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Copyright of China Petroleum Machinery is the property of China Petroleum Machinery Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Sediment erosion around submarine pipelines is a popular topic, widely investigated in both ocean and submarine-pipeline engineering. In this paper, the incompressible smoothed-particle hydrodynamics (ISPH) method is modified for simulation of local scouring process around the submarine pipeline under the action of unidirectional flow. The erosion model is based on the Clear Water Particle–Turbid Water Particle–Critical Shear Stress (CWP-TWP-CSS) concept, and a sand–water two-phase model is proposed to deal with the sediment-entrained flow. The results of the numerical simulation are compared with the experimental data to verify the accuracy and applicability of the numerical model. The scouring process around the pipeline is investigated under different conditions, i.e., pipeline diameters, gap ratios, and flow velocities. The ISPH model is further used to study the flow characteristics of the scour pits around the submarine pipeline and the influence of the vortices on the maximum scour depth, to provide a theoretical basis for the stability design of submarine pipelines. [ABSTRACT FROM AUTHOR]

The anti-corrosive failure of on-site welding points (nodes) of submarine pipelines is the main factor affecting the external anticorrosive failure of pipelines.The quality of anti-corrosive coatings directly affects the safe operation of the entire submarine pipeline.The anticorrosion of nodes in submarine pipelines generally adopts the forms of heat shrink band， fusion bonded epoxy powder， and composite coating.Compared to heat shrink band and fusion bonded epoxy powder， the coating damage rate of composite coating node anti-corrosive materials was the lowest.The anti-corrosive pipe filled with nodes had a lower coating damage rate than the unfilled anti-corrosive pipe.The filling at nodes not only provided mechanical protection， but also affected the current demand value for cathodic protection.In addition， research showed that the coating damage rate of 3LPP coating anti-corrosive pipeline was lower than that of FBE and 3LPE coating anti-corrosive pipeline， and the coating damage rate of insulated pipeline was the lowest.Submarine insulated pipelines had a shielding effect on cathodic protection current.Only when there was a damage to the node anti-corrosive layer， the cathodic protection current flowed into the surface of the protected pipeline to protect the pipeline.

In order to improve the efficiency of submarine pipeline inspection, and manage inspection data more reasonably and effectively, so as to analyze and predict pipeline health status more scientifically, an efficient and intelligent submarine pipeline inspection management platform was constructed by using WebGIS and 3D visualization technology. The platform has functions such as automatic management of job flow, visual monitoring of job site, intelligent analysis and visual display of inspection data. The results of applications show that the platform is advanced and reliable, and can enable the submarine pipeline inspection system to be automated, visualized and intelligent. The improvement and promotion of the platform will be of great significance to ensure the high efficiency and low fault operation of China′s submarine pipelines.

The DNVGL-RP-F105 guidelines provide essential techniques for the preliminary design of undersea pipelines. However, its approximations for static displacement and the natural frequency of the pipe are restricted to cases where the ratio of the pipe's diameter to its length (L/D) is less than 140. This limitation poses challenges for longer spans, which, although rare, can sometimes be unavoidable. This study introduces a novel analytical method, rooted in the energy method and cable theory, for computing the static deformation and natural frequency of long free-span underwater pipelines. We conducted a comprehensive verification of our proposed method by comparing its outcomes with those of 212 finite element analysis simulations. The results reveal excellent predictions for long spans. However, for shorter spans, traditional methods remain more accurate. Additionally, we explored the influence of pipeline's diameter, thickness, and boundary conditions on both static displacement and frequency, providing valuable insights for design considerations. We found that the boundary conditions' impact on the fundamental frequency becomes negligible for long spans, with up to a 10% difference between pinned–pinned and fixed–fixed conditions. In essence, this research offers a vital enhancement to the existing DNV guidelines, becoming particularly beneficial during the preliminary design phases of pipelines with L/D ratios exceeding 140. [ABSTRACT FROM AUTHOR]

Submarine pipelines are the main means of transporting oil and gas produced offshore. The present work proposed a deep learning technology to identify damage caused by characteristic events and abnormal events using pipeline images collected by remotely operated vehicles (ROVs). The EfficientNet and You Only Look Once (YOLO) models were used in this study to classify images and detect events. The results show that the EfficentNet model achieved the highest classification accuracy at 93.57 percent, along with a recall rate of 88.57 percent. The combining of the EfficentNet and YOLOv5 models achieved a higher accuracy of detecting submarine pipeline events and outperformed any other methods. A new decision-making system that integrates the operation and maintenance of the model is proposed and a convenient operation is realized, which provides a new construction method for the rapid inspection of submarine pipelines. Overall, the results of this study show that images acquired via ROVs can be applied to deep learning models to examine submarine pipeline events. The deep learning model is at the core of establishing an effective decision support system for submarine pipeline inspection and the overall application framework lays the foundation for practical application. [ABSTRACT FROM AUTHOR]

Sand waves are commonly formed on the sandy seabed of the continental shelf and characterized by their regular wave-like shape. When a submarine pipeline is laid on this type of seabed, it often experiences free spans due to the unevenness of the seabed. These free spans are particularly vulnerable to vortex-induced vibration (VIV) and the resulting fatigue damage, which have been identified as the primary causes of pipeline failures in offshore oil and gas exploration. This study examines the VIV and fatigue damage of free spans in a submarine pipeline in the Lufeng oilfield, which is located in a large area of sand waves. The assessment conditions encompass the as-laid empty state, the flooded state, and the operational state. Additionally, both the minimum and maximum lay tension are taken into account during the evaluation of VIV and fatigue. The VIV onset screening conducted revealed a considerable number of pipeline free spans exceeding the VIV onset span lengths under both temporary and operating conditions for the non-trench seabed. Furthermore, the analyses indicate that the pipeline does not meet the criteria for VIV fatigue on a non-trenched seabed. Consequently, a proposed solution of implementing a 1 m trench rectification measure for the seabed is recommended. The results demonstrate that this measure effectively mitigates the occurrence of VIV and subsequently reduces fatigue damage across all conditions. [ABSTRACT FROM AUTHOR]

