| 摘要 |
<p><P>PROBLEM TO BE SOLVED: To lessen the maximum outside diameter for a socket portion U of a two-layered tube. <P>SOLUTION: The two-layered tube comprises an inner tube 11 having a socket 13 for piping connection on its end, outer tubes 30, 42, and 44 covering the periphery of the inner tube 11. The two-layered tube has a first outer tube 30 covering at least the maximum outside diameter part 13<SB>S</SB>of the socket 13, and second outer tubes 42 and 44 capable of covering other part excluding a part covered by the first outer tube 30. The first outer tube 30 is made from a material highly tougher than that of the second outer tubes 42 and 44, and its wall is formed thinner than that of the second outer tubes 42 and 44. Consequently, compared with the inner tube 11 wholly covered with an outer tube such as lower tough mortar, the maximum outside diameter of the socket portion U of the two-layered tube can be reduced. <P>COPYRIGHT: (C)2004,JPO</p> |
