Material Family

Nickel-Molybdenum Alloy (Thermally Stable, Low Iron, Low Carbon)

A direct, improved successor to B-2, with optimized chemistry for stability.

Common Forms

Seamless Pipe (SMLS) is strongly preferred. Welded pipe is less common due to the criticality of thermal control.

Seamless construction ensures the most uniform and reliable microstructure for severe service.

Chemical Composition (Typical wt.%)

Ni: ≥ 65.0 (Balance)
Mo: 27.0 - 32.0
Cr: 1.0 - 3.0
Fe: 1.0 - 3.0
Al: ≤ 0.50
Ti: ≤ 0.20
C: ≤ 0.010
Si: ≤ 0.10

High Mo for reducing acid resistance. Controlled, low levels of Cr & Fe and additions of Al/Ti dramatically improve thermal stability over B-2.

Mechanical Properties (Annealed, Room Temp)

Tensile Strength (Rm): 827 - 1034 MPa
Yield Strength (Rp0.2): 414 - 690 MPa
Elongation (A): 40 - 55%

Exhibits higher typical strength than B-2 while maintaining excellent ductility.

Physical Properties

Density: ~9.22 g/cm³
Melting Range: 1370 - 1420 °C

Similar high density to B-2 due to high molybdenum content.

Key Corrosion Resistance

• Equal or superior resistance to B-2 in pure hydrochloric acid (HCl) across all concentrations and temperatures.

• Excellent resistance to sulfuric (H₂SO₄), phosphoric (H₃PO₄), and acetic acids under strictly reducing conditions.

• Same Major Limitation: Poor resistance to oxidizing agents (e.g., Fe³⁺, Cu²⁺ ions, HNO₃, oxygen). Oxidant contamination must be avoided.

Matches B-2's legendary reducing acid performance. The primary difference is not corrosion, but fabricability.

Primary Advancement: Thermal Stability

Dramatically improved resistance to embrittlement caused by precipitation of intermetallic phases when held in or slowly cooled through the 550-1050°C range. This makes it far less sensitive during welding and heat treatment than B-2.

This is the single most important reason to choose B-3 over B-2 for new designs. It enables safer, more reliable fabrication.

Key Standards (Pipe)

Seamless Pipe: ASTM B622 / ASME SB-622 (Standard Specification for Seamless Pipe and Tube - Grade UNS N10675), DIN 2.4600

ASTM B622 is the primary specification for seamless pipe.

Common Sizes & Schedules

OD Range: 1/8" NPS to 8" NPS (Seamless)
Wall Thickness: Sch 10S, 40S, 80S, 160
Length: Random, Cut to Length.

Typically supplied in schedules suitable for pressure and process applications in acid service.

Fittings & Fabrication

Compatible with ASTM B366 wrought fittings. Significantly easier and safer to weld and fabricate than B-2. While controlled procedures are still recommended, the risk of forming brittle phases in the weld zone is greatly reduced.

Post-weld heat treatment is less frequently required, simplifying construction of piping systems.

Typical Applications

• Hydrochloric Acid (HCl) Service: Production, pickling, and handling lines at high temperatures.
• Sulfuric Acid (H₂SO₄) Recovery: Concentration and circulation lines in strictly reducing conditions.
• Acetic Acid & Anhydride Production: Process and transfer piping.
• Chemical Intermediates: Piping for oxygen-free, reducing chemical processes.

Used in the same severe reducing processes as B-2, but where fabricability, weld integrity, and long-term thermal stability are critical concerns.