Computational method to assess the residual stresses of thick plate joined by two-pole tandem EGW in marine vessels

초록

Shear strakes or deck plates of large container carrier and FPSO vessels are joined by ultra-thick plates whose thickness is more than 60mm. Traditionally FCAW(Flux-Core Arc Welding) has been used to join the ultra-thick plates. However, FCAW has been replaced with EGW(Electro-Gas Welding) since the welding efficiency of EGW is higher than that of FCAW. Two-pole EGW has been applied to vertical position welding by several shipyards. EGW requires one or two layers of bead whereas FCAW requires more than 20 layers of weld bead in thick welding. However it uses higher heat input than FCAW. Therefore high welding residual stresses are generated by EGW. It is known that the high residual stress may shorten the fatigue strength of the joined structure. The residual stress should be investigated when EGW is applied to the thick plate joining. Present study explains a computational method to analyze the residual stress of EGW in the thick plates. Based upon the FEA (finite element analysis), both profile and level of the residual stresses are studied for EH40 TMCP (Thermo-Mechanical Control Process) steel plates with thickness of 80mm. Also, peculiar stresses of butt joint specimens are measured by X-ray diffraction method to assure the results of the FEA model