Buried Pipelines Research Articles

Nonlinear structural responses of the buried oval steel pipelines crossing strike-slip faults

The permanent ground deformation may lead to bending failure or fractures of the buried steel pipelines. In practical applications, the buried pipelines may also exhibit ovality defects due to soil pressure, gravity of the pipeline, and misalignment of joints, which have the potential to diminish the load-bearing capacity of the buried pipelines. This paper introduces a comprehensive analytical methodology to examine the dynamic behavior of pipelines with different initial ovality defects subjected to strike-slip faults. A modified permissible lateral displacement function is introduced to determine the strain distribution of the deformed pipelines. One may predict the yield displacement of the oval pipelines accurately based on the yield theory of classical beams and the static equilibrium method. Then, the accuracy of the proposed method was validated by developing a finite element model and other results. Good agreement was reached characterized by the yield displacement and the yield strain, respectively. Finally, a parametric analysis was conducted on the effects of different ovality, steel grades, diameter-to-thickness ratios, fault inclination angles, and soil properties on the displacement and strain distributions of the deformed pipeline.

Ground failure and soil erosion caused by bursting of buried water pipeline: experimental and numerical investigations

Pressurized water pipelines buried in an urban environment are prone to bursting failures, threatening public safety and traffic convenience. The limited studies in literature just focused on soil fluidization while few studies considered ground failure, shear strain, soil erosion and the influence of leakage locations during pipe bursts. In this study, extensive experimental tests along with a finite difference method – discrete element method (FDM-DEM) solid–fluid coupling analysis were conducted to investigate these issues. It was disclosed that the failure development during pipe bursts can be divided into three stages, i.e., seepage diffusion, erosion cavity expansion, and soil fluidization. By digital image correlation (DIC) analysis of the experimental results, a wedge-shaped displacement zone in ground was identified, with peak shear strain near its boundaries. Moreover, it was revealed that leakage locations affected the expansion origin of erosion cavity; as the burial depths increased, the ground heave range increased linearly; the maximum water outflow distance was closely related to the internal pressures of buried pipeline, which could be modeled by a square root formula based on turbulent jet theory. Mesoscopic analyses revealed that finer particles were more susceptible to erosion during pipe bursts because of the low possibility of forming strong connections with surrounding particles. The findings yielded from this study can enhance the understanding of pipe bursts and help professionals mitigate potential damage.

Research on the Dynamic Leaking and Diffusion Law of Hydrogen-Blended Natural Gas under the Soil–Atmosphere Coupled Model

With the breakthrough in mixing hydrogen into natural gas pipelines for urban use, the widespread application of hydrogen-blended natural gas (HBNG) in energy delivery is imminent. However, this development also introduces significant safety concerns due to notable disparities in the physical and chemical properties between methane and hydrogen, heightening the risks associated with gas leaks. Current models that simulate the diffusion of leaked HBNG from buried pipelines into the atmosphere often employ fixed average leakage rates, which do not accurately represent the dynamic nature of gas leakage and diffusion. This study uses computational fluid dynamics (CFD) 2024R1 software to build a three-dimensional simulation model under a soil–atmosphere coupling model for HBNG leakage and diffusion. The findings reveal that, in the soil–atmosphere coupling model, the gas diffusion range under a fixed leakage rate is smaller than that under a dynamic leakage rate. Under the same influencing factors in calm wind conditions, the gas primarily diffuses in the vertical direction, whereas under the same influencing factors in windy conditions, the gas mainly diffuses in the horizontal direction.

Corrosion prediction model for long-distance pipelines based on NLFE-NGO-ELM

Abstract To improve the accuracy of buried pipeline corrosion rate prediction, we developed a Northern Goshawk Optimization-based Extreme Learning Machine (NLFE-NGO-ELM) model enhanced by Non-linear Feature Expansion. Feature selection was used to expand the small dataset and reduce the dimensionality of factors affecting pipeline corrosion. The Northern Goshawk algorithm was used, and 106 sets of pipeline external corrosion detection data were simulated in MATLAB as a case study. The ELM optimizer was analyzed using Grey Wolf Optimization (GWO-ELM), Northern Goshawk Optimization (NGO-ELM), and BP optimization as comparison models. Using NLFE-NGO-ELM significantly improved the model's prediction accuracy and speed. The NGO-ELM model was applied to predict the corrosion rates of 21 pipelines, achieving an absolute error of only 2.40% and an R value of 0.97255, surpassing the predictive performance of NGO-BP and GWO-ELM models. These results indicate that the current model exhibits superior learning performance and stronger fitting capabilities.

