Nonlinear Pipe-soil Interaction Research Articles

Lateral Buckling of Subsea Pipelines Triggered by Sleeper with a Nonlinear Pipe–Soil Interaction Model

Buckle-initiation techniques, such as sleepers, are usually installed to trigger lateral buckling at pre-designated locations to release the axial compressive forces induced by thermal loading. Taking the nonlinear pipe–soil interaction model into account, a mathematical model is proposed to investigate the lateral buckling of subsea pipelines triggered by a sleeper. The numerical solution is validated by comparing the model with solutions in the literature, and the model shows good agreement. The discrepancy between them is analysed by presenting the effect of mobilisation distance during buckling. The influence of the breakout resistance, sleeper height, and sleeper friction coefficient on the buckled configuration, post-buckling behaviour, and minimum critical temperature difference is discussed parametrically. The results show that the deformation of the buckled pipeline shrinks, and both the minimum critical temperature difference and the maximum stress along the buckled pipeline enlarge when the nonlinear pipe–soil interaction model is incorporated. However, the influence of the nonlinear pipe–soil interaction reduces with increasing sleeper height.

Simulation stage-based seabed pre-trenching technique for steel catenary riser touchdown fatigue analysis

ABSTRACT The development of seabed trench by the steel catenary riser (SCR) touch-down zone (TDZ) in its early life can be caused by installation loads, direct hydrodynamic loads, and vessel first and second-order motions on the SCR. This paper presents a numerical technique by which pre-trench can be initiated for fatigue response calculations during SCR detailed design analysis. Examples are presented to demonstrate the new approach and how the SCR fatigue response can be calculated in the presence of the created pre-trench. The SCR (after the pre-trenching process) is allowed to respond to the vessel first order six degrees of freedom motions about its nominal position in the presence of the created pre-trench. As demonstrated in this paper, the pre-trenching technique makes it possible to conduct a full time-domain, irregular wave simulations of the SCR in the presence of a pre-trench created using the hysteretic non-linear pipe soil interaction mode.

Pipeline Lateral Buckling Initiated by the Imposed Residual Curvature Method with Nonlinear Pipe-Soil Interaction

Pipeline Lateral Buckling Initiated by the Imposed Residual Curvature Method with Nonlinear Pipe-Soil Interaction

Effect of nonlinear pipe-soil interaction on lateral buckling of subsea pipelines triggered by a distributed buoyancy section

A distributed buoyancy section is one of the main buckle initiation techniques to trigger a pipeline to buckle laterally to release the high axial force induced by the high temperature of the transported fluid. A key design parameter governing the initiation of the lateral buckle is the breakout resistance. In this study, a nonlinear pipe-soil interaction model is incorporated into the mathematical model to study the lateral buckling behaviour of the subsea pipeline triggered by a distributed buoyancy section. The numerical solution is compared with test results and analytical results in the literature to validate the mathematical model. A parametric discussion is carried out to investigate the breakout resistance, residual resistance and parameters of the distributed buoyancy section on lateral buckling behaviour. The results show that the breakout resistance has a great effect on the minimum critical temperature difference. The influence of breakout resistance on the buckling behaviour is much smaller than the influence of residual resistance. Moreover, the most optimal length of distributed buoyancy section should be equal to the length of the buckled section. Thus, the largest length of the buckled section during design should be estimated first to determine the optimal length of distributed buoyancy section.

Mode jumping in the lateral buckling of subsea pipelines

Unburied subsea pipelines under high-temperature conditions tend to relieve their axial compressive stress by forming localised lateral buckles. This phenomenon is traditionally studied under the assumption of a specific lateral deflection profile (mode) consisting of a fixed number of lobes. We study lateral thermal buckling as a genuinely localised buckling phenomenon by applying homoclinic (‘flat’) boundary conditions. By not having to assume a particular buckling mode we are in a position to study transitions between these traditional modes in typical loading sequences. For the lateral resistance we take a realistic nonlinear pipe-soil interaction model for partially embedded pipelines. We find that for soils with appreciable breakout resistance, i.e., nonmonotonicity of the lateral resistance characteristic, sudden jumps between modes may occur. We consider both symmetric and antisymmetric solutions. The latter turn out to require much higher temperature differences between pipe and environment for the jumps to be induced. We carry out a parameter study on the effect of various pipe-soil interaction parameters on this mode jumping. Away from the jumps post-buckling solutions are reasonably well described by the traditional modes whose analytical expressions may be used during preliminary design.

