Research on the compensatory welding method for preventing welded joints of polyhedral shells from fracturing during hydrobulging

This paper first introduces the basic principle and the main advantages of the new die-less hydrobulging technology for manufacturing spherical vessels. Then, it analyzes the phenomena that result in the fracture of polyhedral shells during hydrobulging, coming to the conclusion that the concentration of plastic strain at the inside weld toe and the reduction in the plasticity of the heat-affected zone (HAZ) are the main reasons for fracturing. Based on the analysis, a new technological method - the compensatory welding method (CWM), which consists of two transferring beads and a tempering bead - is proposed to prevent the welded joints from fracturing. Finally, it establishes, by means of a substantial amount of experimental research, that the reasons why the compensatory welding method is able to improve the plasticity of the welded joints and prevent fracturing are: (i) that the transferring beads change the direction of the inside bond line, improving the shape profile of the weld toe; and (ii) that the tempering bead improves the microstructure of the HAZ, reducing its hardness such that its plasticity is increased.