Pipeline Stability Research Articles

Experimental and theoretical studies on lateral buckling of submarine pipelines

Global buckling of a submarine pipeline during high pressure/high temperature (HP/HT) operation results in a loss of pipeline stability that is similar to a bar in compression; this phenomenon constitutes one of the key factors affecting pipeline integrity and design. To intuitively study the buckling response, a test system was designed that can account for thermal loading and pipe-soil interactions, and this system was used to perform a series of small-scale model tests on the lateral buckling of submarine pipelines with different initial imperfections. Based on the hat-shaped buckling profiles of the test pipelines, a new buckling mode called "hat-shaped buckling" was proposed. In an attempt to study the conditions under which the pipeline exhibits this hat-shaped buckling mode, the changing law of the buckling mode was investigated through finite element analyses of pipelines with different parameters, including the length of the pipeline and the amplitude and wavelength of the initial imperfection. Subsequently, an analytical solution for calculating the buckling amplitude of a pipeline with a hat-shaped buckling profile was proposed. The theoretical solution was compared to the experimental data, which verified the feasibility of the model in calculating pipeline buckling deformation. The experimental data, the buckling mode based on these data and the corresponding analytical model discussed herein may provide a reference for future experimental studies of pipeline buckling.

Program complex for solving of some classes of aerohydroelasticity problems

On the basis of the developed mathematical models, a program complex was created for studying the dynamics and stability of an elastic pipeline, an elastic structural element in supersonic flow, elastic elements of wing profiles of several types with subsonic flow, elastic elements of vibration devices of several types. The complex generates three-dimensional graphs of element deformations, construction of animation graphs of element deformations, construction of flat graphs of deformations and strain rate at a given point or at a given time. On the basis of the constructed graphs, one can study the dynamics and draw conclusions about the stability of vibrations of elastic structural elements.

A study on the flow characteristics of butterfly valve with baffles

In the industry, globe valves, which are commonly used to precise control the flow rate along with opening and closing flow in pipes, are technically and economically limited in valve size due to structural instability related to complex internal flow passage. Butterfly valves, on the other hand, have advantages such as low weight and low manufacturing costs, but it is difficult to control the flow rate at an opening angle of 60°or higher and flow is unstable in the case of butterfly valve. Therefore, the purpose of this study is to have characteristics of flow rate of the globe valve that is used in the industry at the same diameter of pipeline and flow stability due to uniformity of flow through the baffle hole by adding 1/2 baffle to butterfly valve. Hole size of baffles were set at 5, 7 and 9 mm and baffles were set at the rear of the butterfly valve. To verify the method of numerical analysis, the results of experimental study were compared with the results of numerical study. As a results, it is confirmed that characteristics of flow rate of butterfly valve with baffle is similar to globe valve in the case of hole size 5 mm. In addition, flow pattern is to be stable by analyzing turbulence energy. Consequently, when applying baffle to butterfly valve, it is possible to reduce the flow unstability and change the flow rate of butterfly valve.

Relationship between texture of polypropylene coatings and interface friction for sand at low stress levels

Pipelines in the offshore sector make common use of polypropylene (and other polymer) coating systems to protect the infrastructure and provide thermal insulation. High pressure high temperature pipelines are subject to large axial loads due to restraint by seafloor soils of thermal strains in the pipe wall. Friction between pipe coating material and seafloor soil plays a defining role in the build-up of axial stress and the formation of lateral buckling. Accurate quantification of pipe–soil interface friction is key to robust pipeline stability design and possibilities to enhance or manipulate the friction coefficient may be attractive to designers. An extensive campaign of soil and interface tests using a range of granular materials and polypropylene surface specimens engineered to achieve varying surface textures was carried out. The results show that interface friction primarily depends on stress level and the magnitude of the surface texture in relation to the particle size. Herein, a new relative texture parameter, Ta, is developed that, unlike alternative relative roughness parameters, can be obtained using conventional profilometry measurement techniques. An expression for estimating the friction coefficient in relation to texture and stress level is proposed that can serve as a useful predictor of pipe–soil interface friction.

