Patent ID: 8281476

Claim:
A method of manufacturing a multilayered tube, comprising: preparing an outer tube, an inner tube having an outer diameter of 95˜98% of an inner diameter of the outer tube, and dies with a shaping void having a diameter of 100.20˜100.30% of an outer diameter of the outer tube; mounting the outer tube on the shaping void, with the inner tube inserted into the outer tube; plastically expanding the inner tube to be brought into contact with the outer tube by injecting a fluid into the inner tube until a pressure of the fluid reaches a first forming pressure inside the inner tube; elastically expanding the outer tube to be brought into contact with the shaping void by increasing the pressure of the fluid until the pressure of the fluid reaches a second forming pressure inside the inner tube; and elastically recovering the outer tube to allow the outer tube and the inner tube to be coupled to each other by removing the fluid from the inner tube, wherein the first forming pressure is in the range of 10˜20% of yield strength of the inner tube, and wherein the second forming pressure is in the range of 10˜20% of yield strength of the outer tube and is maintained for 2˜3 seconds.