| 摘要 |
<p>In this method for manufacturing a steel pipe, a steel sheet, the edges of which have been bent, is subjected to three-point bending a plurality of times in a widthwise direction so as to form said steel sheet into a cylinder, and after abutting parts are welded together so as to produce a pipe blank (1), a pipe expander provided with a plurality of pieces of expansion hardware (2) is inserted into the pipe blank and the pipe blank is expanded. By expanding the pipe blank with the expansion hardware (2) placed up against each section (9) of the pipe blank that was not deformed by the three-point bending, steel pipes with excellent dimensional precision can be manufactured with high yield. Letting N represent the number of pieces of expansion hardware, the three-point bending is preferably performed aN-1 times (a being an integer, e.g. 1, 2, etc.).</p> |
