Double tube with petal shape and method of manufacturing the same

A method of manufacturing a double tube using a hydroforming method, the double tube comprising:

• an outer tube;
• and
• an inner tube coaxially inserted into the outer tube to be installed, and having a corrugated petal shape in a wave form along a circumferential direction;
• the method comprising:
• an operation of inserting the inner tube into the outer tube and coaxially disposing the inner tube and the outer tube (S1);
• an operation of inserting a plurality of petal forming bars into a space between the outer tube and the inner tube and arranging the petal forming bars along a circumferential direction at predetermined intervals (S2);
• an operation of disposing an assembly of the outer tube, the inner tube, and the petal forming bars in a mold of a hydroforming machine (S3);
• an operation of supplying a fluid into the inner tube while applying a pressure to the inner tube in an axial direction to expand the inner tube (S4);
• and
• an operation of separating the petal forming bars from the space between the outer tube and the inner tube (S5).