the material, which is essential for producing tubing that will be used in high-stress applications.

3. Hot Working: The cast billets are then heated and hot worked, usually by extrusion, to form a cylindrical shape. This step refines the grain structure of the alloy and enhances its mechanical properties, especially its strength and resistance to thermal cycling.

4. Seamless Tubing Formation: Inconel 718 tubing is often produced as seamless tubing, meaning it is created without any welded seams. This is done through extrusion or rotary piercing, followed by elongation. Seamless tubing is preferred in high-pressure applications, as it eliminates the risk of weak points where the material could fail.

5. Cold Working: In some cases, cold working processes such as drawing or pilgering are used to achieve the final dimensions and enhance the tubing’s surface finish. Cold working also increases the strength of the material by refining the grain structure.

6. Heat Treatment: After forming the tubing, it is subjected to heat treatment, typically a solution annealing process followed by aging. Solution annealing helps relieve stresses induced during the forming process, while aging enhances the alloy's strength, particularly at high temperatures. This treatment is critical to achieving the required mechanical properties for high-performance applications.

7. Finishing and Inspection: After heat treatment, the Inconel 718 tubing is further processed to achieve the final dimensions and surface finish required for its specific application. This may include surface treatments to reduce oxidation or enhance corrosion resistance. The tubing is also thoroughly inspected for any internal defects or irregularities using techniques like ultrasonic testing or X-ray inspection.

8. Quality Control: Stringent quality control measures are employed to ensure the tubing meets the exact specifications for strength, corrosion resistance, and mechanical properties. Tensile testing, pressure testing, and dimensional inspections are common steps to verify that the final product is ready for use in critical aerospace or high-pressure applications.

User Requirements

Users of Inconel 718 tubing typically have stringent requirements due to the high-performance nature of the applications. Some of the most common user demands include:

1. High Strength and Fatigue Resistance: Inconel 718 tubing must have excellent tensile strength and resistance to fatigue to withstand the mechanical stresses experienced in jet engines, rocket motors, and high-pressure systems. The tubing must retain its mechanical properties even under dynamic loading conditions and prolonged exposure to high temperatures.

2. High-Temperature Resistance: Inconel 718 is chosen for its ability to perform at temperatures exceeding 700°C (1290°F), which is common in jet engine and gas turbine applications. The tubing must maintain its strength, avoid thermal degradation, and resist oxidation at these elevated temperatures.

3. Corrosion and Oxidation Resistance: Components in high-pressure, high-temperature environments are often exposed to corrosive elements, whether in aerospace, marine, or chemical processing applications. Inconel 718 tubing must provide excellent resistance to both general corrosion and localized forms of corrosion such as pitting or crevice corrosion.

4. Precision and Dimensional Accuracy: Aerospace and industrial users demand that Inconel 718 tubing be manufactured to precise dimensions, with tight tolerances to ensure compatibility and safe integration into complex systems. The material must meet strict quality standards to ensure safe and reliable performance.

5. Weldability and Fabrication Ease: Inconel 718 tubing must be easy to weld and form into the required shapes. The alloy’s good weldability ensures that it can be used in the fabrication of complex structures and components without compromising its strength or corrosion resistance.