Buckle Propagation Research Articles

Propagation buckling failure of a buried offshore pipeline with integral arrestors under external overpressure and strike-slip faulting disturbance

In this study, the propagation buckling failure of a buried offshore pipeline under external overpressure and strike-slip faulting disturbances was investigated numerically. A nonlinear shell model, accounting for geometric, material, self-contact, and pipe-soil interaction nonlinearities, was developed using the vector form intrinsic element method. The arresting performances of the single- and double-integral arrestors were analyzed based on a series of simulations considering various combinations of arrestor diameter-to-thickness ratios, lengths, and sub-arrestor intervals. A comparative analysis was conducted between single- and double-integral arrestors, focusing on their arresting performance, material usage, and manufacturing complexity. The results revealed that pipelines under external overpressure are prone to local collapse and bidirectional buckling propagation under small fault displacements. Reverse ellipticities occur downstream of the buckling propagation and their development leads to flipping propagation. Buckling arrestors function by exhausting the upstream flattening propagation and inhibiting the development of reverse ellipticities downstream. The material consumption of each single-integral arrestor was significantly higher than that of a double-integral arrestor with the same diameter-to-thickness ratio. The weld count of the double-integral arrestors was lower than that of the single scheme, but this difference narrowed as the pipeline mileage increased. These results can serve as valuable guidelines for the design and construction of pipelines crossing seismic zones.

Integrated finite element analysis and machine learning approach for propagation pressure prediction in hybrid Steel-CFRP subsea pipelines

Accurate prediction of the propagation pressure (PP) in hybrid steel-CFRP pipe systems presents a substantial challenge due to intricate interactions and complex collapse failure modes. An efficient FE-based algorithm is programmed using ANSYS to numerically estimate the PP of hybrid steel-CFRP pipe, subjected to external pressure. This study employs a machine learning (ML) framework, addressing the inherent complexity with a three-phase approach: Parameter Design, Buckle Propagation Analysis, and ML Model Development. The dataset, encompassing about two thousand observations with four key features, undergoes k-fold cross-validation and min-max normalization for robust ML performance. Five ML models—Random Forest (RF), K-Nearest Neighbors (KNN), Genetic Programming (GP), Multi-layer Perceptron (MLP), and Support Vector Machine (SVM)—are developed and evaluated. The results revealed a significant influence of Ds/ts, a three-phase relationship with ts/tc, and a substantial decrease in PPh/PPs with increasing σys/σuc, predominantly exhibiting U-shaped or dog-bone failure modes in different scenarios. Proven that GP, KNN, and RF are the superior performers, ranking ahead of SVM with Gaussian Kernel (SVM-GK), MLP, and SVM with Linear Kernel (SVM-LK). Statistical metrics, Taylor Diagram analysis, and comparisons with FE results emphasize the effectiveness of GP, KNN, and RF. Additionally, normality tests and feature importance analysis provide nuanced insights.

Buckle propagation failure of subsea pipelines; experimental, analytical, and numerical simulations

This research program investigates buckle propagation in subsea pipeline systems, The study aims to understand and predict propagation pressure (PP ), essential for ensuring the structural integrity and safe operation of these pipelines, hypothesizing that incorporating strain hardening effects into the strain energy approach can significantly enhance the prediction of propagation pressure (PP ) and that geometric parameters, particularly the diameter-to-thickness (D/t) ratio, play a major role in PP prediction. Accurate PP prediction is essential for ensuring the structural integrity and safe operation of these pipelines. The investigation is conducted through analytical, experimental, numerical, and machine learning approaches. A new analytical solution for PP is proposed, incorporating strain hardening effects using a strain energy approach. Experimental tests conducted using a hyperbaric chamber cover a wide range of pipeline configurations and materials, including steel, aluminum, and stainless steel. Complementing experimental data, numerical simulations using finite element methods facilitate parametric dependence analysis and the visualization of results through 3D charts. More than 600 FE models were simulated to investigate the influence of geometric and material parameters on PP . The findings from both experimental and numerical analyses indicated that the geometric and material properties have a significant impact on PP , specifically, the diameter-to-thickness (D/t) ratio, yield stress (σy ), and tangent modulus (E′). Furthermore, Machine Learning (ML) techniques have been used to predict the PP value and have concluded that the Random Forest (RF) technique outperformed the K-Nearest Neighbors (KNN), and Multi-layer Perceptron (MLP) neural network techniques. Overall, this study concludes that analytical, numerical, and machine learning approaches offer valuable insights into buckle propagation in subsea pipelines, contributing to improved safety and reliability in offshore oil and gas operations.

