METHOD OF MAKING STEEL PIPE AND MATRIX Russian patent published in 2022 - IPC B21D5/01 B21C37/08 

FIELD: storage or distribution of gases or liquids.

SUBSTANCE: invention relates to production of steel pipe. Sheet material is bent three times or more in the direction of its width to form a preform with U-shaped cross-section. Welding gap section is connected to form steel pipe. At that, preform has a slightly curved section with its centre located at a point away from the end over the width of the sheet. Performing pressure treatment of the preform billet, wherein the open pipe section in range of 20 % or more of the sheet width W with the centre located on the lowermost U-shaped section of the preform billet, and the section of the open pipe in range of 10 % or more of the width W of the sheet along the width of the sheet from its end are inscribed in a circle with a diameter equal to or substantially equal to the outer diameter of the steel pipe. Forming is performed with the help of matrix with radius of arc-shaped section in the range of ±3.5 % relative to radius corresponding to outer radius of steel pipe.

EFFECT: forming a steel pipe with proper roundness.

9 cl, 17 dwg, 7 tbl