Greetings Automotive enthusiasts,

I have been thinking about an alternative to the cold working processes that my company uses to form pipe and I've read a little about hydroforming.  I was hoping that someone has expierence in this area.  We expand pipe circumferentially inside another pipe using a cone mandrel.  This reinforces older pipe that has eroded over time due to fluid flow.  Typically this is done without special fixures and only uses pressure behind a solid cone mandrel which is typically 10-15% larger than the ID of the deformable pipe.  Pressures usually rage about 6000psi for a 6 inch pipe that's expanded 12% inside a 6-3/4 inch pipe, for example.  Burst is obviously a concern for the older pipe, however this is overcome by containing the pressure only to the deformable pipe...esentially making it a pressure vessel.  Instead of using pressure behind a solid mandrel, why not use straight pressure in sections???  Questions arise on how to contain the deformation using some sort of dynamic seal.  Any thoughts??