Deep-sea Pipeline Research Articles

Research on the post-buckling deformation of a deep-sea pipeline laid on a sleeper

ABSTRACT Deep-sea pipelines transport oil under high temperature and pressure. Restricted by seabed friction, the deep-sea pipeline cannot expand freely leading to global buckling deformation. Extreme and unexpected global buckling deformation may threaten the integer of the pipeline system. The sleeper is used to release the high axial expansion force. In this study, the post-buckling of deep-sea pipelines was simulated and the vertical and lateral deformation were analysed. The influential factors of vertical displacement were revealed. Impact of pipeline and sleeper geometrical parameters on the stress and strain distribution in the post-buckling stage was calculated and discussed. Results show that the imperfection with large v 0/L 0 can prevent the upheaval deformation. The effect of reducing the bending moment and stress exists by setting sleeper works well when the lateral soil friction is strong. The pipeline with a larger sleeper height needs a larger temperature to trigger global buckling but has a lower bending moment.

Accelerated stress corrosion cracking of X80 pipeline steel under the combined effects of sulfate-reducing bacteria and hydrostatic pressure

The microbially mediated metal stress corrosion cracking (SCC) mechanisms in deep-sea environments remain unclear, hindering the safe use of deep-sea equipment materials. Hydrostatic pressure facilitated microbiologically influenced corrosion resulting in the pitting depth increase. The stress concentration at the pit bottom induced anodic dissolution (AD), leading to ductile fracture. Hydrostatic pressure and iron sulfides both enhanced the hydrogen evolution reaction (HER). The sulfides produced by SRB metabolism inhibit hydrogen atom recombination, leading to a higher hydrogen permeation current and inducing hydrogen embrittlement (HE) fracture. The combined effect of AD and HE increases the SCC susceptibility of deep-sea pipeline steel.

Dynamic response and performance assessment of subsea sandwich pipelines with different interlayer subjected to underwater explosion

The sandwich pipelines have been developed and applied in subsea due to their better resistance than single-layer pipelines. Explosive shock loads can cause fatal damage to subsea pipelines, thus the objective of this paper is to systematically evaluate the safety of subsea sandwich pipelines under explosion loading. The uniqueness of this study is to analyze the dynamic response of sandwich pipeline filled with different interlayer materials subjected to underwater explosion, especially considering the fluid-solid interaction (FSI) effect. Based on the Arbitrary Lagrangian-Eulerian (ALE) algorithm, the propagation of the blast shock wave in sea water and the FSI effect with the pipeline were investigated by using LS-DYNA code. The accuracy of the numerical method was verified, and then the evolution of the explosive pressure in sandwich pipes with different interlayer material was simulated. The energy absorbing capacity of each layer was analyzed. The structural dynamic response and deformation of the subsea sandwich pipelines was investigated by considering the influencing factors including the diameter-to-thickness ratio (λ) of the inner pipe and outer pipe, the interlayer material, and the explosive charge (Me). The results show that with the increase of λ and Me, the ovality of the pipe increase correspondingly. Moreover, the results demonstrate that with different material as the interlayer, each layer of the sandwich pipe shows different ability to absorb the internal energy caused by explosive shock wave, thus the deformation of the pipe differs significantly. This study can provide a reference for the optimized design of subsea sandwich pipelines to support the operational safety of deep-sea pipeline systems.

The influence of erosion manner on the buckling resistance of pipelines

This article establishes a three-dimensional deep-sea pipeline buckling model for the first time based on the simulation results of pipeline erosion. Through calculation and comparison, it was found that the critical buckling load of intact pipelines and pipelines under uniform corrosion and random pitting corrosion is different. Uniform corrosion can reduce the critical load, but random pitting corrosion can improve the buckling resistance of pipelines. This conclusion is the first discovery.

Analysis of anchor force for pipeline walking induced by SCR tension

The deep-sea pipeline exposed on the seabed is prone to pipeline walking under the influence of thermal loading cycles. Anchors are commonly used to prevent the pipeline walking from causing the end connection of the pipeline system to break. The development of a simple and practical method for calculating anchor force is essential for the preliminary design of the project. In this paper, a finite element model for calculating anchor force is established, and the factors affecting the accumulated length of effective axial force are analyzed. A strain diagram method is proposed for calculating the anchor force under partial accumulated length, and an analytical solution for the rigid anchor force is derived based on the strain diagram method. To address the problem of large anchor force at the end anchor, a flexible anchor is proposed to reduce the anchor force, and a formula for predicting the flexible anchor force is fitted. The study shows that the accumulated length proportion of anchor force increases with the increase of loading temperature and SCR tension, and decreases with the increase of pipeline length and friction coefficient. Flexible anchors can significantly reduce the anchor force. The proposed analytical solution for anchor force can comprehensively consider the influence of factors such as pipeline length, SCR tension, loading temperature, and friction coefficient, and has certain advantages over traditional analytical solutions.

