The calamities of oil leaking under water in ocean environments have motivated a number of studies on the theoretical mechanisms of oil jetting, oil leaking and diffusion phenomena from subsea oil pipelines. This paper presents results in terms of theoretical and computational fluid dynamics (CFD). Sensitivity studies of leak hole diameters, leak velocities and ocean current velocities are investigated. The analytical results indicate that the underwater oil leaking processes of subsea oil pipelines manifest two different scenarios (a) the jetting and (b) the diffusion. In the jetting, initial oil momentum is dominant. The larger the leak hole diameter and the leak velocities are, the larger the oil jetting column diameters and the lengths are. Also, significant necking phenomena occur in the oil columns, and significant plumes are developed at both sides of an oil column. In the diffusion scenario, larger ocean current velocities, smaller leak hole diameters and smaller leak velocities give rise to oil droplets' growth. Based on results in this study, constructive suggestions are put forwarded to dispose of oil spill pollution. INTRODUCTION Subsea oil pipelines play a fundamental role for offshore oil and gas field explorations and productions. However, the subsea pipelines buried under water all year round may suffer from corrosion, fatigue damage and damage caused by external forces such as human destruction and natural disasters. These result in serious environmental pollution and immense economic losses. For example, the pipelines in the Gulf of Mexico were torn apart, leaking about 5000 barrels of crude oil every day in April 2010. Although the frequency of underwater oil leaking is relatively lower than that of surface or near-surface oil leaking, it is quite difficult to observe the mechanism of transport and diffusion process. The research on the dispersion process and drift of the leaking oil of subsea pipelines is helpful to understand the distributions of the leaking pollutants in water. The research will be beneficial to estimate the risk of the oil leaks, to take emergency response actions and control of the pollutants released.

In this study, artificial ground motions with temporal-spatial correlation are first synthesized based on a collected offshore recording from Kyoshin Network (K-NET). Second, a finite element model of 400-meter subsea pipeline is created, and the time-domain earthquake analyses are carried out under two patterns of seismic inputs. One is the uniform excitations without considering temporal-spatial variations, whereas the other is the non-uniform multi-point excitations with temporal and spatial coherence functions. Comparisons of the transient dynamic response are therefore conducted. It is shown that the nonuniform excitations tend to trigger a stronger dynamic amplification effect than uniform excitations do in the aspect of maximum acceleration and maximum displacement. Furthermore, the maximum principle stress is approximately 1.33 times under non-uniform excitations as compared to that of the uniform excitations, which is consistent with the trend of maximum relative displacement. The importance to account for the effect of temporal-spatial variations in the seismic ground motions on the dynamic response of subsea seismic pipelines thereby is manifested in this study. INTRODUCTION In earthquake prone countries like China, Japan and the Unites States, the long-span coastal and offshore structures including cross-sea bridges, tunnels, and subsea pipelines are subjected to potential earthquake attack. Especially for subsea pipelines that are commonly employed for oil and gas transportations, most of them are shallowly buried in soft seabed soil or even directly laid on seabed without trenching operations. Oil and gas would leak off once the pipeline is damaged or ruptured by the seismic ground motions. Earthquakes would then cause serious property loss and serious pollution to ocean environment and ecology water. Consequently, it is of great significance to investigate their dynamic responses under strong seismic loading in order to ensure the safety and reliability of subsea pipelines. According to a large quantity of studies based on the strong motion array records (Loh, 1985; Hao, Oliveira, 1989; Roullé and Chávez-García, 2006), it is denoted that seismic ground motions at different sites typically vary in frequency, amplitude and duration, which is known as temporal-spatial correlation. The influence factors are related to the local site effect, incoherency effect and wave passage effect. The local site effect is produced by the anisotropic and damping soil along the wave travelling paths, leading to variation of frequency as well as decay or soil amplification in amplitude. The incoherency effect include reflection, refraction and scattering during the wave propagation, conducing to the frequency variation as well. The wave passage effect accounts for the time delay of the arrival earthquake waves, resulting in phase-lags at different sites. However, in the previous works (Datta and Mashaly, 1990; Wang, et al., 2010; Xue and Wang, 2019; Zhang, et al., 2019), the temporal-spatial correlation of ground motion has been extensively discussed based on the proposed power spectral density (PSD) models (Kanai, 1961; Clough and Penzien, 1975; Du and Chen, 1994), in which the parameters are derived from existing onshore earthquake recordings. In fact, unlike the onshore earthquake ground motions, the offshore earthquake ground motions have unique characteristics in the ratio of vertical-to-horizontal peak ground acceleration and the peak spectrum plateau due to the effects of seafloor soft sediments and water layers (Chen, et al., 2015; Zhang and Zheng, 2019). If the onshore motions are used as seismic inputs, they may lead to erroneous predictions of offshore pipeline seismic responses (Bi, Hao, 2017).

