Research On Weld Residual Stress Analysis And Safety Assessment Of Half-pipe Jacket

The half-pipe jacket is widely used in chemical,pharmaceutical and other industries as heating and cooling equipment because of its advantages such as high strength,high heat transfer efficiency and saving consumption of steel.However,residual stresses are inevitable when half pipe is welded on the cylinder.And welded joint will become the weakest link for complex stress state under the external load,which usually leads to leakage.So it is very meaningful to make research on weld residual stress and safety assessment of half-pipe jacket.This paper analyzed the temperature and stress field fully for three types of groove(45degrees outside groove,no groove and 2mm parallel groove)by the finite element software ABAQUS,and the affect of pipe diameter and distance was also researched.Three types of welding lines and macroscopic structures were compared by experiments.The stress of half-pipe jacket with three different types of groove were analyzed accurately by the linear elastic fracture mechanics method,and safety assessment was also done which regards groove as defect(external crack).The results are as follows.(1)The root of the half-pipe jacket with different groove has different distribution of temperature field,and the highest peak temperature occur at 45 degrees of outer groove and exceeds the melting point.And for no groove or 2mm parallel groove,the temperature of the root didn't reach the melting point and the root was welded incompletely,which reduced the mechanical properties.For 45 degrees of outer groove,excellent weld was formed and the surface metal oxidation for cylinder was also reduced at the welding process,even plasticity,toughness and properties of low temperature of the weld metal was enhanced.However,serious defects of incomplete weld was found for no groove and the weld corner defects exist at the weld root for 2mm parallel groove.The groove reduces the residual stress in the weld root,particularly for stress of thickness direction,which is helpful to reduce the sensitivity ofthe stress corrosion cracking for half-pipe jacket.(2)The half-pipe jackets with the different types of groove have different weld residual stress distribution.The maximum value of residual stress existed at no groove type when the residual stress value of 2mm parallel groove is decreased,and the residual stress value of45°outside groove reduced significantly.Therefore,the 45 degree outside groove is suitable for real conditions.The effect of changes of half-pipe diameter on transversal stress is larger and on longitudinal stress is smaller.However,the total stress is minimum when diameter of half-pipe equal to 25 mm which means it is the optimum choice.Increment or decrement of the half-pipe pitch affected transversal stress and longitudinal stress and its effects on transversal stress larger than longitudinal stress.Considering the total stress,the half-pipe pitch which equal to 30 mm is the best.(3)The stress analysis and safety assessment were done for three types weld joint with different groove.The no groove should be avoided,because the serious defects of incomplete weld were found and the peak stress reached 269 Mpa which exceeded yield strength.And 45 degrees of outer groove and 2mm parallel groove were satisfied with requirements through assessment.Considering the results of weld residual stress,45 degrees of outer groove is the better one.As a conclusion,45 degrees of outer groove and keeping a certain gap should be recommended in the welding process for half-pipe jacket.