Process for producing pipe bends from straight, spiral-welded pipes

摘要

The invented process for producing pipe bends from straight, spiral-welded pipes made of steel coiled strips of the following chemical composition: 0.03 to 0.25 percent by weight of carbon C, 0.5 to 1.7 percent by weight of manganese Mn, 0.0 to 0.5 percent by weight of nickel Ni, 0.2 to 0.7 percent by weight of silicon Si, 0.001 to 0.035 percent by weight of aluminium Al, 0.0 to 0.03 percent by weight of phosphorus P, 0.0 to 0.035 percent by weight of sulfur S, 0 to 0.25 percent by weight chromium Cr, 0.0 to 0.1 percent by weight of molybdenum Mo, 0.0 to 0.3 percent by weight of copper Cu, 0.0 to 0.08 percent by weight of vanadium V, 0.0 to 0.05 percent by weight of niobium Nb, 0.0 to 0.06 percent by weight of titanium Ti, whereby the content of Cr + Cu + Mo is at the most 0.45 percent by weight and the content of Nb + Ti + V is at the most 0.12 percent by weight and the balance being iron Fe and processing impurities. The pipes are welded by double-sided butt weld using filler material of the following chemical composition: 0.04 to 0.08 percent by weight of carbon C, 0.3 to 0.7 percent by weight of silicon Si, 0.9 to 1.7 percent by weight of manganese MN and the remainder being iron and processing impurities. The manufacturing process is characterized in that the weld is carried out in such a manner that it does not project over both inner and/or outer surfaces of the pipe by more than 2 mm, and that tangent to cross section thereof includes at the spot of the welt transition to the pipe base material with the pipe surface an angle 45 degrees at the most, whereupon the pipe welded in such a spiral manner is subjected to bending in an electric induction bending machine with water spray at working temperature T, which is selected in intersection, respectively overlap of temperature intervals [AiC3ZM-(30 to 80)] degC and [AiC3PM-(30 to 80)] degC, wherein AiC3ZM represents the temperature AiC3 of the base steel material and AiC3PM represents the temperature AiC3 of the filler material, whereby AiC3 is equal to 910-(203 C)e1/2-30 Mn + 44,7 Si [degC].