| 摘要 |
PROBLEM TO BE SOLVED: To lower a maximum stress generated at a main pipe rail opening end part of a branch pipe and enhance internal pressure fatigue strength by forming pressure receiving surfaces which cane into contact with the outer peripheral surface of the main pipe rail symmetrically with a shaft core of a branch hole as a center on the inner peripheral surface on the opposite side to a screw wall part of a ring- shaped coupling hardware which is externally fitted to the main pipe rail. SOLUTION: When a branch pipe 2 is branch-connected with a main pipe rail 1, a nut 4 is screw-fastened to a screw wall 3-1 of a ring-shaped coupling hardware 3 which is externally fitted to the main pipe rail 1 after a pressing bearing surface 2-3 of a connection head part 2-2 on the side of the branch pipe 2 is made to abut on a pressure receiving bearing surface 1-3 opening outward in a branch hole 1-2 part. As a result, the main pipe rail 1 is compressed by the pressure receiving surface 3-2 provided symmetrically on the inner peripheral surface of the ring-shaped coupling hardware 3 because the ring-shaped coupling hardware 3 is attracted to the side of the branch pipe 2 at the same time that the pressing bearing surface 2-3 is made press-contact with the pressure receiving bearing surface 1-3. Thus, high compression pressure is imparted to the branch hole 1-2 of the main pipe rail 1 and internal pressure fatigue strength is improved. |