Geophysical investigations for stability and safety mitigation of regional crude-oil pipeline near abandoned coal mines

Abstract This study aims for the protection of a crude-oil pipeline, buried at a shallow depth, against a probable environmental hazard and pilferage. Both surface and borehole geophysical techniques such as electrical resistivity tomography (ERT), ground penetrating radar (GPR), surface seismic refraction tomography (SRT), cross-hole seismic tomography (CST) and cross-hole seismic profiling (CSP) were used to map the vulnerable zones. Data were acquired using ERT, GPR and SRT along the pipeline for a length of 750 m, and across the pipeline for a length of 4096 m (over 16 profiles of ERT and SRT with a separation of 50 m) for high-resolution imaging of the near-surface features. Borehole techniques, based on six CSP and three CST, were carried out at potentially vulnerable locations up to a depth of 30 m to complement the surface mapping with high-resolution imaging of deeper features. The ERT results revealed the presence of voids or cavities below the pipeline. A major weak zone was identified at the central part of the study area extending significantly deep into the subsurface. CSP and CST results also confirmed the presence of weak zones below the pipeline. The integrated geophysical investigations helped to detect the old workings and a deformation zone in the overburden. These features near the pipeline produced instability leading to deformation in the overburden, and led to subsidence in close vicinity of the concerned area. The area for imminent subsidence, proposed based on the results of the present comprehensive geophysical investigations, was found critical for the pipeline.

Response of buried pipelines to repeated shaking in liquefiable soils through model tests

Liquefaction hazard induced by seismic events might affect the stability of buried pipelines, with permanent displacements of the embedded structure as a consequence. In this context, the pipe uplift is of main concern, as already widely discussed in the literature. In this paper, further insights to assess the phenomenon and the related effects on pipelines are provided based on the results of shaking table tests on pipes of different apparent unit weight. A multiple shaking sequence is adopted on each model. Among others, data here reported confirms that, with liquefaction occurrence, upward displacement is expected for a pipe with an apparent unit weight smaller or equal to the unit weight of the sand deposit; the opposite for larger apparent unit weight. The pipe vertical displacement is initiated with the first earthquake that in sequence induces liquefaction extensively in the soil deposit. The uplift rate is higher for this shaking, and then it reduces for the next earthquakes even for bigger shaking amplitude. The onset of uplift varies for successive earthquakes depending on the magnitude of the input motion, the relative density and the weight of the structure. A transient horizontal movement of the transversal cross section of the pipe, due to the earthquake loading inducing liquefaction in the soil deposit, can be significant and induce pipe damages.

Vibration study of a composite pipeline supported on elastic foundation using a transfer matrix method

Efficient and accurate simulation of the vibration characteristics of a composite pipeline system is the key to the study of the stability and vibration control of the pipeline system. A simulation method called transfer matrix method for multibody systems is used to predict the vibration of a composite pipeline resting on an elastic soil. The transfer matrix of the Euler–Bernoulli beams considering the internal fluid velocity and high-efficiency dynamics model of the pipeline system under the action of the elastic foundation are derived. The simulation results have good agreement with that of the literature and commercial software ANSYS Workbench which verified the accuracy of the numerical model. The simulation results show that with the increase of the velocity, the natural frequencies of each mode of the pipeline decrease continuously. When the first frequency is zero, the pipeline buckling occurs and the velocity reaches the critical velocity; the elastic coefficient and shear coefficient in the foundation coefficient are positively related to the stability of the pipeline system. The damping coefficient is negatively related to pipeline stability.

Stability Analysis of Multispan Pipeline Embedded in Temperature-Dependent Matrix

In this paper, dynamic stiffness method is used to study the stability of multispan pipelines in temperature-dependent matrix. The effects of temperature changes and different span combinations on the natural frequency, critical velocity, and critical pressure of pipelines are discussed. The main conclusions are obtained and shown as follows. The increase of temperature will lead to the decrease of the first three order natural frequencies. The first two order critical velocities and critical pressure of the system will also decrease with increasing temperature. The change of span combination has no influence on the first-order critical velocity and first-order critical pressure of the system, but it has influence on the second order. The influence of the change of span combination on the first-order natural frequency is regular, but that on the second-order and third-order is not. The increase of the velocity will change the instability form of systems with different span combinations, while the change of the pressure inside the tube will not change the instability form of the system.

