Material Properties
Chemical Composition
UNS N10276 Hastelloy C276 is a nickel – based superalloy with a complex and carefully balanced chemical composition. Nickel (\(Ni\)) forms the base, present in the largest proportion. Alongside nickel, it contains significant amounts of molybdenum (\(Mo\), 15 – 17%), chromium (\(Cr\), 14.5 – 16.5%), and tungsten (\(W\), 3 – 4.5%). Smaller amounts of iron (\(Fe\), 4 – 7%), carbon (\(C\), 0.010% max), silicon (\(Si\), 0.08% max), manganese (\(Mn\), 1% max), phosphorus (\(P\), 0.04% max), sulfur (\(S\), 0.03% max), and cobalt (\(Co\), 2.5% max) are also part of its makeup. The combination of these elements gives Hastelloy C276 its unique properties. For example, the high molybdenum content contributes to its remarkable pitting and crevice corrosion resistance, while chromium enhances its general corrosion resistance in both oxidizing and non – oxidizing environments.
Physical Properties
- Density: Hastelloy C276 has a density of approximately 8.89 g/cm³. This relatively high density is typical of nickel – based alloys and is important to consider in applications where weight is a factor, such as in some aerospace or marine components.
- Melting Point: It has a melting range of 1325 – 1370 °C (2417 – 2498 °F). This high melting point allows it to be used in applications that involve high – temperature processes.
- Thermal Conductivity: The thermal conductivity of Hastelloy C276 is moderate, which means it can transfer heat at a rate suitable for applications where heat dissipation or heat transfer needs to be controlled, such as in heat exchangers within chemical processing plants.
- Thermal Expansion Coefficient: It has a specific thermal expansion coefficient, which is important to account for in applications where the material will be subjected to temperature variations. This property ensures that the material maintains its integrity and dimensional stability during heating and cooling cycles.
- Electrical Resistivity: Hastelloy C276 has an electrical resistivity of around 1.229 µΩ·m. This property can be crucial in applications where electrical conductivity or resistance is a factor, such as in some electrical components or in environments where electrical interactions need to be managed.
- Magnetic Properties: It is essentially non – magnetic, which makes it suitable for applications where magnetic interference needs to be avoided, like in certain medical devices or in sensitive electronic equipment manufacturing.
Mechanical Properties
- Tensile Strength: In the annealed condition, Hastelloy C276 has a minimum ultimate tensile strength of 690 MPa (100 ksi). This high tensile strength enables it to withstand significant pulling forces without breaking, making it suitable for structural components in various industries.
- Yield Strength: The yield strength (0.2% offset) is typically around 310 MPa (45 ksi) in the annealed state. This indicates the stress level at which the material begins to deform plastically.
- Elongation: It has a minimum elongation at break of 40%, which shows its good ductility. This property allows the material to be formed into various shapes through processes like forging, rolling, or bending without cracking.
- Hardness: The hardness of Hastelloy C276, measured on the Rockwell B scale, is typically around 100 RB minimum. Hardness is an important property as it affects the material’s wear resistance and its ability to withstand indentation and scratching.
- Fatigue Resistance: Hastelloy C276 exhibits good fatigue resistance, meaning it can withstand repeated cyclic loading without failure. This makes it ideal for components that are subject to continuous stress fluctuations, such as in rotating machinery parts.
- Creep Resistance: At elevated temperatures, Hastelloy C276 shows reasonable creep resistance. Creep is the slow, time – dependent deformation of a material under a constant load. In applications where the material is exposed to high temperatures and stress for extended periods, such as in some parts of chemical reactors, creep resistance is crucial to maintain the integrity of the component.
Other Properties
- Corrosion Resistance: Hastelloy C276 is renowned for its outstanding corrosion resistance. It can resist corrosion in a wide range of aggressive environments, including both oxidizing and reducing acids. For example, it shows excellent resistance to sulfuric acid, hydrochloric acid, and phosphoric acid, even at high concentrations and elevated temperatures.
- Oxidation Resistance: It has good oxidation resistance up to approximately 1800 °F (982 °C). This property allows it to be used in applications where exposure to high – temperature oxidizing atmospheres is expected, such as in some parts of industrial furnaces.
- Stress Corrosion Cracking Resistance: The alloy is highly resistant to stress corrosion cracking (SCC), especially in chloride – containing environments. SCC is a phenomenon where a material cracks under the combined action of tensile stress and a corrosive environment. In the oil and gas industry, where chloride – rich brines are common, the SCC resistance of Hastelloy C276 makes it a preferred material for many components.
- Pitting Resistance: Due to its high molybdenum content, Hastelloy C276 has excellent pitting resistance. Pitting is a localized form of corrosion that can lead to the formation of small holes or pits in the material surface. In seawater applications, for example, where pitting corrosion is a major concern, Hastelloy C276 can provide long – term reliability.
- Intergranular Corrosion Resistance: The low carbon content of Hastelloy C276 minimizes carbide precipitation during welding and heat treatment processes. This, in turn, gives the alloy good intergranular corrosion resistance. Intergranular corrosion occurs along the grain boundaries of a material and can severely degrade its mechanical properties.
