Hastelloy B-3 is a nickel-molybdenum alloy (approximately 65 percent nickel, 28.5 percent molybdenum, 1.5 percent iron, with controlled additions of chromium, aluminum, and manganese). It is an improved version of Hastelloy B-2, offering outstanding resistance to pure reducing acids while eliminating the susceptibility to intermetallic phase embrittlement that can occur in B-2 during welding or thermal exposure.

The nominal chemical composition is: nickel 65.0–71.0 percent, molybdenum 27.0–32.0 percent, iron 1.0–3.0 percent, chromium 1.0–3.0 percent, manganese up to 3.0 percent, aluminum up to 0.5 percent, and smaller amounts of carbon, silicon, and cobalt.

Key mechanical properties (typical, annealed condition):

● Tensile strength: 760–860 MPa

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

● Elongation: 40–50 percent

● Hardness: 85–95 HRB

● Density: 9.22 g/cm³

Hastelloy B-3 offers exceptional resistance to hydrochloric acid at all concentrations and temperatures up to boiling, as well as to sulfuric, phosphoric, acetic, and other reducing acids. Unlike B-2, B-3 maintains excellent ductility and corrosion resistance even after exposure to temperatures in the 650–800°C range, making it far more forgiving during welding and hot forming. The alloy remains resistant to stress corrosion cracking and pitting in reducing environments. However, it should not be used in oxidizing acids (e.g., nitric acid) or in the presence of ferric or cupric ions.

Common standards: ASTM B333 (plate, sheet, strip), B335 (rod, bar), B622 (seamless pipe and tube), B619 (welded pipe), B626 (welded tube), ASME SB-333, SB-335, SB-622, and NACE MR0175/ISO 15156 for sour service.

Typical applications include:

● Chemical processing: reactors, heat exchangers, distillation columns, valves, and piping for hydrochloric acid service.

● Pharmaceutical and fine chemical synthesis: equipment handling HCl, H₂SO₄, or other reducing acids.

● Acetic acid and organic acid production.

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

Comparison with Hastelloy B-2: B-3 has significantly better thermal stability, resisting the formation of brittle Ni₄Mo intermetallic phases during welding and high-temperature exposure. It also offers improved resistance to localized corrosion in certain environments. For new designs, B-3 is generally preferred over B-2. For mixed acids containing oxidizing species, Hastelloy C-276 or C-22 are more suitable.

Selection guidance: Choose Hastelloy B-3 for severe reducing acid service, particularly hydrochloric acid at any concentration and temperature, where fabricability and long-term thermal stability are required. For purely reducing environments without welding concerns, B-2 may still be used, but B-3 is the modern, more robust alternative. For oxidizing or mixed acids, select a C-series alloy.