Inconel 718 seamless pipe (UNS N07718) is an age-hardenable nickel-chromium-niobium-molybdenum alloy. It is supplied either in the solution-annealed condition for subsequent ageing by the fabricator, or fully solution annealed plus precipitation hardened for direct use. After ageing it reaches roughly 185 ksi tensile and 150 ksi yield strength while retaining the corrosion resistance and low-temperature toughness of the 700 series.
Typical uses are high-strength bolting and tubing, rocket and turbine components, downhole completion parts, springs and fasteners, and high-temperature clamp and support hardware that must not relax.
Specification and Designation
| Designation | Value |
|---|---|
| UNS number | N07718 (formerly Grade 718) |
| Chemical composition and heat treatment | ASME SB-637 |
| Fittings, flanges and valves | ASME SB-834 |
| Bolting | ASME SA-962 |
| Plate, sheet and strip | ASME SB-906 |
| Delivery condition | Solution annealed (Grade 1) or solution annealed plus precipitation hardened |
On standards: ASME BPVC Section II does not contain a dedicated seamless pipe specification for UNS N07718. The alloy’s governing Section II specifications are SB-637 for bar, forgings and forging stock, and SB-834 for forged fittings and flanges. Where seamless pipe is required, we supply to these same composition and heat-treatment requirements, and we can quote to AMS 5589 or the customer’s own specification on request. Tell us the standard on your enquiry and we will confirm the exact line item.
Chemical Composition (ASME SB-637, Table 1)
| Element | Composition, % | Element | Composition, % |
|---|---|---|---|
| Nickel | 50.0 – 55.0 | Carbon | 0.08 max |
| Chromium | 17.0 – 21.0 | Manganese | 0.35 max |
| Columbium (Nb) + tantalum | 4.75 – 5.50 | Silicon | 0.35 max |
| Molybdenum | 2.80 – 3.30 | Phosphorus | 0.015 max |
| Titanium | 0.65 – 1.15 | Sulfur | 0.015 max |
| Aluminium | 0.20 – 0.80 | Boron | 0.006 max |
| Iron | Remainder (by difference) | Copper | 0.30 max |
| Cobalt (if determined) | 1.0 max |
Note that for UNS N07718 the nickel content carries a range rather than a minimum, and iron is the balance element determined arithmetically by difference. This is unusual in the nickel alloy family and is worth checking against incoming inspection documents.
Mechanical Properties (ASME SB-834, solution annealed plus precipitation hardened)
| Tensile, min ksi (MPa) | Yield (0.2%), min ksi (MPa) | Elongation, min % | Hardness |
|---|---|---|---|
| 185 (1275) | 150 (1034) | 12 | 35 HRC max, typical 28–34 |
Elongation falls to 12% in the aged condition against 30% for solution-annealed N06625, because the gamma double prime precipitate consumes ductility. Design for the aged properties whenever 718 is used in a pressure or load path.
Heat Treatment (ASME SB-637, Table 2)
| Stage | Parameters |
|---|---|
| Solution treatment | 1700 to 1850°F (924 to 1010°C), hold 1/2 h minimum, cool at a rate equivalent to air cool or faster |
| Precipitation hardening | 1325 ± 25°F (718 ± 14°C), hold 8 h, furnace cool to 1150 ± 25°F (621 ± 14°C), hold until total precipitation treatment time reaches 18 h, air cool |
All three precipitation-hardening families (gamma prime, gamma double prime and delta phase) respond to this two-step schedule. The purchaser must designate on the order which partial stages are required for the material to be shipped, so state your condition explicitly.
Supply Range and Conditions
| Parameter | Range |
|---|---|
| Outer diameter | 6 mm – 300 mm, subject to production route |
| Wall thickness | 1.0 mm – 30 mm |
| Condition | Solution annealed (so fabricator can age) or solution annealed plus aged |
| Product forms | Seamless pipe and tube, forged fittings and flanges to SB-834, bar and forging stock to SB-637, bolting to SA-962 |
Testing and Inspection
- EN 10204 3.1 mill test certificate; third-party inspection available on request
- Full chemical analysis with actual heat values on the certificate
- Tensile testing after the specified heat treatment, reported in the delivered condition
- Hardness testing in the aged condition
- Grain size examination where required by the applicable code
- Dye penetrant inspection; ultrasonic testing on bar and forgings
Surface, Marking and Packing
Supplied pickled or bright annealed, capped both ends and sleeved. Marked with heat number, condition, standard, size and works mark. Export packing in wooden cases or on steel pallets with plastic end caps.
Applications
- High-strength tubing, stem and actuator components
- Downhole and completion equipment, packer and mandrel parts
- Bolting, studs and fasteners requiring high yield and stress-rupture resistance
- Springs, clips and fasteners for elevated-temperature service
- Turbine and rocket hardware
- Oil and gas wellhead components and high-temperature hangers
Related Products
If you need corrosion resistance rather than strength, our Inconel 625 seamless pipe is the better choice, being solid solution annealed with no ageing step and far better chloride pitting resistance. For the matching fittings and flanges in 718, ask for our SB-834 line.
Technical Enquiries
Send the required condition (solution annealed or solution annealed plus aged), dimensions, quantity and the standard you intend to purchase against. We will confirm the production route, the exact specification line item and the delivery terms, FOB Shanghai or Ningbo.
Frequently Asked Questions
Which standard should I specify for Inconel 718 seamless pipe?
ASME BPVC Section II has no dedicated seamless pipe specification for UNS N07718. The governing Section II specifications are SB-637 for bar and forgings and SB-834 for forged fittings and flanges. Many buyers specify AMS 5589 or a customer-specific specification for seamless tube. Tell us your standard and we will confirm exactly what we can supply against it.
Should I order 718 solution annealed or aged?
Solution annealed if you intend to cold form, bend, machine heavily or age the part yourself as part of your controlled process. Order solution annealed plus aged if the component goes into service as delivered and you want the full 185 ksi strength without in-house heat treatment.
Why is iron the balance element in 718?
Because nickel in 718 is specified as a range of 50.0 to 55.0% rather than a minimum. The remainder of the alloy balance is iron, which is determined arithmetically by difference. Most other nickel alloys specify nickel as a remainder with a high minimum.
What is the difference between N07718 and N07725 (Waspaloy)?
Waspaloy N07725 has more chromium, more molybdenum and no niobium, relying on gamma prime rather than gamma double prime for strengthening. It has better oxidation and hot-corrosion resistance at the highest temperatures, while 718 has better weldability and lower cost. Choose 718 for complex welded fabrication and N07725 for the hottest oxidising service.
Can 718 be welded?
Yes, and it is widely welded. Use a matching filler such as INCONEL Filler Metal 718, control interpass temperature below about 200°C, and avoid post-weld ageing where the strainer-aged condition would be needed. Always specify the required condition on the order.