Strain demand of elastic pipes subjected to permanent ground displacements using the finite difference method

Long-distance pipelines are one of the primary means of oil and gas transportation. During the construction process, long-distance pipelines are inevitably buried across geohazard zones, which potentially generate permanent ground displacements. These ground displacements can potentially induce excessive strains in the pipe posing a great threat to the pipe’s safety and integrity. In this study, a new numerical methodology for the response analysis of pipes subjected to ground displacements is proposed based on the finite difference method. Simulating the pipeline as a large deformation Euler Bernoulli beam, the finite difference method is used to solve the two interacting nonlinear differential equations of equilibrium in the longitudinal and lateral directions considering the nonlinear pipe-soil interaction induced by the ground displacement. Implemented using the nonlinear equation solver of FindRoot by Mathematica for solving nonlinear equations, the longitudinal strain along the pipeline can be subsequently derived, and the tensile and compressive strain demands can be therefore determined for engineering reference. Finally, the applicability of this method is validated based on two hypothetical study cases involving symmetric and non-symmetric soil resistance on the lateral direction of the pipe. Comparing the results with the finite element analysis solver Abaqus, we demonstrate that this present methodology has excellent predictive capabilities. Our study is carried out for elastic response calculation, but the proposed method shows a great promise for further development involving material nonlinearity, which is appropriate for the preliminary safety evaluation for the design of new pipelines or for risk prescreening of existing pipelines.

Analytical and numerical study on lateral buckling of imperfect subsea pipelines with nonlinear lateral pipe-soil interaction model

The nonlinear pipe-soil interaction model and the initial imperfections are predominantly factors that affect the lateral buckling behaviour of subsea pipelines with a high-temperature. In this study, mathematical models, taking these two factors into account, are proposed to simulate lateral buckling of subsea pipelines. Analytical solutions are derived from the assumption of rigid-plastic pipe-soil interaction, while numerical results are obtained when considering nonlinear pipe-soil interaction. The analytical and numerical results have an excellent agreement except for the negligible discrepancy in the pre-buckling state. The discrepancy is induced by the difference of mobilisation distance in rigid-plastic and elastic-plastic pipe-soil interaction models. After the analysis of snap-through phenomenon, the influence of breakout resistance, amplitude and half-wavelength of imperfection on the post-buckling behaviour is studied. Finally, the upper and lower bound critical temperature differences are discussed as well. The results show that the hysteresis cycle between pre-buckling and post-buckling states may appear under cyclic thermal loading. The snap-through phenomenon and the hysteresis cycle can take place more easily for large breakout resistance, small amplitude and large wavelength of imperfection. In the post-buckling state, the maximum stress uplifts with increasing breakout resistance or amplitude of imperfection, while it reduces with escalating wavelength of imperfection.

Lateral buckling critical force for submarine pipe-in-pipe pipelines

The lateral buckling critical force of a submarine pipe-in-pipe pipeline with symmetrical initial imperfection on soft foundation is determined. The effects of initial imperfection shapes, out-of-straightness, soil parameters as well as lateral nonlinear pipe-soil interaction, and structure parameters (stiffness ratio of inner pipe to outer pipe and clearance between inner and outer pipes) are discussed. A simple formula considering the above factors is proposed to determine the lateral buckling critical force of submarine pipe-in-pipe pipelines based on dimensional analysis and numerical results. The accuracy of the presented formula is shown by a case study.

Lateral Global Buckling of Submarine Pipelines Based on the Model of Nonlinear Pipe–Soil Interaction

With the increasing development and utilization of offshore oil and gas resources, global buckling failures of pipelines subjected to high temperature and high pressure are becoming increasingly important. For unburied or semi-buried submarine pipelines, lateral global buckling represents the main form of global buckling. The pipe–soil interaction determines the deformation and stress distribution of buckling pipelines. In this paper, the nonlinear pipe–soil interaction model is introduced into the analysis of pipeline lateral global buckling, a coupling method of PSI elements and the modified RIKS algorithm is proposed to study the lateral global buckling of a pipeline, and the buckling characteristics of submarine pipeline with a single arch symmetric initial imperfection under different pipe–soil interaction models are studied. Research shows that, compared with the ideal elastic–plastic pipe–soil interaction model, when the DNV-RP-F109 model is adopted to simulate the lateral pipe–soil interactions in the lateral global buckling of a pipeline, the buckling amplitude increases, however, the critical buckling force and the initial buckling temperature difference decreases. In the DNV-RP-F109 pipe–soil interaction model, the maximum soil resistance, the residual soil resistance, and the displacement to reach the maximum soil resistance have significant effects on the analysis results of pipeline global buckling.

Localised upheaval buckling of buried subsea pipelines

Buried subsea pipelines under high temperature conditions tend to relieve their axial compressive force by forming localised upheaval buckles. This phenomenon is traditionally studied as a kind of imperfect column buckling problem. We study upheaval buckling as a genuinely localised buckling phenomenon without making any ad hoc assumptions on the shape of the buckled pipeline. We combine this buckling analysis with a detailed state-of-the-art nonlinear pipe-soil interaction model that accounts for the effect of uplift peak soil resistance for buried pipelines. This allows us to investigate the effect of cover depth of subsea pipelines on their load-deflection behaviour. Furthermore, the influence of axial and uplift peak soil resistance on the localised upheaval behaviour is investigated and the maximum axial compressive stress during the buckling process is discussed. Parameter studies reveal a limit to the temperature difference for safe operation of the pipeline. Localised upheaval buckling may then occur if the pipe is sufficiently imperfect or sufficiently dynamically perturbed.

