Prediction of welding distortion in multipass girth-butt welded pipes of different wall thickness

For a full welded body ball valve, because the last working procedure is the weld, prior to welding, the welding distortion must be accurately predicted to provide preference for welded structure fabrication at the design stage in order to assure spool rotation, valve seal, and non-deformability in active service. Therefore, it is important to select an accurate and efficient method to predict welding distortion. In this study, the finite-element method based on the inherent strain theory was presented to simulate welding distortion in multipass girth-butt welded pipes of different wall thicknesses. For multipass welding, two weld passes at the same layer were combined. The axial distortion of each weld layer was calculated respectively and the radial distortion was calculated for one time. For multipass girth-butt welded pipes of different wall thicknesses, two methods were proposed to predict the axial distortion. The results calculated were compared and better method was confirmed.