I think most titanium welding has to occur in an inert atmosphere. I have heard that titanium bike frames are welded together in setups not too much unlike the picture-- spacesuited welders in a room full of inert gas, or via glove ports into a clear box full of inert gas.

Wikipedia seems to confirm this: "welding of titanium must be done in an inert atmosphere of argon or helium in order to shield it from contamination with atmospheric gases such as oxygen, nitrogen or hydrogen."