Submarine pipelines are widely adopted around the world for transporting oil and gas from offshore fields. They tend to be severely ruined by the extreme waves induced by the natural disaster, such as hurricanes and tsunamis. To maintain the safety and function integrity of the pipelines, porous media have been used to wrap them from the external loads by the submarine environment. The functions of the porous wrappers under the hydrodynamic impact remain to be uncovered before they are widely accepted by the industry. In this study, a numerical wave tank is established with the immersed boundary method as one of the computational fluid dynamics. The submarine pipelines and their porous wrappers are two-way-coupled in terms of displacement and pressure at their interfaces. The impact from the solitary waves, which approximately represent the extreme waves in the reality, on the pipelines with different configurations of the porous wrapper is investigated. The results present significant protective functions of the wrappers on the internal pipelines, transferring the impact forces from the pipelines to the wrappers. The protective effects tend to be enhanced by the porosity and thickness of the wrappers. The influence of the pipeline configurations and the marine environment are then analysed. As for the front pipeline, an increase in the gap leads to a slight increase in the horizontal forces on both the wrapper and the pipeline, but a significant increase in the vertical forces. As for the rear pipeline, because of the shield function of the front pipeline, the velocity within the gap space and the forces on the pipes are decreased with the decrease in the gap size. The complex flow fields around the pipelines with wrappers are also illuminated, implying that the protection function of the wrapper is enhanced by the wave height reduction. [ABSTRACT FROM AUTHOR]

As the lifeline of offshore oil and gas production, a submarine pipeline requires regular safety evaluations with proper maintenance according to the evaluation results. At present, the safety factors based on regional-level commonly used factors in engineering are too many, and this leads to conservative evaluation results with a low acceptance of defects. In this paper, a risk factor evaluation index system for submarine pipeline defects is constructed through an analytic hierarchy process (AHP), and the original safety factors are corrected to achieve accurate evaluations for submarine pipeline safety. By constructing a radial basis neural network (RBFNN), the fast calculation of safety factors for other pipeline defects can be realized. Through comparison, it was found that the values obtained by the machine training were in good agreement with the real values, which reflects the accuracy of the model and provides a basis for the repair of a defective pipeline. [ABSTRACT FROM AUTHOR]

Sediment erosion around submarine pipelines is a popular topic, widely investigated in both ocean and submarine-pipeline engineering. In this paper, the incompressible smoothed-particle hydrodynamics (ISPH) method is modified for simulation of local scouring process around the submarine pipeline under the action of unidirectional flow. The erosion model is based on the Clear Water Particle–Turbid Water Particle–Critical Shear Stress (CWP-TWP-CSS) concept, and a sand–water two-phase model is proposed to deal with the sediment-entrained flow. The results of the numerical simulation are compared with the experimental data to verify the accuracy and applicability of the numerical model. The scouring process around the pipeline is investigated under different conditions, i.e., pipeline diameters, gap ratios, and flow velocities. The ISPH model is further used to study the flow characteristics of the scour pits around the submarine pipeline and the influence of the vortices on the maximum scour depth, to provide a theoretical basis for the stability design of submarine pipelines.

As oil spills cause harm to the survival and environment of the ocean, the objective of the present paper is to study the oil migration range using the key indicator kv, which is defined as the ratio of oil spill speed to ocean current speed. The correctness of diffusion models created and estimated for subsea oil spills can be verified by experiments. We also considered the effect of key indicators on the horizontal and vertical dispersion ranges of oil spills. The study's findings show that, under various kv settings, the horizontal and vertical spreading heights of oil spills both increase as kv rises. When kv is equal, the leakage velocity and water flow velocity increase synchronously, and over time, the horizontal distance and vertical diffusion height of the oil spill gradually increase. In the early stages of an oil spill, when kv = 50, 100, or 150, the vertical spreading velocity will rapidly decrease. The vertical spreading speed of spilled oil increases as kv rises when the water flow rate remains constant. The horizontal migration distance grows as kv decreases when the leakage rate is constant. Fitting curves for the vertical rise height and horizontal spreading distance for the same and various kv settings were also obtained in order to anticipate the migration mode of oil spills. This is critical for dealing with environmental damage caused by maritime oil spills, as well as emergency responses. [ABSTRACT FROM AUTHOR]

The status of pipeline can be effectively evaluated by identifying the defects with inline inspection technology to further improve the integrity management of oil and gas pipelines. For example, a 60 km long submarine pipeline,comprising the onshore and offshore sections, was equipped with compensators composed of hundreds of elbows in whole line, while the submarine pipeline section was seriously deformed, and the inline inspection operation faced a high risk of jamming. In view of the above characteristics, a new mechanical pig with high passing capacity was designed for diameter measurement and pigging, of which the passing capacity was verified by pull test on the test section. Subsequently, the length, flange diameter and weight of the inline detector were improved according to the diameter measurements to enhance the passing capacity of the inline detector and the fatigue resistance of elbows. Finally, the eddy current inline detector was successfully applied to the actual projects based on the progressive pigging, with the complete and effective data of the whole pipeline collected. The results show that the inline inspection technical scheme for long-distance submarine pipelines with many bends and deformation is safe and reliable, which could provide a reference for the inline inspection of other high-risk submarine pipelines.

For formulate an effective maintenance scheme of submarine pipeline and effectively ensure the safe operation of submarine pipeline, a strength evaluation and reliability technology of energy pipeline based on Fuzzy depth learning network algorithm is proposed. Firstly, the influence factors of marine environment on submarine pipeline corrosion are described. Secondly, the reliability model of corroded submarine pipeline is established. Given the uncertainty of the relevant parameters of the corrosion defect, the equation of state of the corrosion protection pipe shall be determined on the basis of the corrosion pressure analysis of the corrosion protection pipe. A vague in-depth networking algorithm is used to calculate the probability of a rusty pipeline failure. The results show that the probability of corrosion of the pipeline increases rapidly over time. When the time is 22 years, the failure probability is 2 × 10−4. When the time is 30a, the failure probability is 3.1 × 10−3. The feasibility of fuzzy deep learning network algorithm is verified.

