In 1984-1986, I welded titanium pipe, 2" thru 6" dia, at the Ammco plant at Isle of Palms outside Charleston, SC. The facility produces a powdered product used in the manufacture of polyester and required great amounts of 100% acytic acid thus the titanium piping.
If you wish more information, just PM me, and I will gladly share my knowledge.
QC Robert
robertp@westernp.com