Large welded tubes are primarily used in oil pipelines and offshore platforms. They are actually produced by the steelmaker industry ILVA-Laminati Piani, Taranto (Italy). The production process is characterised by three phases: (1) forming; (2) welding and (3) calibration. In addition, the first phase is composed by three steps: the forming of the longitudinal border of the blank (C-forming); the air bending of the C-formed blank (U-bending) and the forming inside a circular shaped die of the U-formed blank (O-forming). After the welding phase, the final forming operation (calibration) is performed to correct the tube distortion due to the thermal input using a special purpose machine (expanding machine). In the present work, the calibration phase is investigated using the finite element (FE) method. Both 2D and 3D FE models have been used. The 2D analysis has been aimed to obtain the tube profile after the forming phase (simulation of the C–U–O forming steps); in addition the simulation of the calibration phase has also performed under the hypothesis of plane strain condition, but not accurate results have been obtained. On the contrary, the 3D FE analysis has allowed to accurately investigate the calibration phase; two different numerical models have been used: the first one considering a cylindrical tube (the tube profile obtained by the previous 2D simulation was simply extruded along a straight line); the second one modelling the tube inflections due to residual stress after welding (the real tube section has been extruded along a circular path, according to experimental data). The aim of this search is to investigate stress and strain state in the tube; in particular the action of the expanding machine is simulated and the effect on the tube section end profiles and on the tube lengthwise inflection have been evaluated. The possibility of both obtaining a good circular shape of the tube section and correcting the lengthwise inflection is investigated. The FE model is defined according to data coming from the workshop: the sheet material is X70 steel and initial blank dimensions are 14,000mm×3000mm×27.5 mm.
|Titolo:||Effect of forming and calibration operations on the final shape of large diameter welded tubes|
|Data di pubblicazione:||2005|
|Digital Object Identifier (DOI):||10.1016/j.jmatprotec.2005.02.150|
|Appare nelle tipologie:||1.1 Articolo in rivista|