Koji Yoshizaki

A First Step Towards the Development of a Pipeline Wrinkle Material Ultimate Limit State

While the formation of a wrinkle in an onshore pipeline is an undesirable event, in many instances this event does not have immediate pipeline integrity implications. The magnitude or severity of a wrinkle formed due to displacement controlled loading processes (e.g. slope movement, fault displacement, frost heave and thaw settlement) may increase with time, eventually causing serviceability concerns (e.g. fluid flow or inspection restrictions). Pipe wall damage leading to cracking and eventually a loss of containment involves contributions from the wrinkle formation and growth processes, as well as, wrinkle deformations promoted by in-service line pressure, temperature and seasonal soil displacements. The objective of this paper is to provide an overview of the ongoing research efforts, sponsored by TransCanada PipeLines Ltd. and Tokyo Gas Co. Ltd., towards the development of a mechanics based wrinkle ultimate limits state that may be used in future to evaluate the long term integrity of wrinkled pipeline segments. The research efforts include non-linear finite element modeling to demonstrate the ability of experimentally derived material properties to predict the formation of through wall cracking induced by high and low frequency load effects. This paper outlines the material testing program used to support the development of failure criteria capable of considering the contributions of monotonic deformation, as well as, high and low cycle cyclic loading.Copyright

Large Deformation Behavior of Pipe Bends Subjected to In-Plane Bending

Ground liquefaction during earthquakes can produce a significant amount of lateral ground displacement. For buried gas pipelines, deformation and strain are likely to be concentrated on the pipe bends. Closing and opening in-plane bending experiments were conducted for various kinds of pipe bends until the measured strain exceeded 25% using pipe specimens of a diameter from 100 to 300 mm. The deformation behavior was different between the closing mode and the opening one. In the closing mode, an ovalization was observed in the central cross section of the bend, and internal pressure was maintained in all experiments. On the other hand, unique behavior was observed in the opening mode. When the pipe diameter was 300 mm (Do/t=43), local buckling was observed at the center of the bend. However, when Do/t was less than 32 (200 mm in diameter), the flexural rigidity of the bend became much higher than that of a straight pipe, and buckling and rupture were observed in the straight pipe. Finite element analyses were carried out using linear shell elements, and the validity of the numerical modeling technique over 25% of plastic strain was confirmed.Copyright