A comprehensive study on a propagating buckle in externally pressurized pipelines

Buckle propagation is a unique phenomenon occurring in deep-sea pipelines. In previous works, this phenomenon was investigated using a ring technique in which the pipeline was assumed to be in plane strain condition and the energies absorbed in membrane stretching and longitudinal bending were ignored. This paper presents a three-dimensional analysis of the buckle propagation phenomenon with an emphasis to address more complete factors that were not accounted for in the ring analysis. The analyses are based on the available solutions of the transition zone obtained in our previous works. A comprehensive mechanism for buckle propagation phenomenon is described from the point view of plastic stability theory for shells which enables the incorporation of the effects of transverse and longitudinal bending, membrane stretching and material strain hardening. The nondimensionalized buckle propagation pressure is represented in terms of yield coefficient, strain hardening coefficient and membrane stretching factor. It is found that a buckle once initiated in a pipeline may or may not propagate along the pipeline depending on its radius-to-thickness ratio. By comparing with various experimental results the theoretical predictions from this analysis are shown to provide very accurate estimations of the buckle propagation pressure for different materials with diverse geometric parameters and material properties. This paper points to the need for more complete information regarding the effects of transverse bending, membrane stretching and material strain-hardening on the buckle propagation pressure. Upon the requirement of application variations of the yield coefficient, strain hardening coefficient and membrane stretching factor with respect to the radius-to-thickness ratio are sketched out. This eliminates the need for recourse the curves and allows a fast and convenient resolution of buckle propagation pressure for certain pipeline. Most importantly, the present analysis offers the potential for future design of pipelines being at once more rationally and parametrically complete, and yet compact and simple to apply.