ASTM B392 R04251 Niobium Fittings – Nb-1Zr Socket-Weld, Threaded & Machined
What are ASTM B392 R04251 niobium fittings?
They are socket-weld and threaded fittings, couplings, plugs, bushings, unions and other machined parts made from ASTM B392 bar and rod in UNS R04251. R04251 is reactor-grade niobium-1% zirconium (Nb-1Zr, ASTM Type 3). Machining from solid bar is the standard route for small-bore, high-integrity niobium-alloy fittings.
Note on specifications: ASTM B392 covers niobium and niobium-alloy bar, rod and wire (R04200, R04210, R04251, R04261) – not seamless fittings or pipe. Fittings machined from B392 bar carry its grade, chemistry and test requirements. For an overview of both Nb-1Zr grades, see Nb-1Zr niobium fittings.
R04251 Bar-Machined Fittings – Quick Facts
- Grade: UNS R04251, Nb-1Zr reactor grade (Zr 0.8–1.2%)
- Raw material: ASTM B392 bar and rod, annealed
- Fitting types: socket-weld and threaded elbows, tees, couplings, half couplings, caps, plugs, bushings, unions, nipples and tube connectors
- Dimensions: to ASME B16.11 profiles or customer drawing
- Condition: annealed in vacuum, machined, pickled and clean
- Certificate: EN 10204 3.1 with interstitial (C, O, N, H) analysis
ASC LLP, Mumbai, supplies R04251 fittings machined from bar, formed from tube and formed from plate. Browse all niobium fittings or the full niobium range.
Properties of R04251 Nb-1Zr
- Stronger than pure niobium: 0.8–1.2% zirconium raises room-temperature and high-temperature strength and creep resistance.
- Liquid-metal compatibility: excellent resistance to liquid lithium, sodium and potassium – the main reason R04251 is chosen.
- Corrosion resistance: good resistance to many acids, similar to pure niobium.
- Ductile and machinable: soft, ductile bcc metal that machines well with sharp tools and coolant.
- Oxidation limit: niobium alloys oxidise rapidly in air above about 400 °C – hot service must be in vacuum, inert gas or liquid metal.
How R04251 Fittings Are Machined from B392 Bar
- Bar: R04251 bar or rod to ASTM B392, annealed and certified with interstitial analysis.
- Machining: turned, bored and threaded with sharp carbide or HSS tools, positive rake and plenty of coolant to avoid galling.
- Cleaning: degreased and pickled to remove iron pick-up and machining residue.
- Inspection: dimensional and thread gauging, visual and dye-penetrant check.
- Packing: sealed, clean packing for vacuum or liquid-metal service.
R04251 Bar-Machined Fitting Types
| Fitting type | Typical sizes | Dimensional basis |
| Socket-weld elbows, tees, couplings | ⅛” – 2″ NPS | ASME B16.11 profiles (dimensions only) |
| Threaded elbows, tees, couplings, caps | ⅛” – 2″ NPS | ASME B16.11 / NPT or BSP threads |
| Plugs, bushings, nipples, unions | ⅛” – 2″ NPS | ASME B16.11 / drawing |
| Tube-to-tube connectors and glands | By tube OD | Customer drawing |
| Special machined parts | Any | Customer drawing |
ASME B16.11 has no pressure rating for niobium alloys – it is used for dimensions only; design pressure is set by the purchaser. Butt-weld elbows, tees and reducers are formed from tube instead.
Mechanical Properties – ASTM B392
| Grade (annealed bar) | Tensile strength (min) | 0.2% yield strength (min) | Elongation (min) |
| R04251 / R04261 (Nb-1Zr) | 195 MPa (28 ksi) | 125 MPa (18 ksi) | 20% |
| R04200 / R04210 (pure Nb) | 125 MPa (18 ksi) | 73 MPa (10.5 ksi) | 25% |
Minimum tensile requirements for annealed bar per ASTM B392.
R04251 Bar-Machined Fittings Specifications
| Item | Details |
| Product | R04251 Nb-1Zr niobium fittings machined from bar |
| Material standard | ASTM B392 (bar, rod, wire) |
| Grade | UNS R04251 (reactor grade); R04261 commercial grade on request |
| Fitting types | Socket-weld, threaded, plugs, bushings, unions, connectors, special parts |
| Dimensions | ASME B16.11 profiles or customer drawing |
| Threads | NPT, BSP or special |
| Testing | Chemical incl. interstitials, tensile on bar, dimensional, thread gauging, dye penetrant |
| Certificate | EN 10204 3.1; third-party inspection on request |
R04251 Chemical Composition (ASTM B392)
| Element (max %, unless range) | R04251 – Type 3 (reactor grade) | R04261 – Type 4 (commercial grade) |
| Zirconium (Zr) | 0.8 – 1.2 | 0.8 – 1.2 |
| Oxygen (O) | 0.015 | 0.025 |
| Carbon (C) | 0.01 | 0.01 |
| Nitrogen (N) | 0.01 | 0.01 |
| Hydrogen (H) | 0.0015 | 0.0015 |
| Tantalum (Ta) | 0.1 | 0.5 |
| Tungsten (W) | 0.03 | 0.05 |
| Molybdenum (Mo) | 0.010 | 0.050 |
| Iron (Fe) | 0.005 | 0.01 |
| Silicon (Si) | 0.005 | 0.005 |
| Nickel (Ni) | 0.005 | 0.005 |
| Hafnium (Hf) | 0.02 | 0.02 |
| Titanium (Ti) | 0.02 | 0.03 |
| Niobium (Nb) | Remainder | Remainder |
R04251 is not 99% pure niobium – it contains 0.8–1.2% zirconium, with tighter oxygen, tantalum and metallic limits than commercial-grade R04261.
