Connection between cooled pipe and uncooled pipe in a double-pipe heat exchanger

A heat exchanger comprising:

• an uncooled pipe with an inlet duct of a fluid to be cooled,
• a cooled double-wall pipe with an internal pipe traveled by the fluid to be cooled and an external pipe defining with the internal pipe a space traveled by a cooling fluid, and
• a union connection between said uncooled pipe and cooled double-wall pipe, the union connection including a connection part for connection between one end of the inlet duct of the fluid to be cooled and one end of the double-wall pipe, said connection part also forming a bottom wall of said space virtually transversal to a longitudinal extension of the double-wall pipe, the connection part of the union connection having an annular form with a U-shaped cross section piece having two legs and a perpendicularly extending interconnecting crosspiece to define two annular shanks extending longitudinally to the double-wall pipe with each shank being welded to one end of one of the two pipes of the double-wall pipe, a bottom of the connection part being a bottom wall of the space, and said one end of the inlet duct is welded to a radially inner portion of the connection part at said bottom wall of the space such that an interior diameter of the inlet duct is approximately equal to an internal diameter of the internal pipe of the double-wall pipe;
• the bottom wall of the space having a thickness almost equal to the thickness of a wall of the internal pipe of the double-wall pipe;
• the inlet duct is coaxial with the double-wall pipe.