Modeling and assessment of hydrogen-blended natural gas releases from buried pipeline

Blending hydrogen into natural gas pipelines for transportation reduces costs but increases safety risks. The main objective of this work is to explore the evolution of leakage hazards in hydrogen-blended natural gas pipelines and quantify these risks. To achieve this, multi-stage coupling numerical models are developed to explore the leakage hazards in hydrogen-blended natural gas transportation. The results show that the proposed model accurately predicts leakage rates of hydrogen-blended natural gas pipelines in various soil types. The gas diffusion pattern shifts from spherical to hemispherical, with the hazardous volume increasing linearly overall. The influence of pressure on leakage is amplified in the soil, while the impact of the leakage aperture is diminished. Although increasing the hydrogen blending ratio reduces the leakage rate, it also enhances the hazard evolution. Burial depth primarily affects alarm time, while an increase in leakage angle within 90–180° significantly delays the hazard evolution. Moreover, higher soil resistance not only mitigates the leakage diffusion but also reduces the pressure differential. The leakage aperture exhibits the highest correlation with the hazard evolution.

Multi-physics coupled simulation and experimental investigation of alternating stray current corrosion of buried gas pipeline adjacent to rail transit system

As the gradual emergence of alternating current (AC) electrified rail transit system in urban areas, buried gas pipeline adjacent to the system will be seriously corroded by induced alternating stray current. These buried gas pipelines are at serious risk of electrochemical corrosion, which leads to safety and environmental threaten. In order to study the distribution of alternating stray current corrosion on pipeline surface on a larger spatial scale, this paper conducted numerical simulation and experimental validation of alternating stray current corrosion of buried gas pipeline. In the numerical simulation model, coupling between different physical fields are realized through the relationship between current density of pipe-to-soil interface, electrolyte, and electrodes. Proposed numerical method based on coupled multi-physics in this paper are in good agreement with experimental results under different influencing factors. A novel evaluation index was proposed to assess the corrosion risk within different zones on the pipeline surface. Results show that corrosion distribution is greatly influenced by spatial interaction between buried pipeline and rail transit system including crossing angle and parallel distance. Besides, alternating stray current corrosion on buried gas pipeline are proved to be both affected by dynamic characteristics due to AC fluctuation and operation mode of locomotive.

Experimental study on the leakage identification for the buried gas pipeline via vibration signals

It is difficult to detect and locate small leakages, especially for buried pipelines. Fortunately, a non-intrusive leakage identification method for buried gas pipelines is proposed in this study. Accelerometers were arranged in the soil at a certain distance from the leakage orifice to capture the acceleration signals caused by leakage. A 7-layer wavelet transform was applied to extract the leakage characteristic frequency band. Meanwhile, the attenuation characteristics of vibration signals were analyzed and the signal amplitude attenuation patterns in the axial, radial, and circumferential directions were analyzed. The results show that the leakage recognition rate is nearly 100% by selecting a P-SNR threshold of 7.26. Thus, the non-intrusive method based on accelerometers can be successfully applied for the leakage monitoring of buried gas pipelines.

Discrete element simulation of ground collapse induced by buried sewage pipeline breakage and soil leakage

The rupture of buried sewage pipelines constitutes a primary triggering factor of ground collapse. To investigate the phenomenon of ground collapse resulting from buried sewage pipeline breakage and soil particle leakage, numerical simulations employing the discrete element method (DEM) are utilized. The study focuses on examining the ground collapse mechanisms in both dry and water-rich sand stratum scenarios. A positive correlation is identified between the particle loss rate (PLR) and the magnitude of ground collapse, and a microscopic analysis of the mechanism of particle loss is carried out to visualize the soil arching process. The entire collapse process shows that the formation and destruction of soil arching are clearly accompanied by the particle loss phenomena. Additionally, the computational fluid dynamics (CFD) module is incorporated into the DEM to investigate the collapse of water-rich sand stratum. Parametric studies involving the burial depth of the pipeline, water pressure, the defect radius of the pipeline breakage, and the defect shapes are comprehensively conducted. It is found that the water pressure is the primary factor influencing the PLR, which progressively increases with higher water pressure, larger radius of pipe defect, and shallower burial depth.

