How Titanium Tubing Is Made: From Sponge to Seamless Tube

Step 1: From Titanium Ore to Titanium Sponge

All titanium products begin with titanium sponge. The ore, mainly ilmenite or rutile, is processed to titanium tetrachloride and then reduced by magnesium or sodium in the Kroll or Hunter process to produce porous titanium sponge. The sponge is crushed and purified to remove residual impurities; only purified sponge is suitable for melting, because impurities strongly affect the mechanical properties and corrosion resistance of the final tube.

Step 2: Melting and Ingot Casting

The purified sponge, together with alloying elements such as aluminum, vanadium or molybdenum when required, is compacted into electrodes and melted in a vacuum arc remelting (VAR) furnace or electron beam furnace. Vacuum melting removes gases and volatiles and produces a homogeneous melt. The molten titanium is cast into cylindrical ingots, which become the raw material for the tube blank.

Step 3: Hot Working into Tube Blanks

The ingot is hot worked by rolling or forging at temperatures typically above 900 °C to break down the cast structure and refine the grain size. The resulting billet is then pierced and rolled or forged into a hollow tube blank. In some cases cold working steps are used to achieve the required dimensions and properties of the blank before extrusion.

Step 4: Extrusion of Seamless Pipe

The tube blank is heated to a specific temperature to increase malleability and then pushed through a die under hydraulic pressure in an extrusion press, forming a continuous seamless pipe. Extrusion is carefully controlled to achieve precise dimensions and the required mechanical properties, and it is the key step that distinguishes seamless titanium tubing from welded tubing.

Step 5: Annealing, Cold Drawing and Heat Treatment

After extrusion, the tube is annealed to eliminate internal stress and improve ductility. It is then cold drawn through a series of dies, gradually reducing the diameter and wall thickness while increasing length. Cold drawing improves mechanical properties and surface finish. A final phase-change heat treatment applies controlled heating and cooling cycles to achieve the desired microstructure and hardness, balancing strength and ductility for the intended service.

Step 6: Finishing and Quality Control

Machining and finishing operations bring the tube to the required dimensions and surface quality without leaving defects. Strict quality control and inspection are applied, including dimensional checks, wall thickness measurement, surface inspection, and where required, hydrostatic or eddy current testing and chemical analysis. Only tubes meeting the specification are released for shipment.

FAQ

1. What is the difference between seamless and welded titanium tubing?

Seamless tubing is produced by extrusion and cold drawing from a solid blank and has no longitudinal weld, giving uniform properties around the circumference. Welded tubing is formed from strip and welded longitudinally, which can be more economical for thin walls and large diameters.

2. Why is melting done under vacuum?

Molten titanium reacts readily with oxygen and nitrogen at high temperature. Vacuum arc melting removes gases and volatiles and prevents contamination, which is essential for ductility, weldability and corrosion resistance.

3. What are the common titanium alloys for tubing?

Commercially pure grades (CP1-CP4) are used for corrosion service, while alloys such as Ti-6Al-4V, Ti-3Al-2.5V and Ti-0.2Pd are used where higher strength or special corrosion resistance is required.

4. How is the wall thickness of titanium tube controlled?

Wall thickness is set by the extrusion die and refined by cold drawing passes, then verified by ultrasonic or mechanical measurement on every production lot, with results reported in the inspection certificate.

5. What surface treatment do titanium tubes receive?

Pickling in acid solution removes the oxide scale and oxygen-enriched layer after heat treatment, and additional machining, polishing or grinding is applied where surface finish is specified. The surface must be free of cracks, scratches and pits before acceptance.