I am searching how to bending pipe in a pipe
It is a boat exhaust system,
how they make the bending
inside of the pipe is a smaller pipe
i hope you can help me
I've done a similar type of thing with hygenic tube that holds products that "set" (chocolate Etc..) and its not easy. It's a little hard to explain, but you make the tube up 'bit by bit" and need to get the right size tubes to make it work (one elbow needs to be able to slip over another), and on the inner tube you tack 3 bits of round bar about 8mm od (or what ever fits) x 25mm in a triangle pattern so that it stays central. With regards to bending the tube, someone like Hotrodder or Rick (amongst others) would probably be able to give you more info, but the ones in the foto look like standard short and long radius Elbows cut down (or added onto) to create the required angle, although I could be wrong and it's still early.
Low melting point alloy like 'cerrobend' : The two pipe are held co-axial in a jig, the Cerrobend is poured in hot, the bend is made when it has set, then the Cerrobend is melted out. Cerrobend has a very low meltng point and can melt in very hot water