COLLAPSE LOADS FOR CRACKED ELBOWS UNDER INTERNAL PRESSURE

Elbow is a type of component widely used in a piping system. The existence of cracks in excess of the defect limits can not be excluded. So it is very important to know the effect of cracks on the collapse loads of elbows for integrity assessment of the piping system. The simplified estimation formulas for plastic limit pressure of cracked elbows without the effects of straight pipes were established. The influences of defects on the load carrying capacity of elbows with various bending radius (R=1.0D_i and R=1.5D_i), were investigated in detail, by use of detailed three-dimensional (3D) non-linear finite element (FE) analyses, using elastic-perfectly-plastic material behavior and taking geometric nonlinearity into account. The crack-like defects with different dimensions were focused on axial through-wall cracks, located in extrados, intrados and crown of elbows with the welded tangent straight pipes respectively. The results from comprehensive parametric studies of limit loads of elbows indicate that the limit load capacity of cracked elbows may reduce with the increasing of crack length and these trends are more serious for long radius elbows. These is insignificant effect of t/r_m on the weakening factor (P_L/P_ L0 ) of cracked elbows subjected to internal pressure.