Confined buckle propagation of offshore pipelines under external pressure

Abstract

Offshore pipelines can be protected against collapse and buckling propagation by installing buckle arrestors or restraint cylinders. When the external pressure is high enough, the buckling would penetrate the arrestors or restraint cylinders and propagate along the line inside these protective structures, known as confined buckle propagation. A two-dimensional theoretical model has been proposed to estimate the confined propagation pressure, considering the rigid-perfectly plastic model and the Ramberg-Osgood model, respectively. Subsequently, the hyperbaric chamber test on SS304 confined tubes was conducted under external pressure. The annulus space of test specimens between the internal pipe and the external constraint cylinder was full of high-strength cement mortar and epoxy resin, respectively. Numerical models have been developed to duplicate the local collapse and the confined buckle propagation scenarios, and reasonable consistencies are observed between the tests and the numerical simulations. After that, broad parametric analyses of the confined propagation pressure are implemented to examine the influence of geometry and material property. As a result, an empirical expression is proposed to predict the confined propagation pressure.