Study of contact forces in the bearing part of the protective coating of underground pipelines in gravel and cobbles

In the construction and operation of underground pipelines, the feasibility of engineering methods of protecting the insulation coating from external mechanical impacts should be based on the existing loads. When an underground pipeline is laid on coarse gravel and very coarse soil, the analysis of the support forces at the base of the pipeline is a pressing issue. In particular, the difficult conditions for the construction, reconstruction, repair and operation of underground pipelines include cases when the pipeline route passes through sections of rocky soils. Discrete rocky conditions include large grain content in the form of coarse gravel, cobbles, and boulders. The article analyzes the influence of the size of foundation soil components on the magnitude of force arising in the protective coating of the support part of an underground pipeline depending on the unevenness of the soil and its granulometric composition. One of the directions for studying the distribution of contact-mechanical interaction in granular soils is a discrete model. The distinction of the discrete medium model is that individual elements of its structure are viewed as mechanically interacting bodies. Structural elements are particles of bulk material that can be considered as spheres. The results of modeling the contact problem using the discrete (granular) model of the base of the pipeline are presented. It was found that with the same diameter size and depth of burial, the force varies depending on the pipe diameter chosen in the project (for a pipe of 1420 mm, the maximum difference was 23%). In the case of unevenness of the ground, the force in the supporting part can increase by 3-5 times. The conditions of stability and strength of underground pipelines are formulated taking into account the discreteness of the base particles.

Transverse Vibrations of Underground Pipelines with Different Interaction Laws of Pipe with Surrounding Soils

Studies on the effect of changing the stiffness coefficient along the length of the pipeline on its resonant vibration mode are considered in the paper. A computational model of transverse vibrations of the pipeline located in soil with different properties is created. Theoretical and computational studies to solve the problems of stability of underground pipelines located in the soils with different properties under seismic effects are carried out. It is revealed that the vibratory process of the pipeline can be realized at frequencies close to resonance. The results of the study are presented as curves of distribution of displacements of pipeline sections along the length at dimensionless frequencies. When the pipeline vibrates with a frequency close to the resonant frequency, the displacements of pipeline sections can take very large values. It is shown that at frequencies close to resonance, the values of moments can be large in the pipeline sections, which are the reasons for the loss of pipeline stability.

Safety Assessment of Gas Pipeline Body and Weld Stress in High Fill Area

Gas pipeline is occupied by high-filled soil and a large amount of soil has caused long-lasting additional stress on the pipeline. Under the action of the additional stress of the high fill soil, the pipeline may undergo relatively large displacement and deformation, which will cause harm to the safe operation of the pipeline. In order to clarify the stress and deformation state of gas pipeline body and weld in the high fill area, this paper preliminarily calculated the radial stability of gas pipeline under the action of the high-fill soil and the stress state of the weld under the ovality deformation. According to the actual parameters, boundary conditions and deformation of pipeline, a finite element model is established to calculate and check the stress state of the pipeline in the high fill area. Analyzed the serviceability of the pipeline according to the requirements of gas pipeline integrity management specification. Finally, according to the analysis results, a comprehensive assessment of the high fill area of the pipeline is carried out, and recommendations for the next treatment measures are put forward.

Technology on Settlement Control of Large Diameter Shield Traversing Closely Beneath High-pressure Gas Pipeline for Metro Tunnel

Taking the project of sectional tunnel traversing closely beneath high-pressure gas pipeline on Weiqing Line between Xinglong Station and Tianfuxin Station in Chengdu Metro Line 18 for an example, the technology controlling the settlement is studied. Based on the reinforcement isolation grouting with inclined boreholes, driving control parameters of shield and grouting behind the sectional tunnel lining with deep holes, the control technology on the large diameter shield passing closely beneath high-pressure gas pipeline is established for metro tunnels. The application of this technology controls the settlement of high pressure gas pipe within - 4mm, less than - 5mm, which verifies the practicability of this technology. At the same time, it greatly improves the stability of pipeline, guarantees the safety of pipeline operation, and provides the reference for similar projects in the future.

