This paper examines the characteristics of butt welding joint shrinkage for shipbuilding and marine structures main plate.
The shrinkage strain of butt welding joint which is caused by the process of heat input and cooling, results in the difference between dimensions of the actual parent metal and the dimensions of design. This, in turn, leads to poor quality in the production of ship blocks and reworking through period of correction brings about impediment on improvement of productivity. Through experiments on butt welding joint’s shrinkage strain on large structures main plate, the deformation of welding residual stress in the form of I, Y, V was obtained. In addition, the results of experiments indicate that there is limited range of shrinkage in the range of 1 ∼2 mm in 11 t ∼21.5 t thickness and the effect of heat transfer of weld appears to be limited within 1000mm based on one side of seam line so there was limited impact of weight of parent metal on the shrinkage. it has been learned that Shrinkage margin needs to be applied differently based on groove phenomenon in the design phase in order to minimize shrinkage.
The works for main plate of vessel take place at the time of the cutting for large steel plate and plasma cutting method is mainly used in shipyard in consideration of production efficiency and cost. In case of I and Y type grooves at welding joints in design shape, it has a characteristic that plasma cutting section for butt welding joints is usually cut with round shapes not at a right angle, which also affects the metal dawn for butt welding joints. It is observed that the formation of irregular cutting section provides a phenomenon that materials of butt welding are not completely adhered to each other when tack welding is applied. It is also confirmed that the gap of welding joints brings about the irregular welding deposition and heavily influences welding shrinkage by changing its welding temperature. Thus, it is concluded that a regular inspection of cutting machine and its related correction work are important factors to keep the quality of cutting section by stabilizing welding shrinkage of butt welding.