| 摘要 |
PROBLEM TO BE SOLVED: To provide a method for manufacturing a low yield ratio seam welded steel pipe for a line pipe, which method can manufacture the low yield ratio seam welded steel pipe for the line pipe without requiring additional facilities and without deteriorating production efficiency. SOLUTION: The entrance side of a steel strip 20 is corrected by means of a leveler 2, and then the steel strip is continuously formed into a nearly cylindrical open pipe, and then the steel pipe 30 is formed by seam-welding the circumferential end portions of the open pipe, and then the steel pipe 30 is corrected while being turned by means of a rotary correcting machine 10. In this case, the steel strip has a composition containing 0.1% or less C, and 1.8% or less Mn, and an average strain of 0.2 to 7.0% in the wall thickness direction in the entrance side correction, and the steel pipe 30 has an average strain of 0.2 to 7.0% in the wall thickness direction and a compressive strain of 0.2 to 7.0% in the longitudinal direction of the pipe caused by the repeated bending and return-bending operation in the turning correction. COPYRIGHT: (C)2007,JPO&INPIT
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