Finite Element Analysis Of Magnetic Flux Leakage Testing And Ultimate Bearing Capacity In Pipeline Girth Weld

Pipeline transportation is a main form used to transport liquids and gases on land and sea.Welding is the main connection method for transportation pipelines.Girth weld welding is a key link in pipeline construction.Welding quality control is an important guarantee for the safe operation of oil and gas pipelines.In the process of long-term use,due to various complex conditions inside and outside the pipe,many defects often occur in the weld area of the pipe due to processing,corrosion,and external forces,which lead to a decrease in the strength of the pipe and seriously affect the safety and service life of the pipe.The regular inspection of in-service pipelines is of great significance for pipeline integrity assessment and life prediction.As one of the common methods of pipeline non-destructive testing,magnetic flux leakage internal detection has the advantages of low requirements on the pipeline environment,no coupling,wide application range,low price,etc.and it is widely used.In this paper,based on the principle of magnetic flux leakage detection technology,using finite element method,using ANSYS software to simulate the leakage magnetic field generated by common defects in pipe girth welds and welds,the magnetic flux density radial direction describing the characteristics of magnetic field distribution is obtained.At the same time,using ABAQUS finite element software and referring to the groove shape of the actual pipe girth weld,a nonlinear finite element analysis model for the girth weld of the pipe with defects is established,and the pipes with defects under different loads are established.The stress analysis of the girth weld is carried out,and the influence of the defect type and size,the weld reinforcement,and the material properties of the heat-affected zone on the stress distribution of the girth weld of the pipeline with defects is discussed.The results show:There is a positive correlation between the radial deformation of the defects(wrong edges,undercuts,pits,pores,and crack-like)in the typical defects of the pipe girth weld and the axial component of the magnetic flux density in the magnetic flux leakage distribution curve and the peak value of the radial component.According to the distribution characteristics of the leakage magnetic field of different defects: It can be seen from the distribution characteristics of the leakage magnetic field of different defects: the smoother the transition of the wrong edge defect,the smoother the magnetic flux density distribution curve;the shape of the undercut and pit defects are different,and the undercut is uncontrollable in the actual processing process,and the magnetic leakage signal is Geometry is closely related;because of its location affected by the outer wall material,buried pore defects are more difficult to detect than other types of defects.The ultimate bearing capacity and the peak stress position of the circumferential weld of the defective pipe are related to the load of the pipe.The amount of misalignment is negatively correlated with the ultimate bearing capacity of the pipeline.The calculation results in this paper are consistent with the safety range specified in the pipeline design;the pores cause the local stress around the hole to increase significantly,but the influence range is only within a small range around the pore.The stress distribution of the pipe body is uniform,and the maximum stress position is related to the load.For buried pores,the current standard for pore defects of3 mm size control index is applicable to X60 pipelines,but if it appears near the surface of the pipeline,this value is not applicable;the depth of pits and crack-like defects has the most obvious effect on the stress of the pipe girth weld.As the depth increases,the ultimate bearing capacity of the pipe decreases significantly;an appropriate amount of excess height at the girth weld can effectively play a reinforcing effect,but the girth weld reinforcement exceeds the appropriate height,stress concentration occurs at the weld toe position obviously,and the maximum equivalent stress position of the pipeline under tensile load is transferred to the heat-affected zone,which reduces the joint strength.The paper has 84 pictures,12 tables,and 95 references.