RESIDUAL STRESS IMPROVEMENT IN REPAIR WELDED PLATES USING WATER-SHOWER COOLING DURING WELDING PROCESS

摘要

To reduce tensile residual stress at a repair-welded area, a method that applies water-shower cooling behind a torch was developed. The width of the repair-welded area in this study was 27 mm, while the maximum width of welded areas in previous studies was 18 mm. To examine how much the welding method reduced residual stress at large-width welds, we first applied the method to multipass bead on plate specimens. The first layer consisted of a five-pass bead. A single large-width weld pass was applied with water-shower cooling. To cover the five-pass bead on plate area with a large-width weld, the torch was moved in a weaving motion. Residual stresses were measured. The measurements showed that tensile stresses remained in the five-pass bead on plate specimen. The tensile residual stresses were improved to compressive when our welding method was applied at the large-width weld pass. Then, we applied our method to a repair-welded specimen. The specimen was a butt-welded joint with an X-shaped groove. Repair welding was performed around the boundary of the welded area. A single large-width weld pass with water-shower cooling was applied at the surface. Residual stresses were measured. The measurements showed that tensile stresses remained on the surface of the X-shaped groove welding. Tensile residual stresses increased around the repair-welded area. When our welding method was applied, residual stresses were improved to compressive. Therefore, our welding method can reduce tensile stress in a repair-welded plate.