Tunnelling-induced nonlinear responses of continuous pipelines resting on tensionless Winkler foundation

Prevailing analytical approaches for tunnelling-induced soil-pipeline interactions predominantly rely on linear analyses, limiting their applicability in nonlinear scenarios. This study introduces a novel tensionless Winkler solution that accounts for gap formation and soil yielding, validated against three well-documented experiments and demonstrating superiority over existing Winkler solutions. Additionally, plate load tests refine traditional soil-bearing theories for buried pipelines in sand, providing subgrade stiffness and ultimate bearing capacity values pertinent to tunnelling-induced interactions. Parametric studies highlight amplified nonlinearity in pipeline behaviours with increased pipeline flexural rigidity and tunnel volume loss, due to soil-pipeline separation and subgrade yielding. Notably, ignoring gap formation and soil yielding leads to overly conservative estimations of pipeline deflections and bending moments. Higher subgrade moduli increase pipeline strains, while enhanced subgrade bearing capacity above the pipeline prevents soil yielding, rendering its effect negligible, whereas the bearing capacity beneath the pipeline is inconsequential in tunnelling scenarios.

Seismic Performance Evaluation of Pipelines Buried in Sandy Soils Reinforced with FRP Micropiles: A Numerical Study

Unstable sandy soil poses significant challenges for buried pipelines, particularly due to the increased risk of displacement and stress-induced fractures resulting from soil settlement and earthquake-induced ground deformation. These concerns are especially critical in seismically active regions where underground infrastructure is at higher risk. Fiber-reinforced polymer (FRP) composites present a promising and sustainable alternative for deep foundations, offering durability and reduced maintenance costs compared to conventional materials. This study introduces a novel approach to enhancing the seismic performance of pipelines buried in sandy soils by numerically investigating a three-dimensional (3D) multipipe grouting micro anti-slide pile system, utilizing a polyurethane polymer slurry as the grouting material. Key parameters such as pile spacing, diameter, and length, along with the effects of soil wetting and various earthquake intensities, were examined under the influence of surface loads exerted by a fully loaded truck. The results demonstrate that using polymer micropiles significantly reduces soil and pipeline settlement by 15% to 50%, with larger pile diameters and lengths further decreasing settlement and strain on pipelines. While seismic excitation increases settlement, polymer grouting effectively mitigates this impact, leading to substantial reductions in settlement.

Wave-induced sloping seabed residual response around a buried pipeline

Most studies of the wave interaction with pipeline were conducted on a flat seabed. This paper presents the results from the numerical modelling simulation to investigate the wave induced response around a half-buried pipeline on a sloping seabed. The numerical model is validated using the experimental data of the wave-pipeline-seabed interaction. The validated model is then applied to simulate the wave generated pore pressure distribution around the pipeline buried in the sloping seabed. Effects of the pipeline buried depth, the pipeline position and the slope gradient on the wave generated residual pore pressure as well as the potential soil liquefaction within the sloping seabed are simulated and analyzed. Results demonstrate that the pipeline location on the sloping seabed can significantly affect the residual pore pressure within the sloping seabed. This is particularly true when the pipeline is placed at the junction between the flat seabed and slope.

Earthquake damage mitigation methods for buried pipelines under compressive loads: A case study of the Thames water pipeline

Promoting tensile failure by providing a proper orientation angle between the pipe axis and the fault line is the main seismic design philosophy for buried steel pipelines. However, most of the severe damage and failures experienced by pipelines are mainly due to negative crossing angle and thus compressive loads acting along the pipeline. This paper investigates different earthquake damage mitigation methods such as Carbon Fiber Reinforced Polymer (CFRP) wrapped pipes, Steel Pipes for Fault Crossing (SPF), and corrugated pipes for buried steel pipelines which are mainly subjected to compressive loads. Therefore, the Thames water transmission pipeline, which is a well-known case study, that suffered major and minor damage due to compressive forces in the 1999 Kocaeli earthquake, is considered to simulate and compare the earthquake damage mitigation capabilities of these countermeasures. The numerical studies are performed by using a three-dimensional nonlinear finite element model. The results show that the use of CFRP composites in buried pipelines, regardless of their thickness, wrapping length, or layer orientation, does not have the expected damage reduction effect, but does increase the effective length between major wrinkles or change the type of pipe failure. On the other hand, SPFs and corrugated pipes are more effective in earthquake damage reduction due to their high axial and rotational capabilities.

