ASTM B622 is a standard specification for seamless nickel and nickel alloy pipes and tubes designed for corrosive service environments. Alloy C22 (UNS N06022), commonly known as Hastelloy C-22, is a nickel-chromium-molybdenum-tungsten alloy renowned for exceptional corrosion resistance. It is specifically engineered for heat exchangers operating in aggressive chemical and high-temperature environments.

Material Composition:
Alloy C22’s composition is optimized for performance in oxidizing and reducing media:

Nickel (Ni): ~56% (base element for ductility and corrosion resistance).
Chromium (Cr): 20–22.5% (enhances oxidation resistance).
Molybdenum (Mo): 12.5–14.5% (resists reducing acids and pitting).
Tungsten (W): 2.5–3.5% (synergizes with Mo for localized corrosion resistance).
Iron (Fe): 2–6%, Cobalt (Co): ≤2.5% (trace elements).
Carbon (C), Manganese (Mn), Silicon (Si), Sulfur (S), Phosphorus (P), Vanadium (V): Minimized to enhance weldability and reduce intermetallic phase formation.

Physical and Mechanical Properties:

Tensile Strength: ~100 ksi (690 MPa).
Yield Strength: ~45 ksi (310 MPa).
Elongation: ~45% (excellent ductility).
Thermal Conductivity: 9.8 W/m·K (at 100°C).
Coefficient of Thermal Expansion: 12.2 μm/m·K (20–100°C).
Density: 8.69 g/cm³.
Non-Magnetic: Suitable for sensitive applications.

Application:

Heat Exchangers in Petrochemical Plants: Alloy C22’s resistance to chloride-induced corrosion and its high-temperature strength make it suitable for use in heat exchangers in petrochemical refining processes, such as hydroprocessing, alkylation, and dehydrogenation processes.
Sulfur Recovery Units: In sulfur recovery plants, where acid gases like hydrogen sulfide and sulfur dioxide are common, Alloy C22 tubes are used in heat exchangers to prevent corrosion in these aggressive environments.
Pharmaceutical Manufacturing: Alloy C22’s excellent corrosion resistance and biocompatibility make it suitable for heat exchangers in pharmaceutical and biotechnology applications. It can handle aggressive cleaning agents and sterilization processes, ensuring long-term, reliable operation in these high-purity environments.
Drug Processing: In the drug manufacturing process, where heat exchangers are used to control the temperature of various fluids and chemicals, Alloy C22 offers corrosion resistance, even in highly acidic or chloride-containing environments.