Nickel Alloy Tubes for Aerospace: Inconel 718, 625 and X-750
Recommended Pipe & Tube Materials
Aircraft engines, exhaust systems and space propulsion expose metals to extreme temperature, vibration and corrosion while weight must be kept to a minimum. Nickel-based superalloys keep their strength and oxidation resistance where stainless steels and aluminum cannot. This article explains the main nickel alloy tube grades used in aerospace and what buyers should specify.
Why Aerospace Uses Nickel Alloys
- Strength at high temperature: superalloys retain mechanical properties far above the limits of ordinary steels
- Oxidation and hot corrosion resistance in combustion gas and exhaust streams
- Fatigue and creep resistance under vibration and thermal cycling
- Good fabricability for forming, bending and welding into complex tube assemblies
- Reliability in safety-critical systems where failure is not acceptable
Key Alloys and Their Roles
Inconel 718 (UNS N07718)
A precipitation-hardening alloy with very high strength and good weldability, used up to roughly 650-700 °C (about 1,200-1,300 °F). Typical uses include engine casings, ducting, fuel and hydraulic lines, fasteners and rocket engine components.
Inconel 625 (UNS N06625)
A solid-solution strengthened alloy with excellent fatigue strength, oxidation resistance and formability. It is widely used for exhaust systems, bleed air and ducting, thrust reverser components and bellows, and it welds readily.
Inconel X-750 (UNS N07750)
A precipitation-hardening alloy with good relaxation resistance, used for springs, seals, fasteners and tubing in engine and airframe assemblies.
Other Alloys
Alloy 600/601 for heat-resistant ducting, Alloy 617 and Haynes-type alloys for hot sections, and stainless steels and titanium for lower-temperature parts.
Typical Product Forms
- Seamless tubes and small-diameter precision tubing
- Welded and drawn tubing for ducting and exhaust
- Tubes in solution annealed, or solution annealed and aged condition, according to alloy and application
Specifications and Quality Requirements
Aerospace buyers normally require:
- Conformance to AMS or customer specifications, and ASTM B444 / B167 / B163, as applicable, for the alloy and product form
- Full traceability from melt to finished tube, with certificates such as EN 10204 3.1 or 3.2
- Non-destructive testing: eddy current, ultrasonic and dimensional inspection, and hydrostatic or pneumatic testing where required
- Controlled grain size, cleanliness and mechanical properties verified on test samples
- Quality management aligned with aerospace practice (such as AS9100), and approved special processes where needed
Selection Tips
- Match the alloy to the operating temperature and stress: 718 for high strength, 625 for formability and corrosion, X-750 for springs and relaxation resistance
- Specify heat treatment condition (annealed or aged) and required mechanical properties
- Define tight tolerances on OD, wall thickness, ovality and surface finish
- Confirm testing scope, documentation and the customer’s approval requirements before ordering
- Email: info@duplex-stainless-steel.com
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- Send Your Inquiry →
Frequently Asked Questions
Q1: What is the difference between Inconel 718 and Inconel 625?
718 is precipitation-hardened for very high strength and is used where load-bearing capacity is critical. 625 is solid-solution strengthened, easier to form and weld, and offers excellent oxidation and corrosion resistance, so it is common in ducting and exhaust.
Q2: What temperature can Inconel 718 tube handle?
It is generally used up to about 650-700 °C for load-bearing service. Above that, strength decreases and other alloys may be considered.
Q3: Do you supply tubing with aerospace certifications and traceability?
Please specify the required specification (AMS, ASTM or customer standard), documents and testing in your inquiry, and we will confirm what we can supply.
Q4: Can small quantities or custom sizes be supplied?
Aerospace projects often need small lots and precise sizes; please send drawings or dimensional requirements for a quote.
Request a Quote for Aerospace Nickel Alloy Tubes
Send us your alloy, specification, OD × wall thickness × length, heat treatment condition, quantity and testing requirements, and we will reply within 24 hours.