Experimental and analytical evaluation of the performance of hybrid steel-CFRP pipelines at high external pressures

Behavior of hybrid steel-CFRP pipe systems under external pressures is studied herein using a combination of experimental, analytical, and finite element (FE) methods. Hyperbaric chamber tests are conducted on steel tubes and those wrapped with CFRP of different thicknesses and winding orientations to evaluate their performances. Based on the experimental observations and using analytical methods, new equations are proposed that can predict the collapse and propagation pressures of the hybrid steel-CFRP pipelines. The results revealed a significant enhancement in the collapse and buckle propagation capacities of the hybrid steel-CFRP pipes, with average increases of 60% and 200% respectively, compared to bare steel pipes. The failure mode observed in the hybrid steel-CFRP pipe was characterized by a U-shaped pattern, which occurred at higher pressures than the dog-bone shape mode observed in bare steel pipes. As evidenced in the FE results, the presence of CFRP in the hybrid steel-CFRP pipe system led to improved stress distribution, enhanced buckle propagation capacity, and reduced ovality. These findings demonstrate the effectiveness of CFRP in reinforcing steel pipes and highlight the potential for the hybrid steel-CFRP pipe system to offer superior performance in deep-waters.

Empirical formula of buckle propagation pressure for sandwich pipes with polymer core material

The sandwich pipe, with its high hydraulic pressure resistance and thermal insulation properties, presents itself as a potential choice for deepwater oil and gas exploration. This study developed a 3D finite element numerical model using ABAQUS software to simulate the collapse propagation of sandwich pipes under the high external hydraulic pressure. A parametric analysis was undertaken using a numerical model, which had been calibrated by experimental tests. The study aimed to assess the contributions of material properties, such as yield strength and Young's modulus, as well as geometric dimension, to the collapse propagation behavior of the sandwich pipe. Moreover, a simplified empirical formula was formulated to research the propagation pressure of polymer sandwich pipes. The research also investigated the contribution of the interaction property between the core layer and inner/outer steel layer on the propagation pressure. An interfacial factor was incorporated into the present simplified empirical formula. The empirical formula was validated using experimental results and data from various sources, including real interlayer interactions observed during tests. The results indicate that this formula offers an accurate prediction of the propagation pressure for polymer sandwich pipes.

Confined buckle propagation of offshore pipelines under external pressure

Offshore pipelines can be protected against collapse and buckling propagation by installing buckle arrestors or restraint cylinders. When the external pressure is high enough, the buckling would penetrate the arrestors or restraint cylinders and propagate along the line inside these protective structures, known as confined buckle propagation. A two-dimensional theoretical model has been proposed to estimate the confined propagation pressure, considering the rigid-perfectly plastic model and the Ramberg-Osgood model, respectively. Subsequently, the hyperbaric chamber test on SS304 confined tubes was conducted under external pressure. The annulus space of test specimens between the internal pipe and the external constraint cylinder was full of high-strength cement mortar and epoxy resin, respectively. Numerical models have been developed to duplicate the local collapse and the confined buckle propagation scenarios, and reasonable consistencies are observed between the tests and the numerical simulations. After that, broad parametric analyses of the confined propagation pressure are implemented to examine the influence of geometry and material property. As a result, an empirical expression is proposed to predict the confined propagation pressure.