Localised lateral buckling of partially embedded subsea pipelines with nonlinear soil resistance

Unburied partially embedded subsea pipelines under high temperature conditions tend to relieve their axial compressive force by forming localised lateral buckles. This phenomenon is traditionally studied as a kind of imperfect column buckling problem. We study lateral buckling as a genuinely localised buckling phenomenon governed by a different static instability, with a different critical load. No ad hoc assumptions need to be made. We combine this buckling analysis with a detailed state-of-the-art nonlinear pipe-soil interaction model that accounts for the effect of lateral breakout resistance. This allows us to investigate the effect of initial embedment of subsea pipelines on their load-deflection behaviour. Parameter studies reveal a limit to the temperature difference for safe operation of the pipeline, in the sense that for higher temperature differences a localised buckling mode has lower total energy than the straight unbuckled pipe. Localised lateral buckling may then occur if the pipe is sufficiently imperfect or sufficiently dynamically perturbed.

Numerical study on lateral buckling of fully bonded sandwich pipes

Sandwich pipes (SP) are promising subsea pipelines for deep-water applications. Thus, their lateral buckling response is a significant design aspect. The temperature field of SP denotes the load in lateral buckling analysis, and it is calculated using the heat transfer differential equation in this study. A general temperature field formula is proposed for an arbitrary multilayer SP, and this formula is verified by finite element models. Another finite element model based on the fiber shell element is then constructed to investigate the lateral buckling response of SP. They are validated by existing experimental and numerical results. The evolution of the lateral buckling profiles and of stress distribution are studied in consideration of nonlinear pipe-soil interaction and nonlinear material constitutive law. Moreover, the influence of initial imperfections and pipe-soil interaction on lateral buckling response is examined. Finally, a formula is approximated for a SP with a half-wave sinusoidal imperfection profile on the basis of dimensionless analysis and numerical results. This formula is convenient for engineering applications.

Perturbation analysis for upheaval buckling of imperfect buried pipelines based on nonlinear pipe-soil interaction

Submarine pipelines are often operated under conditions of high temperature and high pressure, which may induce considerable axial compressive force. If the lateral movement is constrained, for instance, burying pipe or dumping gravel, upheaval buckling may happen. Pipe-soil interaction affects the upheaval buckling behavior of submarine pipelines. However, pipe-soil interaction models currently existing fail to reflect the drop process of uplift resistance when the vertical displacement is over mobilization distance. To solve this problem, a new nonlinear pipe-soil interaction model is presented and the governing differential equation of an imperfect pipeline on soft foundation is deduced. The solution to the governing differential equation is proposed based on nonlinear perturbation expansions. The effect of soil conditions, burial depth and initial imperfections on critical force as well as localization pattern of upheaval buckling are discussed. Results show that the capacity of pipeline against thermal buckling increases with the burial depth or maximum uplift resistance and decreases with the OOS of pipeline or mobilization distance. Critical buckling force is almost unaffected by pipe-soil interaction form, but the post-buckling response depends on pipe-soil interaction forms. The pipe-soil interaction model can be used not only in pre-buckling design but also in post-buckling control.

On lateral buckling of subsea pipe-in-pipe systems

Lateral buckling is a common phenomenon in unburied high temperature and high pressure (HT/HP) subsea pipe-in-pipe systems. An effective finite element model based on beam element and tube-to-tube contact element is proposed to study lateral buckling in pipe-in-pipe systems, in which the initial imperfection (out-of-straightness), nonlinear pipe-soil interaction and nonlinear material properties are considered. The results show that it is the resultant axil force of the inner and outer pipe that governs the lateral buckling phenomenon in pipe-in-pipe systems. The initial imperfection and pipe-soil interaction are the most important factors which influence evolution of the displacement and stress in pipe-in-pipe systems. Nonlinear material properties are necessary when plastic strain may occur in post-buckling stage. At last, a simplified model is proposed which can easily calculate the critical buckling temperature of the corresponding pipe-in-pipe system.

A semi-analytical approach to a nonlinear stress–strain analysis of buried steel pipelines crossing active faults

In the present paper a semi-analytical methodology for a nonlinear stress–strain analysis of buried steel pipelines at active fault crossings is presented and verified. The developed model introduces a number of critical refinements to the existing methodologies which extend the application area of analytical models in pipeline design. In particular, a strike-slip and normal-slip fault crossings can be analyzed taking into account material and large displacement nonlinearities, nonlinear pipe–soil interaction. The proposed model is verified against the results by other authors and numerical results, obtained with the finite element method.