Just a little more information. In 1996 I was a member of the Fremont Ca. bicycle club, the west coast Bianchi distributor is in Hayward, just down the freeway.
The club asked Bianchi to do a show and tell about what's new, the rep. brought a down hill racing frame and a down tube from a TI Megatube frame. The down tube was made from two sheets of titanium, formed and welded. The interesting thing was the sheets had small stiffeners formed into the sheet.
I'm a long time welder/fabricator and needed to know how that was done, the Bianchi rep. didn't know, I guess only the factory that made the sheets knew.
Jim