Abstract: It is an object of the present invention to provide a novel roll-forming method for steel pipes and equipment for same with which (1) the evidence that forming work in the FF forming method is mainly carried out at the cluster forming portion showing the poor formability is modified and improved without any deteriorating the advantage of the common-utilization of rolls in the FF forming method which employs basically the circular-bend method, and (2) the forming function at the breakdown forming portion is enhanced. Accordingly, the pinch-point formed by the upper and lower rolls is set at a boundary area between the target forming zone in the material's width direction and previously-formed zone or un-formed zone.

Abstract: In the fin pass forming apparatus, the fin roller is split in two symmetrically with respect to the center line of the flow direction of a steel pipe to be formed, and a plurality of side rollers are arranged on a section perpendicular to the flow direction of the steel pipe. At least one fin roller stand is mixed in a group of roller stands including a cluster mill composed of a lower roller and a plurality of pairs of side rollers. The fin roller arranged in the cluster mill is split in two, one is a roller on the work side and the other is a roller on the drive side. The split fin rollers come into contact with a steel pipe to be formed at arbitrary positions in arbitrary directions in the circumferential direction of the steel pipe to be formed so as to conduct a fin pass formation. The plurality of fin pass forming rollers are arranged on a section different from the flow direction of the steel pipe to be formed.