Scouring, due to the interaction of fluid, pipeline and material of soil, is a complex phenomenon, numerous effective parameters are involved on the scouring phenomenon below the pipelines. In order to predict scour depth accurately, investigators have tried to predict scour depth by artificial intelligence models like support vector machines, radial basis function, genetic programming and group method of data handling. A prediction model of BP neural network is proposed for the pipeline scour depth in this paper, which weights and thresholds of the BP neural network were optimized by genetic algorithm. The scour depth was predicted by this model using nondimensional data sets that were collected from the existing research. The results of the prediction model were compared with empirical equations and BP neural network, which showed that GA-BP neural network predicted the scour depth with R=0.9437(Correlation coefficient), RMSE=0.1072(Root Mean Square Error, RMSE) and MAE=0.0788(Mean Square Error, MAE) compared with empirical equations (R=0.7605, RMSE=0.2662, MAE=0.1730 and R=0.7416, RMSE=0.2790, MAE=0.2015) and BP neural network (R=0.8281, RMSE=0.2323, MAE=0.1736) in live-bed conditions. Thus it can be seen GA-BP neural network has lower error and higher accuracy than the empirical equations and BP neural network. Results of the sensitivity analysis indicated that Fr is the most effective parameter for predicting the scouring depth below the pipeline. Therefore, the method proposed by this paper can be used to accurately predict the scour depth of submarine pipeline, and provide an important role to improve the stability of pipeline. INTRODUCTION Pipelines are used to carry liquids, such as water, oil, and natural gas. These pipelines are basically embedded in the sea bed. When the flood occurs, the water flow oscillation caused by the shedding of wake vortex influence the stability of pipelines, which may cause local scour around the pipe. Therefore, the prediction of the scour depth around the pipeline is an important problem in submarine pipeline engineering. Aiming at the problem of pipeline scour prediction, the experimental research and numerical calculation are carried out(Brørs, 1999; Moncada-M et al, 1999; Chiew, 1990; Myrhaug et al, 2009; Çevik and Yüksel, 1999; Cheng et al, 2014). A large number of empirical equations have been obtained through previous studies. The main disadvantage of these traditional methods is that it is not accurate enough to predict the scour phenomenon. Therefore, artificial intelligence methods are propoesd for predicting this problems. For example, artificial neural networks (ANN), support vector machine (SVM), machine learning methods, adaptive neuro-fuzzy inference systems (ANFIS), genetic programming (GP), group method of data handling (GMDH) have been used to predict scour of underwater structures(Guven et al, 2008; Najafzadeh et al, 2014; Najafzadeh et al, 2015; Azamathulla et al, 2010; Azamathulla et al, 2011; Azamathulla et al, 2015; Etemad-Shahidi et al, 2011; TothE et al, 2011; Parsaie et al, 2019). Recently, the BP neural network optimized by genetic algorithm (GA-BP) are used to solve various problems in engineering field. In this paper, according to the scour influence factors, the BP neural network optimized by genetic algorithm (GA-BP) is used to establish the scour depth prediction model, which is introducing the genetic Algorithm to optimize the weights and thresholds of the network and taking advantage of the characteristics of GA global search, and the generalization performance of the neural network can be improved, so as to improve the prediction accuracy of the network model and provide another scientific method for the prediction of scour depth. The main purpose of this paper is to study the effectiveness of GA-BP model in predicting pipeline scour depth. Also, the results are compared with empirical equations and BP neural network.

