Objectives  The welding distortion of block structures in the fabrication of semi-submersible lifting and disassembly platforms influences their dimensional accuracy and production schedule.

  Methods  Thus, taking a B514 block as the research object, the tendency and magnitude of its out-of-plane welding distortion are predicted in advance, and the influence of inverse deformation and welding sequence are examined for fabrication accuracy enhancement. Next, typical welded joints and their welding conditions are summarized, and effective thermal-elastic-plastic finite element (FE) computation is carried out to examine the thermal-mechanical response and evaluate the inherent welding deformation. With inherent deformation as mechanical loading, elastic FE analysis is then employed to predict the dimensional accuracy of the B514 block. Moreover, the influences of inverse deformation application and different welding sequences on dimensional accuracy are also examined.

  Results  Based on elastic FE analysis with inherent deformation, the computed out-of-plane welding distortion is found to be in good agreement with the measurement, and its generation mechanism is also clarified.

  Conclusions  Effective FE analysis can be employed to predict the inherent deformation and distortion of complex welded structures; moreover, inverse deformation application and an optimized welding sequence can significantly reduce welding distortion.