Temperature Field Simulation And Metallurgical Analysis Of Underwater Wet Welding Process

Underwater welding technology is a key technology widely used in theconstruction, assembly and maintenance of ocean engineering steel structureequipments, which is of great significance to promote china’s marine development.Underwater welding usually can be divided into wet welding, dry welding and localcavity welding. Because of the simple equipment, low cost and strong adaptability,wet welding is the most commonly used welding method in shallow waterenvironment. However, the quality of wet welding joint is usually poor due to theinfluence of water. So how to improve wet welding technology and enhance thequality of welding joint has attracted researchers’ attention. In recent years, with therapid development of computer technology, numerical simulation technology hasbeen extensively applied and become a kind of important means on the research ofwelding process. In this paper, the3D finite element model of underwater wetwelding is established on the basis of experiment and the temperature field of weldingProcess is analyzed. Because the numerical simulation research of wet welding is veryrare, the study in this paper has an important significance and can provide atheoretical reference for choosing reasonable wet welding process and evaluatingwelding joint quality.On the home-made underwater welding experiment platform, underwater overlaywelding tests are performed and the suitable welding process parameters are obtained.Through comparing the macro morphology of wet overlaying welding joint to that ofland welding and observing the metallo-graphs, it is founded that the wet overlayingwelding joint has lager molten wide, shallower penetration and more low temperatureshift substances in the same welding parameter. The hardness test of welding jointalso shows that hardness of wet overlaying welding joint are higher than that of theland overlaying welding joint.Combining the characteristics of underwater welding with heat transfer principle,the heat conduction process of wet welding is discussed. Based on the water boilingheat transfer principle, the water convective coefficient changing with temperaturecurve is gained. Furthermore, it is used to develop a kind of SYSWELD subroutinefor describing the heat boundary condition in underwater wet welding. According to the forming characteristics of wet overlaying welding joint, oneeffective combined heat source model for the temperature field simulation is founded:gauss surface heat source+double ellipsoid heat source, and the power coefficientration of them is1.2:1. After this, the3D FEM model of wet overlaying weldingprocess is set up via SYSWELD and the calculation of temperature field is made. Theresult shows that the molten pool shape of simulation is consistant with theexperimental result. Based on simulation result, the dynamic change of weldingtemperature filed and welding molten pool are analyzed, as well as the characteristicsof temperature change of the points in different regions. Finally, the t8/5values ofHAZ is obtained by studying the temperature variation curves, which are used topredict the organization and performance combining with the CCT diagram of Q345.The predicting outcome is basically the same as the experimental one.