Computer simulation study of the vacuum effect during sewage pipelines annular space backfill in trenchless renovation

The article presents material that may be useful for designers and researchers involved in the pipeline material selection for the water supply and sanitary sewer networks construction and reconstruction. During renovation of a dilapidated pipeline by pulling a new polymer pipeline into it, the annular space is filled with cement mortar. The influence of vacuum effect on the strength characteristics of the pipeline when it is filled with cement mortar is considered. The influence of groundwater on the pipeline stability and vacuum in the annular space is presented.

On-bottom stability design of submarine pipelines: the fundamentals

Pipelines are major cost of items in the oil and gas field development. Poor on-bottom stability design may lead to fatigue, lateral and propagation buckling problems. Consequently, additional cost may be incurred during pipeline design and construction due to critical problems relating to poor design. But cost related to the on-bottom stability problem can be significantly reduced by optimizing design. This paper presents comparative review of submarine pipelines on-bottom stability design methods. Comparing absolute lateral stability, generalized lateral stability and traditional force balance methods show variation in submerged weight and effect of pipe-soil interaction on submerged weight parameters. Overall, most literatures agreed that pipelines lateral stability can be increased by increasing porosity of soil, soil embedment and submerged weight. But steel wall and concrete thicknesses are the major parameters used to establish lateral stability of submarine steel pipelines. Therefore, providing an in depth understanding of on-bottom pipeline stability design is necessary to prevent pipeline movement during operation, its associated risks and optimized design.Keywords: Displacement, lateral stability, on-bottom design, pipeline, submerge weight

Study of Pipeline Penetration Based on CEL in Clay

In deep water, pipelines are usually laid directly on the seabed. During the laying process, the pipe typically penetrates into the seabed by a fraction of a diameter. The vertical embedment of pipeline and formation of berm during penetration have a significant effect on the pipeline stability. This study aims to investigate the vertical pipeline penetration at uniform and normal consolidated clay, by carrying out a series of numerical analyses, in which the coupled Eulerian-Lagrangian method (CEL) is incorporated to enable large deformation simulation. These analyses have been compared with collapse loads calculated using the theory solution. The results show that the CEL method is very suitable for simulating large-deformation pipesoil interaction.

Stability Analysis Of Cross-Section Of Double-Row Large-Diameter Pipeline Based On Bim Technology

In order to improve the efficiency of pipeline stability analysis method, taking X80 pipeline with diameter of 1,219 mm as an example, a stability analysis method of pipeline section based on BIM t...

Hydro-mechanical behavior of unsaturated soil surrounding a heated pipeline considering moisture evaporation and condensation

Pipelines used for the transportation of waxy oil or high viscous oil usually work under high temperature and some of them are buried in unsaturated soils, e.g., in coastal regions or regions where change in groundwater level takes place. The rise and drop in temperature of these pipelines inevitably cause evaporation and condensation of moisture within unsaturated soils, which in turn could possibly lead to significant change in the pore water/gas pressures and subsequently change the soil behavior drastically. This paper describes the establishment of a coupled model of phase transition and mechanical behavior by implementing the Kelvin-Laplace and Clapeyron functions into the finite element method code OpenGeoSys, and the subsequent numerical study on the hydro-mechanical behavior of soils surrounding a heated pipeline. Results show that the thermally induced vapor condensation could yield significant drop in gas pressure and compression of soil, which is deemed beneficial to pipeline stability, and this effect can be enhanced by increasing the pipeline burial depth. There exists a critical initial saturation that can distinguish differing development trends for both gas pressure and ground settlement. Implications regarding the design of high temperature pipelines in unsaturated soils are also discussed.

