What is a Seamless Inconel 718 Tube?
A Seamless Inconel 718 tube (UNS N07718) is a high-performance nickel-chromium-iron superalloy tube manufactured from a solid billet without a longitudinal production weld.
Compared to welded tubes, seamless Inconel 718 tubing avoids a longitudinal production weld. Seamless manufacture avoids a longitudinal production weld. Pressure capability, dimensional accuracy and service reliability depend on the specified material condition, dimensions, inspection requirements, fabrication and applicable design code.
This makes it suitable for high-temperature, high-pressure, and corrosive environments when the ordered condition and acceptance criteria match the service requirements.
Need pipe in nominal NPS / Schedule sizes? See our Inconel 718 seamless pipe range.
Inconel 718 is a precipitation-hardened nickel alloy known for its excellent tensile strength, creep resistance, and rupture strength at temperatures up to 1300°F (704°C).
Key Advantages of Inconel 718 Seamless Tubes
High-Temperature Strength: Maintains useful mechanical properties from cryogenic temperatures to 704°C (1300°F); allowable design values depend on stress, environment and condition.
Corrosion Resistance:
- Resistant to oxidation and scaling
- Good resistance to stress corrosion cracking (SCC) in many media
- H₂S (sour gas) service suitability is not automatic — review the applicable requirements (e.g. NACE MR0175 / ISO 15156-3), material condition, hardness limits and the actual environment
Delivery Conditions: Available routes include aerospace tubing specifications such as AMS 5589 / AMS 5590, with chemistry per ASTM B637 (UNS N07718). Each route defines its own heat-treatment condition, revision and melting practice. Solution-treated delivery is a different condition from aged product — state the required condition and specification revision in the RFQ.
Fatigue Resistance: Used in applications involving cyclic loads, vibration and dynamic stress; performance depends on condition, surface and loading.
Product Specifications and Data
To provide a comprehensive overview of this high-performance material, here are the detailed technical specifications and performance data for Inconel 718.
Equivalent Grade
| UNS | Common grade name | EN material number | EN steel name | JIS grade | GB/T grade |
|---|---|---|---|---|---|
| N07718 | Inconel 718 | 2.4668 | NiCr19Fe19Nb5Mo3 | Not listed in grade index | NS4301 / GH4169 |
Grade correspondence does not make ASTM, ASME, EN, JIS and GB delivery requirements interchangeable. Confirm chemistry, heat treatment, mechanical properties, dimensions, testing and certification against the purchase specification. Approximate or unconfirmed correspondences retain their qualification. See the grade designation index.
Chemical Composition
The composition of Inconel 718 is carefully balanced to achieve its superior high-temperature strength and corrosion resistance.
| Ni | Cr | Fe | Mn | Nb | Mo | Ti | C | Si | S | P | Co | B | Al | Cu |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 50.0-55.0 | 17.00-21.00 | Bal | ≤0.35 | 4.75-5.50 | 2.80-3.30 | 0.65-1.15 | ≤0.08 | ≤0.35 | ≤0.015 | ≤0.015 | ≤1.0 | ≤0.006 | 0.20-0.80 | ≤0.30 |
Chemical composition, wt %. Source: SAE AMS 5589G, Table 1 (composition of the 718 seamless-tubing alloy — 52.5Ni-19Cr-3.0Mo-5.1Cb(Nb)-0.90Ti-0.50Al-18Fe, similar to UNS N07718), consistent with published ASTM B637 limits for UNS N07718. Single values are maximum content unless a range is shown. Aluminium 0.20–0.80 % and copper ≤ 0.30 % are included; iron is determined arithmetically by difference.
Mechanical Properties (Specification Limits)
Inconel 718 is specifically designed to maintain its strength and shape in high-stress, high-temperature environments.
| Condition (AMS 5589G) | Tensile Strength | Yield Strength (0.2% offset) | Elongation in 50 mm (2 in.), min | Hardness |
|---|---|---|---|---|
| Solution heat treated (delivery condition) | 1069 MPa (155 ksi) max | 655 MPa (95 ksi) max | 30 % | — |
| Solution treated + precipitation hardened | 1276 MPa (185 ksi) min | 1034 MPa (150 ksi) min | 12 % | ≥ 36 HRC |
Mechanical properties — specification minimums, room temperature. Source: SAE AMS 5589G, Table 2 (as solution heat treated) and Table 3 (after precipitation heat treatment). Solution heat treated tubing is supplied for subsequent forming and welding and carries maximum tensile/yield limits of 155 ksi (1069 MPa) / 95 ksi (655 MPa) with 30 % elongation minimum; after precipitation hardening the minimums are 185 ksi (1276 MPa) / 150 ksi (1034 MPa) with 12 % elongation minimum and hardness not lower than 36 HRC (AMS 5589G 3.6.2.2). Average grain size ASTM No. 5 or finer. Solution heat treatment 941–996 °C (1725–1825 °F); precipitation treatment 718 ± 8 °C (1325 ± 15 °F) for 8 h, furnace cool to 621 ± 8 °C (1150 ± 15 °F), hold to 18 h total, air cool. Composition per AMS 5589G Table 1, consistent with ASTM B637 for UNS N07718. ASTM B983 does not cover Alloy 718 — it applies to precipitation-hardening cobalt-containing alloys and has been removed from this page.
