Research On Fatigue Properity Of A High Deformablity Pipeline Steel Weld Joins

The pipeline steel’s fatigue property is the important parameters of the pipeline design parameters, but the reserve on the fatigue property of double phase large deformation pipeline steel is less. Therefore, the fatigue property reservation of large deformation pipeline steel and the welding joint on pipeline safety design have important significance.Tensile test, microhardness test, fatigue test are employed in this to test the X80 large deformation pipeline steel weld joint’s properties; metallographic microscope,scanning electron microscope(SEM) are employed to study the X80 pipeline steel, the tissue of welding joint and the fatigue fracture. The experiment results show that the welding joint’s tensile strength is 620 MPa, the relationship between welding joint’s fatigue life and stress is S=4366 ? N-0.18, while the fatigue life is 1 ?106, the fatigue strength is 321 MPa. Compared with the base mental, the fatigue strength is about100 MPa lower in the same fatigue life.The fatigue crack of X80 large deformation pipeline steel welding joint is generated around the weld-fusion line zone, and propagated inward along welding heat affected zone. As the crack propagated to a certain degree, the crack quickly fractures along welded seam. Deposited metal biting edge and inclusions and the stress concentration because of the weld residual high and the HAZ property deterioration were the reason of the fatigue creak generation, the grain of CGHAZ(Coarse Grained HAZ) grow bigger due to rack quickly fractures, the hardness of FGHAZ(Fine Grained HAZ) become lower due to the fatigue creak quickly.