Many oil and gas pipelines have to be laid on the seabed during the deep development of marine oil and gas resources, but the submarine pipeline suspension due to souring under marine hydrodynamic conditions is the important factor that leads to the vortex-induced vibration failure of pipelines. In terms of the poor adaptability of the existing sour protection measures to the submarine pipelines in strong tidal area, a scale physical model test was performed with a bidirectional water channel based on a submarine pipeline in the strong tidal area of Hangzhou Bay. Meanwhile, research was conducted on the sour protection effect of artificial grass for submarine pipelines under alternating tidal current conditions. The test results indicate that the local scour depth of submarine pipelines decreases with the increasing of the density and coverage width of artificial grass. When the coverage width increases to the critical value, the sour depth is reduced to be zero. By fitting the experimental data with the multiple regression fitting method, the relational expression of the density and critical width of artificial grass can be obtained. The research results could provide reference for the design and implementation of sour protection measures for submarine pipelines in strong tidal area.

The beam analysis model and the initial imperfection are predominant factors in analyzing the lateral buckling behavior of submarine pipelines under high temperature. However, the existing beam models do not consider the inhibition provided by the virtual anchor point of the pipeline. In this study, a fixed-fixed beam model is introduced to simulate the lateral buckling response of a submarine pipeline. This model considers the suppression tension provided by the virtual anchor point during the pipeline feeding-in process, which better reduces the buckling response phenomenon of the pipeline. Based on the assumption of rigid-plastic pipe-soil interaction, the analytical solution of the buckling development of pipeline under full-contact repetitive cosine imperfection is derived. The effectiveness of the fixed-fixed model is verified by comparing with the analytical solutions in other literature. The influence of the imperfection model, the temperature difference, and the soil resistance on the pipeline buckling is investigated. Finally, the size effect of the pipeline on the effective axial force development is discussed. The results show that the pipeline undergoes stress vibration under tensile force, and the frequency and density of the pipeline stress vibration increase with the increase of the initial defect amplitude. Increasing the diameter–thick ratio will significantly increase the bending amplitude and bending stress of the pipeline. Attention should be paid to the fatigue damage caused by continuous stress mutations during pipeline buckling, which could further lead to the structural destruction of the pipeline. [ABSTRACT FROM AUTHOR]

A fracture mechanics-based fatigue reliability analysis of a submarine pipeline is investigated using the Bayesian approach. The proposed framework enables the estimation of the reliability level of submarine pipelines based on limited experimental data. Bayesian updating method and Markov Chain Monte Carlo simulation are used to estimate the posterior distribution of the parameters of a fracture mechanics-based fatigue model regarding different sources of uncertainties. Failure load cycle distribution and the reliability-based performance assessment of API 5L X56 submarine pipelines as a case study are estimated for three different cases. In addition, the impact of different parameters, including the stress ratio, maximum load, uncertainties of stress range and initial crack size, corrosion-enhanced factor, and also the correlation between material parameters on the reliability of the investigated submarine pipeline has been indicated through a sensitivity study. The applied approach in this study may be used for uncertainty modelling and fatigue reliability-based performance assessment of different types of submarine pipelines for maintenance and periodic inspection planning. [ABSTRACT FROM AUTHOR]

In order to predict the penetration depth of submarine pipeline on sandy seabed,a coupled Eulerian-Lagranginan finite element model of submarine pipeline penetration on sandy seabed was established under ABAQUS to simulate the process of submarine pipeline penetration into sandy seabed under the loads such as wind,wave,current and self-weight.The effect of the friction coefficient of the pipe-soil interface,the internal friction angle,the dilation angle,and the elastic modulus of sand on the penetration depth of the pipeline was studied.The results show that,during the penetration of the submarine pipeline,the seabed on both sides of the pipeline is uplifted,and the seabed soil forms a continuous sliding surface extending from the bottom of the pipeline to the surface of the seabed.The soil failure is in the form of general shear failure.The friction coefficient of the pipe-soil interface,the internal friction angle and the dilation angle of the sand all affect the penetration depth of submarine pipeline on sandy seabed.The internal friction angle of sand has the greatest impact on the penetration depth of the submarine pipeline,while the elastic modulus of sand has no significant effect on the penetration depth of the submarine pipeline.The penetration resistance of the submarine pipeline increases as a power function with the increase of the friction coefficient of the pipe-soil interface,the internal friction angle and the dilatation angle of the sand.The proposed prediction formula can accurately predict the penetration depth of pipelines on the sandy seabed by considering the effects of pipe-soil interaction and sand mechanical properties, and the calculation results provide basic data for in-situ stability evaluation of submarine pipelines on the sandy seabed.

This work is devoted to the results of experimental studies on the impact of wave loading on a buried pipeline. Currently, there is an active development of large deposits located on the shelf and the northern rivers (Ob Bay, Yenisei), from where delivery to the places of consumption should be made. The most convenient type of transportation is the pipeline. Its route often crosses water areas, the size of which can reach five kilometres or more. Such dimensions allow the occurrence of a wave load acting on the pipeline. The issue of pipeline stability is especially relevant for designers in order to avoid accidents during operation. Nowadays, the regulatory documentation does not address this issue. Only the force of Archimedes is considered, without taking into account the wave action. The causes and process of moving the pipe up in the ground are difficult to theoretically analyze, therefore, it is mainly studied by empirical methods. In this work, the dependence between the wave load and the buoyancy force is established experimentally. The series of experiments was conducted with changing wave parameters and pipeline depth. This article will be useful for submarine pipeline designers.

