Pipeline Spans Research Articles

Calculation and prediction of suspended span caused by erosion of deep water submarine pipelines

Submarine pipelines can be divided into three types based on their laying status: pipelines laid flat on the seabed, pipelines without buried, and pipelines buried in shallow trenches. In addition, there is also a suspended span state caused by waves and currents erosion. The four laying states of submarine pipelines indicate that the seabed, as the foundation supporting the pipeline, must provide sufficient support to ensure the stability of the pipeline. This article studies the erosion span data of existing pipelines, evaluates and predicts the pipeline span state through theoretical calculation and analysis, and then uses numerical simulation calculation methods to predict the pipeline span depth, and compares and verifies it with measured data.

Seismic Response of Cable-Stayed Spanning Pipeline Considering Medium-Pipeline Fluid–Solid Coupling Dynamic Effect

With the aim of determining the influence of the fluid–structure coupling dynamic effect of the oil and gas transmission medium and pipeline on the seismic response, an oil pipeline supported by a cable-stayed spanning structure was taken as the study object. Kinetic equations taking into account the action of oil and gas medium were studied, and a finite element model structure considering the additional-mass method and the fluid–structure coupling effect were established separately. In addition, the mechanism of the oil–gas–pipeline coupling action on the seismic response of pipeline structure was analyzed, and the results were obtained. The results show that the pipeline has a minimal seismic response at the abutment location, the seismic response gradually increases along the abutment to the main tower, and the seismic response reach is maximized at about one-fifth of the bridge platform. The seismic response of the oil and gas pipeline model structure using the additional-mass method is generally more significant than that based on the fluid–solid coupled dynamic model; moreover, the maximum displacement response differs by about 24%, and the maximum acceleration response differs by approximately 30%, indicating that the oil and gas medium has a certain viscoelastic damping effect on the seismic response of the oil pipeline, which provides a reference for the seismic response calculation theory and analysis method of cable-stayed spanning oil pipelines.

悬跨管道极限长度计算方法研究

悬跨管道极限长度计算方法研究

Generalised analytical solution for determining natural frequency of free span offshore pipelines considering non-homogeneity of seabed soil

The free spanning of the offshore pipelines caused by uneven seabed, ocean current and soil erosion, is one of the main factors of fatigue failure. The majority of researchers have presumed that the seabed soil is homogeneous but practically it is not homogeneous. In this article, a generalised analytical model of the free spanning has been proposed considering the effects of axial force, out of straightness and axial restraints for determining natural frequencies of the offshore pipelines. The novelty of this paper is that the developed analytical model is used for non-homogeneous soil conditions at the support of free span pipelines to find the lowest natural frequency. The proposed model has been validated with the well-used code DNVGL-RP-F105: 2017 and finite element analyses. The proposed analytical method has been found to be accurate under real-world circumstances and could be a helpful tool for evaluating the free span pipelines.

Effect of opening and wall boundaries on CFD modeling for submarine landslide-ambient water-pipeline interaction

Submarine landslide-ambient water-pipeline interactions are receiving extensive attention in ocean engineering, especially the impact forces caused by landslides on pipelines. Computational fluid dynamics (CFD) approaches are widely used to obtain these forces; however, as necessary definite solution conditions, the boundary conditions of CFD modeling are challenging to reasonably determine. In this study, the relationship between the finite volume method (FVM) in CFD modeling and boundary conditions is presented, and a classic physical flume experiment is reproduced using CFD modeling, verifying the effectiveness of the established modeling. The quantitative effect of the opening and free slip wall boundaries under variable complex working conditions (i.e., Reynolds number, pipeline span height, landslide impact velocity, and landslide rheological model) is explored via a general geometry model. The evolution characteristics of impact forces on pipelines under different boundary conditions are given. The mechanism caused by impact force changes is explained through the distributions of the velocity field, pressure field and streamlines around pipelines. Furthermore, a method for determining boundary conditions is briefly proposed, providing a basis for optimizing the CFD modeling of submarine landslide-ambient water-pipeline interactions.

