Analysis and Design of Buried Steel Water Pipelines in Seismic Areas

The present paper offers an overview of available methodologies and provisions for the structural analysis and mechanical design of buried welded steel water pipelines subjected to earthquake action. Both transient (wave shaking) and permanent ground actions (from tectonic faults, soil subsidence, landslides and liquefaction-induced lateral spreading) are considered. In the first part of the paper, following a brief presentation of seismic hazards, modelling of the interacting pipeline-soil system is discussed, in terms of either simple analytical models or more rigorous finite elements, pin-pointing their main features. In the second part of the paper, pipeline resistance is outlined, with emphasis on the corresponding limit states. Possible mitigation measures for reducing seismic effects are also presented, and the possibility of employing gasketed joints in seismic areas is discussed. Finally, the above analysis methodologies and design provisions are applied in a design example of a buried steel water pipeline, located in an area with severe seismic action.<br/

Buckling of unconfined and confined thin-walled steel cylinders under external pressure

The present paper investigates the structural stability of thin-walled steel cylinders subjected to uniform external pressure. A brief discussion of unconfined steel cylinder buckling is presented first. Subsequently, motivated by the design of buried pipelines, buckling of confined steel cylinders, surrounded by an elastic medium, is examined. A two dimensional model is developed, assuming no variation of load and deformation along the cylinder axis. The cylinder and the surrounding medium are simulated with nonlinear finite elements that account for both geometric and material nonlinearities. The external pressure response of confined thin-walled steel cylinders is examined, in terms of initial the out-of-roundness of the cylinder, the initial gap between the cylinder and the medium, and the stiffness of the surrounding medium. Numerical results show a rapid drop of pressure after reaching the maximum pressure level. Finally, the numerical results show good comparison with a simplified closed-form expression, proposed elsewhere, which could be used for buried pipeline design purposes. © 2008 ASCE

Stability of confined thin-walled steel cylinders under external pressure

The present paper investigates the structural stability of thin-walled steel cylinders surrounded by an elastic medium, subjected to uniform external pressure. A two-dimensional model is developed, assuming no variation of load and deformation along the cylinder axis. The cylinder and the surrounding medium are simulated with nonlinear finite elements that account for both geometric and material nonlinearities. Cylinders of elastic material within a rigid boundary are considered first, and the numerical results are compared successfully with available closed-form analytical predictions. Subsequently, the external pressure response of confined thin-walled steel cylinders is examined, in terms of the initial out-of-roundness of the cylinder, the initial gap between the cylinder and the medium, and the stiffness of the surrounding medium. Numerical results are presented in the form of pressure-deformation equilibrium paths, and show a rapid drop of pressure after reaching the maximum pressure level, as well as a significant imperfection sensitivity. A plastic-hinge mechanism is developed that results in a closed-form expression and illustrates the post-buckling response of the cylinder in an approximate manner. The distributions of plastic deformation, as well as the variation of cylinder-medium contact pressure around the cylinder cross-section are also depicted and discussed. Furthermore, the effects of uniform vertical preloading on the maximum pressure sustained by the cylinder are examined. Finally, the numerical results show good comparison with a simplified closed-form expression, proposed elsewhere, which could be used for design purposes. (C) 2008 Elsevier Ltd. All rights reserved

Wrinkling of lined pipes under bending

The present study is motivated by the use of lined pipes in energy pipeline applications (oil, gas, etc.) where a corrosion-resistant thin-walled liner is fitted inside a carbon-steel outer pipe. The paper focuses on wrinkling of lined pipes (sometimes referred to as clad pipes), which are candidates for offshore pipeline applications. The pipe is composed by two pipes that are in contact; a thick-walled carbon-steel "outer pipe", and a thin-walled corrosion-resistant inner pipe, referred to as "liner pipe" fitted inside the carbon steel outer pipe. The lateral confinement of the liner pipe due to the deformable outer pipe and its interaction with the outer pipe has a decisive influence on the wrinkling behaviour of the lined pipe. The problem is solved numerically, using nonlinear finite elements to simulate the lined pipe and its interaction with the outer pipe. Nonlinear geometry with large strains is taken into account, and the material of both pipes is elastic-plastic. Stresses and strains are monitored throughout the deformation stage with emphasis on possible detachment of the liner from the outer pipe and the formation of wrinkles. It is shown that the behaviour is characterized by a first bifurcation in a uniform wrinkling pattern, followed by a secondary bifurcation. The values of curvature at which liner wrinkling occurs are determined. Copyright © 2012 by the International Society of Offshore and Polar Engineers (ISOPE)

Buckling of clad pipes under bending and external pressure

The present paper concerns the structural behaviour of clad pipes. This is a double wall pipe, composed by two pipes that are in contact through an appropriate manufacturing procedure; a thick-walled carbon steel "outer pipe", and a thin-walled corrosion-resistant inner pipe, referred to as "liner" pipe. To predict the bending response and the buckling curvature of the thin-walled liner, it is necessary to account for its contact with the confining thick-walled outer pipe. Because of this confinement, existing numerical solutions or analytical predictions for the bending buckling resistance of unconfined thin-walled tubes are inadequate to predict the buckling resistance of the bent liner. In the present work, the problem is solved numerically, using nonlinear finite elements to simulate the clad pipe, accounting for the interaction between the liner and the outer pipe. First, the manufacturing process of the clad pipe is simulated to determine the liner hoop prestressing. Subsequently, bending curvature is applied (with and without the presence of external pressure). Stresses and strains are monitored throughout the deformation stage with emphasis on possible detachment of the liner from the outer pipe and the formation of local buckling on the liner wall. Copyright © 2011 by ASME

Wrinkling of lined steel pipes under bending

Lined pipes are used in energy pipeline applications (oil, gas, etc.); a corrosion-resistant thin-walled liner is fitted inside a carbon-steel outer pipe. The paper focuses on wrinkling of lined pipes (sometimes also referred to as "mechanical clad" pipes), which are candidates for offshore pipeline applications. The lateral confinement of the liner pipe due to the deformable outer pipe and its interaction with the outer pipe has a decisive influence on the wrinkling behaviour of the thin-walled liner. The problem is solved numerically, using nonlinear finite elements to simulate the lined pipe and its interaction with the outer pipe. Nonlinear geometry with large strains is taken into account, and the material of both pipes is elastic-plastic. Stresses and strains are monitored throughout the deformation stage with emphasis on possible detachment of the liner from the outer pipe and the formation of wrinkles. It is shown that the behaviour is characterized by a first bifurcation in a uniform wrinkling pattern, followed by a secondary bifurcation and finally a localization of the buckled pattern. The values of curvature at which liner wrinkling occurs are determined. The numerical results are compared with available experimental results. Copyright © 2013 by ASME

Strain-Based design procedures for spiral-welded steel tubes in combined walls

Spiral-welded steel tubes with diameter to wall thickness ratios between 60 and 140 are often employed in combined wall systems with local buckling as governing failure mode. The current design rules in Eurocode 3 (EN 1993-5 and EN 1993-1-6) are not capable to obtain a good estimate of the real strength and deformation capacity. In a European RFCS project called Combitube, the structural behaviour of spiral-welded steel tubes has been inves-Tigated. An analytical model has been developed that gives more economic designs with a bet-Ter balanced safety level. Copyright ©: SDSS'2016