R04251 Niobium Fittings – Reactor-Grade Nb-1Zr from ASTM B394 Tube
What are ASTM B394 R04251 niobium fittings?
They are butt-weld pipe fittings – elbows, tees, reducers, return bends and caps – formed from ASTM B394 seamless or welded tube in UNS R04251, the reactor-grade niobium-1% zirconium alloy (ASTM Type 3). The 0.8–1.2% zirconium makes R04251 stronger than pure niobium at room and high temperature, and its tight impurity limits suit nuclear, space-power and liquid-metal systems.
ASTM B394 is the standard for niobium and niobium alloy tube; fittings formed from that tube carry its grade, chemistry and test requirements. For an overview of both Nb-1Zr grades, see our Nb-1Zr niobium fittings page.
R04251 Niobium Fittings – Quick Facts
- Grade: UNS R04251, Nb-1Zr reactor grade (ASTM Type 3)
- Raw material: ASTM B394 seamless or welded tube (B392 bar for machined fittings)
- Fitting types: 45° / 90° / 180° elbows, tees, concentric and eccentric reducers, caps
- Sizing: tube OD × wall, or NPS and schedule where pipe sizes are specified
- Condition: annealed (at least 90% recrystallized), pickled and clean
- Certificate: EN 10204 3.1 with interstitial (C, O, N, H) analysis
ASC LLP, Mumbai, supplies R04251 fittings with matching tube, flanges and fasteners. Browse all niobium fittings or the full niobium range.
R04251 Chemical Composition (ASTM B394)
| 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 99.9% pure niobium – it contains 0.8–1.2% zirconium, with tighter oxygen, tantalum and metallic limits than commercial-grade R04261.
Mechanical Properties – ASTM B394
| Grade (annealed tube) | Tensile strength (min) | 0.2% yield strength (min) | Elongation in 1 in (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% |
Tensile requirements for annealed tube per ASTM B394, Table 5. Fittings formed from the tube are supplied annealed.
How R04251 Fittings Are Made from B394 Tube
- Tube: R04251 seamless or welded tube to ASTM B394, annealed and certified.
- Forming: elbows bent or mandrel-formed; tees extruded or fabricated; reducers swaged or spun.
- Welding (fabricated parts): TIG or electron-beam in a high-purity argon chamber or vacuum.
- Annealing: vacuum or inert-gas anneal to restore ductility – never in air.
- Finishing & inspection: pickling, dimensional check, dye penetrant, chemical and interstitial analysis.
Socket-weld and threaded fittings are machined from ASTM B392 bar instead – see R04251 fittings from bar.
R04251 Niobium Fittings Specifications
| Item | Details |
| Product | R04251 (Nb-1Zr reactor grade) niobium butt-weld fittings |
| Material standard | ASTM B394 (tube); ASTM B392 (bar) for machined parts |
| Fitting types | Elbows (45°, 90°, 180° return bends), equal and reducing tees, reducers, caps |
| Sizes | Tube OD × wall to order; small-bore typical (≈ 6 – 100 mm OD) |
| Ends | Square-cut or bevelled for butt welding |
| Condition | Annealed, pickled and clean |
| Testing | Chemical incl. interstitials, dimensional, visual, dye penetrant; tube tested to B394 |
| Certificate | EN 10204 3.1; third-party inspection on request |
R04251 or R04261 – Which Grade?
- R04251 (this page): nuclear, space nuclear power, liquid-metal (Na, K, Li) loops and research systems where low oxygen and impurity levels matter.
- R04261: the commercial Nb-1Zr grade for lamp components, vacuum hardware and general high-temperature service at lower cost – see Nb-1Zr fittings and R04261 flanges.
- Pure niobium: for most acid service, R04200 fittings cost less.
Temperature, Corrosion & Handling
- High temperature: Nb-1Zr is used at high temperature only in vacuum, inert gas or liquid alkali metal. In air it oxidises above about 400 °C.
- Corrosion: resists liquid sodium, potassium and lithium and most acids at moderate temperature; attacked by hydrofluoric acid, hot concentrated sulphuric acid and strong alkalis.
- Hydrogen: avoid galvanic coupling to less noble metals in acid – niobium can absorb hydrogen and become brittle.
- Cleanliness: handle with clean gloves and keep free of oil and iron contamination before welding or vacuum service.
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 |
Applications of R04251 Niobium Fittings
| Industry | Applications of R04251 fittings |
| Nuclear & space power | Liquid-metal coolant loops, heat-pipe and reactor test hardware |
| Research & fusion | High-temperature vacuum and liquid-metal experimental systems |
| Vacuum furnaces | Hot-zone piping and connections in vacuum or inert gas |
| Chemical processing | High-purity acid service needing more strength than pure niobium |
Why Buy R04251 Niobium Fittings from ASC LLP?
- Correct grade and paperwork: R04251 to ASTM B394 with 3.1 certificates showing zirconium, oxygen and other interstitials.
- Complete R04251 line: R04251 flanges, R04251 fasteners and R04251 bar-machined fittings.
- Small quantities and drawings welcome – test loops, prototypes and spares.
- Clean, protected export packing for vacuum and nuclear-grade material.
Send tube OD, wall, fitting type and quantity to sales@amardeepsteel.com or call 022-67439130.
Frequently Asked Questions – R04251 Niobium Fittings
What is UNS R04251?
UNS R04251 is reactor-grade niobium-1% zirconium alloy, ASTM Type 3. It contains 0.8–1.2% zirconium with tight limits on oxygen (0.015% max), tantalum (0.1% max) and other impurities.
What does ASTM B394 cover?
ASTM B394 covers seamless and welded tubes of niobium and niobium alloys in four grades: R04200, R04210, R04251 and R04261. Butt-weld fittings formed from this tube carry its grade and requirements.
What is the strength of R04251 niobium?
Annealed R04251 tube to ASTM B394 has a minimum tensile strength of 195 MPa (28 ksi), minimum yield strength of 125 MPa (18 ksi) and minimum elongation of 20%.
What is the difference between R04251 and R04261?
Both are Nb-1Zr with 0.8–1.2% zirconium and the same minimum strength. R04251 is reactor grade with lower oxygen (0.015%) and tantalum (0.1%) limits; R04261 is commercial grade (0.025% oxygen, 0.5% tantalum).
Can R04251 fittings be used in air at high temperature?
No. Like all niobium alloys, R04251 oxidises in air above about 400 °C. It is used at high temperature in vacuum, inert gas or liquid alkali metals.
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 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.
