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Boiling hydrochloric acid (HCl) is one of the most aggressive chemical environments for metallic materials. Many engineers assume that a premium nickel alloy like Hastelloy C276 can handle anything. But in boiling HCl, C276 fails quickly. The real survivors are the B series alloys – specifically Hastelloy B2 and B3. Here is a straightforward comparison of common Hastelloy grades in this extreme service.
Performance in boiling hydrochloric acid (any concentration, atmospheric boiling point ~110°C)
Alloy Grade | Resistance to Boiling HCl | Key Limitation / Note |
Hastelloy C276 | Poor – high corrosion rate (＞20 mm/year) | Contains molybdenum and tungsten but not designed for reducing acids at high temperature |
Hastelloy C22 | Poor – similar to C276 | Better in oxidising acids, still weak in boiling HCl |
Hastelloy B2 | Excellent – corrosion rate <0.1 mm/year | Extremely sensitive to oxidising impurities (Fe³⁺, Cu²⁺, dissolved oxygen) – can fail rapidly if present |
Hastelloy B3 | Excellent – corrosion rate <0.1 mm/year | Improved version of B2 with better resistance to sensitisation and less sensitivity to oxidising contaminants |
Why B series works
Hastelloy B2 and B3 are nickel-molybdenum alloys with very low chromium. They thrive in pure reducing acids like hydrochloric, dilute sulphuric and phosphoric acids. The absence of chromium prevents the formation of passive films that are unstable in reducing conditions, allowing the alloy to corrode uniformly at extremely low rates.
Why C series fails
C276 and C22 rely on chromium for oxidation resistance. In boiling HCl, the passive layer breaks down, and the alloy suffers rapid general corrosion and sometimes localised attack. They should never be specified for hot concentrated or boiling hydrochloric acid service.
B2 vs B3 – which one to choose
B2 is less expensive but requires strict control of the process fluid – no ferric or cupric ions, no air ingress. Even small amounts of oxidising species can cause catastrophic attack.
B3 is the safer choice. It tolerates minor oxidising impurities and is much less prone to intergranular corrosion after welding or hot forming. For boiling HCl service in real-world plants, B3 is strongly recommended.
If your application involves boiling hydrochloric acid, skip C series entirely. Use Hastelloy B3 for reliable long-term performance. B2 can work only in very clean, reducing conditions with no risk of oxidising contamination.
Need a quote for B3 pipe, plate, or fittings?
Contact us for mill certificates, competitive pricing, and technical support on Hastelloy B3 and other nickel alloys for extreme acid service.
