Pipeline Lateral Buckling Research Articles

Controlled pipeline lateral buckling by reeling induced curvature imperfections

Expansion of pipelines installed on the sea floor due to the passage of high temperature and pressure hydrocarbons leads to lateral buckling. Interaction with a frictional sea floor can result in localization of such buckles, which must be controlled to ensure that the local bending is within acceptable limits. Periodic geometric imperfections introduced to a pipeline installed by reeling using the Residual Curvature Method are modeled and their effectiveness as expansion loops is evaluated. The imperfections are generated by allowing chosen lengths of the line to retain a small curvature by judicious action at the straightener. The model properly accounts for the complex interactions between geometric and material nonlinearities with frictional forces. It is demonstrated that as the temperature increases, the line can buckle in a snap-through manner, or can grow stably usually causing plastic deformation in its crest. The behavior is governed by the length, curvature, amplitude and periodicity of the imperfection, and by the lateral and axial frictional forces that develop. The effect of each of these variables is studied parametrically. Overall, the Residual Curvature Method is found to be a viable and effective method of controlling lateral buckling. The results provide guidance on the optimal periodicity, how to avoid snap-through buckling, and how to simultaneously minimize plastic bending.

Antisymmetric thermal buckling triggered by dual distributed buoyancy sections

Rogue buckles may occur for unburied subsea pipelines operating under high temperature and high pressure conditions. Distributed buoyancy section (DBS) is often installed to trigger pipeline lateral buckling. Single distributed buoyancy section (SDBS) is normally adopted to trigger a symmetric lateral buckling mode. But in some cases, dual distributed buoyancy sections (DDBS) with a gap between them are utilised to trigger an antisymmetric lateral buckling mode. This paper concerns the behaviour of antisymmetric lateral buckling triggered by DDBS. First, the locations of the maxima of the deflection and bending stress are determined. Then, comparisons of the post-buckling behaviour between antisymmetric buckling mode, triggered by DDBS, and symmetric buckling mode, triggered by SDBS, are presented and discussed. The influences of the spacing between dual buoyancy sections and the parameters of the DBS on the buckled configuration and post-buckling behaviour are presented. Finally, the effects of the DBS on the minimum critical temperature difference, the maxima of the deflection and stress are discussed. The results show that the maxima of the deflection and stress of the antisymmetric mode are much smaller than that of the symmetric mode under the same operating conditions. During the design process, the spacing between dual buoyancy sections, the length and the weight ratio coefficient of the DBS should be determined in sequence.

Effects of variability in lateral pipe-soil interaction and pipe initial out-of-straightness on controlled lateral buckling of pre-deformed pipeline

The state-of-the-art method for controlling temperature-induced global lateral buckling of a subsea pipeline is to engineer deliberate buckles at widely spaced locations. These buckles are engineered either by the installation process – i.e. ‘snake-laying’ or by installing subsea structures known as buckle initiators at each intended buckle location. The pre-deformed pipeline is new alternative method that involves continuously pre-deforming the pipeline prior to installation onto the seabed. This pre-deformation causes a significant reduction in axial stiffness and therefore significantly increases the buckle initiation temperature. It also allows thermal expansion to be accommodated throughout the pipe length via expansion of the pre-deformed curvatures, rather than being concentrated at specific buckle locations. This paper presents the influence of two of the variabilities in a pre-deformed pipeline design on the buckling performance: the initial out-of-straightness and the lateral pipe-soil interaction. The results show that the concept of a pre-deformed pipeline is robust and the success of the scheme is not affected by these two uncertainties. The pre-deformed pipeline is shown to be a self-governing system where the maximum strain is self-limited at any location. Pipeline pre-deformation is therefore proven to be a cost effective, safe and valuable tool for controlling pipeline lateral buckling.

Three-Dimensional Explicit Dynamic Numerical Method to Simulate a Deep-Sea Pipeline Exhibiting Lateral Global Buckling

Deep-sea pipelines exhibit lateral global buckling under high temperature and pressure differences. Numerical simulations are an effective and easy way to obtain the deformation and stress distribution of a post-buckling pipeline with a low cost. A relatively accurate and convenient simulation model using the explicit dynamic method was developed based on ABAQUS software to analyse pipeline lateral global buckling. In pipeline global buckling analysis, the dynamic variation of soil resistance as the pipeline moves laterally, the optimized computational length and the use of smooth initial imperfection profiles influence the accuracy of the simulation results. These three key factors were discussed here, and calculation methods were proposed. A CEL simulation model with improved boundary conditions that reduce the influence of wave reflection with a low calculation time cost was built to calculate the variation dynamics of soil resistance throughout the buckling process. Different computational lengths for pipelines with different parameters were simulated, and a fitting function to obtain an optimized computational length was proposed. A method to build the profiles of a pipeline with smooth imperfections was developed. Based on these analyses of the three impact factors, a relatively accurate and convenient simulation model for pipeline global lateral buckling analysis was established. Finally, an engineering case was evaluated to show the application of the simulation model and to test the reliability of this model.

