On the dynamics and arrest of propagating buckles in offshore pipelines

A design methodology for integral buckle arrestors for offshore pipelines was presented in a previous study (Kyriakides et al. [1997]). It was based on experiments and analyses in which buckles penetrated the arrestors quasi-statically. In this dissertation, the performance of the same arrestors is reevaluated under the more realistic dynamic buckle propagation conditions encountered in the sea. The problem is studied through a combination of experiment and analysis.;The quasi-static arresting efficiency of buckle arrestors is first established experimentally as a function of the arrestor thickness. The same arrestor designs are then tested again in constant pressure environments where buckles propagate at velocities of 400 to 1100 ft/s. Experiments are conducted using both water and air as pressurizing media. For all cases considered, the dynamic crossover pressure was found to exceed the corresponding quasi-static value.;Models for reproducing the quasi-static and dynamic propagation and arrest of buckles in pipelines are developed within the framework of the finite element code ABAQUS. In the quasi-static model, the tube and arrestor materials are modeled as J2 flow theory solids with isotropic hardening. In the dynamic models, the rate dependence of SS-304 is assumed to exhibit an overstress power-law behavior. The pressurizing medium is assumed to be vacuum.;The dynamic model is shown to reproduce accurately the conditions of steady-state buckle propagation as well as the dynamic engagement of a buckle with an arrestor. The profile of running buckles was found to sharpen considerably compared to the quasi-static one. The numerical results showed the same dynamic enhancement of arrestor performance observed in the experiments, and revealed that this improvement is primarily related to the differences between the quasi-static and dynamic buckle profiles. Based on the results of this study, it is concluded that quasi-static design procedures for integral buckle arrestors proposed previously are conservative.;The mechanical model consisting of a beam on a nonlinear foundation with an up-down-up response developed by Chater et al. [1983] is revisited and used to study the dynamics of propagating buckles. The foundation is altered in order to allow variation of ratio of the propagation pressure to the collapse pressure within a range typical to pipelines and the pressurizing fluid is modeled as an acoustic medium. The model is initially used to study the steady-state dynamic propagation of buckles where the fluid properties are shown to play a decisive role on the buckle velocity. The full dynamic problem is then analyzed, including the transient dynamic initiation of a buckle by a point load in a structure under uniform pressure.