Using dimpled-pipe surface to reduce submarine landslide impact forces on pipelines at different span heights

The interaction between submarine landslides and pipelines has attracted widespread attention. For a pipeline designer, generalizing practical analysis models, obtaining accurate dynamic forces (i.e., the drag force and lift force), and proposing effective pipeline protection measures are prerequisites for ensuring their safe operation. In this paper, a computational fluid dynamics approach is employed to investigate if a golfball-type dimpled pipeline surface reduces impact forces induced by submarine landslides. Considering technology suspension, geomorphology suspension, environmental erosion suspension and acquired suspension, numerical models are generalized to allow prescribing different pipeline span heights, and are impacted by fluidized homogeneous submarine landslides. For the given Reynolds numbers and span heights, golfball-type dimpled pipelines experience a reduced peak drag force than standard circular pipelines. In addition, the pipeline dimple suppresses the lift force variation and greatly reduces the force amplitude. As a result, pipeline damage could be lessened or even avoided. Also, a methodology for predicting the drag reduction of dimple-surfaced pipelines under various conditions is provided, and the two necessary conditions for the periodic vibration of the lift force are proposed. Finally, the full life cycle of vortices shed from the pipeline and the hydrodynamics during landslides impact on pipelines are revealed providing the needed insights to prevent future submarine pipeline failures.

Optimized transportation of bitumen, a case study for Nigeria

Nigeria meets the bulk of her bitumen demand through importation despite her vast raw deposits. The country is now looking towards its local production by harnessing these vast deposits to change this narrative. The exploration of her abundant deposits of bitumen will however require high-temperature sustenance capable pipelines to ensure uninterrupted flow. Hitherto, this is not a challenge with the transportation of her light crude due to the favorable ambient temperature greater than 25 °C. The solution lies in either with heated pipelines or an optimized insulated pipeline at an extra cost. The goal of this study is to determine a cost estimate for Agbabu Nigeria bitumen transportation. The optimum thickness of pipeline insulation is determined numerically using COMSOL Multiphysics Version 5.5 software heat transfer – pipe flow module. The pipeline span of 150 km with a flow rate of 5 Million Metric Tonnes Per Annum (MMTPA) and needs to be maintained at 68 °C. The calculated cost of insulation is compared with existing data of a heated pipeline. The optimized insulation thickness for the bitumen average flow temperature of 68 °C through the pipe subjected to an ambient temperature of 25 °C is 0.105 m. The transportation of a barrel of bitumen will cost USD 1.25 for an optimized insulation pipeline and USD 1.44 for a heated pipeline. This study provides a decision base for an economical means of transporting the country’s vast bitumen resources.

Risk Based Inspection using API RP 580 and DNV RP F116 Towards Free Spanning Pipelines

The free s pan that occurs in the subsea pipeline can cause fatigue due to vortex induced vibration and local buckling. From the risk of failure that may occur, a risk-based inspection scheduling required. The 14" Underwater pipe belongs to PT. The X located in the Madura Strait is used to transmit gas from the CPP to ORF with a length of 65 km which has 554 free spans . In scheduling inspections, the commonly used codes are API RP 580 and DNV RP F116. Th is journal will discuss the difference between these two codes. Reliability calculations use Monte Carlo simulation with VIV failure mode and local buckling failure mode. The consequences of failure are reviewed on safety, environmental and asset aspects. API RP 580, shows the environmental aspect and the safety aspect of both modes of failure has the next inspection in 6 years, while the asset aspect is 3 years. At DNV RP F116, scheduling inspection of safety aspect on both modes is 3 years and environmental aspects is a year later , while the asset aspect would be better to change the pipe

Dynamics of a Pipeline Span on an Elastic Seabed

Natural frequencies, mode shapes and modal damping ratios must be estimated to assess subsea pipeline spans for vortex-induced vibrations (VIV) and response to direct wave loading. Several approximate solutions exist for a linearly elastic pipe under constant axial force supported by linearly elastic springs beyond the span's shoulders. An exact analytical solution has only recently been published. That solution is used here in a Rayleigh-Ritz approximation to account for arch action arising from combined effects of sag under gravity loads and axial restraint at the shoulders. The method allows survey data to be used directly to quantify arch action. Its accuracy is confirmed by finite element analysis. Further, the modal damping ratio is estimated based on the fractions of the potential energy in bending, the axial force, and the soil springs, all of which are determined analytically. Thus, it is found that the effective modal damping ratio increases without a bound as the axial load approaches the buckling load in compression.

