What is Hastelloy B-3?

Hastelloy B-3 (UNS N10675) is a nickel-molybdenum alloy developed as the next-generation successor to Hastelloy B-2. While B-2 delivered outstanding resistance to hydrochloric acid across the full concentration and temperature range, its Achilles' heel was a severe susceptibility to β-Ni₄Mo embrittlement during welding and exposure to temperatures between 550°C and 800°C. This forced fabricators to perform mandatory post-weld solution annealing — a costly and geometrically restrictive requirement. B-3 solves this problem at the metallurgical level. By adding small controlled amounts of chromium (1–3%) and iron (1–3%) to the Ni-Mo base, the alloy dramatically slows the kinetics of beta-phase and Ni₃Mo ordering, extending the time-temperature envelope for safe fabrication by orders of magnitude.

The practical result is that B-3 fabrications can enter service in the as-welded condition — matching B-2's HCl performance without requiring post-weld heat treatment. This thermal stability advantage reduces fabrication costs, eliminates the size limitations of solution-annealing furnaces, and removes the risk of in-service embrittlement from hot spots and excursions into the 550–800°C range. With a tensile strength of ≥760 MPa, yield strength of ≥350 MPa, and elongation exceeding 40%, B-3 is both formable and strong. HT PIPE supplies B-3 mill products for HCl distillation columns, welded reactors, pharmaceutical vessels, and acid recovery systems worldwide.

Chemical Composition

Per ASTM B333 / ASTM B335. Weight percent. The chromium and iron additions distinguish B-3 from its B-2 predecessor — they are the alloying strategy that suppresses beta-phase embrittlement and enables as-welded service.

★ Elements that distinguish B-3 from B-2 — responsible for the thermal stability breakthrough

Mechanical Properties

Minimum properties per ASTM B333 for solution-annealed plate at room temperature. B-3 offers higher tensile strength than B-2 (760 vs 760 MPa typical) with comparable ductility — and critically, these properties are maintained in the as-welded condition without post-weld heat treatment.

* As-welded properties are comparable to solution-annealed base metal — the defining advantage of B-3 over B-2. No post-weld solution anneal required.

Physical Properties

Heat Treatment Procedure

The heat treatment sequence for B-3 is simpler than B-2 because post-weld annealing is no longer mandatory. However, proper parameter control during solution annealing remains critical for achieving optimum corrosion resistance:

Corrosion Resistance

B-3 preserves B-2's standout HCl resistance while adding better tolerance to oxidizing contaminants and — critically — maintaining this performance in as-welded fabrications without preferential HAZ attack.

Hydrochloric Acid (HCl)

Outstanding resistance to pure HCl at all concentrations up to the boiling point. General corrosion rates below 0.13 mm/year (5 mpy) are achievable across the concentration range up to ~70°C. At boiling temperatures, B-3 delivers B-2-equivalent performance in the parent metal — with the critical difference that the weld HAZ shows no preferential attack. This is the single most important practical advantage: B-3 welded vessels survive in HCl service without the post-weld solution anneal that B-2 demands. ASTM G28 Method A testing (boiling 20% HCl) is the standard acceptance criterion — B-3 as-welded corrosion rates typically pass at <0.5 mm/yr.

Sulfuric Acid (H₂SO₄)

Good resistance in air-free (reducing) conditions up to moderate temperatures. The high molybdenum content provides reducing-acid immunity similar to pure HCl. However, B-3 is NOT recommended for hot concentrated H₂SO₄ with aeration — the oxidizing nature of aerated sulfuric acid can attack the Ni-Mo matrix. In air-free or mildly aerated sulfuric acid below 60°C, B-3 performs well. For hot concentrated sulfuric with oxidizing conditions, consider C-276 or C-22 instead.

Oxidizing Media

The 1–3% chromium addition gives B-3 modest oxidizing-media tolerance — better than B-2's near-zero oxidizing resistance, but far below C-series alloys. B-3 can tolerate trace oxidizing contaminants (e.g., ferric ions in HCl) that would cause rapid attack on B-2. For environments with significant oxidizing species (nitric acid, wet chlorine, hypochlorite), select C-276, C-22, or C-2000. B-3 remains the choice for reducing acid service — HCl, HBr, and certain organic acids — where the high Mo content drives immunity that chromium-based alloys cannot match.

Hastelloy B-3 vs Similar Grades

B-3 occupies the Ni-Mo reducing-acid niche with as-welded capability. Here's how it stacks up against the alternatives engineers consider for HCl and reducing acid service:

→ For a side-by-side technical deep-dive: Hastelloy B-2 vs B-3 — Full Comparison Guide

Typical Applications by Industry

Applicable Standards & Specifications

Available Product Forms from HT PIPE

We carry Hastelloy B-3 in solution-annealed condition. EN 10204 3.1 certification on every shipment; 3.2 available on request. ASTM G28 Method A corrosion testing available as an optional certification.

HT PIPE Project Experience

In 2024, we supplied 5.2 tons of Hastelloy B-3 plate (ASTM B333, 6 mm, 8 mm, and 10 mm thickness, 2000 × 6000 mm) to a Southeast Asian chemical plant for a new HCl distillation column. The project specification required ASTM G28 Method A corrosion testing on welded coupons — with as-welded corrosion rates below 0.1 mm/year as the acceptance criterion. Our B-3 plate passed at 0.07 mm/year as-welded and 0.04 mm/year solution-annealed. Supplied with EN 10204 3.1 certification, ultrasonic testing per ASTM A435, and PMI on every plate. Delivered in 10 weeks — two weeks ahead of the project schedule.

For pharmaceutical HCl recovery systems, we regularly ship B-3 seamless pipe (ASTM B335, 1″ to 6″ NB) and butt-weld fittings (ASTM B366) to European and North American clients. All material is solution-annealed, water-quenched, and supplied with full traceability to the mill heat number. Contact our sales engineers for reference cases matched to your process conditions.

Frequently Asked Questions