langdahl,
I disagree with the above comments. The methods referenced are for custom designs of vessels, which, I do not believe you are really interested in....
You must tell us the design pressure and temperature of the system !!!
First, please note that this is not large pipe...... 3 inch NPS to 12 inch NPS titanium pipe is very common in the pulp and paper industry. There are standard industry pipe flanges that are used for this pipe that are very economical.
Secondly, I am assuming you are dealing with modest pressures and thin walled piping (Schedule 5S or 10S)........ Commonly, these systems are joined with "lap-joint flanges" ( also called Van Stone Flanges) and cheaper carbon steel backup rings. The premium material, titanium in your case, is the only material to touch the fluid.
Try contacting the Felker Bros 800-826-2304 or see the
website.
Also try the Flowline Corp, in Newcastle, PA on 412.658.3711 for more info on these flanges.....
Good Luck !!!! MJC