Method and welding system for welding inner angles of in-service steel structure bridge U ribs

The invention provides a method for welding inner corners of an in-service steel structure bridge U rib, the head end and the tail end of the U rib are each provided with a partition plate, and the method comprises the following steps that S1, a welding construction section is formed, specifically, a construction window used for welding is formed in the in-service U rib, the construction windows are located between two partition plates on the two sides of a welding seam of the U-shaped ribs and located on the two sides of a butt welding seam of the plate units where the U-shaped ribs are welded, and a welding construction section is located between every two adjacent construction windows. S2, the partition plates on the two sides of the construction window are cut, and the cut partition plates are taken out; s3, the cutting boundaries of the plate units and the U-shaped ribs are polished in one construction section, and the interiors of the U-shaped ribs of the welding construction section are cleaned; s4, ov