Alloy B-2 is a solid-solution-strengthened nickel–molybdenum alloy, unique in that it contains essentially no chromium — an element common to nearly all other corrosion-resistant alloys. This datasheet presents the material within the American (ASTM / ASME / UNS) standard system.
The high nickel and molybdenum contents give it superior resistance to hydrochloric acid at all concentrations and temperatures, and to other reducing environments such as hydrogen chloride gas, sulphuric, acetic and phosphoric acids. It is an improved version of the original alloy B, with lower carbon and iron contents that resist carbide precipitation in the weld heat-affected zone, making it resistant to knife-line and HAZ attack and suitable for most chemical-process applications in the as-welded condition.
Because it contains no chromium, the alloy is vulnerable to attack in reducing acids contaminated with oxidising salts such as ferric or cupric chloride, and should not be used with iron or copper piping in hydrochloric-acid systems. In oxidising environments it should not be used above 540 °C, and prolonged exposure to 540–815 °C should be avoided to prevent loss of ductility. In reducing gas or vacuum it can be used to higher temperatures, and its low coefficient of thermal expansion is an asset in some high-temperature applications. It is listed in NACE MR0175 / ISO 15156 for sour service.
Typical values, solution-annealed condition.
| Property | Value | Unit |
|---|---|---|
| Density | 9.22 | g/cm³ |
| Melting range | 1330–1370 | °C |
| Young's modulus (20 °C) | 217 | GPa |
| Specific heat capacity (20 °C) | 373 | J/kg·K |
| Thermal conductivity (20 °C) | 11.1 | W/m·K |
| Electrical resistivity (20 °C) | 1.37 | µΩ·m |
| Coefficient of thermal expansion (20–100 °C) | 10.3 | µm/m·°C |
| Maximum service temperature (oxidising) | ~540 | °C |
| Structure | Austenitic (FCC) | — |
Limiting composition per ASTM B333 (UNS N10665).
| Element | Symbol | Min % | Max % | Role in Alloy |
|---|---|---|---|---|
| Nickel | Ni | Balance | — | Base element; reducing-acid resistance |
| Molybdenum | Mo | 26.0 | 30.0 | Primary alloying element; HCl + reducing-acid resistance |
| Iron | Fe | — | 2.0 | Controlled low (vs original alloy B) |
| Chromium | Cr | — | 1.0 | Essentially chromium-free (defining feature) |
| Cobalt | Co | — | 1.0 | Residual |
| Carbon | C | — | 0.02 | Ultra-low; prevents HAZ carbide precipitation |
| Manganese | Mn | — | 1.0 | Deoxidiser |
| Silicon | Si | — | 0.10 | Controlled low |
| Phosphorus | P | — | 0.04 | Residual impurity |
| Sulphur | S | — | 0.03 | Residual impurity |
Typical room-temperature properties, solution-annealed condition (per ASTM B333).
| Property | Value | Source |
|---|---|---|
| Ultimate tensile strength | ≥760 MPa (110 ksi) | ASTM B333 minimum |
| 0.2% proof strength (yield) | ≥350 MPa (51 ksi) | ASTM B333 minimum |
| Elongation at break | ≥40 % | ASTM B333 minimum |
| Hardness | ~95–100 HRB | Typical |
The alloy is solid-solution-strengthened (not age-hardenable) and can be strengthened by cold work. It has a low coefficient of thermal expansion. Values are typical or specified minima; confirm against the mill test certificate for each delivery.
| Environment | Performance | Notes |
|---|---|---|
| Hydrochloric acid (all conc. / temps) | Outstanding | Highest resistance of any nickel alloy |
| Hydrogen chloride gas | Outstanding | Exceptional resistance |
| Sulphuric acid (pure) | Excellent | Resists pure (uncontaminated) H₂SO₄ |
| Acetic / phosphoric acid | Excellent | Strong resistance |
| Reducing environments | Outstanding | High Ni + Mo |
| Pitting / crevice / SCC | Excellent | Resists chloride SCC, pitting, crevice |
| HAZ / knife-line attack | Excellent | Low C/Fe; usable as-welded |
| Oxidising media / ferric or cupric salts | Poor | No chromium — avoid oxidising contaminants, Fe/Cu salts |
A solid-solution nickel–molybdenum alloy; not age-hardenable. Heat treatment is solution annealing only.
