Physical and chemical properties of Inconel718 alloy tube
1. Physical properties
Density: The density of Inconel 718 alloy tube is about 8.22 g/cm³. This density value makes it have good application potential in fields such as aerospace and energy that have strict requirements on material weight and performance. Compared with some metal materials with higher density, it can effectively reduce the weight of the structure, improve energy utilization efficiency and equipment operation performance while meeting the performance requirements such as strength.
Melting point: Its melting point range is roughly 1260-1340℃. The higher melting point enables Inconel 718 alloy tube to maintain a stable solid structure in a high temperature environment and withstand high temperature without melting and deformation, which provides a solid foundation for its application in high temperature conditions such as high temperature components of gas turbines and high temperature reaction equipment in petrochemical industry.
Thermal expansion coefficient: In the temperature range from room temperature to 100℃, the average linear expansion coefficient of Inconel 718 alloy tube is about 12.3×10⁻⁶/℃. As the temperature rises to 500℃, the average linear expansion coefficient increases to about 13.3×10⁻⁶/℃. The reasonable thermal expansion coefficient makes the alloy tube have good thermal matching with other components in a temperature-changing environment, and it is not easy to produce excessive internal stress due to thermal expansion and contraction, thereby ensuring the overall structural integrity and reliability of the equipment.
Thermal conductivity: At 20℃, the thermal conductivity of Inconel 718 alloy tube is about 11.4 W/(m・K). As the temperature rises, the thermal conductivity will increase. For example, at 500℃, the thermal conductivity is about 17.5 W/(m・K). The relatively low thermal conductivity means that the alloy tube has a certain thermal insulation performance. In some occasions where heat transfer needs to be controlled, such as the piping system of a high-temperature furnace, it can reduce heat loss and improve energy utilization.
Conductivity: The conductivity of Inconel 718 alloy tube is low. At 20℃, its conductivity is about 0.62×10⁶ S/m. This feature makes it valuable in the manufacture of some electrical equipment components that require electromagnetic shielding, which can effectively prevent electromagnetic interference and ensure the normal operation of the equipment. At the same time, low conductivity also indicates that it has a large resistance when used as a conductor in the electrical system. In practical applications, it needs to be reasonably selected according to specific needs.
2. Chemical properties
Anti-oxidation performance: Inconel 718 alloy tube has excellent anti-oxidation performance in high temperature environment. In the air, when the temperature is lower than 650℃, a dense Cr₂O₃ oxide film will form on the surface of the alloy. This oxide film has a stable structure and can effectively prevent oxygen from further diffusing inward, thereby protecting the alloy matrix from oxidation. As the temperature rises to 700-800℃, although the oxidation rate will increase, a composite oxide film composed of various oxides such as Cr₂O₃, Al₂O₃ and TiO₂ will gradually form on the alloy surface. This composite oxide film further enhances the oxidation resistance, so that the Inconel 718 alloy pipe can still maintain good performance when used for a long time in a high temperature environment below 800℃, and will not cause problems such as thinning of wall thickness and strength reduction due to severe oxidation.
Corrosion resistance:
General corrosion: In most conventional atmospheric environments and fresh water, Inconel 718 alloy pipes have good general corrosion resistance. The synergistic effect of nickel, chromium, molybdenum and other elements in its alloy composition improves the thermodynamic stability of the alloy and reduces the corrosion tendency in these environments. For example, after being exposed to industrial atmospheric environments for many years, the corrosion degree of the alloy pipe surface is very slight and hardly affects its normal use.
Seawater corrosion resistance: For complex corrosive media such as seawater, Inconel 718 alloy pipes also show good tolerance. The chromium element in the alloy can form a passivation film on the surface to resist the corrosion of chloride ions in seawater. The molybdenum element further enhances the alloy's resistance to chloride ion pitting and crevice corrosion. In the field of marine engineering, such as the pipeline system of offshore oil drilling platforms and the pipelines of seawater desalination equipment, Inconel 718 alloy pipes can maintain structural integrity in the case of long-term contact with seawater, reducing maintenance and replacement costs.
Resistance to stress corrosion cracking: Inconel 718 alloy pipes have high resistance to stress corrosion cracking. When subjected to tensile stress and in a specific corrosive medium environment (such as high-temperature water medium containing chlorides), the alloy pipe is not prone to stress corrosion cracking. This is mainly due to its reasonable alloy composition design and organizational structure. The γ'' phase and γ' phase formed by the niobium element in the alloy improve the microstructure of the alloy while improving the strength of the alloy through precipitation strengthening, thereby reducing its sensitivity to stress corrosion cracking. This property enables Inconel 718 alloy pipes to operate reliably under harsh working conditions such as petrochemicals and nuclear industries where stress and corrosion are combined.
Intergranular corrosion resistance: Through appropriate heat treatment processes, Inconel 718 alloy pipes can obtain good intergranular corrosion resistance. In the sensitization temperature range (generally 600-950℃), the chromium element in the alloy will not be depleted at the grain boundaries due to the precipitation of carbides, thereby maintaining the corrosion resistance of the grain boundary area. For example, Inconel 718 alloy pipes that have been solution treated and aged show no tendency to intergranular corrosion in the E method (oxalic acid electrolytic etching test) and A method (sulfuric acid-copper sulfate test) of ASTM A262 standard, which can meet the use requirements in some chemical production environments that are sensitive to intergranular corrosion.
Chemical stability: Inconel 718 alloy pipes show good chemical stability in many common chemical media. At room temperature, it has good tolerance to most organic acids (such as acetic acid, citric acid, etc.), dilute sulfuric acid, dilute hydrochloric acid, etc. In these acid solutions with lower concentrations, a passivation film will form on the surface of the alloy tube, preventing further chemical reactions. Even in some medium-concentration acid solutions, within a certain temperature range, the Inconel 718 alloy tube can remain relatively stable and have a low corrosion rate. However, in strong oxidizing acids (such as concentrated nitric acid) and high-temperature, high-concentration acidic environments, the corrosion resistance of the alloy tube will be challenged to a certain extent, and it needs to be evaluated and selected according to specific working conditions. In addition, in alkaline media, the Inconel 718 alloy tube also has good chemical stability. In general alkaline solutions such as sodium hydroxide and potassium hydroxide, it is not easy to undergo corrosion reactions, and can be used in related application scenarios such as alkaline material transportation pipelines.
