1. Alloy Designation and Standards

NiMo28 is not a universally standardized name but typically refers to Hastelloy B-2. Its standard designations are:

• UNS Number: N10665

• ASTM Standards: B335 (bars), B622 (seamless pipes), B619/B626 (welded pipes)

• EN/DIN: 2.4617

• Chinese Standard: NS322 (GB/T 15007)

2. Chemical Composition

• Typical composition of NiMo28 (Hastelloy B-2), in weight percent (wt%):

Ni (Nickel)：~65–70%

Mo (Molybdenum)：26–30%

Fe (Iron)：1–6%

Cr (Chromium)：≤1.0%

C (Carbon)：≤0.01%

Mn (Manganese)：≤1.0%

Si (Silicon)：≤0.1%

Co (Cobalt)：≤1.0%

V (Vanadium)：≤0.3%

S (Sulfur)：≤0.01%

P (Phosphorus)：≤0.03%

• Key Design Considerations:

High Molybdenum (26–30%): Ensures resistance to hydrochloric, sulfuric, and other reducing acids.

Ultra-low Carbon (≤0.01%): Prevents carbide precipitation and weld sensitization.

Low Chromium (≤1%): Ensures stability in reducing environments but limits oxidation resistance (e.g., against nitric acid or oxidizing ions like Fe³⁺/Cu²⁺).

3. Physical and Mechanical Properties

(1) Physical Properties

Density：9.24 g/cm³

Melting Range：1330–1380°C

Thermal Expansion (20–100°C)：11.5 ×10⁻⁶/°C

Thermal Conductivity (20°C)：10.1 W/(m·K)

Electrical Resistivity：1.25 μΩ·m

(2) Mechanical Properties (Annealed Condition)

Tensile Strength (Rm)：690–790 MPa

Yield Strength (Rp0.2)：310–380 MPa

Elongation (A₅)：≥40%

Hardness (HB)：180–220

Elastic Modulus (E)：210 GPa

(3) Highlights:

Combines high strength with good ductility.

Strong work-hardening tendency—intermediate annealing is required during cold forming.

High-temperature service: Short-term use up to ~1000°C is possible, but long-term applications should not exceed 600°C to avoid brittle phase precipitation.

4. Corrosion Resistance

NiMo28 (Hastelloy B-2) is engineered for resistance in strongly reducing environments:

(1) Acid Resistance

• Hydrochloric Acid (HCl)：

Excellent at all concentrations and temperatures—even at boiling point; superior to stainless steels and most nickel alloys

• Sulfuric Acid (H₂SO₄)：

Excellent in low to moderate concentrations (≤60%), but susceptible to oxidizing impurities like Fe³⁺ and Cu²⁺

• Phosphoric Acid (H₃PO₄)：

Outstanding performance, ideal for wet-process phosphoric acid

• Hydrofluoric Acid (HF)：

Good resistance; avoid high concentrations and temperatures

• Organic Acids (e.g., Acetic, Formic)：

Excellent resistance

(2) Unsuitable Media

Oxidizing acids: Nitric acid (HNO₃), chromic acid (H₂CrO₄), hypochlorous acid (HClO)

Acids containing oxidizing ions (Fe³⁺, Cu²⁺, dissolved oxygen)

High-temperature alkaline media: NaOH, KOH (risk of stress corrosion cracking)

(3) Localized Corrosion Resistance

Pitting：Excellent in reducing environments

Crevice Corrosion：Better than stainless steel, but caution still needed

Stress Corrosion Cracking (SCC)：Resistant in chloride media; sensitive in alkalis

5. Processing and Welding

(1) Forming

Cold Working: Feasible, but requires intermediate annealing (1065–1120°C, rapid quench).

Hot Working: Recommended range is 1050–1200°C. Avoid prolonged exposure between 700–900°C to prevent brittle phase formation.

(2) Welding

Recommended Methods: GTAW (TIG), GMAW (MIG), SMAW (Stick)

Filler Metal: ERNiMo-7 (AWS A5.14) or dedicated Hastelloy B-2 filler

(3) Welding Guidelines:

Use ultra-low carbon and low-sulfur/phosphorus filler to avoid contamination.

Rapid cooling after welding to prevent μ-phase formation in the heat-affected zone.

Avoid preheating or post-weld heating to reduce sensitization risk.

6. Typical Applications

NiMo28 (Hastelloy B-2) is ideal for equipment exposed to strongly reducing acids:

• Chemical Processing: Hydrochloric acid reactors, heat exchangers, pipes, valves

• Petrochemical Industry: Alkylation units, catalyst recovery systems

• Pharmaceuticals: Reactors handling high-purity acid media

• Hydrometallurgy: Phosphoric acid extraction, spent acid recovery

• Environmental Engineering: FGD (flue gas desulfurization) systems

7.Comparison with Other Ni-Mo Alloys

• Hastelloy B-2 (NiMo28)

Main Composition：Ni-28Mo-1Cr, ultra-low C

Features：Best for hydrochloric acid, excellent weldability

Suitable Environments：Reducing acids, no oxidizers

• Hastelloy B-3

Main Composition：Ni-28.5Mo-1.5Cr

Features：Improved resistance to intergranular corrosion, more thermally stable

Suitable Environments：Similar to B-2 with better high-temp performance

• Hastelloy B-4

Main Composition：Ni-28Mo-1Cr

Features：Enhanced SCC resistance

Suitable Environments：Sulfur-bearing reducing environments

8. Summary

NiMo28 (Hastelloy B-2)sets the benchmark for corrosion resistance in reducing acid environments—especially hydrochloric, sulfuric, and phosphoric acids. Its high molybdenum and ultra-low carbon design ensures excellent performance in welded structures and long-term service, though it is not suitable for oxidizing agents or prolonged high-temperature exposure above 600°C.

Best suited for:

• All concentrations and temperatures of hydrochloric acid

• Low to moderate sulfuric acid (without oxidizers)

• Wet-process phosphoric acid and organic acid production

Not recommended for:

• Nitric, chromic, or other oxidizing acids

• Acid solutions containing Fe³⁺/Cu²⁺

• Long-term service above 600°C

9. About Suzhou Bolaibao Metal

As corrosion challenges intensify across industries, Suzhou Bolaibao Metal has built an integrated service system centered on high-performance alloys like NiMo28—spanning material development, custom fabrication, and technical support. We not only supply reliable, high-quality alloys, but also partner closely with our clients to deliver tailored engineering solutions. With our philosophy of “Material Expertise, Application Focus”, Bolaibao is committed to becoming your most trusted partner in corrosion-resistant materials.

Bolaibao Metal – Solving Complex Problems with Specialized Materials, Empowering Critical Industries to Withstand Corrosion.

• Tel: +86 15366282159

• Email: sale@bolaibao1.com

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