PRODUCTION METHOD OF LONGITUDINALLY WELDED MAIN PIPES Russian patent published in 2015 - IPC B21C37/00 

FIELD: metallurgy.

SUBSTANCE: method involves moulding of the main outline of a tube workpiece of rolled plates, further connection of longitudinal side edges of the moulded tube workpiece, welding to them of process planks and welding of the above side edges in a closed position with formation of a longitudinal connecting joint, as well as expansion of the obtained tube to provide an outline of its circle. After moulding of the main outline of the tube working, its additional moulding is performed at least at two stages; with that, at the first stage from an initial position with a connector of side edges of the tube workpiece, which is located at the upper point of the perimeter, it is turned about the axis through an angle of 15…60° and fixed in this position, a compressive force uniformly distributed throughout the length of the tube workpiece is applied to the upper zone of its external surface, which provides vertical displacement of this zone in the direction of the tube workpiece axis by the specified value, and at the second stage of additional moulding the tube workpiece is turned about the axis to an opposite side through the same angle and the similar force is applied to the upper zone of its external surfacee. Additionally, at least two additional moulding stages are performed.

EFFECT: reduction of residual inner stresses in a zone of a longitudinal weld.

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