Hastelloy B-2 is a nickel-molybdenum alloy (approximately 65 percent nickel, 28 percent molybdenum, 2 percent iron, with small amounts of chromium and other elements). It is designed for exceptional resistance to pure reducing acids, particularly hydrochloric acid (HCl) at all concentrations and temperatures, as well as sulfuric, phosphoric, and acetic acids. The alloy is solid-solution strengthened and is not precipitation hardenable.

The nominal chemical composition is: nickel 65.0–72.0 percent, molybdenum 26.0–30.0 percent, iron up to 2.0 percent, chromium up to 1.0 percent, cobalt up to 1.0 percent, and smaller amounts of carbon, manganese, and silicon.

Key mechanical properties (typical, annealed condition):

● Tensile strength: 760–850 MPa

● Yield strength (0.2% offset): 350–450 MPa

● Elongation: 40–50 percent

● Hardness: 85–95 HRB

● Density: 9.22 g/cm³

Hastelloy B-2 offers outstanding resistance to hydrochloric acid across the full concentration and temperature range (up to boiling). It also resists sulfuric acid (up to moderate concentrations), phosphoric acid, and organic acids. However, it has very poor resistance to oxidizing media (e.g., nitric acid, ferric ions, dissolved oxygen) and should not be used in such environments. The alloy is susceptible to the formation of intermetallic phases (Ni4Mo) if exposed to temperatures between 650–800°C, which can embrittle the material; careful fabrication and heat treatment are required.

Common standards: ASTM B333 (plate, sheet, strip), B335 (rod, bar), B622 (seamless pipe and tube), B619 (welded pipe), ASME SB-333, SB-335, SB-622.

Typical applications include:

● Chemical processing: equipment handling hydrochloric acid (any concentration) at elevated temperatures, such as reactors, heat exchangers, valves, and piping.

● Pharmaceutical and fine chemical synthesis: where HCl is used as a reactant or byproduct.

● Acetic acid and other organic acid production.

● Flue gas desulfurization (FGD) in reducing scrubber environments.

Comparison with other alloys: Hastelloy B-3 is a newer, more thermally stable version with improved resistance to embrittlement during welding and thermal exposure. For most new designs, B-3 is preferred. Hastelloy C-276 or C-22 are better for oxidizing or mixed acids. For dilute HCl at low temperatures, zirconium or tantalum may be alternatives.

Selection guidance: Choose Hastelloy B-2 for severe reducing acid service, especially hydrochloric acid, where oxidizing contaminants are absent. For improved fabricability and resistance to intermetallic phase formation, use Hastelloy B-3. For mixed acids (oxidizing + reducing), select Hastelloy C-276 or C-22.