To provide a producing method for a steel pipe, which becomes a more preferable quality control method and further enhances productivity by distinguishing a defective joined part at an early stage (for example, before passing through a straightening machine) with a more inexpensive, simpler method and by rejecting it, and to provide a device for the method.
In the producing method, an original sheet is prepared by successively welding and joining end parts, in a longitudinal direction, of a plurality of steel strips, and steel pipes are successively produced by heating and forming the original sheets. The producing method includes: a marking step, in which a welded and joined part of the original sheet is marked; a marked portion identifying step, in which the marked part is detected before entering a heating furnaces 5, 6 (A), tracking is performed from the detected position till the outlet side of a reducer 8 (C, D), and the portion marked at the outlet side of the reducer is identified by the tracking; a step, in which the identified marked portion is marked again; and a step, in which the portion marked again is rejected at a cooling bed or at its outlet side.
Akihiko Yamashita
Kishimoto Tatsuto