Structural behavior of buried pipe bends and their effect on pipeline response in fault crossing areas

Abstract

Pipe bends, often referred to as ''elbows'', are special pipeline components, widely used in onshore buried steel pipelines. They are sensitive to imposed deformations and their structural behavior is quite flexible and associated with the development of significant stress and strain, which may lead to failure. In the present paper, the mechanical performance of buried steel pipeline bends is investigated first, using rigorous finite element models that account for the pipe-soil interface. Three 36-inch-diameter pipe elbows are considered, subjected to pull-out force and embedded in cohesive soils. The elbows have bend angles equal to 90°, 60°and 30°, and bend radius-over-diameter ratio (R/D) equal to 5. The results show the increased flexibility of the pipeline bend with respect to the straight pipe, and are reported in the form of force-displacement diagrams. Furthermore the deformation limits of each elbow are identified in terms of appropriate performance criteria. The second part of the paper investigates the effect of pipe bends on the response of pipelines crossing active faults using a three-dimensional rigorous finite element model. The numerical results refer to a 36-inch-diameter pipeline crossing a strike-slip fault, and show that the unique mechanical response of pipe bends, in terms of their flexibility, may offer an efficient tool for reducing ground-induced deformations. The three-dimensional model employs the load-displacement curves of the first part of the paper as end conditions through nonlinear springs. Furthermore, the results show that there exist an optimum distance of the elbow from the fault plane, which corresponds to the maximum allowable ground displacement. Therefore, pipeline elbows, if appropriately placed, can be employed as ''mitigating devices'', reducing ground-induced action on the pipeline at fault crossings.

Numerical study of semi-elliptical cracks in the critical position of pipe elbow

“…Figs. (4)(5)(6) show the distribution of pressure, velocity and Von-Mises stress along the pipe elbows, respectively. The Effect of elbow radius was investigated in order to obtain the radius value at which the stress is stabilized.…”

“…Due to a mixed mode loading, the non-dimensional crack driving force kr is defined as the ratio of maximum equivalent stress intensity factor, K eq,max , to the fracture toughness of material in mode K IC . kr=Keq/KIc (6) Here in this particular FAD Non-dimensional load Lr is defined as the ratio of maximum circumferential stress max and flow stress  o : Crack orientation (°) a/t=0.5…”

“…Indeed, the piping systems including the elbows are subjected to severe factors which may menace the integrity and safety of the pipe [4][5]. Due to the importance of elbows in the petroleum industries including their geometry and location, they are considered to be as critical parts in piping systems [6][7]. Due to their geometry, stress amplification occurs which promote failure and leak.…”

Research on Vibration Characteristics of Typical Pipe

“…The ground pipe mainly concerns the influence of corrosion and flow induced vibration on the pipe. [1][2] The main part of the spacecraft pipe is the external tension, sound and vibration environment, which affects the pipe. [3][4] In the study of the vibration characteristics of the pipe, there are mainly theoretical analysis, finite element simulation, test verification and other means.…”

Local Buckling Behavior and Plastic Deformation Capacity of High-Strength Pipe at Strike-Slip Fault Crossing

“…Zhang et al discussed the collapse behavior of pipeline buried in rock under strike-slip fault movement and reverse fault displacements [27,28]. Vazouras conducted series of numerical models to investigate the failure behavior of pipeline under strike-slip fault movement in detail [29][30][31][32]. Trifonv et al also built a rigorous numerical model to analyze the influence of the trench on the pipeline performance at fault crossing [7].…”