Design and Testing of Real-Time Sensing System Used in Predicting the Leakage of Subsea Pipeline.

This study integrates the array sensing module and the flow leakage algorithm. In this study, a real-time monitoring deep-sea pipeline damage sensing system is designed to provide decision-making parameters such as damage coordinates and damage area. The array sensor module is composed of multiple YF-S201 hall sensors and controllers. YF-S201 hall sensors are arranged inside the pipeline in an array. The flow signal in the deep-sea pipeline can be transmitted to the electronic control interface to analyze the leakage position and leakage flowrate of the pipeline. The theory of this system is based on the conservation of mass. Through the flow of each sensor, it is judged whether the pipeline is damaged. When the pipeline is not damaged, the flowrate of each sensor is almost the same. When the pipeline is damaged, the flowrate will drop significantly. When the actual size of leakage in the pipeline is 5.28 cm2, the size calculated by the flowrate of hall sensors is 2.58 cm2 in average, indicating the error between experimental data and theoretical data is 46%. When the actual size of leakage in the pipeline is 1.98 cm2, the size calculated by the flowrate of hall sensors is 1.31 cm2 in average, indicating the error between experimental data and theoretical data is 21%. This can accurately confirm the location of the broken pipeline, which is between sensor A and sensor B, so that the AUV/ROV can accurately locate and perform pipeline maintenance in real time. It is expected to be able to monitor the flowrate through the array magnetic sensing module designed in this study. It can grasp the status of deep-sea pipelines, improve the quality of deep-sea extraction and pipeline maintenance speed.

Study of the deep-sea pipeline walking with the consideration of the influence of pre-determined global buckling

Deep-sea pipelines are important facilities for transporting hydrocarbon resources in offshore oil development projects. Due to the weak axial soil resistance and the cyclic variation of temperature, the deep-sea pipeline walks axially after several loading cycles, threatening the integer of the connecters. The walking phenomenon is well studied in recent years, while the walking with consideration of the influence of buckling deformation is barely considered. This paper analysed this topic with theoretical method, and the analytical solutions for predicting walking distances of each pipeline sections are proposed. Then, the finite element (FE) method is used and a serious of FE models are established to verify the proposed analytical solutions. Meanwhile, the related three issues are discussed based on the analytical and FE method. The coupled walking and buckling deformation is studied, and the interaction between the walking and buckling is revealed.

Research on Improving the Accuracy of Welding Residual Stress of Deep-Sea Pipeline Steel by Blind Hole Method

For a typical pipeline-lifting deep-sea mining system, marine mining pipelines have higher requirements for steel welding. After the pipeline steel is welded, a large amount of residual stress will be generated inside the component because the heat treatment is not carried out, causing the pipeline to form stress corrosion cracks in the seawater environment. For high residual stress, the blind hole method has inaccurate measurement accuracy. Based on the theory of solid mechanics, this paper comprehensively considers the distance between the strain grid and the center of the hole. It introduces the ratio γ of the applied stress to the yield strength of the specimen. The strain relief coefficients under the values were investigated. The variation trend of the strain release coefficient distribution with the γ value of the three kinds of strain gauge flowers commonly used in China was discussed. Finally, the variation law of strain release coefficient with γ value was obtained by fitting. The strain release coefficient was corrected to improve the accuracy of the blind hole method for measuring high residual stress, which provides a reference value for the engineering application of the blind hole method. This has important theoretical significance and engineering value for guiding the welding construction of high-strength pipeline steel in a deep-sea environment.

Effect of V Content and Heat Input on HAZ Softening of Deep-Sea Pipeline Steel.

In this paper, the welding thermal cycle process of deep-sea pipeline steel was investigated by welding thermal simulation. The microstructure evolution, crystallology and second-phase precipitation behavior of the soft zone of the heat-affected zone (HAZ) were characterized and analyzed by combining scanning electron microscopy, electron back-scattered diffraction, transmission electron microscopy and hardness testing. The results show that HAZ softening appeared in the fine-grained zone with a peak temperature of 900–1000 °C for deep-sea pipeline steel, the base metal microstructure of which was the polygonal ferrite and acicular ferrite. Using V microalloying and low welding heat input could effectively decrease the softening of the HAZ fine-grained region, which was achieved by reducing the effective grain size, increasing the proportion of the dislocation substructures, and precipitating the nanoscale second-phase particles.