Simple Fusion of Object Detectors for Improved Performance and Faster Deployment

Object detectors often suffer from multiple performance limitations which may be attenuated with larger training datasets, improved training techniques, and complex detection models. However, such strategies are complex and time-consuming for applications requiring fast deployments. We propose a Simple Fusion of Object Detectors (SFOD) late ensemble method to combine existing pre-trained, off-the-shelf, fine-tuned object detectors and leverage on their divergences to improve the overall detection performance. Comprehensive experimental evaluations, based on PASCAL VOC07 challenge, demonstrate SFOD’s ability to improve mean average precision ( ${mAP}$ ) for different fusion sizes and base detector combinations, reaching an absolute 84.08% ${mAP}$ and an improvement of 3.97% ${mAP}$ . The improvements extend to most classes, fusion sizes, and base detector combinations, revealing $AP$ improvements up to 17.35% over baselines, for particular object classes. Practical application evaluations, based on optimal threshold selection, also reveal improvements of 10.54% and 8.36% of mean recall ( $mR$ ) and ${mAP}$ , respectively. Our approach does not require additional training and is quickly deployable, yet providing a few adjustable hyperparameters to optimize the recall-precision relation for specific applications. Improvements obtained from our proposed SFOD fusion pipeline span across a broad range of object classes and are important for a wide variety of critical applications where every successful detection is treasured.

不考虑内流影响的悬跨管道涡激振动模态分析

不考虑内流影响的悬跨管道涡激振动模态分析

Flow around two elastically-mounted cylinders with different diameters in tandem and staggered configurations in the subcritical Reynolds number regime

Flow around two cylinders with different diameters undergoing Flow-Induced Vibrations (FIV) in the subcritical flow regime is investigated using two-dimensional Unsteady Reynolds Averaged Navier-Stokes (URANS) approach. Physical parameters of the system are chosen to represent the free spanning pipelines laid in proximity. The two cylinders are initially placed at various tandem and staggered positions with one in the wake of the other, and subject to steady current flows. The two cylinders are free to respond in both in-line and transverse directions. The investigated Reynolds numbers (Re) are Re1=1.4×105 based on the diameter of the larger cylinder and Re2=1.15×105 based on the diameter of the smaller cylinder. A parametric study investigating the effects of relative spacing of the cylinders on the vibration response of the system is performed. First and second order statistics of the flow, frequency domain analysis and flow field visualizations are used to characterize the dynamic behavior of the system. It is found that the motion trajectories of the downstream cylinder show a qualitative difference depending upon whether it is in tandem with the upstream cylinder or in the wake with a transverse offset. A large amplification of the in-line response is observed in the positions with a transverse offset. The vibration response of the upstream cylinder is affected by the presence of the downstream cylinder only when the horizontal center-to-center distance is small (L/D1=2.06 where D1 is the diameter of the larger cylinder) and is largely unaffected when the horizontal distance is increased to L/D1=3.22.

Forced Vibration Tests for In-Line Vortex-Induced Vibration to Assess Partially Strake-Covered Pipeline Spans

AbstractHelical strakes can suppress vortex-induced vibrations (VIVs) in pipelines spans and risers. Pure in-line (IL) VIV is more of a concern for pipelines than for risers. To make it possible to assess the effectiveness of partial strake coverage for this case, an important gap in the hydrodynamic data for strakes is filled by the reported IL forced-vibration tests. Therein, a strake-covered rigid cylinder undergoes harmonic purely IL motion while subject to a uniform “flow” created by towing the test rig along SINTEF Ocean's towing tank. These tests cover a range of frequencies, and amplitudes of the harmonic motion to generate added-mass and excitation functions are derived from the in-phase and 90 deg out-of-phase components of the hydrodynamic force on the pipe, respectively. Using these excitation- and added-mass functions in VIVANA together with those from experiments on bare pipe by Aronsen (2007 “An Experimental Investigation of In-Line and Combined In-Line and Cross-Flow Vortex Induced Vibrations,” Ph.D. thesis, Norwegian University of Science and Technology, Trondheim, Norway.), the IL VIV response of partially strake-covered pipeline spans is calculated. It is found that as little as 10% strake coverage at the optimal location effectively suppresses pure IL VIV.

