A Seismic Design Method for Subsea Pipelines Against Earthquake Fault Movement

As there are no specific guidelines on design of subsea pipelines crossing active seismic faults, methods for land buried pipelines have been applied to. Taking the large seismic fault movement into account, this paper proposes improved methods for seismic designs of subsea pipelines by comprehensively investigating the real constraining of soil on the pipelines, the interaction processes of soil with the pipeline, the plastic slippage of the soil, and the elastic-plastic properties of the pipeline materials. New formulas are given to calculate the length of transition section and its total elongation. These formulas are more reasonable in mechanism, and more practical for seismic design of subsea pipelines crossing active faults.

Collapse Analysis of Imperfect Subsea Pipelines Based on 2D High-Order Nonlinear Model

To study the collapse of imperfect subsea pipelinos, a 2D high-order nonlinear model is developed. In this model, the large deformation of the pipes is considered by raiaining the high-order nonlinear terms of strain. In addi-tion, the J2 plastic flow theory is adopted to describe the elasioplastic constitutive relations of material. The quasi-static process of collapse is analyzed by the increment method. For each load step, the equations based on the principle of virtual work are presented and solved by the discrete Newton＇s method. Furthermore, finite element simulations and full-scale experiments were preformed to validate the results of the model. Research on the major influencing factors of collapse pressure, including D/t, material type and initial ovality, is also presented.

Structure Design and Optimization of a New Type of Subsea Pipeline Connector

The basic configuration of a new type of subsea pipeline connector was proposed based on the press-fitting principle, and a parametric finite element model was created using APDL language in ANSYS. Combining the finite element model and optimization technology, the dimension optimization aiming at obtaining the minimum loading force and the optimum sealing performance was designed by the zero order optimization method. Experiments of the optimized connector were carried out. The results indicate that the optimum structural design significantly improved the indicators of the minimum loading force and sealing performance of the connector.

Real-time Monitoring of Subsea Gas Pipelines,Offshore Platforms,and Ship Inspection Scores Using an Automatic Identification System

The aim of this research is to develop an algorithm and application that can perform real-time monitoring of the safety operation of offshore platforms and subsea gas pipelines as well as determine the need for ship inspection using data obtained from automatic identification system(AIS).The research also focuses on the integration of shipping database,AIS data,and others to develop a prototype for designing a real-time monitoring system of offshore platforms and pipelines.A simple concept is used in the development of this prototype,which is achieved by using an overlaying map that outlines the coordinates of the offshore platform and subsea gas pipeline with the ship’s coordinates(longitude/latitude)as detected by AIS.Using such information,we can then build an early warning system(EWS)relayed through short message service(SMS),email,or other means when the ship enters the restricted and exclusion zone of platforms and pipelines.The ship inspection system is developed by combining several attributes.Then,decision analysis software is employed to prioritize the vessel’s four attributes,including ship age,ship type,classification,and flag state.Results show that the EWS can increase the safety level of offshore platforms and pipelines,as well as the efficient use of patrol boats in monitoring the safety of the facilities.Meanwhile,ship inspection enables the port to prioritize the ship to be inspected in accordance with the priority ranking inspection score.

Simplified Technique for Predicting Offshore Pipeline Expansion

In this study,we propose a method for estimating the amount of expansion that occurs in subsea pipelines,which could be applied in the design of robust structures that transport oil and gas from offshore wells.We begin with a literature review and general discussion of existing estimation methods and terminologies with respect to subsea pipelines.Due to the effects of high pressure and high temperature,the production of fluid from offshore wells is typically caused by physical deformation of subsea structures,e.g.,expansion and contraction during the transportation process.In severe cases,vertical and lateral buckling occurs,which causes a significant negative impact on structural safety,and which is related to on-bottom stability,free-span,structural collapse,and many other factors.In addition,these factors may affect the production rate with respect to flow assurance,wax,and hydration,to name a few.In this study,we developed a simple and efficient method for generating a reliable pipe expansion design in the early stage,which can lead to savings in both cost and computation time.As such,in this paper,we propose an applicable diagram,which we call the standard dimensionless ratio(SDR)versus virtual anchor length(LA)diagram,that utilizes an efficient procedure for estimating subsea pipeline expansion based on applied reliable scenarios.With this user guideline,offshore pipeline structural designers can reliably determine the amount of subsea pipeline expansion and the obtained results will also be useful for the installation,design,and maintenance of the subsea pipeline.