Effectiveness of concrete grouting method for deep-sea pipeline repairs

This study aims to assess the effect of a concrete grouted layer on the collapse pressure of pipes under external pressure. The system consists of a concrete grouting layer and a high-strength plastic jacket. Six specimens with varying degrees of defects are tested to obtain their collapse pressures under external pressure, and four specimens are then repaired. The results show that the repair method restores the collapse pressure of the pipe to 39.15%–100% that of the undamaged pipeline. In addition, a numerical model is established and validated, and systematic parametric studies are conducted to supplement the test results. The experimental and numerical results show that the ultimate collapse pressure of the pipe is significantly influenced by the repair measures of the concrete grouted layer. Based on the parametric study, the main parameters that affect the collapse pressure of the repaired pipes are identified. The relationship between the collapse pressure and the geometry of the concrete grouted layer is analysed, and optimal parameters for the concrete grouted layer are obtained. The results show that installing concrete reinforcement is an effective technology for the rapid repair of defective pipes.

Safety analysis of deep-sea mining pipeline deployment operations considering internal solitary waves

Internal solitary waves bring great challenges to the safety of deep-sea mining pipeline deployment operations. The three-dimensional finite element model of deep-sea mining pipeline system under the action of internal solitary waves is established and solved. The shape, tension, stress, upper rotation, offset, and transient response of the pipe string during the deployment process of the deep-sea mining system under the internal solitary wave environment are analysed, and dangerous stages and risk factors are obtained. The envelopes of deployment operations under different internal solitary waves are calculated, and the technical measures to enlarge the operation envelope are discussed. The results show that the upper rotation and offset at moon pool position are more easily affected by internal wave energy relative to stress and tension, and they are the main factors affecting the safety of operation. The stage that the mining vehicle passes through the high-velocity zone of internal solitary waves is the high-risk stage. The operation envelope is the smallest when the IW-OC direction angle is 0°, and is the largest when the angle is 180°. Strengthening the upper restraint has limited effect on improving the operation envelope, in contrast, turning on the propellers of mining vehicle to resist the internal wave when necessary can effectively expand the operation envelope.

Development of Deep Sea Pipeline Position and Attitude Measuring Device Based on Flange Center Positioning

In order to reduce the measurement uncertainty of deep sea pipeline position and attitude measuring device based on flange centre positioning, this paper evaluates the solution process of pipeline pose and proposes a positioning method based on flange centre positioning. The problem of deep water riser measurement operation is solved on the basis of reducing the uncertainty. The final design-related prototype verifies that the measurement method can effectively reduce the uncertainty based on the accuracy.

Development of a Position Measuring Device of a Deep-Sea Pipeline Based on Flange Center Positioning

A deep-sea pipeline position and attitude-measuring device based on pipeline outer circle positioning can measure the spatial relative positions of the end faces of two oil pipelines in the deep sea. This device can provide the necessary data to make a transition pipeline connecting two sections of oil pipelines together. However, after analyzing the data measured by this device, it is found that the measurement data has a large error because the error transmission coefficient of the measurement value is too large. In order to reduce the error transfer coefficient, a new measuring device for measuring the posture of deep-sea pipelines by a tensioning rope was proposed. Unlike previous measuring devices, this measuring device is based on the positioning of the flange center of the pipe instead of the pin on the outer circle of the pipe. With the comparison of positioning methods between fixing in the center of flange and fixing the outer wall of pipeline, the former can reduce the transition matrix in the process of solving the relative position of the two pipes, and then reduce the magnification of the measurement sensor error. It also reduces two measurement parameters. The solving formula of the position and attitude of the measuring device based on the outer circle positioning of the pipeline is analyzed. It is proved that the error transmission coefficient of the measuring device based on the flange center positioning is smaller. Experiments show that compared with the positioning method based on the outer circle of the pipe, the positioning method based on the flange center has a higher accuracy.

Dynamics analysis of deep-sea mining pipeline system considering both internal and external flow

The transportation pipeline subsystem is an essential part of the deep-sea mining system. In order to explore the internal flow field of the pipeline, the internal flow simulation is carried out by CFD-DEM coupling method. The pressure and wall shear stress of the pipe are computed to show the influence of internal flow on the pipelines. Moreover, a novel multi-body dynamic model of the pipeline system is established by the lumped-mass finite element method (LM_FEM) considering both internal and external flow to investigate its dynamic performance. The model includes a 900 m lifting rigid pipe, a 400 m conveying flexible hose and a simplified buffer. The results show that the dynamic performance of pipeline system is greatly affected by ocean current angle, sea depth and buoyancy module distribution. As the ocean current angle increases, the maximum bending moment of rigid pipe is significantly reduced, and the value of flexible hose is gradually increased. This study provides an important theoretical basis and technical references for the pipeline design, performance evaluation and coordinated motion control of the practical deep-sea mining system.

