Welding titanium

Titanium welds excellently, provided it is completely shielded from the air. Above roughly 400 degrees it absorbs oxygen, nitrogen and hydrogen, and that absorption embrittles the material irreversibly. Unlike steel, no post-treatment repairs it.

That makes welding titanium less a matter of welding skill than of gas control. This article covers the method and how the result is assessed.

Why shielding governs everything

At elevated temperature, oxygen and nitrogen dissolve in the titanium lattice and raise strength while drastically reducing ductility and toughness. Hydrogen causes longer term embrittlement. No heat treatment removes those elements again.

Shielding must therefore continue until the material is below roughly 400 degrees. The torch cup alone is insufficient for that: the weld cools more slowly than the torch travels.

Trailing shield, backing and chamber

The standard solution is a trailing shield behind the torch, continuing to protect the still hot weld metal, combined with backing purge on the root side. On pipework the whole pipe is purged.

For critical work, welding takes place in a chamber that is first evacuated and then filled with argon, or in a flexible tent with controlled oxygen content. Residual oxygen is measured, typically below 50 ppm and lower under the strictest requirements.

Colour as an acceptance criterion

Weld colour directly indicates how much oxygen was absorbed. Bright silver is good, light straw still acceptable, dark yellow borderline, and blue, purple or grey white powder means rejection. AWS D18.2 and the common specifications attach numbers to this.

That assessment covers the weld face, the root side and the heat affected zone. A bright bead with a blue root is not a sound weld. Agree in advance which number is still accepted.

Cleanliness and tooling

Titanium is extremely sensitive to contamination. Grease, fingerprints, iron particles and residues of other metals cause embrittlement and cracking. Degrease with a suitable solvent, work with gloves and use only tooling dedicated to titanium.

Iron particles from a shared brush or grinding disc are the classic cause of rejected titanium work. Maintain a separate work area, as with stainless but stricter.