Physical Properties (Reference)
These physical properties highlight the material’s ability to perform reliably under a wide range of conditions.
| Density | Melting Point | Thermal Expansion | Thermal Conductivity | Modulus of Elasticity | Electrical Resistivity |
|---|---|---|---|---|---|
| 8.22 g/cm³ | 1260 – 1336 °C | 13.0 μm/m°C (20-100°C) | 11.4 W/m·K (20°C) | 200 GPa | 1.2 × 10⁻⁶ Ω·m (20°C) |
Physical properties (reference values).
Size Tolerance Chart (mm)
| Specified/Calculated Nominal OD (Inches) | Permissible Variation (Inches) | Specified/Calculated Nominal OD (mm) | Permissible Variation (mm) |
|---|---|---|---|
| 0.500 to 5⁄8, excl. | ±0.005 | 12.7 to 15.8, excl. | ±0.127 |
| 5⁄8 to 1 1⁄2, incl. | ±0.0075 | 15.8 to 38.1, incl. | ±0.190 |
| Over 1 1⁄2 to 3 1⁄2, incl. | ±0.010 | Over 38.1 to 88.9, incl. | ±0.254 |
| Over 3 1⁄2 to 4 1⁄2, incl. | ±0.015 | Over 88.9 to 114.3, incl. | ±0.381 |
| Over 4 1⁄2 to 6, incl. | ±0.020 | Over 114.3 to 152.4, incl. | ±0.508 |
| Over 6 to 6 5⁄8, incl. | ±0.025 | Over 152.4 to 168.3, incl. | ±0.635 |
| Specified/Calculated Nominal OD (Inches) | Permissible Variation (Inches) | Specified/Calculated Nominal OD (mm) | Permissible Variation (mm) |
|---|---|---|---|
| 2 1⁄2 to 5 1⁄2, excl. | ±0.031 | 63.5 to 139.7, excl. | ±0.787 |
| 5 1⁄2 to 9 1⁄4, incl. | ±0.047 | 139.7 to 234.9, incl. | ±1.19 |
| Condition | Specified/Calculated Nominal OD (Inches) | Permissible Variation (Wall Thickness) |
|---|---|---|
| Cold-Finished | 0.500 to 5⁄8, excl. | ±15.0% |
| 5⁄8 to 4 1⁄2, incl. | ±10.0% | |
| Over 4 1⁄2 to 6 5⁄8, incl. | ±12.5% | |
| Hot-Finished | 2 1⁄2 to 9 1⁄4, incl. | ±12.5% |
Common Industrial Applications
Alloy 718 tube is used where high strength must be combined with corrosion resistance from cryogenic to elevated temperatures. Typical application areas for the tube product form include:
Aerospace Industry
- Jet engine components
- Rocket motors
- High-temperature fasteners
Power Generation
- Gas turbines
- Nuclear reactor systems
Oil & Gas (HPHT Applications)
- Downhole tubing
- Wellhead components
- Subsea valves
Cryogenic Systems
- LNG storage
- Low-temperature piping
Why Choose Our Inconel 718 Seamless Tube?
- Supplied against AMS 5589 / AMS 5590 aerospace routes with general requirements per ASTM B829 — state the revision in the RFQ
- Suitable for marine, offshore, and aerospace applications
- Third-party inspection by recognized agencies can be arranged per order; PED conformity assessment, where applicable, is a separate regulatory process agreed for the specific product and category
- Full traceability and high-performance reliability
Frequently Asked Questions
What sizes are available for Inconel 718 seamless tube?
The overall range is OD 6–257 mm; WT 0.5–35 mm. Requirements outside this range are reviewed against mill capability on request.
Which specification governs Inconel 718 seamless tube?
ASTM B637 / ASME SB637 is the governing specification for Inconel 718 seamless tube. The edition in force at order time is stated on the quotation and purchase order; chemistry, mechanical properties, heat treatment, dimensions and testing are reported against the ordered standard and material heat.
What inspection documents are provided?
Each order is documented with a mill test certificate stating heat chemistry and mechanical test results. EN 10204 3.1 certification, hydrostatic testing, eddy-current or ultrasonic inspection and PMI are performed when specified in the purchase order.
Ready to Request a Quotation?
Send the NPS and schedule (or actual OD and wall), quantity, length, end finish and the inspection items you need as acceptance criteria — you will get a written quotation stating the specification and edition, delivery condition, documents included and lead time.