Nonlinear Contact Between Pipeline's Outer Wall and Slip-on Buckle Arrestor's Inner Wall During Buckling Process

In order to theoretically study the buckle propagation of subsea pipelines with slip-on buckle arrestors, a two-dimensional ring model was set up to represent the pipeline and a nonlinear spring model was adopted to simulate the contact between pipeline's inner walls and between pipeline's outer wall and slip-on buckle arrestor's inner wall during buckle propagation. In addition, some reverse springs are added to prevent the wall of left and right sides separating from the inner wall of slip-on buckle arrestors. Considering large deformation kinematics relations and the elastic-plastic constitutive relation of material, balance equations were established with the principle of virtual work. The variation of external pressure with respect to the cross-sectional area of pipelines was analyzed, and the lower bound of the crossover pressure of slip-on buckle arrestors was calculated based on Maxwell's energy balance method. By comparing the theoretical results with experiment and finite element numerical simulation, the theoretical method is proved to be correct and reliable.

Corrosion-Based Integrity Analysis of Offshore Pipeline for Hydrocarbon Transportation

Conventional pipeline corrosion assessment methods result in failure pressure predictions that are conservative, especially for pipelines that are subjected to internal pressure and axial compressive stress. Alternatively, numerical methods may be used. However, they are computationally expensive. This paper proposes an analytical equation based on finite element analysis (FEA) for failure pressure prediction of a high toughness corroded pipeline with a single corrosion defect subjected to internal pressure and axial compressive stress. The equations were developed based on the weights and biases of an Artificial Neural Network (ANN) model trained with failure pressure from finite element analysis (FEA) of a high toughness pipeline for various defect depths, defect lengths, and axial compressive stresses. The proposed model was validated against actual burst test results for high toughness materials and was found to be capable of making accurate predictions with a coefficient of determination (R2) of 0.99. An extensive parametric study using the proposed model was subsequently conducted to determine the effects of defect length, defect depth, and axial compressive stress on the failure pressure of a corroded pipe with a single defect. The application of ANN together with FEA has shown promising results in the development of an empirical solution for the failure pressure prediction of pipes with a single corrosion defect subjected to internal pressure and axial compressive stress.

采用阻流器的近壁面海底管道绕流研究

为深入了解采用阻流器的海底管道自埋机制,基于Fluent软件,结合标准k-ε湍流模型,建立了高雷诺数下安装阻流器的近壁面海底管道绕流数值模型,研究了阻流器长度和间隙比对管道尾流与壁面边界层之间复杂的相互作用以及时空演化的影响.研究结果表明采用阻流器可以显著增大管道与壁面之间流速以及管道附近脉动速度,但当阻流器长度达到临界值时,管道尾部会形成稳态结构.随着间隙比的增大,尾流演化可以分为4个区域:稳态结构、两次诱导壁面涡、单次诱导壁面涡、卡门涡街.适当的间隙比有利于诱导壁面旋涡的产生,从而加快管道周围沉积物冲刷.

Installation Strength Analysis of Subsea Flowline Jumpers

A subsea flowline jumper （FJ） is a basic connected component for the wet oil tree, subsea pipeline and riser base, and it plays an irreplaceable role in the subsea production system. During the installation of FJ, collisions often happen between FJ and other equipment, which may cause serious damage. Besides, as the operating water depth increases, the demand for the installation equipments, such as the crane and winch, will increase. The research of deepwater FJ installation in China is still in the primary stage, thus an installation method for the deepwater FJ is proposed in this paper. Finite element models of a typical M-shaped FJ installation system are built to simulate the installation procedures. Analysis results show that the installation steps designed are feasible and valid for the deepwater FJ. In order to ensure the safety of the installation process, the collision-sensitive analysis for the FJ is conducted, and results show that it is necessary to set the pick up speed at a proper value, in order to avoid collision in the installation process. Besides, the mechanical characteristics of FJ during the installation are investigated under a range of environmental conditions and it is found that the maximum stress of the FJ always happens at its central position. The basic requirements for the installation equipment are also obtained through the analysis of the main installation steps.

跨斜滑断层非埋设海底管道局部屈曲分析

利用有限元软件ABAQUS,建立跨斜滑断层非埋设海底管道数值分析模型,考虑管道材料非线性、几何大变形和管土非线性作用的影响,模拟跨斜滑断层海底管道在正常操作阶段的局部屈曲响应。针对管道壁厚、铺设残余张力、穿越断层角度等敏感性参数变化下海管局部屈曲失效、侧向位移和轴向拉伸应变等进行分析,为跨斜滑断层非埋设海底管道的前期设计、安全评价、维修保护等提供参考。

浅剖管道图像零样本深度学习自动检测研究

针对现有海底管道检测通过人工判读浅地层剖面仪(sub-bottom profiler,SBP)影像带来的检测低效和低精度问题,提出了一种顾及成像机理的基于零样本深度学习SBP图像中海底管道自动检测方法。首先研究了SBP工作原理及管道成像特点;其次顾及成像背景及各种实际影响因素,基于成像机理生成了管道样本图形;之后利用生成的管道样本,训练YOLOv5神经网络,构建了SBP图形中管道的检测模型,实现了SBP图形中管道的自动检测,取得了优于90%的正确检测率,提出的方法为基于SBP图形的海底管道自动检测提供了一种新途径。

