Patent UA-96097-C2 (UA)
Title: Method for production of steel high-strength electric-welded double-seam pipes of large diameter for main pipelines
Inventor: LIVSHYTS DMITRII ARNOLDOVICH
IPC: B21B1/22
Filed: 2010-09-27
Abstract: The invention relates to production of high-strength electric-welded double-seam pipes of large diameter manufactured from hot-rolled sheet that are used for construction of main gas and oil pipelines, as well as for production of hot-rolled sheets for the pipes. A method includes manufacture of a steel slab by steel melting in a converter with its subsequent out-of-furnace processing and casting on a machine for continuous casting of blanks, the slab austenitizing and its subsequent multistage rolling on a reverse mill into a thick sheet, preliminary preparation of the thick sheet for subsequent processing the pipe, forming the sheet into a pipe blank, welding the pipe and its further expansion. The steel of certain chemical composition is produced, after casting on the continuous casting machine of blanks the slab is cooled at a rate of 1 ÷ 25 °C/h to the temperature not above , then it is heated to the temperature that is for 150 ÷ above Ac3, after which pre-rolling is carried out, at which the metal starts to be deformed in the upper part of the austenite region under the temperature that is for 20 ÷ below the temperature of the slab heating to the temperature that is for 20 ÷ above the recrystallization temperature, then the final rolling is performed in the lower part of austenite region in the temperature range A+(20÷100)C÷ A-(10÷90)C, while between the last and final stages of rolling an intermediate cooling of metal is carried out at a rate of 0.5 +8.0 °C/s, a reduction per pass makes 5 ÷ 20 %, while the overall degree of reduction at final rolling is 50 ÷75 %, and after final rolling cooling of the rolled products is carried out up to 650÷350 °C at a rate of 1.0 ÷ 8.0 ° C/s, then the rolled metal is subject to final cooling to 100 ÷150 °C at a rate of 0.5 ÷6 °C/ h, and then the rolled metal is subject to final cooling, after which the obtained rolled metal is forwarded for pipe production, where first two longitudinal edges of the sheet are subject to edge-planing processing to obtain given sizes of edges and sheet width, after which the sheet with machined longitudinal edges is fed to a seven-stand continuous roller-forming mill, in which it is formed into a semi-cylindrical pipe blank with subsequent submission to an assembly device, in which two semi-cylindrical workpieces are connected into one cylindrical workpiece and sent to the assembly and welding line, where the connected longitudinal edges of pipe blank are welded along entire length by the first technological seam by automatic arc carbon dioxide shielded welding, and after turning the pipe blank for 180° they are welded by the second technological seam, and then welding of internal and external working seams is performed by arc welding under a layer of flux with use of a welding wire, then the pipes are expanded on a hydromechanical expander with plastic deformation for 0.8 ÷ 1.2 %, and then the tests by internal hydraulic pressure are carried out followed by control of metal of welds and base metal by non-destructive tests, stippling and removal of the bevel on the pipe ends. Due to the formation of mechanical properties of sheet rolled metal taking into account further impact of pipe processing a complex of mechanical properties of pipe is provided.