Structural optimization of an encased bi-material FGP-GNF pipeline-liner system with novel polyhedral configurations

This article proposes a novel thin-walled polyhedral functionally graded porous (FGP) liner consolidated by graphene nanofillers (GNF) to rehabilitate the cracked pipeline. A buckle propagation may occur since the liner is subjected to hydrostatic pressure and temperature variational field simultaneously. A cosine function is developed to describe the deformed shape of the liner. Both pores and the GNF are distributed symmetrically on the cross-section of the liner, which also has a polyhedral profile to improve its bending stiffness. The nonlinear equilibrium equations are accurately obtained by introducing the thin-walled shell theory and the principle of minimum potential energy. The critical buckling pressure is obtained by solving the nonlinear equilibrium equations. Analytical solutions are compared successfully with other closed-form results to accomplish the verification when the FGP-GNF polyhedral liner reduces to an isotropic circular one. Furthermore, one improvement factor is proposed to analyze the effect of different polyhedral shapes on the buckling pressure of the encased polyhedral FGP-GNF liner. Finally, parameters are evaluated to further understand the buckling behavior of the FGP-GNF polyhedral liner, including the number of polygons, porosity coefficient, mass fraction, geometric shape of the GNF, radius-to-thickness ratio, temperature field, etc.

Water nanolayer facilitated solitary-wave-like blisters in MoS2 thin films

Solitary waves are unique in nonlinear systems, but their formation and propagation in the nonlinear fluid-structure interactions have yet to be further explored. As a typical nonlinear system, the buckling of solid thin films is fundamentally related to the film-substrate interface that is further vulnerable to environments, especially when fluids exist. In this work, we report an anomalous, solitary-wave-like blister (SWLB) mode of MoS2 thin films in a humid environment. Unlike the most common telephone-cord and web buckling deformation, the SWLB propagates forward like solitary waves that usually appear in fluids and exhibits three-dimensional expansions of the profiles during propagation. In situ mechanical, optical, and topology measurements verify the existence of an interfacial water nanolayer, which facilitates a delamination of films at the front side of the SWLB and a readhesion at the tail side owing to the water nanolayer-induced fluid-structure interaction. Furthermore, the expansion morphologies and process of the SWLB are predicted by our theoretical model based on the energy change of buckle propagation. Our work not only demonstrates the emerging SWLB mode in a solid material but also sheds light on the significance of interfacial water nanolayers to structural deformation and functional applications of thin films.

Premothballing, Mothballing, and Recommissioning Method for 762-mm and 102-km Offshore Gas Pipelines

In the coming years, gas production in Indonesia is projected to decrease so that the option to abandon a plant and temporary shut down will increase. The 762-mm and 102-km offshore gas pipeline is planned to be shut down for 4 years. Therefore, the comprehensive method from the premothballing, mothballing, and recommissioning stages should be developed. In this study, these methods have been developed and the pipeline can be preserved for 4 years with some remarks where the coating repairs, freespan rectification, and analysis of the sacrificial anode remaining life must be performed before premothballing stage. In the premothballing stage, 4 different pigs are used to clean the pipeline until the deposit released is less than 20 L. In mothballing, the internal pipeline is filled with nitrogen gas to prevent the corrosion. The injection of nitrogen gas will be conducted by the train pig method, where each train pig is pushed by nitrogen gas. The internal pressure of the pipeline must be maintained at 1.1 MPa and should not be less than 0.9 MPa to avoid buckle propagation. Continuous maintenance and monitoring should be conducted on the pipeline. The corrosion coupon monitoring should be performed every six months, pressure and right of way (ROW) monitoring should be carried out every two weeks, and regular monitoring and maintenance reports should be conducted at least once a year. Recommissioning begins with evaluating data and conducting remotely operated vehicle (ROV) inspections. Nitrogen gas displacement is performed using a train pig driven by fresh nitrogen gas on two pigs and the production gas should be streamed to push the third pig. The inline inspection (ILI) must be performed to determine the percentage of actual metal loss. The ILI results can be used to perform remaining life analysis and as requirements for pipeline recertification so that the pipeline can be reoperated.

