Ti-6Al-4V ELI (Grade 23) Titanium Pipe for Aerospace and Medical Applications

What Is Grade 23 (Ti-6Al-4V ELI)?

Grade 23 titanium, also known as Ti-6Al-4V ELI or TC4ELI, is the extra low interstitial version of the most widely used titanium alloy. Its composition - approximately 6% aluminum and 4% vanadium on a titanium base - is the same as Grade 5, but oxygen, nitrogen, carbon, and iron are held to tighter limits. The result is improved ductility, fracture toughness, and fatigue resistance at a small cost in static strength. Grade 23 is covered by ASTM B265 for sheet, B348 for bar, B861 and B862 for pipe and tube, and F136 for implant material.

Composition and Mechanical Properties

Typical composition limits for Grade 23 include aluminum 5.5-6.5%, vanadium 3.5-4.5%, oxygen 0.13% max, iron 0.25% max, carbon 0.08% max, and nitrogen 0.05% max. Minimum tensile properties for annealed bar per ASTM B348 are 860 MPa (125 ksi) ultimate tensile strength and 795 MPa (115 ksi) yield strength, with 10% elongation. The material also maintains good toughness down to cryogenic temperatures, which is why it appears in both aerospace and medical specifications.

Aerospace Applications

In aerospace, Grade 23 is used where a crack must not grow: airframe fittings, pressure vessel liners, cryogenic fuel ducting, and exhaust components that see thermal cycling. Titanium's high strength-to-weight ratio and corrosion resistance make it attractive for ducting systems, and the ELI chemistry ensures the ductility needed for forming complex shapes such as exhaust pipes and manifolds. Welded Grade 23 tube made to ASTM B862 is used in fluid systems where weight saving justifies the material cost.

Medical Applications

For surgical and medical use, Grade 23 material certified to ASTM F136 is the standard choice for implants, including hip stems, bone plates, and spinal systems. Its biocompatibility, low modulus relative to steel, and fatigue resistance suit long-term implantation. The same alloy in wire and tube form is used for surgical instruments and medical device components, where corrosion resistance and clean processing matter.

Pipe Fabrication: Welded and Seamless

Grade 23 pipe and tube are produced both seamless (ASTM B861) and welded (ASTM B862). Welded tube is formed from strip and longitudinally welded under argon shielding, then sized and annealed. Cold drawing improves dimensional accuracy and mechanical properties. Because the alloy work-hardens and has low thermal conductivity, fabrication requires controlled parameters, but the ELI chemistry makes the weld zone more forgiving than standard Grade 5. For critical aerospace and medical parts, full traceability from ingot to finished tube is maintained.

Frequently Asked Questions

Is Grade 23 the same as TC4ELI?

TC4ELI is the Chinese designation for Ti-6Al-4V ELI, equivalent to Grade 23 in the ASTM system; the chemistry and properties correspond.

Why is Grade 23 used for both aerospace and medical parts?

The ELI chemistry gives a combination of high strength, toughness, and biocompatibility that is rare among metals, so the same alloy serves both demanding fields.

Can Grade 23 pipe be welded?

Yes. Grade 23 is weldable by GTAW with argon shielding, and welded tube is supplied to ASTM B862 with the weld seam tested by eddy current or ultrasonic methods.

What is the difference between Grade 5 and Grade 23 pipe?

Grade 23 has lower oxygen, nitrogen, carbon, and iron limits, giving better toughness and ductility; Grade 5 has slightly higher strength and lower cost.

What surface finish is typical for medical-grade tube?

Medical components are usually supplied pickled, polished, or with controlled surface finish to remove contamination and improve cleanability.

Is Grade 23 suitable for exhaust systems?

Yes, its high-temperature strength, oxidation resistance, and fatigue performance suit exhaust ducting and manifolds in aerospace and high-performance applications.