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Leakage in submarine oil and gas pipelines can result in financial losses and marine environmental pollution.Timely detecting, analyzing and locating leaks can minimize losses and strengthen pipeline quality control. In this paper, theleak detection system of submarine pipeline in offshore oil jetty projects was studied. By comparing and analyzing existing leakdetection technologies, a practical application solution for the submarine pipeline leak detection system in offshore oil jettyprojects was proposed. The combination of negative pressure wave method and flow balance method can improve the accuracy ofleak detection and reduce false alarm rates, providing a reliable and efficient solution for the project. [ABSTRACT FROM AUTHOR]

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.)

A dent is a common type of defects for submarine pipeline. For submarine pipelines, high hydrostatic pressure and internal pressure are the main loads. Once pipelines bend due to complex subsea conditions, the compression strain capacity may be exceeded. Research into the local buckling failure and accurate prediction of the compressive strain capacity are important. A finite element model of a pipeline with a dent is established. Local buckling failure under a bending moment is investigated, and the compressive strain capacity is calculated. The effects of different parameters on pipeline local buckling are analyzed. The results show that the dent depth, external pressure and internal pressure lead to different local buckling failure modes of the pipeline. A higher internal pressure indicates a larger compressive strain capacity, and the opposite is true for external pressure. When the ratio of external pressure to collapse pressure of intact pipeline is greater than 0.1, the deeper the dent, the greater the compressive strain capacity of the pipeline. And as the ratio is less than 0.1, the opposite is true. On the basis of these results, a regression equation for predicting the compressive strain capacity of a dented submarine pipeline is proposed, which can be referred to during the integrity assessment of a submarine 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. [ABSTRACT FROM AUTHOR]

Copyright of Coatings & Protection / Tuceng yu Fanghu is the property of Coating & Protection Editorial Office 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.)

Buckling initiation devices/techniques, including sleepers, distributed buoyancy, snake lay, and residual curvature method (RCM), have recently been widely applied in engineering. These initiated buckles may induce a long pipeline to transform into multiple short pipeline segments, which promote the occurrence of pipeline walking. Thus, a pipeline, which is designed to buckle laterally, may laterally and axially displace over time when subjected to repeated heating and cooling cycles. This study aims to reveal the coupling mechanism of pipeline walking and global lateral buckling. First, an analytic solution is proposed to estimate the walking of pipeline segments between two adjacent buckles. Then, the sensitivity of this method to heating and cooling cycles is analyzed. Results show the applicability of the proposed walking analytical solution of buckling pipelines. Subsequently, an influence analysis of walking on global buckling, including the capacity of buckling initiation, buckling amplitude, buckling mode, and failure assessment of the buckling pipeline, is performed. The results reveal that the effect of walking on the buckling axial force is negligible. However, pipeline walking will aggravate the asymmetry of the pipeline buckling and the failure parameters of the pipeline during the post-buckling. [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]

Copyright of Coatings & Protection / Tuceng yu Fanghu is the property of Coating & Protection Editorial Office 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.)

To figure out the law of diffusion of suspended sediment in water, researchers have tracked and monitored the diffusion of suspended sediment during thetrenching of submarine pipeline in Beibu Gulf based on the actual analytical results on ocean currents adjacent to the project area. Research findings indicate that during the procedures of tracking and monitoring, the average velocity of ocean current amounted to 19 cm/s, 30 cm/s and 22 cm/s, respectively, whereas the average direction of ocean current amounted to 228°, 226°and 231° respectively. In addition, the average content of suspended sediment of seawater in the surface layer, middle layer and bottom layer amounted to 1.8mg/L and 3.7 mg/L, 5.9 mg/L, respectively. In the ascending order, the relationship of the content of suspended sediment was: surface layer seawater < middle layer seawater < bottom layer seawater. [ABSTRACT FROM AUTHOR]

Oil spills endanger the survival of marine species and the maritime environment. As a result, this study constructs a three-dimensional diffusion model of oil spills from pipeline ruptures and analyses the diffusion law of oil films created on the sea surface under various conditions. The model's accuracy was validated using actual oil spill tests, and the oil spill similarity model was further established using similarity theory. The results show that as the leaking aperture grows within 2–3 s, the high concentration centre area of the oil film on the sea surface expands, and the oil film protrudes to the right. From the inside out, the oil film produces a convex elliptical oil film with a high-low concentration form. As the leakage rate rises, a convex, elliptical, large-area oil film of low-high-low concentration forms. During this time frame, the oil leak has not yet developed an oil film at a flow rate of 0.3 m/s. This is due to the fact that horizontal migration speed has a large influence on vertical migration speed, increasing the horizontal migration distance underwater and lengthening the time needed to achieve the development of the sea surface oil film area. With increasing leakage aperture and leak rate, the lateral diffusion length, longitudinal diffusion breadth, and oil spill area of the oil film rise. However, when the velocity of the water flow increases, it decreases. Furthermore, the quadratic fitting curves of the longitudinal expansion length, longitudinal diffusion width, and oil spill area of the oil film were fitted under various influencing factors to predict the diffusion law of the oil film on the sea surface, which is critical for protecting the marine environment. [Display omitted] [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]

Copyright of Coatings & Protection / Tuceng yu Fanghu is the property of Coating & Protection Editorial Office 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.)