Response analysis of pipeline crossing structure with earthquake

Pipeline spanning structure has the characteristics of small overall stiffness, poor resistance to deformation, and large slender-length ratio with poor stability. It is a vulnerable part of long distance pipeline engineering under earthquake action, so it is necessary to analyze the response of pipeline spanning structure under earthquake action. In this paper, the structure model of pipeline span is established through ANSYS, and numerical simulation analysis is carried out under seismic action to explore the influence law of pipeline span structure under seismic action of different pipeline span length and different pipeline span form. The results show that the middle span is the most unfavorable position for pipeline crossing. In the same span, with the increase of span length, the natural frequency of pipeline decreases and the period increases. When the span length of pipeline is fixed, the natural frequency of straight pipeline is obviously higher than that of other pipelines, and the seismic performance is the best. It provides a theoretical basis for seismic design of pipeline crossing structure.

Nonlinear Span Assessment by Amplitude-Dependent Linearization

Abstract Although it has long been recognized that vortex-induced vibrations of subsea pipeline spans involve nonlinear and inelastic behavior, the current practice to assess such spans for fatigue and ultimate loading conditions is based on the modal analysis assuming linear behavior. Nevertheless, nonlinearity can be captured approximately by making the linearization amplitude dependent. The eigenvalue problem to be solved for the natural frequencies and mode shapes then involves a stiffness matrix that depends on the mode shape and amplitude of vibration. An important part of the nonlinearity comes from the soil, which is generally represented by springs. This paper presents a simple and particularly effective algorithm to solve this nonlinear eigenvalue problem by using the same algorithm that serves to track the bifurcated solution branches in quasi-static structural stability (buckling) analyses. This method is applied to an example in which the nonlinearity comes from the soil springs. The results demonstrate the importance of the nonlinearity, even at relatively low vortex-induced vibrations (VIV) amplitudes typical of the pure inline response. The inelasticity of the soil springs is also used to calculate the associated contribution to the modal damping ratio.

Comparing the Utility of Industry ROV and Hybrid-AUV Imagery for Surveys of Fish Along a Subsea Pipeline

AbstractIn recent years, video footage obtained from routine industry surveys using remotely operated vehicles (ROVs) has been used to assess fish assemblages associated with offshore oil and gas infrastructure. However, as industry moves towards using autonomous underwater vehicles (AUVs), it is important to understand how such a change may affect assessments of fish assemblages and whether these data collected from AUVs can be directly compared to those collected from historic and future ROV footage. In an extremely rare opportunity, we compare fish assemblages surveyed by an industrial ROV and an industrial hybrid-AUV (H-AUV) along the same 2,060-m section of subsea pipeline, at the same time of day, within 1 day of each other. A total of 206 transects, each 20 m in length, were analyzed, recording 406 fish from 10 species. The H-AUV recorded all 10 fish species, while the ROV recorded seven. Mean species richness was ~4% higher for H-AUV, and mean abundance was ~21% higher for ROV; these differences can be considered negligible. Multivariate analysis revealed nonsignificant differences in species composition between survey methods. This result suggests that future surveys of fish at this pipeline using a similar H-AUV can yield comparable results to ROV and, as such, facilitate comparison to historical ROV imagery. Future surveys of pipelines with AUV should consider adding extra lighting and high-definition cameras onto booms similar to those operating on ROVs, which will provide a useful field of view into pipeline spans and make it easier to identify fish. Our study provides insight into the utility and comparability of industry ROV and AUV pipeline inspection footage for the assessment of fish assemblages associated with subsea pipelines, which is used to inform policies and practices on the installation and decommissioning of subsea infrastructure.

Probabilistic modelling of free spanning pipelines considering multiple failure modes

Free Spanning occurs due to unevenness of seabed, artificial supports and etc. Based on DNV-OS-F101, free spanning may cause Vortex-Induced Vibration (VIV), local buckling and pipeline bursting. The purpose of this study is to present a methodology for assessing free spanning pipelines in terms of Probability of Failure (POF). In order to assess VIV fatigue of subsea pipelines, a Finite-Element Reliability based method with aim of Artificial Neural Network (ANN) is proposed. For training ANN, 560 different ABAQUS FE scenarios with different pipeline configurations are defined, and their results are transferred to MATLAB. According to the recommended criteria, ANN is optimized. For determining reliability level of VIV fatigue, Monte-Carlo Sampling (MCS) is used to optimize ANN, and POF is determined consequently. In addition, using recommended method by DNV-RP-F105, Fatigue Life Capacity (FLC) of pipeline is determined for different conditions. For assessment of pipeline bursting and local buckling, recommended models by DNV-OS-F101 is adopted to determine their relevant POF using First-Order Reliability Method (FORM) and MCS. Furthermore, the effect of different operating pressure on reliability level of pipeline is investigated. Finally, in order to determine the effect of each parameter on POF of pipeline bursting and local buckling sensitivity analysis is carried out, using alpha index.