Applications
Chemical Processing
In the chemical processing industry, Hastelloy C276 is used in a wide variety of applications. It is commonly used in the construction of chemical reactors, heat exchangers, and piping systems. For instance, in the production of organic chemicals, where highly corrosive reactants and products are involved, Hastelloy C276 reactors can withstand the harsh chemical environment, ensuring long – term operation and minimizing the risk of leaks or failures. In sulfuric acid production plants, heat exchangers made of Hastelloy C276 are used to transfer heat between different process streams while resisting the corrosive effects of sulfuric acid at various concentrations and temperatures.
Oil and Gas Industry
The oil and gas industry also relies heavily on Hastelloy C276. It is used in subsea pipelines, wellhead components, and valves. Subsea pipelines need to resist the corrosive effects of seawater, as well as any corrosive substances present in the transported oil or gas, such as hydrogen sulfide (\(H_2S\)) and chlorides. Hastelloy C276’s excellent corrosion resistance, including resistance to \(H_2S\) stress corrosion cracking, makes it a suitable material for these critical applications. Wellhead components, which are exposed to high – pressure, corrosive fluids, also benefit from the use of Hastelloy C276 to ensure reliable operation in challenging downhole conditions.
Pollution Control
In pollution control applications, Hastelloy C276 is used in flue gas desulfurization (FGD) systems. FGD systems are designed to remove sulfur dioxide (\(SO_2\)) from the flue gases of power plants and industrial boilers. The process involves exposure to highly corrosive environments, including sulfuric acid mist and chloride – containing solutions. Hastelloy C276 is used in the construction of absorption towers, re – heaters, and fans in FGD systems due to its ability to resist corrosion in these aggressive conditions, thus ensuring the efficient and long – term operation of the pollution control equipment.
Pulp and Paper Industry
In the pulp and paper industry, Hastelloy C276 is used in equipment that comes into contact with corrosive chemicals during the pulping and paper – making processes. For example, in the digesters where wood chips are cooked with chemicals to break them down into pulp, the harsh chemical environment can cause severe corrosion. Hastelloy C276 is used in the construction of digester linings and other components to resist corrosion and maintain the integrity of the equipment. It is also used in bleach plants, where the presence of chlorine – based bleaching agents creates a highly corrosive atmosphere, and Hastelloy C276 can withstand these conditions better than many other materials.
Pharmaceuticals
The pharmaceutical industry requires materials that are both corrosion – resistant and meet strict purity standards. Hastelloy C276 is used in pharmaceutical processing vessels, piping, and fittings. In the production of drugs, the process often involves the use of corrosive chemicals and solvents. Hastelloy C276 ensures that the equipment does not corrode and contaminate the pharmaceutical products, while also maintaining its structural integrity over time. Its ability to be easily cleaned and sterilized also makes it suitable for use in pharmaceutical manufacturing facilities.
Food Processing
In food processing, where hygiene and corrosion resistance are crucial, Hastelloy C276 is used in equipment such as heat exchangers, valves, and piping. The food processing environment can be corrosive due to the presence of acidic or alkaline food products, cleaning agents, and sanitizers. Hastelloy C276’s corrosion resistance ensures that the equipment does not leach harmful substances into the food products, while also providing long – lasting performance. It can withstand the repeated cleaning and sanitization processes required in the food industry without corroding or degrading.
Aerospace
Although less common than in some other industries, Hastelloy C276 can be used in certain aerospace applications. For example, in components that are exposed to corrosive environments, such as in some parts of aircraft engines where hot, corrosive gases are present, or in aerospace fuel systems where the fuel may contain trace amounts of corrosive substances. Its high strength, corrosion resistance, and ability to maintain its properties at elevated temperatures make it a viable option for these specialized aerospace applications.
Marine Applications
In marine applications, Hastelloy C276 is widely used. It is used in shipbuilding for components such as propeller shafts, seawater piping systems, and marine hardware. Seawater is a highly corrosive medium, containing salts, dissolved oxygen, and other corrosive agents. Hastelloy C276’s excellent corrosion resistance, especially its resistance to pitting and crevice corrosion in seawater, makes it a reliable choice for marine applications. Propeller shafts made of Hastelloy C276 can withstand the abrasive and corrosive forces of seawater, ensuring smooth operation of the ship’s propulsion system over long periods.
Manufacturing Techniques
Casting
Casting is one of the methods used to shape Hastelloy C276. In this process, molten Hastelloy C276 is poured into a mold of the desired shape. The high melting point of the alloy requires careful control of the casting temperature. Casting can be used to produce complex – shaped components, such as some parts of chemical reactors or marine propellers. However, it is important to ensure proper cooling and solidification to avoid defects such as porosity.
Forging
Forging involves shaping the Hastelloy C276 by applying compressive forces. This can be done hot (at elevated temperatures) or cold. Hot forging is often preferred as it allows for better formability due to the reduced strength of the material at high temperatures. Forged Hastelloy C276 components, such as shafts and gears, can have improved mechanical properties compared to cast components as the forging process can align the grain structure of the material, enhancing its strength and fatigue resistance.