To investigate the different influencing characteristics of local scour around submarine pipelines, hydrodynamic and sediment transport two-dimensional models based on Flow-3D are used to numerically simulate the local scour around the pipeline under steady currents. An RNG k-ε turbulence model is applied to simulate the turbulent flow field around the pipeline. The instantaneous shear stress of the bed surface is taken as the starting and transporting conditions of the sediment. The simulation results of the equilibrium scour depth and terrain around the pipeline are verified with the previous experimental results, which perform with good agreement. Then, the numerical simulation method is applied to investigate the local scour process around the pipeline. The results show that shear stress is the main driving force of scour around a pipeline. The velocity, sediment grain size, pipeline diameter, and the initial gap between the pipeline and the seabed, significantly affects submarine pipeline equilibrium scour depth and terrain in varying degrees. [ABSTRACT FROM AUTHOR]

Submarine pipeline is one of the most popular research filed that many researchers focus on solving the issue of buckling of pipeline. The snaked laying is an effective method to control the lateral buckling. The scour below offshore pipeline may affect the efficiency and performance of the snake lay pipeline. The objective of this study was to investigate the effect of scour hole on the buckling of seawater pipelines. A three-dimensional numerical model developed to investigate the effect of scour below offshore pipeline subjected to wave and current by using Abaqus software and Aqua Module. The results indicated that vertical deformation of straight pipeline increased by increasing scour hole depth. This value changed 4.85 cm to 32.87 for holes 11 to 200 cm respectively, but these parameters of the snake lay pipelines were not affected by the presence of scour hole. Moreover, the effective axial force of snacked lay pipelines reduced 5 times in comparison to straight pipeline by applying wave and current. The results indicated that the value of stress of snaked-lay pipeline was independent on scour hole depth. Therefore, this pipeline was effective method to limit and control buckling even in the presence of scour below it

The DNVGL-RP-F105 guidelines provide essential techniques for the preliminary design of undersea pipelines. However, its approximations for static displacement and the natural frequency of the pipe are restricted to cases where the ratio of the pipe’s diameter to its length (L/D) is less than 140. This limitation poses challenges for longer spans, which, although rare, can sometimes be unavoidable. This study introduces a novel analytical method, rooted in the energy method and cable theory, for computing the static deformation and natural frequency of long free-span underwater pipelines. We conducted a comprehensive verification of our proposed method by comparing its outcomes with those of 212 finite element analysis simulations. The results reveal excellent predictions for long spans. However, for shorter spans, traditional methods remain more accurate. Additionally, we explored the influence of pipeline’s diameter, thickness, and boundary conditions on both static displacement and frequency, providing valuable insights for design considerations. We found that the boundary conditions’ impact on the fundamental frequency becomes negligible for long spans, with up to a 10% difference between pinned–pinned and fixed–fixed conditions. In essence, this research offers a vital enhancement to the existing DNV guidelines, becoming particularly beneficial during the preliminary design phases of pipelines with L/D ratios exceeding 140.

Sand waves are commonly formed on the sandy seabed of the continental shelf and characterized by their regular wave-like shape. When a submarine pipeline is laid on this type of seabed, it often experiences free spans due to the unevenness of the seabed. These free spans are particularly vulnerable to vortex-induced vibration (VIV) and the resulting fatigue damage, which have been identified as the primary causes of pipeline failures in offshore oil and gas exploration. This study examines the VIV and fatigue damage of free spans in a submarine pipeline in the Lufeng oilfield, which is located in a large area of sand waves. The assessment conditions encompass the as-laid empty state, the flooded state, and the operational state. Additionally, both the minimum and maximum lay tension are taken into account during the evaluation of VIV and fatigue. The VIV onset screening conducted revealed a considerable number of pipeline free spans exceeding the VIV onset span lengths under both temporary and operating conditions for the non-trench seabed. Furthermore, the analyses indicate that the pipeline does not meet the criteria for VIV fatigue on a non-trenched seabed. Consequently, a proposed solution of implementing a 1 m trench rectification measure for the seabed is recommended. The results demonstrate that this measure effectively mitigates the occurrence of VIV and subsequently reduces fatigue damage across all conditions.

Submarine pipelines are widely adopted around the world for transporting oil and gas from offshore fields. They tend to be severely ruined by the extreme waves induced by the natural disaster, such as hurricanes and tsunamis. To maintain the safety and function integrity of the pipelines, porous media have been used to wrap them from the external loads by the submarine environment. The functions of the porous wrappers under the hydrodynamic impact remain to be uncovered before they are widely accepted by the industry. In this study, a numerical wave tank is established with the immersed boundary method as one of the computational fluid dynamics. The submarine pipelines and their porous wrappers are two-way-coupled in terms of displacement and pressure at their interfaces. The impact from the solitary waves, which approximately represent the extreme waves in the reality, on the pipelines with different configurations of the porous wrapper is investigated. The results present significant protective functions of the wrappers on the internal pipelines, transferring the impact forces from the pipelines to the wrappers. The protective effects tend to be enhanced by the porosity and thickness of the wrappers. The influence of the pipeline configurations and the marine environment are then analysed. As for the front pipeline, an increase in the gap leads to a slight increase in the horizontal forces on both the wrapper and the pipeline, but a significant increase in the vertical forces. As for the rear pipeline, because of the shield function of the front pipeline, the velocity within the gap space and the forces on the pipes are decreased with the decrease in the gap size. The complex flow fields around the pipelines with wrappers are also illuminated, implying that the protection function of the wrapper is enhanced by the wave height reduction.