Numerical analysis of cross-section ovalization in the deep-sea pipeline lateral buckling process

The deep-water pipeline is the main means of transportation in offshore oil and gas development engineering. The deep-water pipeline may incur lateral global buckling due to the high temperature and pressure that are applied on the pipeline to ensure the contents’ liquidity. With the increasing operating water depth, a higher temperature and pressure are applied to the pipeline, causing large lateral deformation and a large bending moment. Due to the inhomogeneous distribution of the bending moment on the cross-section, different points on the cross-section will deform differently. This kind of deformation causes the cross-section to turn into an oval ring. The cross-section ovalization caused by global buckling was rarely analyzed in former engineering practice since the load is relatively low. With the increase in operation water depth and operation load, the ovality caused by global buckling is noticeable. This article analyzed cross-section ovalization caused by pipeline lateral global buckling with a numerical simulation method. The pipelines with different initial cross-section shapes were simulated, and the influence of several impact factors, including load, pipeline and soil factors on the ovality of the cross-section, were analyzed. The results show that the initial cross-section shape type has little effect on the pipeline ovalization pattern. The initial ovality of the pipeline with an oval ring cross-section shape has little influence on the residual ovality. Among all the factors analyzed in this paper, the pressure difference is the primary factor that should be considered in a pipeline ovalization check.

Study on snaked laying method and the influence to control lateral buckling

The snaked laying is an effective method to control the submarine pipeline lateral buckling and widely used in the pipeline projects. In order to control the lateral buckling, the snaked lay method is investigated theoretically and numerically. Because of the special configuration of the snaked laying pipeline routine, the lateral global buckling can be easily triggered with a small compressive stress and the bending stress on the pipeline cross-section can be maintain at a low level. This paper analysed the impact factors of snaked laying pipeline on the lateral global buckling especially the laying wavelengths, amplitudes of curve and curve shapes. And the comparison between snaked laying and regular laying pipeline are discussed.

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.

Subsea Pipeline Lateral Buckling Design—Strain Concentration or Strain Capacity Reduction Factors

A strain concentration factor is typically incorporated in the higher-pressure and high-temperature (HPHT) pipeline lateral buckling assessment to account for nonuniform stiffness or plastic bending moment. Increased strain concentration can compromise pipeline low cycle fatigue and lateral buckling capacity, leading to an early onset of local buckling failure. In this paper, the philosophy of local buckling mitigation using the strain concentration factor is examined. The local buckling behavior is evaluated. Global strain reduction and evolution against buckling are analyzed with respect to varying joint mismatch level. The concept of a strain reduction factor (SNRF) due to joint mismatch is developed based on the global strain capacity reduction with reference to the uniform configuration. It is demonstrated that the SNRF in terms of strain capacity reduction is a unique characteristic parameter. As opposed to strain concentration, it is an invariant insensitive to evaluation methods and design strain demand level, hence more representative as a limiting design metric to maintain the safety margin. The rationale for its introduction as an alternative to the strain concentration factor is outlined and its benefits are established. The method for obtaining the SNRF and its application is developed. The discernible difference and scenarios for application of either factor are discussed, including low and high cycle fatigue, linearity and stress concentration, engineering criticality assessment (ECA), and lateral buckling. Additional causal factors giving rise to mismatch such as pipe schedule transition and buckler arrestor are also discussed. Iterations of finite element (FE) analyses are performed for a pipe-in-pipe (PIP) configuration in a case study.

