| 摘要 |
PURPOSE:To prevent the generation of a microcrack and to obtain the welding pipe of smooth bead shape by forming the cross section of the open pipe immedi ately before coming into a welding position in the shape specifying the ratio of the diameter in the height direction to the diameter in the horizontal direction and joining it by welding by making it in nearly roundness state at the welding position. CONSTITUTION:In the case of the diameter in the height direction being taken in Dv and the diameter in the horizontal direction Dh on the open pipe section immediately before coming in a welding executing position, Dv/Dh<1.0, and by forming the open pipe F1 in an oblong shape of an opening length C between edges the rise amt. E of the edge can be restrained lower, the seam opening amt. W distribution is improved as well and the deterioration of a bead shape and the generation of a microcrack are constrained.
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