| 摘要 |
PURPOSE:To determine a securing position of accessories, and make the connecting position of pipes correspond with each other correctly by forming projections showing reference positions in the circumferential direction at each predetermined position of the inner peripheral surface. CONSTITUTION:On each position of the inner peripheral surface of a pipe is formed projections 2 showing the reference positions in the circumferential direction. The projections 2 are formed M e.g. in eight places, and each projection is formed over the entire length along the direction of an axis 3 of the pipe 1. In this way, when accessories are provided on the predetermined position in the circumferential direction of the pipe 1, the securing position can be determined correctly on the basis of projections 2. When the pipe 1 is laid so that two pipes 1 can be connected in the form of registering the upper and lower positions, by fitting the projections 2 of one pipe 1 and projections 2 of the other pipe 1, the upper and lower positions of both the pipes 1 can be registered with each other correctly. The height of projections is determined to be a dimension (e.g. of the order of 1mm) in such an extent that it does not obstruct the flow of fluid. |
