Research On The Influence Of Welding Process On Residual Stress Of Composite Pipe Joint

The safety end of the connecting pipe is a dissimilar steel welded structure in the steam generator.The shell structure of the pressure vessel is made of low alloy steel,and the circuit pipeline connected to it is generally made of austenitic stainless steel material that is resistant to high temperature and high pressure corrosion.When welding low alloy steel pressure vessel and stainless steel pipeline,due to significant differences in chemical composition,physical properties,and mechanical properties of different materials,the residual stress generated by welding and the high temperature and high pressure working conditions of the component service make the welded joint prone to cracking.Therefore,it is necessary to explore the influence of welding process on the residual stress in composite pipe welding.This article takes composite pipe joints as the main research object,with a low alloy steel side of 10 Mn Ni2Mo V.It has undergone E16-25 Mo NA507 pre surfacing,E318 V surfacing layer surfacing,heat treatment,and E318 V docking processes.Numerical simulation and experimental methods are used to explore the influence of different processes on residual stress in joints.The microstructure analysis of the composite pipe joint using the original welding process shows that the microstructure of the pre deposited edge is austenite,and the microstructure of the deposited layer is austenite+ferrite.Obvious intergranular cracks can be observed on the axial section and outer surface of the pre stacked edge.In order to accurately analyze the residual stress of the joint,this article tested the physical and mechanical properties of the base metal,pre stacked edge,and welding layer.The results showed that the elongation after fracture of the pre stacked edge was significantly reduced at high temperature,exhibiting obvious hightemperature brittleness,making the pre stacked edge prone to producing micropores and possibly further expanding into cracks under welding stress.Analyze the effect of the number of layers of overlay welding on the residual stress of composite pipe joints.Compared with the two layers of overlay welding,the peak stresses in circumferential,axial,and radial directions are all reduced in the three layers of overlay welding;The stress reached its peak in the pre stacked edge area,and the equivalent stress peak decreased from 552 MPa to 447 MPa.It exceeded the yield strength of the material when welding two layers,and the optimized welding process was welding three layers.On the basis of three layers of overlaying welding,the heat treatment process was carried out,and the stress distribution of the joint was uniform.The effective force of pre stacking edge was reduced to 230 MPa,and the heat treatment significantly eliminated the residual stress level after overlaying welding.After the heat treatment process,the effect of the number of butt welds on residual stress was analyzed.The equivalent stress was mainly distributed in the bottom area of the pre stacked edge.The peak stress of the pre stacked edge of the 19,26,and 37 butt welds was 382 MPa,365 MPa,and 291 MPa,respectively.The optimized number of butt welds was 37.Under the optimized process,the equivalent stress distribution of the composite pipe joint and the flat plate joint is consistent,reaching the peak stress in the bottom area of the pre stacked edge.The peak stresses of the two types of joints are 291 MPa and 306 MPa,respectively,indicating that the residual stresses of the two types of joints are basically the same;The contour method was used to validate the optimized welding process,and it was found that the longitudinal stress level of the flat plate joint was high in the surface layer area of the butt welding cover.The peak stress at the pre stacked edge was 252 MPa,which was not significantly different from the numerical simulation result of 268 MPa.Moreover,no cracks were found in the pre stacked edge area of the optimized welding process for the flat plate joint,indicating the accuracy of the optimized welding process.