Abstract: For big diameter full welded body ball valve, welding is the last process. Because it is sealed with rubber grommet, in order to prevent the grommet from damaging and assure the tightness, post-weld heat treatment (PWHT) method cannot be used to relieve the residual stress. Therefore, mechanical stress relieving method (MSR) is selected to control the welding residual stress of valve body and the relationship between load and time is established. The effect of mechanical stress relieving method on the welding residual stress is researched through both finite element method (FEM) and test. The residual stresses on the outer surface of valve body are measured using the blind hole drilling method before and after welding. The results show that the mechanical stress relieving method can be simulated by 2-D axisymmetric finite element method. MSR treatment can decrease the peak value of axial residual stresses and hoop residual stresses on the outer surface and make the residual stresses distribution more uniform. MSR treatment can replace the PWHT method to relieve the residual stress.

Key words: Finite element method, Full welded-body ball valve, Mechanical stress relieving method, Welding residual stresses