Study On The Effect Of Weld Reinforcement On Fatigue Properties Of Welded Joint Of X80 Welded Pipe

With the continuous improvement of human demand for energy,humans have gradually put forward higher requirements for the transportation volume of natural gas.Therefore,the large-diameter,thick-walled,high-strength X80 pipeline steel has become the first choice for long-distance transportation of natural gas.At present,welded steel pipes are used in such pipelines.A large number of existing studies have shown that X80 welded pipes that have been in service for a long time are prone to fatigue failure at the welded joints.Therefore,research on the fatigue properties of the welded joints of X80 welded pipes has important engineering practical significance.In order to study the property changes of X80 welded pipe before and after the pipe end weld grinding,X80 welded pipe used in engineering project is taken as the research object in this work,and focuses on the influence of the X80 welded pipe's pipe end weld grinding and other processes on its structure and properties.Using experimental methods such as mechanical properties test,fatigue test,metallographic observation,scanning electron microscope observation,etc.,through processing the experimental results,the effect of weld reinforcement on the mechanical properties,fatigue properties,fatigue fracture and hardness of welded joints is analyzed.The results show that after removing the weld reinforcement,the mechanical properties of the welded joints of X80 welded pipes are basically unchanged,but their fatigue life has been greatly improved.After performing the above-mentioned butt-welded joint experiments,this paper establishes a finite element analysis model for the actual welded joint specimens of the X80 welded pipe and the welded joint specimens without reinforcement.The effect of weld reinforcement on the fatigue properties of the welded joint of X80 welded pipe was studied by finite element analysis method.The results show that the stress concentration at the welded joint due to the weld reinforcement caused fatigue cracks to initiate at the weld toe of the inner weld and expanded along with the coarse-grains zone,when the weld reinforcement is removed,due to the weakening of the strength of the fine-grained zone and the hardness difference between the coarse-grained zone and the fine-grained zone,fatigue cracks are initiated in the coarse-grained zone next to the fine-grained zone,and it expands along the fine-grained zone in the heat-affected zone,and the fatigue strength of the welded joint of the X80 welded pipe increases after removing the weld reinforcement.The simulation results obtained through finite element analysis are compared with the results obtained through experiments,and it is found that it is basically the same as the results obtained in the experiment,which further confirms that the established finite element analysis model is feasible and the results obtained are reliable,and further analysis the mechanism of the weld reinforcement on the fatigue properties of the welded joint of X80 welded pipe and the influence range of the stress concentration at the weld toe are discussed.