Solution Anneal Temperature: ~1066 °C (1950 °F), followed by rapid cooling (water quench) Purpose: dissolves secondary phases, restores maximum corrosion resistance and ductility.
Service caution: avoid prolonged exposure to 540–815 °C (1000–1500 °F), which reduces ductility unless Fe + Cr are carefully controlled. In oxidising atmospheres limit to ~540 °C.
Good weldability; usable in the as-welded condition. The low carbon and iron contents prevent carbide precipitation in the heat-affected zone, giving resistance to knife-line and HAZ attack.
| Welding Process | Applicability | Filler / Consumable |
|---|---|---|
| GTAW / TIG | Excellent | AWS A5.14 ERNiMo-7 (matching B-2 filler) |
| GMAW / MIG | Good | AWS A5.14 ERNiMo-7 (matching B-2 filler) |
| SMAW / stick | Good | AWS A5.11 ENiMo-7 |
Use matching Ni-Mo filler. Keep the joint clean and free of iron/copper contamination, which is detrimental in subsequent acid service.
Machining Guidelines
| Parameter | Recommendation |
|---|---|
| Work hardening | High rate (typical of Ni-Mo alloys); rigid setup, sharp tooling, positive rake |
| Cutting | Low speed, sufficient feed/depth to cut below work-hardened layer |
| Coolant | Ample flood coolant |
| Preferred condition | Solution-annealed |
Forming Processes
| Process | Notes |
|---|---|
| Hot forming | Followed by solution anneal + rapid cool |
| Cold forming | Readily cold-formed; high work-hardening rate; intermediate anneals for heavy reductions |
| Cleanliness | Keep tooling free of iron contamination to protect acid-service performance |
| Industry | Typical Components | Key Requirements |
|---|---|---|
| Chemical processing | HCl reactors, heat exchangers, storage tanks, piping, valves, pumps | HCl + reducing-acid resistance |
| Acetic / phosphoric acid | Process vessels and piping | Reducing-acid resistance |
| Pharmaceutical | Reactors, pressure vessels | Corrosion resistance + cleanliness |
| Petrochemical | Reducing-environment process hardware | Sulphuric/acetic acid resistance |
| High-temperature (reducing/vacuum) | Components needing low thermal expansion | Low CTE; reducing-atmosphere stability |
| Product Form | ASTM Standard | ASME Code |
|---|---|---|
| Rod and bar | ASTM B335 | ASME SB-335 |
| Plate, sheet and strip | ASTM B333 | ASME SB-333 |
| Seamless pipe and tube | ASTM B622 | ASME SB-622 |
| Welded pipe | ASTM B619 | ASME SB-619 |
| Welded tube | ASTM B626 | ASME SB-626 |
| Fittings | ASTM B366 | ASME SB-366 |
| Welding consumables | AWS A5.14 ERNiMo-7 · AWS A5.11 ENiMo-7 | — |
Listed in NACE MR0175 / ISO 15156 for sour service. UNS N10665.
| Alloy | Ni % | Cr % | Mo % | Other | Best Used For |
|---|---|---|---|---|---|
| Alloy B-2 | bal | ≤1.0 | 26–30 | — | HCl all conc.; reducing acids (chromium-free) |
| Alloy B-3 | bal | 1.0–3.0 | 28.5 | Fe 1–3 | Improved thermal stability vs B-2; HCl service |
| Alloy C-276 | bal | 14.5–16.5 | 15–17 | W 3–4.5 | Both oxidising + reducing; broad corrosion |
| Alloy C-22 | bal | 20–22.5 | 12.5–14.5 | W 2.5–3.5 | Best pitting/crevice; mixed acids |
| Alloy 625 | ≥58 | 20–23 | 8–10 | Nb | Seawater + strength; oxidising tolerant |