海底气液多相流混输管道电伴热的热能节省特性研究

针对海底气液混输管道面临的结蜡、胶凝、摩阻过大等流动安全保障问题,提出了热能较为节省的电伴热方式。相对于常见的平台加热方式,基于海管系统总的热平衡原理,采用微积分方法推导出了电伴热相对热耗率的数学解析式,澄清了影响电伴热热能节省效果的主要因素,证明了电伴热与平台加热在加热能耗方面的优劣,并探明了总传热系数等关键因素对电伴热热能节省特性的影响规律。结果表明:在确保质量流量、保温措施及出口温度均相同的条件下,电伴热的热耗总是小于平台加热的热耗,具体的热能节省效果仅跟总传热系数、输送距离、管径、质量流速、液相质量分数5个关键因素有关。电伴热相对热耗率与总传热系数和输送距离近似呈线性负相关关系,与管径和质量流速近似呈指数式正相关关系,与液相质量分数近似呈线性正相关关系。采用电伴热方式时,由于不需要额外掺水确保管道的“最小安全输量”,在极低输量条件下的热能节省效果将更加显著。本研究成果可为海底气液多相流混输管道电伴热的热能节省特性认知提供理论依据。

海洋CO_(2)管道输送技术现状与展望

管道输送是经济高效的CO_(2)运输方式,海洋CO_(2)运输是离岸碳捕集、利用与封存(CCUS)产业链的关键环节和规模化开展离岸CCUS工程建设所需的核心技术。本文明晰了我国实施离岸CCUS的优势、典型海洋碳运输情境和海洋CO_(2)运输方式,剖析了国内外海洋CO_(2)管道输送的技术与工程概况;从CO_(2)流体相态及流动安全,沿程腐蚀风险评估、监测及预警,CO_(2)泄漏实时监测技术,高压CO_(2)泄放及对环境的影响等方面梳理了海洋CO_(2)管道输送工艺技术现状;从CO_(2)管道材料断裂行为及止裂措施、高耐蚀及密封材料、碳钢管道长寿命运行的关键腐蚀控制技术、注采井筒的腐蚀风险评估等方面梳理了海洋CO_(2)管道材料技术现状。研究认为,加快发展适应海洋CO_(2)管道输送复杂工况的材料体系、全流程CO_(2)管道的智慧管理与数字孪生技术、海底CO_(2)管道全生命周期运行关键技术、在役海底管道改输评估与保障技术,采取加快推动我国近海碳封存CO_(2)管网规划、拓展和深化跨行业/跨机构合作模式创新、系统建设海陆统筹的标准体系、引导专业化技术服务企业深度参与海底CO_(2)管网建设等举措,促进我国海洋CO_(2)管道输送体系高质量建设。

Seabed structures and foundations related to deep-sea resource development:A review based on design and research

The deep‐sea ground contains a huge amount of energy and mineral resources,for example,oil,gas,and minerals.Various infrastructures such as floating structures,seabed structures,and foundations have been developed to exploit these resources.The seabed structures and foundations can be mainly classified into three types:subsea production structures,offshore pipelines,and anchors.This study reviewed the development,installation,and operation of these infrastructures,including their structures,design,installation,marine environment loads,and applications.On this basis,the research gaps and further research directions were explored through this literature review.First,different floating structures were briefly analyzed and reviewed to introduce the design requirements of the seabed structures and foundations.Second,the subsea production structures,including subsea manifolds and their foundations,were reviewed and discussed.Third,the basic characteristics and design methods of deep‐sea pipelines,including subsea pipelines and risers,were analyzed and reviewed.Finally,the installation and bearing capacity of deep‐sea subsea anchors and seabed trench influence on the anchor were reviewed.Through the review,it was found that marine environment conditions are the key inputs for any offshore structure design.The fabrication,installation,and operation of infrastructures should carefully consider the marine loads and geological conditions.Different structures have their own mechanical problems.The fatigue and stability of pipelines mainly depend on the soil‐structure interaction.Anchor selection should consider soil types and possible trench formation.These focuses and research gaps can provide a helpful guide on further research,installation,and operation of deep‐sea structures and foundations.

