Finite Element Analysis On Stress Intensity Factors Of Piping Branch Junctions With Cracks

Branch junction is an engineering component widely used in petroleum chemical industry and it is of great significance for branch junction to operate safely. Using ANSYS finite element technique and 3D singularity element, numerical simulations have been conducted towards d/D=0.5 welded branch junction to get stress intensity factor of the through-wall crack tip under the combined effect of internal pressure and moment load of the tip on the main pipe. Under the load of internal pressure, when cracks are in the middle of the run pipe, typeⅠcrack is the dominant crack and the numerical value is hundreds times of typeⅡand typeⅢ. The situation of the cracks in the branch pipe and the situation of the cracks in the run pipe are almost same, both the dominant crack type is the typeⅠcrack.When the positions of the cracks are getting transformered and the branch junctions are under the load of internal pressure, the crack position transformation parameters alpha in the range of 0°～60°. It is not that the closer the position of the crack to the weld area, the stress intensity factor is becoming lager, that is, the more dangerous the crack is. But the alpha crack position in 52 degrees nearby and the typeⅠandⅡstress intensity factor has a minimum value, when crack appeared in this area,it is is not in very danger, and then as to weld area and increased gradually. And with the alpha increases in the weld area, the value of stress intensity factor has increased gradually.When the cracks are in the shoulder of the branch pipe, the typeⅠand typeⅢcrack are the dominant crack type, because of the crack symmetry place is a symmetric constraint, under the load of internal pressure in the area of crack tips there has the typeⅢcracks.When the branch junctions with cracks in the shoulder of the run pipe are under the load of in-plane bending moment, the dominant crack type is typeⅢcrack and the value stress intensity factor of typeⅠis small.When the branch junctions with cracks in the abdominal area of the run pipe are under out-of-plane moment on the run pipe, the crack of typeⅡis the dominant crack type and the value of stress intensity factor of typeⅡand typeⅢare small.Type crack and three type crack stress intensity factor of the numerical smaller. In the surface bending moment, abdominal cracks crack end of the crack, two numerical sliding type crack is bigger. When the branch junctions with cracks in the abdominal area of the run pipe are under in-plane moment on the run pipe, the crack of typeⅡis the dominant crack type and has a high value.Meanwhile, the thesis presents the stress intensity factor of abdominal part of the dominant crack under the combined influence of internal bending moment, out-of-plane bending moment of shoulder part of the dominant crack. The results of the thesis could provide reference value to the actual engineering operation.