Holistic Design of HTHP Pipeline: PETRONAS’ Experience

When the oil and gas price was declining rapidly in 2016, it is prudent for global oil operator to identify opportunity to reduce the development cost. This is where all form of cost optimisation and holistic design approach have to be conducted, especially when dealing with High Pressure and High Temperature (HPHT) pipeline which normally requires higher CAPEX. Referring to a field case example from one of PETRONAS’s HPHT pipeline project in Malaysia waters, initial analysis had identified that a 24-inch subsea FWS HPHT pipeline with 40mm concrete coating thickness (for its on-bottom stability requirement), requires three numbers of ‘buckle trigger’s in order to manage the pipeline lateral buckling issues. Hence, a holistic design approach had been conducted to re-evaluate such requirement, commenced with detail assessment to look for all possible opportunities to reduce the pipeline temperature, one of it is to have a greater heat transfer from the pipeline. This exercise had landed into detail assessment on the pipeline on-bottom stability requirement which resulted in indication that the 24-inch FWS pipeline, that have a thicker wall thickness at the upstream portion, would be self-stabled - no requirement for concrete weight coating. Thus, benefitting from the results, further detail analysis had been conducted to assess the overall heat transfer from the pipeline as well as the impact towards the pipeline lateral buckling design, which lead to elimination of lateral buckling mitigation requirement. Unfortunately, further analysis had shown that in the absent of concrete weight coating, the pipeline un-concrete weight coated section i.e. hot end area and the field joints, would have rapid condensation and exposed to the intolerable top of line corrosion risk. Also, based on past experience with local installation contractor, there will be possibility of installation issue for the un-concrete coated pipeline with the tapered bracelet anode. Following that, thorough analysis had been performed and successfully mitigated the issue by applying field joint coating material with U-Value of 52 W/m2K to the 3LPP-Coated linepipe. As for the subsea flange connection, it is covered with thermal insulation, whereas the anode at the un-concrete coated section utilized anode sled mechanism. This holistic design approach had successfully reduced the project cost in line with PETRONAS’ aspiration i.e. low cost development project; and most importantly the ‘body of knowledge’ i.e. experiences, lessons learnt and good practices are captured in PETRONAS Technical Standard for future replication

Analytical solution for controlled lateral buckling of unburied subsea pipelines

Unburied subsea pipelines designed to operate under high temperature and high pressure (HT/HP) conditions tend to relieve their axial compressive force by forming lateral buckles. Uncontrolled lateral buckling can lead to pipeline failure, such as collapse. Thus, controlled lateral buckling is an effective and inexpensive method to accommodate axial thermal expansion and to control pipeline lateral buckling. In this study, analytical solutions for uncontrolled and controlled lateral buckling of unburied subsea pipelines are derived. And the interaction between two adjacent buckles for controlled lateral buckling is considered. The typical behaviors of uncontrolled and controlled lateral buckling with different lengths of feed-in zone are illustrated and analyzed. The effects of length of feed-in zone and lateral soil resistance on controlled lateral buckling are also presented. The results show that shorter length of feed-in zone and smaller lateral soil resistance will lead to smaller lateral buckling amplitude, maximum bending moment and maximum axial compressive stress. Therefore, reducing the length of feed-in zone or lateral soil resistance can be an appropriate method to be used to control lateral buckling. Finally, the analytical solutions are validated by use of the finite element modelling. The analytical results show good agreement with finite element analysis results.

Limit Analysis Method for Evaluating Soil Resistance to Lateral Motions of Pipelines Partially Embedded in a Seafloor

The lateral soil resistance available to pipelines partially embedded in a seafloor is of interest in evaluating pipeline lateral buckling capacity, stability under forces resulting from current loads, or route pullout loads. An upper-bound limit analysis method, including equilibrium requirements in a manner common to lower-bound theories, was used to evaluate lateral soil resistance to pipe displacements. The method is applicable to sand and clay foundations with homogeneous or layered conditions. Comparisons with results from physical tests and other limit analysis and finite-element investigations are presented. The numerical limit analysis procedure was implemented through numerical-computing software. An optimization procedure was used to identify the minimum resistance satisfying the governing objective equations. The seafloor surface geometry may include soil berms or other features. The soil strength may be described by a linear Mohr-Coulomb criterion or a curved criterion representing a varying material friction angle.

Control Method of Subsea Pipeline Lateral Buckling

Lateral buckling must be considered in exposed HP/HT pipeline design. Snaked-lay method is an effective lateral buckling control method, a new shape of snaked-lay pipeline is presented. Using ANSYS, nonlinear finite element model exposed on even seabed is built. Based on the FEM, sine length and snaked-lay radius are all studied. Sensitivity analyses show that critical buckling is reduced with sine length increasing when lay radius is fixed, but when sine length exceeding a certain value, there is no further reduction in resulting critical buckling force. Maximum moment and critical buckling force are all increased with snaked-lay radius increasing, but for maximum moment when snaked-lay radii exceeding a certain value, the increment is small.