Study On The Coupling Effect Of Cutting Residual Stress On Crack And Subsequent Welding Residual Stress Of Offshore Platform Leg Slab

The processing of offshore platform leg rack involves two processes that cutting and welding,machining process is complex,there are a great impact on the life of the marine platform because of the thermal cutting,welding residual stress and the initial defects.Thermal cutting and welding are often orderly acting on the rack structure,In the process of processing and shaping rack structure,the residual stress field of cutting and the welding residual stress will happen the coupling effect,the formation of residual stress distribution form complex coupling.At present,there are few studies about the cutting and welding residual stress of the pile leg plates at home and abroad,so it is necessary to study the distribution of residual stress in the plate cutting and welding process.This article is based on the characteristics of the marine pile legs cutting and welding process,conducting the thermal elastic-plastic finite element analysis,and carry out numerical simulation about the oxygen cutting and welding process by ANSYS,the main contents are as follows:First of all,build the oxygen cutting heat source model that is applying to marine pile legs,and based on the life and death element technology,simulation flat cutting and tooth plate cutting process,and explore the regularities of distribution of residual stress of plate cutting.The results show that the residual stress is mainly longitudinal residual stress,and the residual stress in the heat affected zone is larger.And when the rack plate cutting,the residual stress in root place is the biggest,in the thickness direction,the maximum residual stress on the surface is greater than the middle region.Secondly,based on the numerical calculation of the cutting plane,the cutting crack model is introduced.By the numerical simulation,the residual stress redistribution law of cutting plane with initial crack is analyzed.The results show that cutting crack induces the residual stress redistribution.For the crack located perpendicular to the cutting direction,the residual stress in the surface of the crack front on the top surface of the model changes from tensile stress to compressive stress,and at the deepest depth of the crack front,the maximum tensile stress exists.The tensile stress decreases rapidly and is smaller than the ini tial stress value in the region approaching the crack front.For the cracks located parallel to the cutting direction,tensile stress near thesurface of the crack front on the top surface of the model is larger than the one before the crack is introduced.The tensile stress decreases rapidly and is smaller than the initial stress value in the region approaching the crack front.At last,the welding model of the rack plate,the tube and the continuous machining model of the cutting and welding are established.By the numerical simulation,the welding residual stress distribution law and the coupled residual stress evolution rule during the continuous welding process are analyzed.The results show that stress superposition phenomenon in the cutting and heating regions,and the trend of residual stress distributions during welding and cutting are similar,and the peak value of welding residual compressive stress is smaller than the welding residual compressive in single process.