Impact of flood water on the technical condition of natural gas transmission pipeline valves

Maintaining the reliability of a transmission system's operation is an extremely important issue in the context of ensuring the continuity of gas delivery to customers. Threats to maintaining the reliability of a transmission system's operation may appear at any stage of transmission, and the most common reasons for this are corrosion, material defects or accidental damage. The paper presents the impact of flood water on transmission valves in the context of possible threats to ensuring the technical safety of gas supplies. Hazards are described which relate to the chemical composition of flood water, which may cause corrosion of valve elements and risk of loss of gas pipeline stability caused by flooding. In the context of the design of a natural gas transmission network, the strength aspects and the phenomenon of corrosion are described. The results of tests related to a specific example are presented. The finite element method (FEM) is used to build ball valve models. Two types of valves are modelled for nominal pipeline diameters of 50 mm (DN50) and 200 mm (DN200). The results of the presented analysis show that the leak tightness of the tested valve flange connections was mainly influenced by changes in their operating conditions because the occurring additional forces and moments caused significant changes in the load balance of the flange connections.

ABOUT SUSTAINABILITY OF TRUNK PIPELINE ON SOFT SOILS

Background One of the main tasks in the construction and operation of trunk pipelines is to ensure the stability of their position. This is a complex problem, its solution depends on the specific construction conditions and the complicating factors, one of them is soft soils. Currently, to ensure the stability of the trunk pipelines, restraint devices are used, which are divided into two groups according to the method of influencing the structure: due to their own weight; due to the bearing capacity of soils and the design features of the device. Each type of device has its own advantages and disadvantages, taking into account which a decision is made on their use in construction in specific conditions, but as practice shows, all these methods are not able to sufficiently ensure the stability of trunk pipelines for the entire duration of their operation. Aims and Objectives The purpose of this article is to present the design of restraints of the second group, working in conjunction with a matrix grid system. An anchor, including left and right anchor blocks, an upper coupling, is installed together with a ballasting half ring fixed to the pipeline and connected to the anchor blocks via clamps. In addition, each anchor in the group is associated with neighboring grid systems. Methods To solve the tasks, engineering methods to calculate the stability of the pipeline were used. Results 1. It has been found that to date, there is no universal solution to ensure the design position of trunk pipelines on weakly bearing soils. The existing designs and methods do not allow us to sufficiently ensure reliable fulfillment of the main function of the pipeline transport system of our country - uninterrupted and trouble-free delivery of the product to the final consumer. 2. The system proposed by the authors of this article, consisting of anchors, combined into groups by a matrix-grid system can solve one of the main problems of the second type of holding devices, namely, ensuring the stability of the position of the main pipeline for the entire period of its operation. At the same time, in especially dangerous sections of the route (for example, when there is a large subsidence of permafrost, in wetlands with an increased risk of pipeline emergence), the design can be supplemented by a ballasting device that increases the carrying capacity of the system due to its own weight on the pipeline. 3. The objectives of further research are the analytical and empirical determination of the values of a number of derived stability parameters, the determination of the optimal number of anchors combined into one matrix-grid system, and the quantitative assessment of the increase in the carrying capacity of the pipeline when using the matrix grid system.

Remote inspection by the magnetic tomography method (MTM) to prevent the risks imposed by exploitation of Arctic offshore pipelines

Cold climate areas that provide opportunities for the remote inspection of pipelines include the Barents Sea, the Russian Arctic, the Alaskan Chukchi Sea, the Beaufort Sea and the Canadian Arctic offshore. First, an analysis of several actual projects of contactless diagnostics using the magnetic tomography method of pipelines in Arctic conditions is done. Second, the Risk-Based Inspection methodology for Arctic offshore pipelines is discussed. It involves ensuring pipeline reliability on the basis of data on the technical condition of the metal in actual operating conditions. The magnetic tomography method allows not only to remotely identify areas of anomalies with metal defects, but also to register mechanical stress levels taking into account actual loads. This reduces the risk for the structure to come to the critical state in terms of exceeding local loads. Finally, magnetic tomography technology allows managing risks in cases of local corrosion, stress cracking or loss of stability of underwater pipelines in areas with free spanning. The qualitative indicators of the inspection include the probabilities of identifying, interpreting the degree of danger, missing a dangerous defect. The pipeline diagnostics report provides the parameters of reliability forecasting: the period of incident-free operation, safe working pressure, and pressure coefficient.