Submarine pipelines are the main means of transporting oil and gas produced offshore. The present work proposed a deep learning technology to identify damage caused by characteristic events and abnormal events using pipeline images collected by remotely operated vehicles (ROVs). The EfficientNet and You Only Look Once (YOLO) models were used in this study to classify images and detect events. The results show that the EfficentNet model achieved the highest classification accuracy at 93.57 percent, along with a recall rate of 88.57 percent. The combining of the EfficentNet and YOLOv5 models achieved a higher accuracy of detecting submarine pipeline events and outperformed any other methods. A new decision-making system that integrates the operation and maintenance of the model is proposed and a convenient operation is realized, which provides a new construction method for the rapid inspection of submarine pipelines. Overall, the results of this study show that images acquired via ROVs can be applied to deep learning models to examine submarine pipeline events. The deep learning model is at the core of establishing an effective decision support system for submarine pipeline inspection and the overall application framework lays the foundation for practical application.

Waves and currents coexist widely in the ocean, and the interaction of waves and currents plays an important role in the instability of submarine pipelines. So far, most studies have concentrated on discussing the dynamic reaction within the seabed around a pipeline under pure wave action, monotypic sediment, and an exposed or fully buried condition. In this study, the effect of current characteristics (e.g., current velocity and propagation direction) and backfilling conditions (e.g., backfill depth and sand property) on the dynamic response around the submarine pipeline is investigated by conducting laboratory experiments. Pipeline was buried in the excavated trench using three types of sand with the median size of 0.150 mm, 0.300 mm and 0.045 mm, respectively. Five relative backfilled depths, with the ratios of backfill depth over the pipeline diameter being 0, 1/2, 1, 3/2 and 2, were tested. The excess pore pressure was measured simultaneously by using the pore pressure sensors installed around the pipeline surface and beneath the pipeline. Results show that both the pore pressure amplitude and its descent rate gradually decrease with an increasing backfill depth, which decreases the soil liquefaction potential. Under the co-current actions, the decrease rate of the pore pressure along the vertical direction increases with an increasing current velocity. However, the increased current velocity leads to a decrease of the attenuation rate under the counter-current actions compared with the pure wave actions, and the counter-current effect on the pore pressure within the seabed is greater than the co-current. The results indicate that the dynamic response around the pipeline in coarse sand is close to that without the backfill scenario, even if the backfill depth reaches up to two times that of the pipeline diameter. It is found that the larger the median particle size of backfill sand, the smaller the impact on pore pressure within the seabed beneath the pipeline. [ABSTRACT FROM AUTHOR]

As an indispensable part of the lifeline for the offshore gas and oil industry, submarine pipelines under long-term marine environmental loadings have historically been susceptible to earthquakes. This study investigates the impact of trench backfilling on the residual liquefaction around a pipeline and the induced uplift of a pipeline under the combined action of an earthquake, ocean wave and current loading. A fully coupled nonlinear effective stress analysis method, which can consider the nonlinear hysteresis and the large deformation after liquefaction of the seabed soil, is adopted to describe the interaction between the seabed soil and the submarine pipeline. Taking a typical borehole in the Bohai strait as the site condition, the nonlinear seismic response analysis of the submarine pipeline under the combined action of seismic loading and ocean wave and current is carried out. The numerical results show that trench backfilling has a significant impact on the seismic response of the pipeline. The existence of trench backfilling reduces the accumulation of the residual excess pore water pressure, so that the seabed liquefaction around the pipeline is mitigated and the uplift of the pipeline is also decreased. [ABSTRACT FROM AUTHOR]

The occurrence of a buried submarine pipeline crossing a channel becoming damaged by the impact of a falling anchor is becoming more common. It is important to analyze the dynamic response of pipelines exposed to such impact and develop effective protection methods to ensure the safe operation of the pipelines exposed to the impact of falling anchors. In this study, different protection methods, including pure rock, concrete mattress + rock, concrete mattress + rock + rubber pad, and compound flexible pad + rock, are physically tested. The strains at the impacting point and along the pipeline were measured with the fiber Bragg grating (FBG) sensors. The effectiveness of the protection methods is analyzed based on the maximum strain and its affected length on the pipeline. Then, a theoretical model is established to analyze the deformation and strain of a pipeline. Through curve-fitting the experimental results, the bearing capacity coefficients for different protection methods are determined. The protection method of compound flexible pad + rock has the best performance to protect the pipeline from the impact of a falling anchor. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Hebei University of Science & Technology is the property of Hebei University of Science & Technology, Journal of Hebei University of Science & Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Pipelines are widely used in recent decades because their eco-friendliness, safety and profitability of transportation. Their length can be more than hundreds and thousands of kilometers. Submarine pipelines got wide distribution. Their constructing must comply with regulatory documents. But even it cant guarantee no problems during operation. This study contains review of the different research, connected with floating of a submarine pipeline problem. Information about conducted research and their conclusions is summarized in this paper. Direction for the future investigations is shown. Submarine pipelines are subjected to vertical movement (floating). Pipeline ballasting method is used to avoid this situation. Ballasting by loading bags is considered in this article. This study contains review of the different research, connected with floating of a submarine pipeline problem. Calculations required for the correct selection of the loading bags weight are performed, possible reasons for floating are described. This article will be useful for submarine pipeline designers.

Corrosion is one of the important causes for submarine pipeline failure. Accurate prediction of the residual strength of corroded submarine pipelines is a key to evaluate the integrity and the subsequent service ability of submarine pipelines. Based on the nonlinear finite element method, a residual strength analysis model was established for the corroded submarine pipelines to predict their residual strength, and the impact of the depth, length and width of the external corrosion on the residual strength of the corroded pipelines was analyzed. Besides, a residual strength prediction model was also established based on the deep learning theory, the residual strength of the corroded submarine pipeline was predicted by the deep learning model that is trained with a dataset comprising 114 groups of calculation results, and the prediction results of the model were compared with the finite element calculation results. The results indicate that the deep learning model has a rapid calculation speed and high prediction precision, which verifies the feasibility and effectiveness of the evaluation method of the residual strength of externally-corroded submarine pipelines based on deep learning.

