| 摘要 |
PURPOSE:To obtain an electric welded steel pipe for an oil pipe, etc., with high precision of shape size by deforming an electric welded blank pipe before reaching sizer rolls to a specific ratio of a longitudinal diameter to a lateral diameter previously. CONSTITUTION:Steel pipe is formed into a cylinder successively and both edge parts are welded to form the blank pipe 11B. This blank pipe 11B is passed through a postanneler 17 to perform a heat treatment of the weld zone locally and passed through an air cooling zone; and the pipe is passed through a water cooling zone 18, side rolls 10, and sizer rolls 19 and then cut, and the cut pipes are passed through a straightening machine 20. In this process, predeformation is carried out so that the ratio (r) of the lateral diameter of the blank pipe 11B to the longitudinal diameter is regulated to 1.04<=gamma<=1.10 in the heat treatment. This predeformation uniforms a lengthwise residual stress distribution at each circumferential position of the blank pipe 11B and prevents the generation of local bending moment to suppress bending. |
