Alloy C-276 - The True Workhorse of the Chemical Industry

Alloy C-276 

W.Nr.: 2.4819

UNS: N10276

Alloy C-276 (2.4819/N10276) is a nickel-chromium-molybdenum alloy containing tungsten. It exhibits excellent resistance to localized pitting and crevice corrosion, uniform corrosion, and stress corrosion cracking in a wide range of chemical process media, especially in reducing acidic environments. Due to its outstanding corrosion resistance, even in the presence of halogens, this alloy has become the true workhorse for various applications in the chemical industry.

Chemical Composition (% by weight):

Material Characteristics

• Excellent corrosion resistance in a wide range of corrosive media, including oxidizing and reducing acids.

• Particularly high resistance to crevice corrosion, pitting, and stress corrosion cracking caused by chlorides.

Corrosion Resistance

Alloy C-276 can be used in many chemical processes involving both oxidizing and reducing media. The high chromium and molybdenum contents enable the alloy to resist chloride ion attack. The addition of tungsten further enhances this resistance. Alloy C-276 is one of the few materials resistant to chlorine gas, hypochlorite solutions, and chlorine dioxide solutions. Additionally, the alloy exhibits excellent corrosion resistance in high-concentration oxidizing salt solutions, such as ferric chloride and copper chloride solutions.

Fabrication and Heat Treatment

Alloy C-276 is well-suited for processing using standard industrial techniques.

Heating

It is crucial that the workpiece is kept clean and free of any contaminants before and during heating. Sulfur, phosphorus, lead, and other low-melting-point metals can cause damage to VDM® Alloy C-276 during the heating process.

Such contamination can also be present in paints or coatings used for marking and temperature indication, as well as in lubricants, oils, fuels, and similar materials. The sulfur content of the furnace fuel must be controlled to the lowest possible level. The sulfur content of natural gas used as fuel should be less than 0.1% (by weight). Heating oil with a sulfur content not exceeding 0.5% (by weight) can also be used as fuel. Electric furnaces are the preferred heating method, as they allow for precise temperature control and avoid fuel-related contamination. The furnace atmosphere should be set between neutral and slightly oxidizing, and should not fluctuate between oxidizing and reducing conditions. The workpiece must not come into direct contact with the flame.

Hot Forming

Alloy C-276 should be hot-formed in the temperature range of 950 to 1200°C (1742 to 2192°F), followed by rapid cooling in water or air. It is recommended to perform a heat treatment after hot forming to achieve optimal corrosion performance. During heating, the workpiece should be placed in a furnace that has already reached the target temperature.

Cold Forming

The workpiece should be in the annealed condition for cold working. Alloy C-276 has significantly better cold forming properties compared to widely used austenitic stainless steels, which must be considered in the design and selection of forming tools and equipment.

Intermediate annealing is necessary during major cold working operations. A final solution annealing treatment must be performed if the cold forming rate exceeds 15%.

Heat Treatment

Solution annealing should be carried out at a temperature of 1,100 to 1,160°C (2,012 to 2,120°F). The holding time during the annealing process depends on the thickness of the semi-finished product and can be calculated as follows:

• For thickness d < 10 mm (0.4 in), the holding time is t = d ∙ 3 min/mm

• For thickness d = 10 to 20 mm (0.4-0.8 in), the holding time is t = 30 min + (d - 10 mm) ∙ 2 min/mm

• For thickness d = 20 mm (0.8 in), the holding time is t = 50 min + (d - 20 mm) ∙ 1 min/mm

Applications

Alloy C-276 is widely used in the chemical and petrochemical industries and is applied in organic chemical processes involving chlorides, as well as in catalytic systems. The material is particularly suitable for use in high-temperature, contaminated inorganic acid, solution, organic acid (e.g., formic and acetic acid), or seawater environments.

• Pulp and paper industry, e.g., for digesters and bleaching tanks

• Scrubbers, agitators, and wet scrubbers in flue gas desulfurization systems

• Acid gas equipment and components

• Acetic acid production reactors

• Sulfuric acid coolers

• Methylene diphenyl isocyanate (MDI) production

• Manufacture and handling of contaminated phosphoric acid

Typical applications of Alloy C-276 include plate-type heat exchangers operating at low temperatures in sulfuric acid production. Other applications, such as VCM production, utilize the alloy's resistance to hydrochloric acid corrosion. Additionally, this alloy exhibits good corrosion resistance to acetic acid of various concentrations and temperatures, making it suitable for use in oxidizing acetic acid solutions. Alloy C-276 can also be used in mixed acid environments, such as acetic acid with inorganic acids and mixtures of inorganic salts, where stainless steels are not suitable.

Extensive practical experience has also shown that this material is suitable for environmental protection equipment, such as flue gas desulfurization. In such applications, the material is widely used for the manufacture of inlet piping, scrubbers, dampers, agitators, and ductwork. Alloy C-276 has been certified for pressure vessel applications in the temperature range of -196 to 400°C (-335 to 752°F).

Available Products

Shanghai COCESS Special Alloy Co., Ltd. can supply Hastelloy C-276 in the form of bars, plates, strips, tubes, capillaries, fittings, flanges, forgings, fasteners, and welding materials. Please contact us for more product details.