METHOD OF MAKING STRAIGHT-SEAM ELECTRICALLY WELDED LARGE-DIAMETER TUBES Russian patent published in 1996 - IPC

FIELD: tube production. SUBSTANCE: method comprises steps of applying on a composite sheet, consisting of sheet strips and being used as a blank for making a tube, an additional sheet; welding the last to the composite sheet after the additional sheet had been placed symmetrically relative to a longitudinal axis of the sheet strip; using the additional sheet with a length, equal to a length of the sheet strip, and a width, being less, than a width of the sheet strip; selecting a total thickness of both sheets according to a condition, that the total thickness is more, than a standard thickness of the sheet strip at least by 1.5 times; making the tube by its edge forming, by preliminary bending of a mean portion of the sheet by a punch in a press with subsequent final formation in a closed gage of the press and reduction operation; after formation had been finished, welding the blank by an outer and inner seams; then milling ends of the inner seams, expanding the tube blank with use of special cones and performing its hydraulic testing by an inner pressure. EFFECT: enhanced reliability of tube seams. 2 cl, 9 dwg