Investigating the Effect of UOE Forming Process on the Buckling of Line Pipes Using Finite Element Modeling

Buried line pipe are often subjected to compressive and/or bending loads at locations of ground movements. Those loads might increase the strain of the pipe at some location beyond a critical value and thus a buckle is formed on the pipe wall. Finite element modeling is an excellent numerical technique that can predict the values of the critical strains that a pipe can withstand before buckling. However, these numerical models require an accurate representation of the spatial material behaviour. Tensile specimens taken from the longitudinal and the transverse directions of a line pipe formed using the UOE process often exhibit different behaviour. Finite Element Models of buckling of line pipe often use the tensile properties exhibited by longitudinal specimens without taking into consideration the effect of the different behaviour in the transverse direction. In order to investigate the effect of the forming process a finite element model of forming a plate into a pipe was analyzed. The model was analyzed twice, once with isotropic hardening material properties and the other with kinematic hardening material properties with a constant size for the yield surface. The behaviour under tensile loading of the formed pipe in both the longitudinal direction and the transverse direction were quite different between the two models. The results show that the kinematic hardening material model can predict the difference in the tensile properties often seen between specimens taken from the longitudinal versus the transverse direction of the pipe. The material model is extended further to model the buckling of line pipe. The results show that the buckling of line pipes is dependent on the behaviour of the pipe in both the longitudinal and the transverse direction.