Physical Properties of Nb-1Zr
| Property | Value (approx.) |
| Density | 8.6 g/cm³ |
| Crystal structure | Body-centred cubic |
| Coefficient of thermal expansion | ≈ 7 µm/m·°C |
| Magnetic | Non-magnetic |
| Oxidation in air | Above about 400 °C – use hot only in vacuum, inert gas or liquid metal |
Applications of R04251 Bar-Machined Fittings
| Industry | Applications of R04251 machined fittings |
| Nuclear & space power | Instrument and small-bore connections in liquid-metal loops and heat-pipe systems |
| Research & fusion | Valves, ports and connectors on vacuum and liquid-metal test rigs |
| Vacuum furnaces | Threaded connectors, plugs and supports in the hot zone |
| Chemical processing | Small-bore acid-service fittings needing more strength than pure niobium |
Nb-1Zr is not used for aircraft engines, oil & gas, marine hardware or medical implants.
Our R04251 / Nb-1Zr Fittings Range
| Page | What it covers |
| Nb-1Zr niobium fittings | Overview of both Nb-1Zr grades (R04251 and R04261) |
| R04251 fittings from tube | Butt-weld elbows, tees and reducers formed from ASTM B394 tube |
| R04251 plate-formed fittings | Caps, stub ends and large-bore fittings from ASTM B393 plate |
| This page | Socket-weld, threaded and machined fittings from ASTM B392 bar |
Why Buy R04251 Fittings from ASC LLP?
- Correct grade and paperwork: R04251 bar to ASTM B392 with 3.1 certificates showing zirconium, oxygen and other interstitials.
- All three routes: bar-machined, tube-formed and plate-formed fittings from one supplier.
- Matching parts: R04251 flanges and R04251 fasteners.
- Drawings, prototypes and small quantities welcome, with clean export packing.
Send drawing, size, thread and quantity to sales@amardeepsteel.com or call 022-67439130.
Frequently Asked Questions – ASTM B392 R04251 Niobium Fittings
What does ASTM B392 cover?
ASTM B392 covers niobium and niobium-alloy bar, rod and wire in grades R04200, R04210, R04251 and R04261. It does not cover pipe or seamless fittings – R04251 fittings are machined from B392 bar.
What is R04251?
UNS R04251 is reactor-grade niobium-1% zirconium alloy (ASTM Type 3), with 0.8–1.2% zirconium and tight limits on oxygen (0.015%), tantalum (0.1%) and other impurities.
Which R04251 fittings are machined from bar?
Socket-weld and threaded elbows, tees and couplings, caps, plugs, bushings, unions, nipples, tube connectors and other small-bore or special parts are machined from ASTM B392 bar.
What are the mechanical properties of R04251 bar?
ASTM B392 requires annealed Nb-1Zr bar to have a minimum tensile strength of 195 MPa (28 ksi), yield strength of 125 MPa (18 ksi) and elongation of 20%.
Is niobium oxidation resistant?
No. Niobium and Nb-1Zr oxidise rapidly in air above about 400 °C, so hot R04251 fittings must be used in vacuum, inert gas or liquid metal.
Can ASME B16.11 be used for niobium fittings?
Only for dimensions. ASME B16.11 gives no pressure-temperature rating for niobium alloys, so pressure capability is set by the purchaser’s design calculation.
Global Reach
ASC LLP supplies niobium, tantalum and other refractory-metal products to nuclear, research and high-temperature industries worldwide, with secure packing and full documentation. Buyers in the USA, Europe, the Middle East and Asia rely on our ASTM B392 R04251 niobium fittings for certified material and traceability.
Countries We Export To
UNITED STATES, EUROPE, UK, UAE, SAUDI ARABIA, OMAN, KUWAIT, JORDAN, QATAR, INDONESIA, MALAYSIA, BRAZIL, SPAIN, ITALY, FRANCE, GERMANY, BAHRAIN, SRI LANKA, AZERBAIJAN, AUSTRALIA, AUSTRIA, PHILIPPINES, TURKEY, RUSSIA, IRAN, IRAQ, CANADA, KOREA, JAPAN, YEMEN, FINLAND, ZIMBABWE, HUNGARY, PORTUGAL, VIETNAM, MOROCCO, THAILAND, SOUTH AFRICA, MEXICO, SINGAPORE, GREECE, KUWAIT, POLAND, NEW ZEALAND, SWEDEN, SWITZERLAND, BELGIUM, BHUTAN, BANGLADESH, TAIWAN, ROMANIA, CAMBODIA, KAZAKHSTAN, AFGHANISTAN.
