بررسي تاثير تنش هاي پسماند ناشي از فرآيند جوشكاري در خمكاري سرد لوله هاي قطور

چكيده انگليسي :

Effect of Welding Residual Stress in Cold Bending of Large Diameter Pipes Ali Mokhtari a mokhtari@me iut ac ir June 6 2011 Department of Mechanical Engineering Isfahan University of Technology Isfahan 84156 83111 IranDegree M Sc Language FarsiSupervisor Dr M R Forouzan Email Forouzan@cc iut ac irAbstractNowadays using large diameter seam welded pipes in order to transfer oil and gas between cities orcountries is greatly increased Because of the high speed and efficiency of submerged arc welding SAW this method is widely used in production of spiral SSAW and direct seam pipes LSAW The qualitycontrol of the welded pipes usually consists of a hydrostatic test in which water is pumped into the pipe High pressure hydrostatic tests can moderate tensile residual stress caused by the welding process This isof great importance because the test can increase the pipe lifetime by decreasing the rate of stress corrosioncracking and or fatigue Cold bending of large diameter pipes is depended to the local topology Bend angle and curvature is limitedin cold bending This process is generally performed at the assembly site with special pipe bending machinebased on three roll bending The main goal of this dissertation is to study the effect of welding residualstresses in cold bending process of large diameter pipes Therefore a good estimation of welding residualstress fields in the whole length of the pipe is needed In the first step of the present study three dimensional model of submerged arc welding in spiral and directseam pipes are simulated by using Ansys commercial software A decouple thermal mechanical model isdeveloped in welding simulations and Thermo physical and mechanical properties used for weldingsimulations are depending on the temperature In thermal analysis the weld heat source model based on theGoldak s double ellipsoid power density distribution was applied After the thermal model was analyzedand the temperature history was achieved the mechanical model was investigated Finally the weldingresidual stress distributions were calculated It was seen from the longitudinal principal stress that there wasa huge tensile residual stress near the welding zone After welding simulations the effect of hydrostatic testprocess in decreasing the residual stresses is evaluated The welding simulation in spiral pipe is validatedusing hole drilling measurements performed before and after hydrostatic test in this research Then residualstresses are determined according to ASTM standard E837 Comparison between residual stressdistributions which measured by experimental and the numerical analysis are shown that obtained resultsfrom the FE simulations are in relatively good agreement with the experimental measurements Also theresults of this research show that applying a hydrotest pressure after welding process can reduce weldingresidual stresses up to 70 In the second step residual stress and strain fields which have been obtained in the former step aregeneralized to the whole length of LSAW and SSAW pipes Then the effect the resulted residual stresses ofwelding process are surveyed on the bending of LSAW and SSAW pipes and geometrical defects such aspipe ovality Results show that the spiral seam pipes are more sensitive to bending ovality than direct seampipes Key wordsSpiral pipe Direct seam pipe Submerged arc welding Hole drilling method Residualstress Hydrostatic test Cold bending

مختاري، علي

بررسي تاثير تنش هاي پسماند ناشي از فرآيند جوشكاري در خمكاري سرد لوله هاي قطور

لوله اسپيرال , لوله درز جوش مستقيم , جوشكاري زير پودري , روش كرنش سنجي سوراخ هايد روتست