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A Study on Remaining Efficiency of Thermal Straightening after Block Lifting
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 Title & Authors
A Study on Remaining Efficiency of Thermal Straightening after Block Lifting
Ha, Yunsok; Yi, Myungsu;
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Deck plates of ships or offshore structures would make out-of-plane distortion for their thin thickness. These distortions are usually straightened by thermal straightening such as flame heating method. After thermal straightening, the blocks are lifted and moved by cranes to assemble it at dry-dock stage. After this lifting process, out-of-plane deformation again happens frequently. And then, they continuously cause quality and accuracy problems in the final dry-dock process. So, it takes more time for repair and correction working. According to preceding research, the lifting process by cranes would offset the effect on thermal straightening. The target of this study is to develop a methodology analyzing the remaining efficiency of thermal straightening after block lifting. The development was based on the assumption of yield state at straightening region. Therefore the remaining efficiency was obtained by different stiffness slope while lifting & relieving. The efficiency formula was designed using inherent strain, and we made a table of zero-efficiency by cooling speed and class rule's steels. As a result, if the stress orthogonal to straightened line is calculated during lifting analysis by FEA, the efficiency can be obtained linearly to the values in the table. Finally, even optimized carling position can be designed by considering the regional data from series project and welding region on deck.
Thermal Straightening;Lifting;Inherent Strain;Welding Deformation;Strain-stress Curve;Carling;FEA (Finite Element Analysis);
 Cited by
Ha, Y.S., Jang, C.D., Kim, J.T., and Mun, H.S., Analysis of Post-Weld Deformation at the Heat-Affected Zone Using External Forces Based on the Inherent Strain. International Journal of Precision Engineering and Manufacturing, 8(4) (2007) 56-62.

Ha, Y.S., and Jang, C.D., An Improved Inherent Strain Analysis for Plate Bending by Line Heating Considering Phase Transformation of Steel. International Journal of Offshore and Polar Engineering, 17(2) (2007) 139-144.

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Shin, S.B., and Lee, D.J., A Structural Design Approach for Controlling Welding Distortion at the Upper Deck of a Hull Structure in the Erection Stage. Metals and Materials International Journal, 17(1) (2011)123-130. crossref(new window)

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