An Investigation of Welding Brittle Fracture of Titanium Spherical Tank Fabricated by TIG

In this study, the cause of brittle fracture at the main weld line of a spherical pressure vessel made of Ti-۶Al-۴V alloy has been investigated. To fabrication of pressure vessel, two hemispheres of Ti-۶Al-۴V alloys welded together by gas tungsten arc welding. Due to sensitivity of titanium welding to oxygen, nitrogen, hydrogen, and carbon elements, and solving of the elements as interstitial, the fusion zone, solid zone which hot till ۵۰۰°C, must be protected with high purity argon gas from these elements. Insufficient protection and higher heat input, resulted in formed brittle compounds in the fusion zone.In further studies, the cause of the failure of the welding region has been determined that the outer layer of the fusion zone is oxidized due to inadequate protection. At high pressures inside the vessel, this oxide layer is cracked due to its brittleness and then the crack is grown at αcase with high speed and entered into a welded area.

Keywords:

Titanium Alloy , Gas Tungsten ArcWelding , Tank , Titanium Oxide , Brittle Fracture