Hastelloy C-22 is a nickel-chromium-molybdenum alloy with the addition of tungsten. It is an improved version of Hastelloy C-276, offering superior resistance to pitting, crevice corrosion, and stress corrosion cracking in a wider range of aggressive environments, including oxidizing acids. The alloy is solid-solution strengthened and is not precipitation hardenable.

The nominal chemical composition is: nickel 56.0 percent (balance), chromium 20.0–22.5 percent, molybdenum 12.5–14.5 percent, iron 2.0–6.0 percent, tungsten 2.5–3.5 percent, cobalt up to 2.5 percent, and smaller amounts of carbon, manganese, and silicon.

Key mechanical properties (typical, annealed condition):

● Tensile strength: 690–790 MPa

● Yield strength (0.2% offset): 310–360 MPa

● Elongation: 45–50 percent

● Hardness: 85–100 HRB

● Density: 8.69 g/cm³

Hastelloy C-22 offers excellent resistance to both reducing acids (hydrochloric, sulfuric) and oxidizing acids (nitric, chromic, ferric). It is highly resistant to pitting and crevice corrosion in chloride-containing environments and to stress corrosion cracking. The alloy maintains outstanding corrosion resistance in the as-welded condition (no sensitization) and has better thermal stability than C-276, making it suitable for higher-temperature applications (up to about 400°C continuous).

Common standards: ASTM B575 (plate, sheet, strip), B574 (bar, wire), B622 (seamless pipe and tube), B619 (welded pipe), B626 (welded tube), ASME SB-575, SB-574, SB-622, and NACE MR0175/ISO 15156 for sour service.

Typical applications include:

● Chemical processing: reactors, heat exchangers, piping for mixed acids, bleach plants, and flue gas desulfurization (FGD) systems.

● Pharmaceutical and food processing: equipment requiring high purity and corrosion resistance.

● Oil and gas: downhole tubing, flowlines, and components in sour (H₂S, CO₂, chlorides) environments, especially where oxidizing agents are present.

● Waste treatment: incinerators, scrubbers, and handling of aggressive waste streams.

Comparison with Hastelloy C-276: C-22 has higher chromium and lower molybdenum than C-276, giving it superior resistance to oxidizing acids and better overall performance in mixed acid environments. C-22 also has better thermal stability and resistance to pitting and crevice corrosion. C-276 remains preferred in highly reducing environments (e.g., concentrated hydrochloric acid) and is often lower in cost. For most chemical process applications requiring broad corrosion resistance, C-22 is the superior choice.

Selection guidance: Choose Hastelloy C-22 for environments containing both oxidizing and reducing species (e.g., mixed acids, chlorides with oxidizing contaminants). For purely reducing conditions (e.g., dilute HCl without oxygen), C-276 or Alloy B may be more suitable. For less demanding service, stainless steel or Incoloy 825 may suffice.