Finite Element Analysis on the Collapse Loads for Cracked Elbows Under Internal Pressure

Elbow is a type of component widely used in a piping system. So it is very important to know the effects of cracks on the collapse loads of elbows for integrity assessment of the piping system. The influences of defects on the load carrying capacity of elbows with various bending radius (R/=1.0 D_i and R/=1.5 D_i), were investigated in detail, by 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 elbow with the welded tangent straight pipes respectively. The results from comprehensive parametric studies on limit loads of elbows indicate that the limit load capacity of cracked elbows may be reduced with the increasing of crack length and these trends are more serious for long radius elbows. These is insignificant effects of t/r_m on the weakening factor (P_L/P_(LO) ) of cracked elbows subjected to internal pressure. This paper is useful for safety assessment of the cracked elbows.