Design Equation of Buckle Propagation Pressure for Pipe-in-Pipe Systems

This paper focuses on the buckle propagation pressure of a pipe-in-pipe system under uniform external pressure. After the validation of the finite element model used in this research, several effects were studied. At first, the effects of the initial imperfection of the inner pipe, including the ovality and eccentricity, were checked out. Second, the influence of the scantling of the inner and outer pipes was tested. It was found that the dominant factor which affects the buckle propagation mode is changeable. Then, the boundary value of the above factor was investigated by varying the ratio of the outer and inner diameters. Finally, after a summary of the calculation results, an empirical formula was proposed to illustrate the relationship between the buckle propagation pressure and the geometrical parameters of the pipe-in-pipe system. Utilizing this formula, the buckle propagation pressure of the pipe-in-pipe system can be estimated rapidly with good accuracy.

On the dynamics of nanoscale structures upon a novel mixture model of elasticity: buckling analysis, vibration analysis, and wave propagation

In this study, a novel mixture model of elasticity, that can cover all size-dependent theories together with simultaneously taking of softening and stiffening impacts, is regarded as mathematical modeling and dynamic analysis of Timoshenko nanobeams. Since the mixture model is the combination of Eringen's two-phase theory with two-phase stress-driven theory, therefore, there are four parameters containing two various types of nonlocal parameters and two additional local phase fraction factors. In this work, after introducing the mixture model together with essential assumptions and relations, the integral form of relations with an equivalent differential form of ones is illustrated. Next, essential conditions are considered and satisfied to match the integral relations with differential relations without any conflict of restrictions are obtained. Finally, through some examples, the essential relations together with compatibility boundary conditions are derived to analyze the buckling, vibration, and wave propagation of Timoshenko nanobeams. Utilizing an efficient numerical solution, the results are achieved, and the validity as well as integrity of the constitutive differential relations are examined through some validation studies. The output results disclose that the previous results in the field of contemporary continuum theories are the particular state of dynamic response of the nanobeams.

Second-order computational homogenisation enhanced with non-uniform body forces for non-linear cellular materials and metamaterials

Although “classical” multi-scale methods can capture the behaviour of cellular, including lattice, materials, when considering lattices or metamaterial local instabilities, corresponding to a change of the micro-structure morphology, classical computational homogenisation methods fail. On the one hand, first order computational homogenisation, which considers a classical continuum at the macro-scale cannot capture localisation bands inherent to cell buckling propagation. On the other hand, second-order computational homogenisation, which considers a higher order continuum at the macro-scale, introduces a size effect with respect to the Representative Volume Element (RVE) size, which is problematic when the RVE has to consider several cells to recover periodicity during local instability. In this paper we reformulate in a finite-strain setting the second-order computational homogenisation using the idea of equivalent homogenised volume. From this equivalence, arises at the micro-scale a non-uniform body force that acts as a supplementary volume term over the RVE. In the presented method, this non-uniform body-force term arises from the equivalence of energy, i.e. the Hill–Mandel condition, between the micro- and macroscopic volumes and depends mainly on the relation between the micro-scale and macro-scale deformation gradient. We show by considering elastic and elasto-plastic metamaterials and cellular materials that this approach reduces the RVE size dependency on the homogenised response.

