B-2/N10665, B-3/N10675... The B series is mainly used in reducing acid environments such as hydrochloric acid evaporators and hydrofluoric acid reaction kettles.

 Hastelloy B-2 (UNS N10665) is a nickel-molybdenum alloy that takes an extreme 'specialization' approach in the field of corrosion resistance—focusing exclusively on reducing acids but absolutely avoiding oxidizing environments.
???? Core Properties
The core design philosophy of B-2 is to achieve ultra-strong corrosion resistance through high molybdenum (26-30%) and extremely low carbon (≤0.02%).
· Excellent resistance to reducing acids: It performs exceptionally well in hydrochloric acid (full concentration range) and medium-concentration sulfuric acid. It also exhibits outstanding resistance to organic acids such as phosphoric acid and acetic acid.
· Good resistance to localized corrosion: It offers good resistance to stress corrosion cracking (SCC) and pitting caused by chloride ions.
· Excellent weldability: The extremely low carbon and low silicon design significantly reduces intergranular precipitates in the welding heat-affected zone, meaning corrosion resistance can be maintained in the welded condition.
· ⚠️ Critical Limitation: It must never be used in media containing oxidizing ions (such as Fe³⁺, Cu²⁺), e.g., nitric acid. Otherwise, it will rapidly undergo intergranular corrosion, leading to premature equipment failure. It is also not suitable for long-term service at high temperatures (>650°C) as brittle phases may precipitate.
???? Main Application Industries
Its applications are almost entirely concentrated in the chemical industry where handling of strong reducing acids is required:
· Production and transportation equipment for hydrochloric acid, sulfuric acid, phosphoric acid, and acetic acid.
· Chemical process systems containing hydrogen chloride gas.
· Reactors and components for strongly reducing chemical environments such as those involving aluminum chloride catalysts.
In summary: The only reason to choose B-2 is to handle reducing acids, especially hydrochloric acid. If there is even a slight risk of oxidation in the operating conditions, it must be avoided, and more 'versatile' alloys like C-276 should be considered instead.