WELDING METHOD OF THICK WALLED STEEL PIPE FOR BENDING ROLL WITH HIGH EFFICIENCY

摘要

PURPOSE:To eliminate welding defects and to improve welding efficiency in the stage of subjecting the inside surface of the groove of a blank steel plate to multi-electrode submerged arc welding by specifying root pass conditions and sepcifying the angle of the butt part on the outside surface side and the quantity of welding heat input. CONSTITUTION:The inside surface side 2 of a blank steel plate 1 for a steel pipe having a prescribed thickness is beveled 4 at such an angle alpha (about 25-40 deg.) at which a groove depth of about 0.4-0.6 times the plate thickness is attained. Such plate 1 is formed and the ends are butted to each other. The outside surface side 3 is partially tack welded and the groove 4 on the inside surface side is subjected to multi-electrode submerged arc welding. The 1st electrode current is set at <=750A and the current of the 2nd and succeeding electrodes is set at 0.70-0.90 times the electrode current just before the same as root pass conditions in this stage. The root pass is accomplished in such a way that the relation between the angle theta at the butt part on the outside surface side and the quantity of welding heat input (H.I.kJ/cm) attains -3.67theta+69<=H.I.- 3.67theta+99, when theta<=10 deg., 32<=H.I..-36.7theta+99 when 10 deg.<=theta<=16 deg. and H.I. <=32 when 16 deg.<=theta. The quantity of heat input for the 2nd and succeeding leayers is set according to the plate thickness.