Analysis And Study For Stresses And Limit Load Of Reducer

Reducer is one of ordinary and important components for pressure piping, but little study about it has been done. Stresses analysis and limit load of bend reducer, concentric reducer and eccentric reducer under internal pressure, bending moment in plane and torque have been studied separately. The results have been examined by finite element method and experiment. The main results were summarized as follows.i. The formulas used for calculating the circumferential stress and meridian stress of bend reducer under internal pressure were inferred. The circumferential stress formulas of bend reducer may be change into the circumferential stress formulas of concentric reducer and eccentric reducer or elbow under internal pressure. The formula used for calculating limit pressure that all of concentric reducer and eccentric reducer and bend reducer were inferred. The limit pressure is generally controlled by the cross section of larger end.ii. The formula used for calculating limit bending moment that all of concentric reducer and eccentric reducer and bend reducer were inferred. The limit bending moment is generally controlled by the cross section of smaller end. The limit bending moment for both of concentric reducer and eccentric reducer is equal to the limit bending moment of pipe that has the same dimension with the small end. The limit bending moment of bend reducer is equal to a basic bending moment multiplied by bending moment coefficient. The basic bending moment is the limit bending moment of concentric reducer or eccentric reducer that has the same dimension with the small end. The bending moment coefficient should be calculating by four different formula that according to bending coefficient.iii. The formula used for calculating limit torque that all of concentric reducer and eccentric reducer and bend reducer were inferred. The limit torque is generally controlled by the cross section of smaller end regardless the torque is acting on the larger end or on the smaller end. It is equal to a basic torque multiplied by a coefficient. The basic torque is the limit torque of pipe that has the same dimension with the small end of bend reducer. The limit torque on the larger end of bend reducer is some smaller than the limit torque on its small end. The torque on one end of 90°elbow can not transfer into the other end perfectly, and it would change into bending moment. The bend moment on one end of 90°elbow may change from the torque on the other end.iv. The methods set up corresponding finite element models of bend reducer and concentric reducer and eccentric reducer were provided. Some important features about stress distribution or deformation is as follows: (a) The bending moment tend to open the larger end and to close the small end relatively when concentric reducer is under internal pressure, which induced by the area difference between the diameter of transverse cross section at larger end and the diameter of transverse cross section at small end; (b) The largest stress is circumferential stress which occur at inside in the larger end or at outside on the middle of eccentric sides when eccentric reducer is under internal pressure.v. The academic analysis was identified with the FEM and experiments. The result of experiment also show that both bending radius of ring shell and radius of its cross section should augment as the increasing of internal pressure, but the bending coefficient of ring shell should reduce.