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چكيده انگليسي :

Simulation of Geometrical Imperfections Due to Cold Field Bending of Large Diameter Pipes Mahdi Bonyadi m bonyadi@me iut ac ir Date of Submission 2011 07 9 Department of Mechanical Engineering Isfahan University of Technology Isfahan 84156 83111 Iran Degree M Sc Language Farsi Supervisor Mohammad Reza Forouzan forouzan@cc iut ac ir Abstract In recent years with the increase in demand for the conveyance of energy the technology of designingand manufacturing of seam welded steel pipes has been developed prominently During the operations ofthe establishment of water or oil conveying pipes the topography of the course necessitates that somepercentage of the pipes need to be bent This bending is done mostly at the site of the pipelinesestablishment with the cold field bending machine During the bending some defects such as ovality wallthinning wall flattening and wrinkling are made and these defects limit the bending angle To prevent theoccurrence of such defects the manufacturers of cold bending machines suggest the use of a mandrel whichis settled inside the pipe in the bending zone and it reduces the formation of geometrical imperfections toan acceptable extent In Iran installer companies refrain from using mandrel in bending of large diameterpipes The absence of mandrel is more apparent in bending of spiral pipes and the geometrical defectscaused in them are more prominent Therefore installer companies in Iran choose straight seam pipes forbending and of course they reduce the extent of bending in order to lower occurrence of geometricaldefects This case is a limiting factor in the use of spiral pipes The main goal of this dissertation is thesimulation of the cold bending process of large diameter straight and spiral pipes with the purpose of theprediction of geometrical imperfections in these pipes In this research the cold bending of straight and spirally welded pipes has been modeled in the ANSYSSoftware for pipes with 12 meters length 48 inches in diameter and thickness of 20 6 mm The pipes usedin this research have been of the Type X65 steel and in order to consider the Baushinger Effect kinematichardening model has been used In the finite element simulation of pipe bending the effect of parameterssuch as curve radius and Die length pipe material weld stiffness diameter of the pipe and also anisotropyon geometrical defects has been studied In addition with the suggestion of a model for a mandrelsimulation the extent of producing an effect on geometrical defects has been explained In the modelsuggested the mandrel has been modeled with spring elements and its elastic modulus has been calculatedin the way that its hardness be equivalent to that of the mandrel s Also in this dissertation process of spiralpipe manufacturing has been modeled and the residual stresses have been calculated The results of this research show that increasing the bending radius causes an improvement in thequality of the bend Besides the consideration of the welding stiffness in the bending simulation of straightseam pipes causes a reduction in the ovality and wall thinning but increasing the weld stiffness in spiralpipes contrary to straight seam pipes increase the ovality and intensifies geometrical imperfections in thesepipes Simulations show that sheet anisotropy pipe does not have a prominent effect on the extent ofdefects while applying anisotropy on a spiral pipe has disturbed the symmetry of the residual stresses in thepipe wall Using a mandrel inside the pipe has severely reduced the extent of ovality By using a mandrel wrinkling and flattening have been completely removed and a perfect bend has been shaped Keywords Spiral Pipe Straight Seam Pipe Residual Stress Cold Field Bending Mandrel Geometrical Imperfection Weld Stiffness Plastic Anisotropy

بنيادي، مهدي

شبيه سازي عيوب هندسي در خمكاري سرد لوله هاي قطور

لوله اسپيرال , لوله درز جوش مستقيم , تنش پسماند , مندرل , سختي جوش , ناهمسانگردي پلاستيك