The interaction between the pipeline and the surrounding soil is a critical factor in the buckling analysis of the pipeline operating at high temperatures and pressures. The heating pipeline alters the temperature and induces excess pore pressure in the surrounding soil, which in turn affects the mechanical properties of the soil. Therefore, a comprehensive understanding of the thermo-mechanical response of the soil surrounding the pipeline during operation and shutdown is essential. To address this issue, this study developed a temperature-controlled pipe model test device that simulates the heating and cooling cycle of the pipe and the temperature field and pore pressure response of the surrounding kaolin clay. The test results showed that the soil temperature at the closest location to the pipe (0.1 D) reached a peak value of approximately 48.7°C when the pipe was heated from 12.5°C to 55°C. The peak temperature decreased with increasing distance, reaching 22.5°C at 0.875D. Heat transfer analysis using ABAQUS software revealed that the influence range of the pipeline on the soil temperature field during the heating cycle was about 2D. Additionally, a parametric study focused on the thermal conductivity (λsoil) of kaolin, and the best-fit value was determined to be 0.6 W/(m·°C. The excess pore pressures were generated in the kaolin surrounding the pipes during the heating cycle, and negative pore pressures were observed after cooling cycle. Furthermore, a theoretical solution for calculating the thermally induced pore pressure was derived, and preliminary verification showed good agreement between the theoretically computed and experimentally measured results. These findings provide valuable insights into the thermo-mechanical response of the soil surrounding pipelines during operation and shutdown, which can improve the design and safety of oil and gas pipelines. [ABSTRACT FROM AUTHOR]

Because non-buried submarine pipelines under cyclic thermal loading are prone to global buckling, sleepers are commonly laid along the pipeline route to induce a series of relatively small and controllable lateral buckling. A finite element model which can simulate the transformation of pipeline laid on a sleeper from vertical buckling to lateral buckling is established in this work. The parameters of sleeper affecting pipeline buckling modes are analysed, and a new kind of sleeper is proposed aimed at avoiding antisymmetric buckling. Results show that the lateral trigger force can avoid antisymmetric lateral buckling when acting between 1°C and 13°C before the critical buckling temperature. The range increases slightly with increasing trigger force. Compared with an ordinary sleeper, the proposed new sleeper with slider can reduce the critical buckling temperature by 25%, which significantly improves the success rate of sleepers. [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.

In recent years, due to the large‐scale construction of wind power and shore power projects, the amount of submarine high‐voltage AC cables has been increasing year by year, and they often form a "common corridor" in parallel with adjacent submarine pipelines, resulting in AC interference on pipelines. A lot of research has been carried out on the AC interference law of buried pipelines onshore. However, there is a lack of discussion on the AC interference suffered by submarine pipelines from high‐voltage AC cables. How to understand the AC interference law of high‐voltage AC cables to submarine pipelines and determining the safe distance has become an urgent demand in practical production. Based on this, this paper established a calculation model for AC interference suffered by submarine pipelines from high‐voltage AC cables on through CDGES software. Through simulation calculation, the influence laws of many factors such as parallel distance between AC cables and pipelines, parallel length, cable load current, anticorrosive coating resistivity, and longitudinal pipeline resistance per unit length on AC interference parameters of pipelines were investigated. It was found that the degree of AC interference increases with the increase of the anticorrosive coating resistivity, the load current, and the longitudinal pipeline resistance per unit length, as well as the decrease of the parallel interval. However, with the increase of the parallel length, the AC interference voltage and current density of the pipeline increase firstly, then decrease, and at the end remains unchanged, and it was found that there existed the parallel length with the maximum AC interference and the saturation parallel length with unchanged AC interference. Based on the principles of electromagnetic induction and AC circuits, the main reasons for the parallel length with maximum AC interference and the saturation parallel length were analyzed in this paper. The safe distances avoiding AC corrosion under different parallel lengths and load currents were discussed, which can provide a reference for the evaluation of AC interference of submarine pipelines and the selection of submarine routing. [ABSTRACT FROM AUTHOR]

In offshore engineering, the phenomenon of free span often occurs, and the pipeline may have multiple free spans adjacent to each other, forming a multi-span pipeline. The interaction of different spans makes the structural vibration characteristics more complex, which may change the fatigue characteristics of the pipeline and affect the safety of the structure. In this paper, model tests were designed to explore the vortex-induced vibration (VIV) characteristics of multi-span pipelines and investigate the multi-span interaction mechanism. The experimental study mainly focused on the dynamic response of double-span pipelines, and further extended to triple-span pipelines, hoping that the results can be applied to more complex environment. The effects of span-length ratio, buried depth and axial force on VIV of the pipeline were investigated and discussed. The dynamic response of the pipeline varied with the span length. There was obvious interaction between different spans of multi-span pipelines, and the pipe-sediment interaction obviously affected the vibration characteristics of pipeline. The differences of pipeline burial depth and axial force changed the structural stiffness. With the increase of buried depth, the response amplitude presented a downward trend. The spanwise evolutions were asymmetric caused by the pipe-sediment interaction and multi-span interaction. The results can help to identify multi-span pipelines in engineering, and realize the prevention and control of free spans. [ABSTRACT FROM AUTHOR]

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.