Due to the change of sea conditions, suspended sections will appear to a submarine pipeline, and its safety has attracted great attention. Herein, by adopting the side scan sonar detection technology and the sub-bottom profiling technology, a submarine pipeline was detected, with the buried, bare and suspended states of the whole pipeline learned. Meanwhile, the in-filled detection was performed for the suspended sections, with the seabed condition verified. In addition, a stress analysis model and a vortex-induced vibration analysis model were established for the submarine suspended pipeline, and based on the actual detection results, the suspension stress analysis and the vortex-induced vibration analysis of the submarine pipeline were carried out. The results show that the detection technology can accurately get the state change of pipeline. Definitely, one of the suspended sections of the whole pipeline is in dangerous state and the rest is in safe state. Conclusively, the research results could provide technical support to the safe operation of the submarine pipeline.

The beam analysis model and the initial imperfection are predominant factors in analyzing the lateral buckling behavior of submarine pipelines under high temperature. However, the existing beam models do not consider the inhibition provided by the virtual anchor point of the pipeline. In this study, a fixed-fixed beam model is introduced to simulate the lateral buckling response of a submarine pipeline. This model considers the suppression tension provided by the virtual anchor point during the pipeline feeding-in process, which better reduces the buckling response phenomenon of the pipeline. Based on the assumption of rigid-plastic pipe-soil interaction, the analytical solution of the buckling development of pipeline under full-contact repetitive cosine imperfection is derived. The effectiveness of the fixed-fixed model is verified by comparing with the analytical solutions in other literature. The influence of the imperfection model, the temperature difference, and the soil resistance on the pipeline buckling is investigated. Finally, the size effect of the pipeline on the effective axial force development is discussed. The results show that the pipeline undergoes stress vibration under tensile force, and the frequency and density of the pipeline stress vibration increase with the increase of the initial defect amplitude. Increasing the diameter–thick ratio will significantly increase the bending amplitude and bending stress of the pipeline. Attention should be paid to the fatigue damage caused by continuous stress mutations during pipeline buckling, which could further lead to the structural destruction of the pipeline.

A fracture mechanics-based fatigue reliability analysis of a submarine pipeline is investigated using the Bayesian approach. The proposed framework enables the estimation of the reliability level of submarine pipelines based on limited experimental data. Bayesian updating method and Markov Chain Monte Carlo simulation are used to estimate the posterior distribution of the parameters of a fracture mechanics-based fatigue model regarding different sources of uncertainties. Failure load cycle distribution and the reliability-based performance assessment of API 5L X56 submarine pipelines as a case study are estimated for three different cases. In addition, the impact of different parameters, including the stress ratio, maximum load, uncertainties of stress range and initial crack size, corrosion-enhanced factor, and also the correlation between material parameters on the reliability of the investigated submarine pipeline has been indicated through a sensitivity study. The applied approach in this study may be used for uncertainty modelling and fatigue reliability-based performance assessment of different types of submarine pipelines for maintenance and periodic inspection planning.

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Submarine pipeline is one of the most popular research filed that many researchers focus on solving the issue of buckling of pipeline. The snaked laying is an effective method to control the lateral buckling. The scour below offshore pipeline may affect the efficiency and performance of the snake lay pipeline. The objective of this study was to investigate the effect of scour hole on the buckling of seawater pipelines. A three-dimensional numerical model developed to investigate the effect of scour below offshore pipeline subjected to wave and current by using Abaqus software and Aqua Module. The results indicated that vertical deformation of straight pipeline increased by increasing scour hole depth. This value changed 4.85 cm to 32.87 for holes 11 to 200 cm respectively, but these parameters of the snake lay pipelines were not affected by the presence of scour hole. Moreover, the effective axial force of snacked lay pipelines reduced 5 times in comparison to straight pipeline by applying wave and current. The results indicated that the value of stress of snaked-lay pipeline was independent on scour hole depth. Therefore, this pipeline was effective method to limit and control buckling even in the presence of scour below it. [ABSTRACT FROM AUTHOR]

This paper aims to establish a direct method for evaluating the internal corrosion in submarine pipelines, including four steps: pre-assessment, indirect inspection, detailed inspection, and post-assessment. The evaluation of corrosion severity and the determination of key monitoring points are particularly important in indirect detection. Taking CO2 gathering and transmission pipeline of an offshore oil field as an example, the overall internal corrosion rate of the pipeline is calculated to be 0.253 mm/a. The 12–45 m long pipeline is selected as the focus of corrosion monitoring. Through the comparative analysis of internal detection data and loss wall thickness, it is found that the results of indirect evaluation and direct evaluation are consistent, indicating the correctness of corrosion rate prediction model and loss wall thickness calculation method. The pipeline reevaluation time is five years. The evaluation method can accurately predict the corrosion status of multiphase flow pipeline and locate the corrosion.

As the service condition is harsh, the submarine pipeline is hard to be monitored and maintained. Therefore, oncean accident occurs, the consequence will be very serious. In order to ensure the safe operation of submarine pipelines, thedomestic and international research progress of submarine pipeline integrity evaluation technology was discussed from theaspects of the overall construction of the submarine pipelines, various safety evaluation systems and integrity standardsthrough the study on current situation of submarine pipeline integrity evaluation. At the same time, considering the serviceconditions and operation characteristics of submarine pipeline in China, the study route and development trend was definedbased on a series of problems such as the unsound submarine pipeline management mode, weak integrity evaluation technologyand inadequate standards in China, to realize the evaluation and analysis of various failure modes and the integrity evaluation ofthe submarine pipeline as soon as possible, and to establish an integrity evaluation system of submarine pipeline. The researchresults could provide references for the safe and reliable operation of the submarine pipelines and have a guiding effect on thedevelopment of submarine pipeline integrity evaluation in China.

