The invention discloses a longitudinal
seam welding device and method for a cylinder of a
pressure vessel, and relates to the technical field of longitudinal
seam welding of pressure vessels. The four pairs of
welding guns are arranged and define a rectangle, the
welding guns at the two ends synchronously face the center of a
welding seam to conduct welding, welding stress is concentrated towards the middle of the welding seam, the pressing wheels are arranged on the two sides of the welding guns, the rotating directions of the pressing wheels point to the welding seam, and welding seam fusion materials are promoted to flow towards the center of the welding seam. By simultaneously applying internal and external synchronous welding and welding two longitudinal seams from the two ends to the center, heat input and cooling in the
welding process are symmetrical in the circumferential direction, and then transverse contraction force and
longitudinal contraction force generated by contraction of the welding seams are equal in magnitude and opposite in direction in the symmetrical positions; the mutual restraining and counteracting capacities are greatly enhanced, so that the influence of welding stress is reduced, shearing force generated by rotation of the pressing wheels drives
molten metal to migrate towards the center of a welding seam, and the
undercut defect is reduced.