Pipeline Wall Thickness Assessment of Various Material Grades and Water Depths Using American and Norwegian Standards

Two standards that are widely used by many countries in designing offshore gas transmission pipelines are American Standard – ASME B31.8, Gas Transmission and Distribution Piping Systems and Norwegian Standard – DNVGL-ST-F101, Submarine Pipeline System. A thorough understanding of these standards is vital in determining optimal pipeline design to ensure pipeline integrity for safe and sustainable operations, as well as striving for economic efficiency. This study aims to evaluate the wall thickness required for pipeline designs using American and Norwegian pipeline standards under different steel grades and water depth conditions. Pipeline costs are then compared for both standards at each water depth condition for commercial evaluation. Through this, the optimal pipeline standard for wall thickness design can be determined. Mathcad software was used for data analysis in accordance with the standards mentioned and all design requirements including pressure containment, collapse, and propagation buckling. Ultimately, the American Standards was able to provide a total cost that was 2.5% lower than the Norwegian Standard for a pipeline project with a combination of shallow, medium, and deepwater depths along its route. However, a combination of Norwegian Standards for medium and deepwater depths and American Standard for shallow water depth can further reduce total costs to 2% compared to only using the American Standard. This study highlights the importance of considering several design standards for a pipeline project instead of strictly adhering to a single standard for better technical and commercial benefit.

Buckling initiation and propagation in pipes under external pressure

A universal plastic ring-beam model is presented considering the longitudinal stretching effect in the transition zone based on the pipes' deformation mode analysis. An improved ring model is applied to the pipe's propagation pressure problem. The closed-form solutions are significantly improved compared to previous studies and are much closer to the FEM or experimental results, especially for medium-thick or thin-walled pipes. The proportion of longitudinal stretching effect in propagation pressure decreases with the increase of diameter-thick-ratio, accounting for 20%–30% of thin wall pipes (25≤ D/t ≤ 40), and 30%–40% for medium-thick-walled pipe (15≤ D/t ≤ 25). Buckling triggers simultaneously in the multiple equal ovalities along the pipe's axial direction. Oval defect deviation angle leads to generating torsional moments in the propagation buckling process, which in turn produces a flip phenomenon, propagation flip-flop mode occurs when the defect deviation angle is a right angle. Whether multipoint trigger mode, flip-flop mode or other axial factors of oval defects in pipes affect buckling initial pressure to different degrees but seem to have no effect on the propagation pressure.

Unfolding the dynamics of free-falling folded chain: Experiments and simulations

Contrary to educated intuition, the tip of a free-falling U-folded chain accelerates faster than gravity without violating the Newtonian laws. In the current work, we study the dynamics of a free-falling U-folded chain experimentally as well as numerically. To this end, high-speed imaging (up to 10000 fps) is used to capture the chain’s falling tip by using different openings between the two tips of the chain. Thanks to high-speed digital imaging, the detailed geometry of the dynamic unfolding is captured. The post-processing of captured images has provided detailed quantitative temporal data for displacement, velocity, and acceleration of the falling tip of the chain. The experimental observations have revealed the various phases of dynamics of the falling U-folded chain, including unfolding, whipping, and rebounding phases for the first time. Furthermore, a Henky-type model is developed to capture the associated phenomena related to these phases, such as rebound effect, whip effect, local buckling, and transverse wave propagation. The model that includes nonlinear elastic, dissipative and bilateral gap-contact features, could successfully capture the experimentally observed phases and phenomena of the unfolding dynamics qualitatively.

Influence of FRP arrestors on the dynamic collapse and implosion of underwater pipelines

The dynamic collapse of pipelines in deep water can create pressure pulses that affect the performance of surrounding structures. In this study, the pipe implosion process was analysed using the Lagrangian–Eulerian method. The numerical model was calibrated using the experimental data, and the responses of the pipelines and surrounding fluid during pipeline collapse and buckle propagation were obtained. The fluid–structure interaction mechanism of the composite arrestors attenuating the pressure pulse was investigated. The simulation results showed that the implosion of a pipeline was a transient high-energy dynamic event. The fluid surrounding the pipe rushed towards the pipe surface at a high velocity during implosion and dynamic buckle propagation, which resulted in a spatial change in pressure distribution. Notably, the unidirectional fibre reinforced polymer (FRP) arrestor had a positive effect on reducing the peak pressure of the pulse wave. Furthermore, the effects of different arrestor spacings and materials on pipe buckling and implosion pressure were discussed, and the design of FRP arrestors was optimised.

