Study On The Law Of Welding Stress And Strain In Circumferential Joint Of Low Alloy Steel Pipes

Pipes structures are widely used in the vital departments of national economy, such as chemical and oil industries. The residual stress and strain produced during the welding process will affect the service life of components. So, carrying out the study on the law of welding stress and strain in circumferential joint, discuss the effect of material properties, pre-deformation, prestress, heat treatment, etc. and compare the results under different models can provide theoretical basis to control, adjust and reduce the welding residual stress and strain, which are of important academic value and practical significance.This paper is based on the thermal-elastic-plastic theory and the platform of ANSYS finite element software. Plate element model, shell element model and three-dimensional model element model of welding temperature field and stress-strain field in circumferential joint of Low Alloy Steel Pipes are founded and influence law of various parameters on the welding stress and strain is discussed. The residual stresses of circumferential joint are measured using the blind hole method, which are compared and verified with values of the finite element method. The paper covers the following aspects concerning the main work and research in the project.A two dimensional plate element axisymmetric model of welding temperature field and stress-strain field in circumferential joint is founded and the distribution of temperature field and stress-strain field during the welding process are obtained. Parameters such as the mesh density, weld model, heat source model are optimized and the influential trend of thermal conductivity, specific heat, thermal expansion coefficient to the welding strain are obtained in this paper.A shell element model of welding temperature field and stress-strain field is founded, whose welding residual stress and strain distribution are obtained. The distribution of axial stress is related to the "additional bending stress" caused by the radial contraction around the welding seam. The influence of pre-deformation, prestress, heat treatment on the welding stress and deformation are analyzed in detail, which proves the feasibility to decrease the deformation near the weld seam, using the process above.A thress dimensional model with moving heat sources of welding temperature field and stress-strain field is founded and the "deposition" phenomenon during the welding process is realized with the help of"birth and death"method. Apparently,"concave"radial deformation at the weld and weld vicinity and axial contraction in the joint at both ends are produced. The hoop residual stress on inner surface of pipe is large, which manifested as tensile stress and they are gradually transferred into compressive stress with the increase of the distance from the weld seam. On the inner surface, the hoop residual stress at the weld and weld vicinity is smaller relatively. The axial residual stress at the weld and weld vicinity on the inner surface manifested as large tensile stress while the axial residual stress manifested as compressive stress.The simulation of plate element and shell element models can be used for references with three-dimensional solid element model. But the plate element model can not realize the movement of heat source and the shell element model can not achieve the relation between layers of multilayer welding. So when carrying out the simulations for large diameter or thin thickness pipes, three-dimensional solid model should be used for finite element analysis to ensure accuracy.The welding residual stresses of circumferential joint are measured and calculated, using blind hole method. By comparing the welding residual stresses, the experimental and calculated values agree well, which verifies effectiveness and correction in the calculation of three dimensional finite element models.