N10629 is a solid-solution nickel–molybdenum alloy of the "B" family, developed (as UNS N10629) with tighter alloy-composition control than alloy B-2 to further suppress thermomechanical cracking during fabrication and stress-corrosion cracking in service. This datasheet presents the material within the American (ASTM / ASME / UNS) standard system.
Like all B-family alloys it is essentially chromium-free and derives its corrosion performance from a high nickel and molybdenum content, giving outstanding resistance to hydrochloric acid at all concentrations and temperatures, and to other strongly reducing media such as hydrogen chloride gas, sulphuric, acetic, formic and phosphoric acids. The controlled, low carbon, iron and silicon levels minimise carbide and intermetallic-phase precipitation, improving thermal/structural stability and weld heat-affected-zone behaviour relative to the earlier alloy B-2.
Being chromium-free, the alloy must not be used in oxidising environments or in reducing acids contaminated with oxidising salts (e.g. ferric or cupric chloride), and should not be combined with iron or copper piping in hydrochloric-acid systems. It is used in chemical-process-industry equipment for pure, reducing-acid service — reactors, heat exchangers, columns and piping — and 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 | 1370–1418 | °C |
| Young's modulus (20 °C) | 216 | GPa |
| Specific heat capacity (20 °C) | 379 | J/kg·K |
| Thermal conductivity (20 °C) | 11.5 | W/m·K |
| Electrical resistivity (20 °C) | 1.37 | µΩ·m |
| Coefficient of thermal expansion (20–100 °C) | 10.4 | µm/m·°C |
| Maximum service temperature (oxidising) | ~550 | °C |
| Structure | Austenitic (FCC) | — |
Limiting composition per ASTM B335 (UNS N10629).
| 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 | — | 3.0 | Controlled low |
| Chromium | Cr | — | 1.5 | Essentially chromium-free; trace addition aids stability |
| Cobalt | Co | — | 3.0 | Residual |
| Manganese | Mn | — | 3.0 | Deoxidiser |
| Carbon | C | — | 0.01 | Ultra-low; thermal stability + HAZ resistance |
| Aluminium | Al | — | 0.50 | Deoxidiser |
| Titanium | Ti | — | 0.20 | Carbide/nitride former |
| Silicon | Si | — | 0.10 | Controlled low |
| Phosphorus | P | — | 0.025 | Residual impurity |
| Sulphur | S | — | 0.010 | Residual impurity |
Typical room-temperature properties, solution-annealed condition.
| Property | Value | Source |
|---|---|---|
| Ultimate tensile strength | ≥760 MPa (110 ksi) | Typical / Ni-Mo B-family |
| 0.2% proof strength (yield) | ≥350 MPa (51 ksi) | Typical |
| Elongation at break | ≥40 % | Typical |
| Hardness | ~95–100 HRB | Typical |
The alloy is solid-solution-strengthened (not age-hardenable) and can be strengthened by cold work. Its tighter composition control gives thermal stability comparable to alloy B-3 and better than B-2. Values are typical; confirm against the mill test certificate for each delivery.
| Environment | Performance | Notes |
|---|---|---|
| Hydrochloric acid (all conc. / temps) | Outstanding | Among the highest of any nickel alloy |
| Hydrogen chloride gas | Outstanding | Exceptional resistance |
| Sulphuric acid | Excellent | Strong resistance to non-oxidising H₂SO₄ |
| Acetic / formic / phosphoric acids | Excellent | Reducing-acid resistance |
| Reducing environments | Outstanding | High Ni + Mo |
| Chloride SCC | Outstanding | Improved composition control vs B-2 |
| Thermal / structural stability | Outstanding | Controlled C/Fe/Si; better than B-2 |
| 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: ~1060–1080 °C, followed by rapid cooling (water quench) Purpose: dissolves secondary phases, restores maximum corrosion resistance and ductility.
Forming note: after significant cold work, a final solution anneal is recommended before welding/service to restore optimum corrosion resistance. The improved composition control reduces embrittlement and cracking concerns relative to B-2.
Good weldability; the controlled low-carbon chemistry resists carbide precipitation in the weld heat-affected zone, giving improved fabrication behaviour relative to alloy B-2. GTAW and GMAW are commonly used.
| Welding Process | Applicability | Filler / Consumable |
|---|---|---|
| GTAW / TIG | Excellent | AWS A5.14 ERNiMo-7-type matching filler |
| GMAW / MIG | Good | AWS A5.14 ERNiMo-7-type matching filler |
| SMAW / stick | Good | AWS A5.11 ENiMo-7-type electrode |
Solution-anneal after heavy cold work before welding. 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 | Hot-formable; followed by solution anneal + rapid cool |
| Cold forming | Cold-formable; high work-hardening rate; final solution anneal after heavy reductions |
| Cleanliness | Keep tooling free of iron contamination to protect acid-service performance |
| Industry | Typical Components | Key Requirements |
|---|---|---|
| Chemical processing | Reactors, heat exchangers, columns, piping for pure reducing acids | HCl + reducing-acid resistance + stability |
| Hydrochloric acid | Process vessels, storage, piping | Extreme HCl resistance |
| Sulphuric / acetic / formic acid | Process equipment | Non-oxidising acid resistance |
| Pharmaceutical | Reactors, pressure vessels | Corrosion resistance + fabricability |
| Petrochemical | Reducing-environment process hardware | Reducing-acid resistance |
| 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-type matching filler | — |
Listed in NACE MR0175 / ISO 15156 for sour service. UNS N10629.
| UNS | Ni % | Cr % | Mo % | Other | Best Used For |
|---|---|---|---|---|---|
| N10629 | bal | ≤1.5 | 26–30 | C ≤0.01 | Improved composition control vs B-2; reducing acids |
| N10675 | bal | 1–3 | 27–32 | C ≤0.01 | Best thermal stability; pure reducing acids |
| N10665 | bal | ≤1.0 | 26–30 | C ≤0.02 | Low-C; as-welded HCl service |
| N10001 | bal | ≤1.0 | 26–30 | Fe 4–6 | Original Ni-Mo (largely superseded) |
| N10276 | bal | 14.5–16.5 | 15–17 | W 3–4.5 | Oxidising + reducing; broad corrosion |