The submarine oil pipeline has many advantages, such as large oil transportation capacity, and being fast and economical. However, long-term laid submarine oil pipelines are affected by reciprocating load of water flow, subsidence caused by soil liquefaction, ship anchorage operation, etc. In severe cases, it causes overall distortion of a small section of the submarine pipeline, profoundly affecting the safety of the submarine pipeline, which is a significant safety hazard for the health of the marine environment and potentially impacting social and economic benefits. Taking the Cezi-Zhenhai submarine pipeline in the sea area between Ningbo and Zhoushan as an example, many deformation defects in the pipeline have been found through internal inspection, and there is a trend of further deterioration. However, the existing external detection of submarine pipeline deformation can only collect limited data through mechanical dots for rough inversion. This does not meet the accuracy requirements of repairing existing submarine pipeline clamps. Therefore, we propose a real-time visualization surveying and mapping system for the submarine pipeline based on a 3-D laser and a separately designed electronic control system. Our research team performed actual mapping work for the Cezi-Zhenhai submarine pipeline and achieved an excellent mapping control effect. A steady monitoring image and good control effect of moving parts are obtained, and the data obtained by 3-D laser processing perfectly represent the actual state of the submarine pipeline. Predictably, the large-scale application of this system will provide a solid technical guarantee for the health of submarine pipelines. [ABSTRACT FROM AUTHOR]

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]

Copyright of Corrosion & Protection in Petrochemical Industry is the property of Corrosion & Protection in Petrochemical Industry Editorial Office 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.)

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

• Laboratory model tests were conducted on scaled-down pipe sections with integrated fins, placed on a remoulded Kaolin clay bed, to investigate the on-bottom stability of surface-laid submarine pipelines during vertical penetration under thermal-induced buckling. • The study demonstrated the effectiveness of radial fins in enhancing the stability and resistance of submarine pipelines against vertical penetration, suggesting potential improvements in submarine pipeline design and deployment. • The variation of soil-surface heaving and pressure around the pipe section with variation of the fin configurations were also explored. • An improvement on the penetration resistance was observed with the integration of the fin in the pipe section. Depending on the degree of the improvement, an optimised pipe configuration was proposed for resisting vertical penetration on very soft seabeds. This study focuses on the on-bottom stability of surface-laid submarine pipelines during vertical penetration under thermal-induced buckling. Submarine pipelines are susceptible to buckling due to their high slenderness ratio, and the resistance to such displacement relies on pipeline stiffness and soil resistance. To investigate this, laboratory model tests were conducted using a scaled-down pipe section placed on a clay bed. The clay bed was prepared with remoulded Kaolin clay, ensuring uniform moisture content, and the model pipe was scaled down from a typical industry prototype. These tests were conducted in 2D plane strain conditions within a tank, equipped with observation windows to monitor pipe movement and soil behaviour. A significant improvement in the pipe section's penetration resistance and on-bottom stability was observed after incorporating fin in the pipe. The addition of fins altered the earth pressure distribution beneath the vertically loaded pipe, leading to a larger failure mechanism in the adjacent soil. Furthermore, the soil-surface-heaving progressed towards the tank wall with increasing angular distance between the radial fins. Thus, the research demonstrated the effectiveness of radial fins in enhancing the stability and resistance of submarine pipelines against vertical penetration, shedding light on potential improvements in submarine pipeline design and deployment. [ABSTRACT FROM AUTHOR]

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.

Copyright of Journal of China University of Petroleum is the property of China University of Petroleum 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.)

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.)

The objective of this study was to demonstrate the feasibility of localising and detecting hydrate plugs inside submarine pipelines, in situ and contactless, using neutron-induced analytical techniques. Cold and fast neutron-beam instruments at Heinz Maier-Leibnitz Zentrum (MLZ) were used to show that neutrons penetrate through the thick wall and the insulation of such pipes and even the induced gamma radiation can be detected outside to perform a non-destructive chemical analysis within the pipe. It was found that the change in the hydrogen concentration caused by a possible hydrate plug can be detected in seconds; while with a detailed analysis at a given spot lasting for a few hours, it is possible to unambiguously identify the hydrate phase inside the hydrocarbon phase. [ABSTRACT FROM AUTHOR]

Copyright of Computer Measurement & Control is the property of Magazine Agency of Computer Measurement & Control 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.)