Experimental Substantiation of Using Acoustic Noise in Above-Ground Pipeline Diagnostics

The full-scale experiments on acoustic noise recording on the surface of an above-ground pipeline are carried out on operating heating main. The tests were performed in the pipeline branches with different style attachment between pipe and support—rigid (the pipe is welded to the support) and flexible (the freely supported heat-insulated pipe). The experiments show that collection of recorded noise amplitude spectra makes it possible to determine natural frequencies and forms of flexural coincident waves generated by noise in the pipeline spans. Both frequencies and forms of the waves depend on the style of the pipe attachment at the span ends, which may be used in diagnostics of pipeline branches by acoustic noise to detect damaged stiffness of the pipe-support attachment and/or instability of the supports. The computer modeling using the finite element method yields flexural wave frequencies similar to the experiment results. The distributions of nodes and antinodes of flexural coincident waves along pipeline spans at different style pipe-support attachments qualitatively agree with the earlier lab test data.

Review of pipeline span analysis

PurposeThe purpose of this paper is to mainly review the state-of-the-art developments in the field of hydrodynamics of offshore pipelines, identifying the key tools for analysis of pipeline free spans, their applications, their qualifying characteristics and capabilities and limitations.Design/methodology/approachThese different analytical, numerical and semi-empirical tools available for predicting such hydrodynamic loads and their effects include VIVANA, PIPESIN, VIVSIM, SIMULATOR, FATFREE, amongst others. Inherent in these models are current effects, wave effects and/ or pipe–soil interactions.FindingsAmongst these models, the most attention was given to the new VIVANA model because this model take into account the vortex-induced effects with respect to free-spanning pipelines (which have dominant effect in the span analysis in deep water) better than other semi-empirical models (such as Shear 7). Recent improvements in VIVANA include its ability to have arbitrary variation in speed and direction of current, as well as the ability for calculation of pure IL and combined IL-CF response. Improvements in fatigue assessments at free spans, i.e. pipe–soil interaction have been achieved through the combined frequency domain and non-linear time domain analysis methodology adopted. Semi-empirical models are still the de facto currently used in the design of free-spanning pipelines. However, there is need for further research on free-span hydrodynamic coefficients and on how in-line and cross-flow vibrations interact. Again, there is still the challenge due to VIV complexity in fully understanding the fluid structure interaction problem, as there is no consolidated procedure for its analysis. It has been observed that there is large scatter between the different codes adopted in the prediction of fatigue damage, as there lacks full-scale test data devoted to determination/validation of the coefficients used in the semi-empirical models. A case study of the preliminary design of a typical 48 in. pipeline has been presented in this study to demonstrate the use of the free-span analysis tool, DNV RP F105. Excel spreadsheet has been applied in the execution of formulas.Originality/valueThis review paper is the first of its kind to study the state-of-the-art development in pipeline free-span analysis models and demonstrate the use of analysis tool, DNV for MAFSL calculation. Hence, information obtained from this paper would be invaluable in assisting designers both in the industry and academia.

Pipeline Slug Flow Dynamic Load Characterization

Flow of gas in pipelines is subject to thermodynamic conditions which produces two-phase bulks (i.e., slugs) within the axial pipeline flow. These moving slugs apply a moving load on the free spanning pipe sections, which consequently undergo variable bending stresses, and flexural deflections. Both the maximum pipeline stress and deflection due to the slug flow loads need to be understood in the design of pipeline spans. However, calculation of a moving mass on a free spanning pipeline is not trivial and the required mathematical model is burdensome for general pipeline design engineering. The work in this paper is intended to investigate the conditions under which simplified analysis would produce a safe pipeline design which can be used by practicing pipeline design engineers. The simulated finite element models presented here prove that replacing the moving mass of the slug by a moving force will produce adequately accurate results at low speeds where the mass of the slug is much smaller than the mass of the pipe section. This result is significant, as the assumption of point load simplifies the analysis to a considerable extent. Since most applications fall within the speed and mass ratio which justify employing this simplified analysis, the work presented here offers a powerful design tool to estimate fatigue stresses and lateral deflections without the need of expensive time-consuming inputs from specialized practitioners.