The Effect Of Machinery Expand On The Residual Stress Of X80 LSAW Pipe

Along with the pipeline manufacture technical development, the long-distance transportation pipeline plays more and more important role in our country energy strategy. Starts along with the"transporting natural gas from west to east"project, the domestically produced LSAW pipe has began to be used, and develops rapidly. during the construction of LNG and ocean oil project, not only has provided the turning point to the domestically produced LSAW pipe, simultaneously the high grade of steel, large diameter, great wall thickness using need also set a higher request to the pipeline quality.Residual stress is an important base value in LSAW pipe quality evaluation. Residual stress and deformation has affected the pipeline intensity gravely, and as initiation of weld crack, has become the significant incipient fault in pipeline safety uses. The expand in LSAW pipe production not only compliance to the geometry dimension request but also reduce the residual stress which generated in forming and welding steps significantly, having raised the pipeline working performance.This thesis provides an anylisis which specifically for the effect of expanding in reducing the residual stress in forming and welding stage. Based on the elasticity-pla -sticity deformation theory and heat elasticity-plasticity theory, using finite element software ANSYS make a simulation of forming,welding and expanding process, get the following achievement:Build up a 3-D finite element method model of forming,welding and expanding stage in LSAW production. Based on plasticity large deformation theory, contact fric- tion theory and heat-plasticity theory,made a global simulation of LSAW production process,got the residual stress distribution in each process.Simulating the machinery expanding process of different expanding rates ( 0.8%,1.0%,1.2% and 1.4%) for the LSAW pipe with forming residual stress and welding residual stress. On the different rates, residual stresses of weld-pipe are obtained. Analysis the fore-and-after changes of residual stresses for expanding and the different effect for releasing residual stresses.Residual stress testing having carried out to domestic X80 LSAW, the result shows that the FEM calculate result match the testing results accurately. The model-building and calculating work in this paper correspond to the actual process , have important guiding significance to LSAW production.The result shows that expanding technique have good effects on reducing the residual stresses that caused in the process of forminging and welding. After the reasonable expanding, peak value of residual stresses on the pipe wall obviously descend. In the range of this reseach, results show that the bigger the expanding ratio is and the effect on releasling residual stresses is better. For the X80 LSAW pipe, as considering the effects of releasing stress and remaining plastic, 1.2% expanding ratio is the best.