A 10-in (1 in = 2.54 cm) subsea oil pipeline and a 14-in gas pipeline of an oilfield crosses a shallow gassubsidence area at about 53 km (KP53) away from the landing point of Hangzhou Gulf. These two pipelines have beenin service for nearly 20 years, but each damaged happened after typhoon. Cause analysis was carried out based on theinvestigation data of damage accidents of oil pipeline crossing the shallow gas subsidence area, and it was found that thepipeline fracture was caused by the fatigue load due to soil liquefaction and subsidence during typhoon. Thereby, a repairplan was designed according to the engineering characteristics for guidance of pipeline repair construction. The repairedpipeline has been subject to several times of typhoon and it is still in good conditions. The research results are of guidingsignificance to the construction of submarine pipeline crossing shallow gas geological hazard area or the seabed with soilliquefaction trend.

The large diameter pipelines, compared to conventional diameter pipelines, are more likely to cause local buckling instability in case of point load subjected during its installation of submarine pipelines. In the local buckling check on submarine pipelines, the correction method, though, has been given in DNVGL-ST-F101-2017 for point load, the protection of concrete counterweight layer on the pipeline has been ignored, the method is therefore considered to be incompatible with the actual structure of large diameter pipelines, and the calculation results are conservative. With finite element analysis method, the local buckling, which is resulted from point load in the installation process of large diameter submarine pipelines, was systematically studied with actual engineering pipeline structure taken into consideration during analysis. Engineering examples were provided to compare the calculation results from finite element method with those from the DNV standard, allowing supplement to the DNV standard in terms of analysis method. This is of good popularization value for local buckling design of large diameter submarine pipelines.

To avoid accidents such as perforation leakage caused by submarine pipeline corrosion, and to timely maintain and protect submarine pipelines, the prediction method for submarine pipeline residual life based on parameter-optimized GM-Markov model was proposed in combination with the characteristics of traditional grey system to process little data, poor data and Markov theory to predict the future state. The feasibility of building the grey GM (1, 1) model was firstly analyzed, then the GM (1, 1) model with optimized parameters was built, and the initial conditions of the model were changed to predict the corrosion depth of submarine pipelines. According to the predicted corrosion depth, Markov model was used to quantitatively analyze the future corrosion state of submarine pipelines and predict their residual life. Some submarine pipeline test section was selected as an example to predict the residual life of the pipeline. The results show that the model with the initial conditions changed enables higher prediction accuracy with only a small amount of sample data, demonstrating its worth of popularization and application.

Local or overall initial geometric defects may inevitably occur in the manufacturing, laying and operation of submarine pipelines. To study the transverse buckling behavior of pipelines with defects laid on the seabed surface, the nonlinear numerical model for transverse thermal buckling of pipelines with 5 kinds of initial geometric defects was established firstly, and then the accuracy of the finite element model was verified. The influence of defect types and nonstraightness on the transverse buckling behavior of pipelines was emphatically analyzed. The results show that the transverse buckling deformation poses a great threat to the safe operation of submarine pipelines. The greater the nonstraightness, the smaller the critical temperature rise will be, and the more prone the pipelines will be to the transverse thermal buckling. Under the condition of the same nonstraightness, the smaller the absolute value of curvature at the center of the initial geometric defect of the pipeline, the stronger the transverse thermal buckling resistance will be. Finally, based on the dimensionless analysis method, the general expression was proposed for calculating the critical temperature rise of submarine pipelines with various common initial geometric defects, and it is anticipated to provide a reference for the thermal buckling design of submarine pipelines.

In view of the characteristics of strong penetration and extremely sensitive to delamination of materials, ultrasonic wave has unique advantages in coating defect detection. In order to quickly and accurately detect the defects of the outer coating of submarine oil and gas pipelines, and make up for the weakness of the existing coating detection technologies for oil and gas pipeline, such as low reliability, vulnerable to external interference, inaccurate positioning, etc., a pipeline coating defect detection method using ultrasonic pulse echo was proposed. Through ANSYS modeling and simulation calculation, the attenuation characteristics of reflected echo between intact coating interface and defective coating interface were compared, and obvious differences can be seen in the amplitude of echo after multiple reflections. The fifth echo signal was selected as the basis for determining the coating defects, and the reliability of simulation results was verified by designed test. This study shows that the method has high sensitivity to accurately detect coating defects. The operation is simple and reliable, not affected by the submarine complex environment, and meets the needs of continuous detection, so it can guarantee the safe and efficient operation of submarine oil and gas pipelines.

Active fault is a major geological hazard threat to submarine pipelines, which may subject to excessive axial deformation and fail from the faulting. Thus an improved analytical method for strain of submarine pipeline under strike-slip faulting was proposed in this paper. The nonlinear constitutive relation of pipeline materials was considered based on the linear strengthening model, and the influence of soil nonlinear constraint on the response of the pipe structure was accurately calculated through the nonlinear soil spring model with ideal elastic-plastic constitutive relation. From the differential control equation of the pipeline stress, analytical results of the axial strain in the pipeline were derived and the expression of the pipe elongation was obtained. Based on the equilibrium equation and iterative calculation, the stress and strain of the pipeline can finally be accurately calculated. Compared with the finite element calculation results, the improved analytical method for pipe strain has higher calculation accuracy than the existing recommended method (i.e. Newmark method).

To investigate the different influencing characteristics of local scour around submarine pipelines, hydrodynamic and sediment transport two-dimensional models based on Flow-3D are used to numerically simulate the local scour around the pipeline under steady currents. An RNG k-ε turbulence model is applied to simulate the turbulent flow field around the pipeline. The instantaneous shear stress of the bed surface is taken as the starting and transporting conditions of the sediment. The simulation results of the equilibrium scour depth and terrain around the pipeline are verified with the previous experimental results, which perform with good agreement. Then, the numerical simulation method is applied to investigate the local scour process around the pipeline. The results show that shear stress is the main driving force of scour around a pipeline. The velocity, sediment grain size, pipeline diameter, and the initial gap between the pipeline and the seabed, significantly affects submarine pipeline equilibrium scour depth and terrain in varying degrees.