Efficient finite element reliability analysis employing sequentially-updated surrogate model for fragility curve derivation

As the threat of natural disasters to structures intensifies, risk assessment of infrastructure has gained much importance. Fragility curves are essential tools in predicting disaster-related losses and making disaster mitigation decisions. In this paper, we propose a new method to efficiently derive accurate fragility curves for structures with high levels of nonlinearity or complexity, addressing the computational challenges of conventional finite element reliability analysis (FERA). To reduce the computational cost for calculating probability of failure in FERA, the proposed method utilizes the first-order reliability method (FORM). However, even with this approach, the computational cost of deriving the fragility curve may remain high; therefore, a surrogate model is used to further reduce costs. By training the surrogate model using the initial structural damage probabilities for a few hazard intensities, an optimal starting point can be calculated for the subsequent FORM analysis. During the fragility analysis, the surrogate model can be updated sequentially to increase the efficiency of FORM analysis continuously. In particular, the training process of the surrogate model requires no separate or additional finite element analysis because it is constructed using previous FERA results. The accuracy and efficiency of the proposed method are tested using conventional FERA and Monte Carlo simulations through a hypothetical short-column example. In addition, fragility curves are derived through a bridge flood fragility assessment considering the scour and seismic vulnerability assessment of a buried gas pipeline considering soil-structure interactions. The derived fragility curves closely match those derived using the conventional FERA, and the computational costs are reduced by 36.54 % and 52.38 %, respectively, compared with the conventional FERA, confirming its cost-effectiveness.

Analysis of Leakage and Diffusion Characteristics and Hazard Range Determination of Buried Hydrogen-Blended Natural Gas Pipeline Based on CFD.

Injecting hydrogen into natural gas pipelines is an economical and efficient method of hydrogen transportation. However, the addition of hydrogen leads to significant hydrogen corrosion and embrittlement in the pipelines, especially in harsh and concealed underground conditions, where leak accidents are frequent and difficult to detect. This Article uses Le Chatelier's Principle to determine the hazardous range of hydrogen-blended natural gas (HBNG) by employing numerical simulation, it examines the gas leakage and diffusion characteristics before and after hydrogen injection as well as under different hydrogen blending ratio (HBR). Additionally, considering the density of the mixed gas, a prediction model for the diffusion hazard range of hydrogen-mixed natural gas is established based on multivariate regression theory. The results show that after a leakage occurs in HBNG the diffusion range in soil is wider compared to methane, with higher corresponding pressure and velocity values. Moreover, as the HBR increases, the farthest danger range (FDR) of the HBNG also increases. When the leakage of the buried HBNG pipeline occurs for 1 min, the difference in FDR between HBR 25% and HBR 5% is 0.005 m. After 30 min, this difference increases to 0.019 m, indicating that with longer leakage duration, the potential explosion risk resulting from increased HBR becomes greater. Factors such as pipeline pressure increase, larger leak hole size, and decreased burial depth all contribute to an increase in FDR, with pipeline pressure change having the greatest impact and burial depth change having the smallest impact. The maximum error of the predicted model for the diffusion hazard range of hydrogen-mixed natural gas is 9.385%, and the average error is 2.376%, demonstrating the accuracy of the prediction results. This study provides guidance for monitoring underground hydrogen-blended natural gas pipeline leaks, offers a basis for determining the repair range of pipelines, and ensures the safe transportation of hydrogen-mixed natural gas pipelines.

Accurate modeling and safety evaluation of dented pipeline with internal pressure based on reverse modeling technique

ABSTRACT As a common form for pipeline geometric defects, dents can induce the local stress concentration of the pipeline, which would result in the debilitation of the bearing capacity and bring huge safety hazards. In this paper, the accurate surface profiles of dented pipeline are acquired based on the 3D scanning technology and deformation detection technology, respectively. Then, the dented pipeline models are constructed by the reverse modeling technique, and the stress distribution characteristics of the dented pipeline in the operation condition are simulated using ABAQUS. The maximum von Mises stresses of a dented pipeline obtained from two proposed modeling techniques are basically consistent. However, the deformation detection technology can effectively avoid the excavation work for buried pipelines. Therefore, the reverse modeling technique based on the deformation detection technology has strong feasibility in practical projects and significant application value in the safety assessment of submarine pipelines, where excavation work is impractical.