Vortex-induced vibration of a full-diamond textured cylinder at subcritical Reynolds numbers

Textured pipe has been proposed to improve the propagation buckling capacity of subsea pipelines recently. Due to its special geometry, textured pipe may have the potential to mitigate the vortex induced vibration (VIV) by altering the wake vortex street formation. In the present study, the effectiveness of using a full-diamond textured pipe for VIV suppression is numerically investigated in a coupled fluid-structure interaction (FSI) framework. Three-dimensional (3D) Computational Fluid Dynamics (CFD) analyses are performed by using the Reynolds-Averaged Navier-Stokes (RANS) turbulence model equipped with shear stress transport (SST)K−ω model at the subcritical Reynolds numbers (Re) with Re∈[2000,12000]. The results are compared in detail with an equivalent conventional smooth cylinder subjected to the same flow conditions. Numerical results show that the textured cylinder can significantly mitigate the undesired VIV and the associated hydrodynamic forces. It eliminates the upper excitation regime in the conventional smooth cylinder and the width of the synchronization regime is also remarkably reduced.

Propagation pressure collapse in conventional pipelines and MLPs: Numerical investigation

The collapse of submarine pipelines can have immense economic and environmental impacts, and understanding the mechanical behavior of such structures under extreme external pressure is vital for the design, fabrication, installation, and operation. The pipe's outer surface is susceptible to damage/impacts due to uncontrolled circumstances, possibly leading to structural changes. This work applies numerical tools to evaluate the collapse and buckle propagation in steel pipes, considering the effects of an initial known deformation caused by different puncher's shapes. Therefore, the structure assumes a new geometry leading to modification in the capacity to withstand external pressure. The analysis applies and compares two numerical methods: the arc-length (Riks) and dynamic-explicit approaches. This comparison allows establishing a direct association between the observed features of the two methodologies. In a general manner, the observation indicates that an increasing indentation causes a reduction in the collapse pressure but also significant changes in the propagation pressure. The similar results between the two methods applied in steel pipes permitted extending this concept to estimate the propagation pressure in Mechanically Lined Pipes (MLPs), where the Riks method is unstable, and the dynamic approach is suitable. In this scenario, the possibility of the internal liner buckling before the external backing steel and the appearance of new failure modes is part of a new complex scenario where the number of variables grows significantly, and the collapse circumstances must be reassessed. The boundary conditions, interface state, and other structural parameters increase the difficulty in this type of analysis, showing that in MLPs the number of variables associated with propagation pressure is much higher than in steel pipes.

Modeling the delamination failure under compressive loads in CFRP laminates based on digital image correlation analysis

Laminate composite materials such as CFRPs are highly susceptible to delamination, being one of the common failure modes in composite laminates. The combination of severe delamination with uniaxial compressive loads leads to the loss of stability and structure failure. In this study, the authors present an experimental and numerical analysis of this effect in laminates. A series of tests were carried out with four different specimens including delamination-free plates and plates with incipient delamination with different damage size and location. 3D Digital Imagen Correlation technique was applied to predict the buckling initiation and propagation and to validate the numerical models implemented, showing good agreement between the numerical and experimental results. Model material failure includes Hashin criterion and cohesive zone model (CZM) to predict delamination. Finally, numerical models have been used to predict the crack initiation and progression in the rest of samples.

BUCKLE PROPAGATION OF SANDWICH PIPES UNDER EXTERNAL PRESSURE

Buckle propagation of local collapse appearing in the damaged pipes is one of the failure modes that are of particular interest for deepwater application. The local collapse can propagate along the pipeline for long distances in both directions when the external pressure magnitude is up to the propagation pressure. In this paper, the buckle propagation pressure of sandwich pipes (SP) with different material properties and geometric characteristics is investigated by numerical simulation using Python programming language based on general finite element code. The results of the pressure history data obtained are verified by comparing those published previously. The effect of material properties, geometric characteristics and adhesion conditions on the propagation pressure are analyzed.