南海海底输气管线永久修复方案研究

海底管线是海上油气田生产的重要设施,一旦发生损坏将可能造成油田停产并带来重大损失。海底管线的维修方案重点考虑的是作业难度、作业风险、作业时间等因素。本文根据南海某海底输气管线修复的作业要求,对舷侧提吊、开孔封堵等维修方案进行了研究,通过方案的对比分析,分析研究了适用的维修方案。

流动条件下X65钢在含氧体系下的腐蚀行为及腐蚀预测模型

X65钢注水海管介质含有溶解氧,导致管道内发生严重腐蚀。针对该问题,基于现场注水海管基础数据,考虑流速、温度、溶解氧浓度和Cl^(-)浓度对X65钢腐蚀行为的影响,设计9组正交试验,采用高温高压反应釜、扫描电子显微镜和X射线衍射仪进行失重测试和腐蚀产物表征;结合多元线性回归法,建立腐蚀预测模型。结果表明:4种影响因素对腐蚀速率的影响程度由大到小排序为:溶解氧浓度>温度>流速>Cl^(-)浓度,溶解氧浓度是腐蚀主控因素;随着流速、温度、溶解氧浓度和Cl^(-)浓度的增大,腐蚀速率增大;腐蚀产物表征结果表明,腐蚀产物主要为Fe3O4和Fe2O3;考虑上述4个因素的影响,基于7组均匀腐蚀速率值,建立腐蚀预测模型;采用剩余2组均匀腐蚀速率值对腐蚀预测模型进行验证,误差最大为8.9%,表明该腐蚀速率预测模型的准确性较高。

Cost consequence-based reliability analysis of bursting and buckling failure modes in subsea pipelines

Risk assessment is a fundamental activity to evaluate the integrity of pipeline systems during their life cycle,which allows pipeline operators to focus attention on integrity management activities in order to prevent and mitigate failure and maintain the design safety level.Risks for materials and contractor’s quality are a major source of concern about the integrity of pipelines and have a remarkable influence on the optimized balance between capital expenditure(CAPEX)and operation expenses(OPEX)in risk-based integrity management of pipeline.While other sources of risks to pipelines have been investigated thoroughly,the impacts of construction and material quality have not been well studied yet.This paper addresses the influence of construction accuracy/quality and corresponding uncertainties on the failure of submarine pipelines in the presence of corrosion.Corrosion-bursting and corrosion-buckling failure modes(which are addressed as ultimate limit states of subsea pipeline in DNV-OS-F101)are investigated in a reliability analysis to predict critical failure year of the pipe.Sensitivity analysis is also implemented to estimate the importance of parameters on failure probability using Monte Carlo Simulation(MCS).The results show a high sensitivity of failure probability to construction accuracy,which defines contractor quality.

Predicting scour beneath subsea pipelines from existing small free span depths under steady currents

An equation was developed to predict current-induced scour beneath subsea pipelines in areas with small span depths,S.Current equations for scour prediction are only applicable to partially buried pipelines.The existence of small span depths(i.e.S/D<0.3)are of concern because the capacity for scour is higher at smaller span depths.Furthermore,it is impractical to perform rectification works,such as installing grout bags,under a pipeline with a small S/D.Full-scale two-dimensional computational fluid dynamics(CFD)simulations were performed using the Reynolds-averaged Navier-Stokes approach and the Shear stress transport k-ωturbulence model.To predict the occurrence of scour,the computed maximum bed shear stress beneath the pipe was converted to the dimensionless Shields parameter,and compared with the critical Shields parameter based on the mean sediment grain size.The numerical setup was verified,and a good agreement was found between model-scale CFD data and experimental data.Field data were obtained to determine the mean grain size,far field current velocity and to measure the span depths along the surveyed pipe length.A trend line equation was fitted to the full-scale CFD data,whereby the maximum Shields parameter beneath the pipe can be calculated based on the undisturbed Shields parameter and S/D.

聚脲在海管节点补口防腐涂层中的应用研究

为简化海管节点施工工艺,同时降低节点补口成本,开展了喷涂聚脲在节点补口防腐涂层中的适用性研究。以国内A公司和国外B公司的喷涂聚脲分别制备海管节点防腐涂层,并对涂层性能进行系统全面的分析研究。结果表明:聚脲涂层均表现出优异的力学性能、电绝缘性、耐水性及热处理后拉伸强度保持率,但是其与基材的界面黏结在阴极剥离试验后会出现失效的情况,同时2种涂层经盐、碱、酸处理后拉伸强度保持率也较差。

某油气水混输不保温海底管道的腐蚀原因及控制措施

对某油气水混输不保温海底管道开展了多次智能内检测,发现在不同时间段海底管道前段及中段存在大量局部腐蚀缺陷点。通过腐蚀模拟试验、通球清管产物及微生物测试分析、海底管道温度变化曲线分析等手段,对该海底管道腐蚀原因进行了系统分析。结果表明:海底管道前段及中段产生大量腐蚀缺陷点的原因是硫酸盐还原菌和腐生菌,以及沉积物垢下腐蚀相互作用,不同时间段海底管道缺陷点发生位置不同是由物流入口温度变化从而改变管道沿程温降引起的。近年来,采取了加强通球清管措施、调整杀菌剂的注入、监测杀菌剂杀菌效果等措施后,海底管道腐蚀状况得到了缓解,腐蚀状况未见明显加剧。