The implementation of corrosion detection in submarine pipelines is difficult, and a combined PCA-MLP prediction model is proposed to improve the accuracy of corrosion prediction in submarine pipelines. Firstly, the corrosion rate of a submarine multiphase flow pipeline in the South China Sea is simulated by the De Waard 95 model in the multiphase flow transient simulation software OLGA and compared with the actual corrosion rate; then, according to the corrosion data simulated by OLGA, principal component analysis (PCA) is used to reduce the dimensionality of the corrosion factors in the pipeline, and the multiple linear regression model (MLR), multi-layer perceptron neural network (MLPNN), and radial basis function neural network (RBFNN) were optimized. The PCA-MLPNN model has an average relative error of 3.318%, an average absolute error of 0.0034, a root mean square error of 0.0082, a residual sum of squares of 0.0020, and a coefficient of determination of 0.8609. Compared with five models, including MLR, MLPNN, RBFNN, PCA-MLR, PCA-MLPNN, and PCA-RBFNN, PCA-MLPNN has higher prediction accuracy and better prediction performance. The above results indicate that the combined PCA-MLPNN model has a more reliable application capability in CO2 corrosion prediction of submarine pipelines.

Waves and currents coexist widely in the ocean, and the interaction of waves and currents plays an important role in the instability of submarine pipelines. So far, most studies have concentrated on discussing the dynamic reaction within the seabed around a pipeline under pure wave action, monotypic sediment, and an exposed or fully buried condition. In this study, the effect of current characteristics (e.g., current velocity and propagation direction) and backfilling conditions (e.g., backfill depth and sand property) on the dynamic response around the submarine pipeline is investigated by conducting laboratory experiments. Pipeline was buried in the excavated trench using three types of sand with the median size of 0.150 mm, 0.300 mm and 0.045 mm, respectively. Five relative backfilled depths, with the ratios of backfill depth over the pipeline diameter being 0, 1/2, 1, 3/2 and 2, were tested. The excess pore pressure was measured simultaneously by using the pore pressure sensors installed around the pipeline surface and beneath the pipeline. Results show that both the pore pressure amplitude and its descent rate gradually decrease with an increasing backfill depth, which decreases the soil liquefaction potential. Under the co-current actions, the decrease rate of the pore pressure along the vertical direction increases with an increasing current velocity. However, the increased current velocity leads to a decrease of the attenuation rate under the counter-current actions compared with the pure wave actions, and the counter-current effect on the pore pressure within the seabed is greater than the co-current. The results indicate that the dynamic response around the pipeline in coarse sand is close to that without the backfill scenario, even if the backfill depth reaches up to two times that of the pipeline diameter. It is found that the larger the median particle size of backfill sand, the smaller the impact on pore pressure within the seabed beneath the pipeline.

Submarine pipelines are important resource delivery devices between land and ocean. For safety reasons, pipelines are often embedded beneath the seabed at a certain depth, to reduce the risk of direct damage to the pipeline. In the past, various kinds of detection equipment have been used for pipeline inspection, to ensure the normal operation of pipelines in practical applications. Acoustic detection technology is the dominant method to monitor buried submarine pipelines. Extracting and integrating the information in acoustic images, such as the route and burial depth, can help to monitor the status of a pipeline. However, most of the existing methods are based on limited parameters, and they cannot be used to precisely detect and locate a submarine pipeline under complex conditions. In this study, a multi-sensor surveying system was used, which integrates a sub-bottom profiler (SBP) and the Shipborne Over- and Under-Water Integrated Mobile Mapping System (SiOUMMS) on the same ship. The data acquired in this system include acoustic profile images and the over- and under-water topography of the pipeline route area. We also designed a position deviation correction method to improve the accuracy of the pipeline detection positioning, i.e., pipeline positioning correction in the real-time kinematic (RTK) positioning data and pipeline horizontal route correction in the integrated data. Compared with the uncorrected pipeline detection positioning result, the reliability of the pipeline inspection result is greatly improved, and the effectiveness and merit of the proposed method are clearly demonstrated. Finally, we conducted a buried pipeline safety assessment for the installation of newly designed wharf piles at Mawan Port of Shenzhen, China, where the results showed that one of the first rows of wharf piles would collide with the sewage pipeline.

The occurrence of a buried submarine pipeline crossing a channel becoming damaged by the impact of a falling anchor is becoming more common. It is important to analyze the dynamic response of pipelines exposed to such impact and develop effective protection methods to ensure the safe operation of the pipelines exposed to the impact of falling anchors. In this study, different protection methods, including pure rock, concrete mattress + rock, concrete mattress + rock + rubber pad, and compound flexible pad + rock, are physically tested. The strains at the impacting point and along the pipeline were measured with the fiber Bragg grating (FBG) sensors. The effectiveness of the protection methods is analyzed based on the maximum strain and its affected length on the pipeline. Then, a theoretical model is established to analyze the deformation and strain of a pipeline. Through curve-fitting the experimental results, the bearing capacity coefficients for different protection methods are determined. The protection method of compound flexible pad + rock has the best performance to protect the pipeline from the impact of a falling anchor.

This paper aims to establish a direct method for evaluating the internal corrosion in submarine pipelines, including four steps: pre-assessment, indirect inspection, detailed inspection, and post-assessment. The evaluation of corrosion severity and the determination of key monitoring points are particularly important in indirect detection. Taking CO2 gathering and transmission pipeline of an offshore oil field as an example, the overall internal corrosion rate of the pipeline is calculated to be 0.253 mm/a. The 12–45 m long pipeline is selected as the focus of corrosion monitoring. Through the comparative analysis of internal detection data and loss wall thickness, it is found that the results of indirect evaluation and direct evaluation are consistent, indicating the correctness of corrosion rate prediction model and loss wall thickness calculation method. The pipeline reevaluation time is five years. The evaluation method can accurately predict the corrosion status of multiphase flow pipeline and locate the corrosion. [ABSTRACT FROM AUTHOR]