METHOD FOR MAKING HELICAL-SEAM TUBES OF ROLLED SHEETS Russian patent published in 2004 - IPC

FIELD: metallurgy, namely manufacture of helical-seam tubes for gas and oil pipelines. SUBSTANCE: method for making helical-seam tubes of rolled sheets comprises steps of butt welding of sheets to strip; shaping tube; welding it by helical seam; cutting welded tubular blank by measured-length tubes; finishing them; using for tube making steel composition at next relation of ingredients, mass%: carbon, 0.03 - 0.15; silicon, 0.1 -0.7; manganese, 0.6 - 2.0; vanadium, 0.01 - 0.15; niobium, 0.01 - 0.12; chrome, 0.01 - 0.3; nickel, 0.01 -0.6; copper, 0.01 - 0.6; aluminum, 0.01 - 0.1; titanium, 0.01 - 0.1; calcium, 0.0005 - 0.02; nitrogen, 0.003 - 0.012; sulfur, 0.001 - 0.01; phosphorus, 0.001 - 0.02; iron, the balance; welding sheets to strip only by inner butt joint while using sheets whose length is normalized with use of mathematical relation; cutting blank by measured-length tubes including portion of shell containing butt joint. Steel may contain in addition molybdenum in quantity 0.01 - - 0.5 mass%. EFFECT: lowered number of flaws of butt welded seam, especially in zone of tube helical seam. 2 cl, 1 ex