| 摘要 |
<p>PURPOSE:To improve the efficiency in treating an improvement by giving the tensile stress exceeding a yield point to the vicinity of a welding joint by narrowing the inner peripheral dimension of a ring as well as outer fitting a constraining ring to the base pipe wall, then expanding the diameter of the ring. CONSTITUTION:A constraining ring 9 split in the length direction and peripheral direction of a base pipe 4 is provided so as to surround the base pipe 4. The diameter contraction by the ring 9 is executed at the position separated by a specific dimension from the center of a welding joint 7. In this case, a bend moment M is caused at the joint part 7 by the pressure to the inner part, the stress exceeding a yield point is caused at a point A and the joint part 7 is plastically deformed. The ring 9 is then expanded and the wall of the base pipe 4 is restored with elastic deformation, and a compression stress is left at the vicinity of the joint part 7. The residual compression stress can thus be formed at and in optional position and size, and the improvement treating efficiency is improved with the simplification of the treating method.</p> |