Welding
Welding Hastelloy C276 requires careful consideration. The alloy can be welded using common welding methods such as tungsten inert gas (TIG) welding, metal inert gas (MIG) welding, and shielded metal arc welding (SMAW). However, due to its chemical composition, special precautions need to be taken. For example, excessive heat input during welding should be avoided to prevent carbide precipitation, which can reduce the corrosion resistance of the welded joint. Post – weld heat treatment may also be required in some cases to relieve stress and optimize the properties of the welded area.
Machining
Machining Hastelloy C276 can be challenging due to its high strength and work – hardening characteristics. Special cutting tools and machining parameters are often required. High – speed steel or carbide – tipped tools are commonly used. Machining operations such as turning, milling, and drilling are used to create precise dimensions and features on Hastelloy C276 components, such as in the production of parts for the oil and gas industry or in the manufacturing of medical devices.
Heat Treatment
Heat treatment of Hastelloy C276 is mainly used to relieve stress, improve ductility, or control the microstructure. Annealing is a common heat treatment process. The alloy is typically annealed at temperatures around 1121 °C (2050 °F) and then rapidly quenched. This helps to dissolve any precipitates that may have formed during previous manufacturing processes and restores the material’s optimal properties, such as its corrosion resistance and ductility.
Cold Working
Cold working involves deforming the Hastelloy C276 at room temperature. This process can increase the strength and hardness of the material through work – hardening. Cold rolling, for example, is used to produce sheets and strips of Hastelloy C276 with specific thicknesses and surface finishes. However, excessive cold working can reduce the ductility of the material, so the process needs to be carefully controlled.
Hot Working
Hot working is carried out at elevated temperatures above the recrystallization temperature of Hastelloy C276. This process allows for easier deformation of the material compared to cold working. Hot rolling, forging, and extrusion are examples of hot – working processes. Hot working can improve the mechanical properties of the alloy by refining the grain structure and reducing internal stresses.
Surface Treatment
Surface treatment of Hastelloy C276 can be done to further enhance its corrosion resistance or to improve its appearance. Electroplating, for example, can be used to deposit a thin layer of a more corrosion – resistant metal on the surface of Hastelloy C276 components. Passivation is another common surface treatment method. In passivation, the surface of the alloy is treated with a chemical solution to form a thin, protective oxide layer, which can further improve its corrosion resistance.
Case Studies
Chemical Reactor Linings
A chemical plant was producing a variety of organic chemicals using highly corrosive reactants. The previous reactor linings, made of a different material, were experiencing frequent corrosion failures, leading to production downtime and costly repairs. After switching to Hastelloy C276 linings, the corrosion rate decreased significantly. In a five – year period, the number of corrosion – related shutdowns dropped from an average of three per year to only one. The cost savings from reduced maintenance and increased production uptime were substantial, demonstrating the effectiveness of Hastelloy C276 in such a harsh chemical environment.
Oil Refinery Components
In an oil refinery, the components in the desalination unit were constantly exposed to a corrosive mixture of oil, water, and salts. The original carbon – steel components were suffering from severe corrosion, with some parts needing to be replaced every few months. When these components were replaced with ones made of Hastelloy C276, the service life increased dramatically. The new components lasted for over three years without significant corrosion, reducing maintenance costs and ensuring more reliable operation of the desalination unit.
Flue Gas Desulfurization Systems
A power plant’s flue gas desulfurization system was experiencing corrosion problems in the absorption tower. The combination of sulfuric acid mist and chloride – containing solutions was causing rapid corrosion of the tower’s interior. After installing Hastelloy C276 panels in the absorption tower, the corrosion rate was reduced to a negligible level. The plant was able to operate the FGD system continuously for over four years without major maintenance due to corrosion, resulting in improved environmental performance and reduced operational costs.
Pulp Mill Equipment
A pulp mill was using equipment made of stainless steel in its digester and bleach plant. However, the stainless steel was not able to withstand the highly corrosive chemicals used in the pulping and bleaching processes. After replacing the key components with Hastelloy C276, the equipment’s lifespan increased significantly. In the digester, the Hastelloy C276 linings lasted for more than five years, compared to less than two years for the previous stainless – steel linings. This led to reduced equipment replacement costs and increased production efficiency in the pulp mill.
Pharmaceutical Processing Vessels
A pharmaceutical company was facing issues with contamination of its products due to corrosion of the processing vessels. The previous material used was not resistant to the corrosive solvents and chemicals used in the drug – making process. After switching to Hastelloy C276 processing vessels, the problem of contamination was eliminated. The vessels also showed no signs of corrosion after several years of use, ensuring the purity and quality of the pharmaceutical products and reducing the risk of product recalls.
Marine Corrosion Protection
A shipyard was building a new vessel and wanted to ensure long – term corrosion protection for its seawater piping system. By using Hastelloy C276 pipes, they were able to prevent corrosion even in the harsh marine environment. Over a ten – year period, the Hastelloy C276 pipes showed no signs of pitting or crevice corrosion, while other vessels in the same fleet with different piping materials experienced significant corrosion and required frequent repairs. This not only saved maintenance costs but also improved the overall reliability of the ship’s seawater systems.
