Study on improvement of Locally Drying Underwater Welding Joint by Retarted Cooling Method

Abstract

A retarded cooling method was conceived to improve the quality of the welded joints obtained with the "locally drying underwater welding method", and underwater welding test using this retarded cooling method was carried out. The test results are summarized as follows:
1) From the heat conduction analysis of the instantaneous plane heat source and the base metal around which was cooled with water, it was clarified that when the ideal insulation material of 100 mm wide and 300 mm long at maximum was applied around the groove to be welded, the welds obtained with the above underwater welding method were cooled to 300°C at nearly the same rate as that on land.
2) In the test, the insulation material of l mm thick and 100 mm wide was firmly applied on either side of the groove to be welded on both of the top and bottom surface, and also the shielding material which traveled with the welding torch was provided. When underwater welding was made using these insulators, the validity of the above heat conduction model was almost proved. Further the welded beads produced by this method had a hardness similar to those made on land.
3) Significant improvements were observed in the mechanical properties, such as elongation, reduction of area tensile strength, bending ductility, and Charpy absorved energy of the joints welded by the locally drying underwater welding system using this retarded cooling method, as compared with those of the welds obtained by the same system not using the retarded cooling method. The values obtained by the test were quite near to those of air welds.
4) In the three-point bending COD test, the temperature at, which stable slow crack occurred in the weld produced by this method prior to brittle fracture was 30°C lower than that in the weld obtained by the previous method, namely; -130°C--110°C. These values are little different from thosee of air welds.