YAG Laser Welding Certification Test Results in Underwater Environment

摘要

This paper is a sequel to "Development of Underwater YAG Laser Repair Welding Robot for Tanks" presented in ICONE-7. There are 2 purposes in this new study, the one is an evaluation of certification test results, and the other is a verification of this technology applying to the actual RW (Radioactive Waste) tanks. The most serious concern of applying this underwater YAG Laser welding to the actual tanks is the possible penetration to the tank wall. Generally, repair-welding work is performed according to these steps below, degradation area detection, crack removal and edge preparation, repair welding, and inspection. If remained tank wall thickness is thinner than 2 mm, underwater repair welding can not be applied because the tank wall will be penetrated by the laser beam. Therefore the minimum wall thickness of after-edge preparation, which we can apply this technology is determined as 2 mm. Still more in this case, the heat input of YAG Laser should be also lower. We had performed YAG Laser welding certification tests with 3 kinds of welding positions (flat, horizontal, and vertical upward) in 2 kinds of environment. In one case welding torch's side is underwater environment, and the opposite side is air environment (actual case in tank inner wall weld repairing). In the other case both sides are underwater environments. We found there is a difference between their welding beads. The bead penetration depth of the former is deeper than that of latter. After all it is easy to penetrate in which the welding torch's opposite side is air environment. So we had performed a lot of certification tests with the former condition. And also we compared the mechanical properties between YAG Laser welding beads in underwater environment and conventional TIG welding beads in air environment. We found the corrosion tests results and the residual stress are almost same.