Development of a device for position and bearing measurement of deep sea pipeline based on uncertainty analysis

In order to reduce the uncertainty of the deep sea pipeline attitude measurement, a device based on the positioning of the outer wall of the pipeline was developed. The theory of error and uncertainty was used to analyze the factors affecting the measurement accuracy of this device. Based on this, a new measurement scheme based on flange center positioning was proposed, and the structural and the magnetic coupling drive design were performed. The strength check of key components was carried out using the finite element method, and the equations for solving posture were derived. Finally, a prototype was fabricated, and an experimental platform was set up to validate the measurement of the length and orientation of the pipeline. It is verified that the measurement method could effectively reduce the measurement error and ensured the measurement accuracy. We believe that this method will be suitable in the measurement of deep sea flat pipes and risers, and has potential application prospects.

Ultimate External Pressure Capacity of Deepsea Dented Pipeline with Combined Axial Compressive Force

As a common defect of deepsea pipeline, dents will weaken the residual strength of the pipeline. In this paper, nonlinear finite element method is adopted to investigate the collapse failure of deepsea dented pipeline under the combined external pressure and axial compressive force. The influence of the axial compressive force on the collapse pressure of dented pipelines with different diameter-thickness ratio and dent depth are investigated based on numerical simulation. It is concluded that relative large axial compressive force will reduce the collapse pressure capacity significantly for deep dent case.

Landslides impact reduction effect by using honeycomb-hole submarine pipeline

Abstract Submarine landslide impact is a threatening load in the service lifecycles of deep-sea pipelines and has attracted tremendous attention in scientific research and engineering construction. However, no effective deep-sea pipeline protection measures are applied in engineering practice. In this paper, a submarine pipeline with honeycomb holes is proposed. This pipeline design standard is quantified by defining three parameters. Based on the computational fluid dynamics method, numerical calculations of common circular and new cross-section pipelines that are impacted by landslides were systematically investigated using a low-temperature rheological model. The results demonstrate that the higher is the Reynolds number, the larger the resistance reduction effect, and the peak drag force on the pipeline with honeycomb holes can be reduced by 20%. Simultaneously, the vibration effect of the pipeline that is caused by the lift force can be effectively suppressed. Further, the relevant resistance reduction mechanisms are revealed using the theories of boundary layer separation and turning point delay. This paper proposes a preliminary design concept of a submarine pipeline with honeycomb holes that effectually reduces the impact of landslides, sand waves and bottom currents on the pipeline to protect the operational safety.

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

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

The method and error analysis of deep-sea pose measurement system

The deep-sea pose measurement system can measure the relative distance and angle of two subsea pipelines which the connection of submarine pipelines project need, and the success of connection is mostly decided by high measurement accuracy. According to deep-sea environment, paper designs a measuring method by deep-sea pipeline pose measurement system which bases on the stretching wire. In order to increasing measurement accuracy, paper analyses the transitive relation of error source which impact system measurement accuracy, and gets the impact laws of error sources which include the orthogonal angle, extension arm vertical pitching angle and horizontal swing angle, etc. We revise the measuring result by binary linear regression analysis to improve the measurement accuracy. Through constructing the test platform, we compare measuring value and true value of the pipelines pose parameters. The experimental results show that the distance error is ±30 mm inside, and that the angle error is ±0.7° inside within 7 m after correction. We reduce the measurement error of the pose measurement system, and verify the correctness of the theoretical.

Microstructure and Properties of Longitudinal Submerged Arc Welded Linepipes for Deep-Sea Pipeline

This paper provides description of deep-sea JCOE process of longitudinal submerged-arc welded pipe.The test methods including optical microscopy and tensile,toughness,drop weight tear are applied, the microstructure and properties of deep-sea pipeline steel and deep longitudinal submerged arc welded pipe with thick wall are studied. The results indicates that pipeline steel of substrate organization to acicular ferrite mainly and deep with longitudinal submerged-arc welded thick wall pipe welding HAZ of rough crystal area and fine crystal area respectively main for granular bainite and associate polygon ferrite organization; Deep-sea LSAW steel pipe has reasonable control parameters for process, and its performance meets DNV-OS-F101:2007 specification and user project technology conditions,used for materiels of pipeline steel for China deep-sea oil and gas pipeline project.