Influence of crossing fault position and site soil on the mechanical properties of bellows joint connected buried pipelines under direct shear

Buried pipeline systems are vulnerable to joint damage in earthquakes. Previous studies have shown that bellows joints are effective in increasing deformation capacity and reducing the axial force of the main pipeline. However, the effectiveness of bellows joints in enhancing the deformation capacity of the pipelines is affected by the location of the crossing fault and the soil at the site. This paper constructs and validates a finite element model of a buried steel pipeline connected by a bellows joint using ABAQUS to investigate this issue. The effects of fault location, soil properties, and internal pressure on the bellows joint connected pipelines were analyzed using a finite element model. The results indicate that the bellows joints exhibit the best energy dissipation and deformation enhancement when the fault passes directly through the joints. Bellows joints in soft soil are better at dissipating energy, reducing pipe deformation, and mitigating pipe damage compared to those in hard soils. The internal pressure is helpful to increase the mechanical properties of the pipelines. The findings can provide some guidance for pipeline design and mitigation strategies for ensuring the reliability and safety of buried pipeline systems in earthquake-prone areas.

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.

Centrifuge tests on the deformation law of pipelines crossing slopes with different water contents

The deformation law of pipelines crossing landslide areas is an important prerequisite for the scientific design of pipelines. Most current studies find it difficult to simulate the real stress and strain state of pipelines on site. This study conducted two centrifuge model tests to observe pipeline failure indicators (deformation, stress, strain) and slope failure indicators (crack width, soil pressure, landslide displacement) in response to changes in acceleration. The experimental findings align with the results obtained from numerical simulations. The findings indicate that slope failure with high moisture content is more serious. At a moisture content of 15%, the slope has a maximum displacement of 70 mm in close reach to the buried pipeline. The pipeline has a “bimodal distribution” of strain along its axial length. The largest amount of deformation occurs at a distance of L/4 from the center of the pipeline, and the deformation value is 9000 με. Moreover, the maximum deformation in the mid-span is 21 mm, which corresponds to the result accumulated from the numerical simulation. Thus, the pipeline needs to improve the disaster prevention capabilities at the mid-span and L/4 of the pipeline.

Novel hybrid XGBoost-based soft computing models for predicting penetration resistance of buried pipelines in cohesive soils

In this paper, both the finite element limit analysis (FELA) and soft computing techniques of four hybrid XGBoost (XGB) models, namely, GA-XGB, optimized with Genetic Algorithms; SMA-XGB, optimized with Slime Mould Algorithms; PSO-XGB, optimized with Particle Swarm Optimization; ACO-XGB, Ant Colony Optimization; and one Genetic Programing model (GP), are employed to develop surrogate models for predicting the undrained penetration resistance of buried pipelines embedded in clays. The penetration resistance of pipelines is caused by internal and external pressures, resulting in a force that acts on the pipeline in the downward and inclined directions at the same time. The penetration resistance factor (N) of a buried pipeline is determined based on four dimensionless variables, namely, the buried depth ratio (H/D), the inclination angle of the applied load (β), the soil strength or overburden ratio (γH/c), and the adhesion factor at soil-pipeline interfaces (α). The findings of this study are presented and summarized in the form of charts for dimensionless penetration resistance factors (N) and failure mechanisms of pipelines. Furthermore, the results from this study are compared with the results from previous studies and agrees well with those of previous studies. According to the results of the four developed hybrid XGBoost-based models, SMA-XGB outperforms GA-XGB, PSO-XGB, and ACO-XGB with no symptoms of overfitting, while the GP model resulted in an adequately accurate model with the advantage of a closed-form equation; its determination correlation coefficient of training and testing equals 0.98 (R2 = 0.980).

Layered seabed effects on buried pipeline response to ice gouging

In ice gouging analyses, the seabed is often simplified as a uniform material domain, over-looking the potential complexities inherent in layered seabed formations, which are wide-spread in numerous Arctic regions. This study investigates the pipeline response into the distinct seabed configurations, including layered soft over stiff clay, layered stiff over soft clay, and uniformly soft and uniformly stiff compositions, to ice gouging. This was achieved through comprehensive large deformation finite element (LDFE) analysis, employing a Coupled Eulerian Lagrangian (CEL) algorithm. Incorporation of the strain-rate dependency and strain-softening effects involved the development of a user-defined subroutine and incremental update of the undrained shear strength within the Abaqus software. The pipeline is explicitly incorporated into the model, allowing for a detailed investigation of its response to ice gouging phenomena within these layered seabed scenarios. This research demonstrates that simplifying a layered seabed into a uniform can be misleading. Such an approach can lead to significant errors, potentially overestimating or underestimating pipeline response to ice gouging. By incorporating these complexities, engineers can develop more optimized designs with enhanced safety margins in Arctic environments prone to ice gouging phenomena.