The critical incidents of the brash ice accumulation are considered using the port of Sabetta as an example. The heat volume, required for the keeping the certain thickness of the brash ice layer is determined using a thermodynamic simulation. The simulation results determine the power capacity of the required heat producing generator. The various methods, that can be used to reduce the energy consumption costs are described, such as: scheduling of the vessels traffic, change of the vessel movement scheme, optimization of the location of the bubbling lines and discharge points of the heated water. INTRODUCTION Currently, active development of the Arctic coast of Russia is under way. Mining companies developed the vigorous activities for development of oil, gas, gas-condensate and other fields. A maritime transport plays an important role in these works. It delivers consumables, machinery and ready-made structures to the Arctic to build the infrastructure. The developed fields begin to supply the raw materials (hydrocarbons and other) to markets by sea. The largest economic activity is observed in the Ob-Yenisei region. It includes the construction of ports and other hydraulic facilities. The port of Dudinka has long operated on the Yenisei River. It provides a transportation of finished products from Norilsk mining and metallurgical plant. The port of Sabetta and the terminal "Arctic Gate" in the Ob' bay had already built for LNG and oil offloading. The design and construction of other facilities, mainly in the northern part of the Ob' bay, continues. The "Utrennyi" terminal is being built on the Gydan Peninsula and it is part of the port of Sabetta. The LNG carrier vessels will be loaded with liquefied natural gas at this terminal. The development of the region is causing a transfer from seasonal sea transportations to year-round traffic. In the Yenisei Gulf, a regular winter sea navigation from the port of Dudinka is carried out since 2008. In the Ob'Bay, a regular winter navigation is carried out from the port of Sabetta since 2013 and from the oil terminal "Arctic Gate" near Kamennyi Cape since 2015. During this time, a sea traffic, for example, in Sabetta, has grown from single calls to several hundred vessels per season.

Marginal oilfield is becoming the primary alternative oil and gas resources in Bohai Oilfield as most of the existing oilfields are entering the middle-late development phase. In general, the development of marginal oilfield relies on other oilfields or facilities due to low IRR (internal rate of return) if developed independently. However, the existing pipe networks of Bohai Oilfield are rather complicated. A number of problems would need to be resolved if marginal oilfields were connected to these networks. These problems are illustrated with a given marginal oilfield in Bohai Bay of China, which would be developed by three production wells and two water injection wells. The nearest existing platform is about 16.1 km away from the marginal oilfield and the existing pipe network contains five pipelines. In order to realize the development of this marginal oilfield, the problems requiring attention include the pressure change caused by the change of fluid properties of the marginal field, and the influence on flow assurance of the original pipeline and existing platform. Feasible and safe solutions are proposed in this paper to resolve these problems, which could help provide useful references to other marginal oilfields. INTRODUCTION Marginal oilfield is becoming the primary alternative oil and gas resources in Bohai Oilfield as most of the existing oilfields are entering the middle-late development phase. The proved reserves of marginal oilfield in Bohai can be rather large (Wan, Qian and Wang, 2018). However, the degree of difficulty in developing these oilfields is rather high due to many factors, such as environment, higher technology requirement and low IRR. In order to develop marginal oilfield economically, a strong reliance on existing infrastructure is often required. However, the existing pipe networks of Bohai Oilfield are rather complicated. A number of problems will need to be resolved if a marginal oilfield were to connect to these networks. A comprehensive assessment of these pipe network issues is required before proceeding with the development of a marginal oilfield.

Three surveys of an 8km long subsea pipeline laid on a soft clay seabed were performed using side scan sonar profiler. The free span characteristics over the field surveys were examined and compared with the conventional free span design criteria. The comparison results indicate some shortcomings in the conventional design approach, with more refined evaluation of the critical spans allowing for optimization of intervention works. A refined free span acceptance criterion is developed based on the field observations. INTRODUCTION The presence of a pipeline on a seabed promotes local sediment transport that leads to scouring of sediment from around and underneath the pipeline. The scouring causes the pipeline to develop a free span. The scour problem around subsea pipelines has been studied extensively by researchers (e.g. Fredsoe, 1988; Mork, 1999) as well as in the SCARCOST project (Sumer et al. , 2001), MOBILEspan Joint Industry Project (Madeley et al. , 2015) and research work on studying the existing Woodside North West pipeline behaviour by University of Western Australia (Leckie et al. , 2015). The conventional approach to design a pipeline assumes that the seabed itself is stable and so the pipeline span remains stationary. This assumption is difficult to justify because substantial experiments and field evidence have demonstrated that the seabed becomes unstable under severe wave and current condition (Leckie et al. , 2015; Teh et al. , 2003). Because of the uncertainties of the pipeline span characters, Mork (1999) and Madeley et al. (2015) proposed probabilistic assessment to simulate the span development process. However, the probabilistic approach is not commonly used, which may be because of the limited availability of reliable statistical distributions of span characteristic data to consider in the pipeline design. The objective of this paper is to present the field observation of a pipeline from three surveys and to discuss the shortcomings in the pipeline free span design. It is motivated by questions about what the actual behavior of pipeline free spans is over the design life and its impact on the pipeline integrity.

Consolidation settlements of a dual suction anchor (DSA) functioning as foundation structure (FST) of a pipeline end manifold (PLEM) on a soft clayey seabed during different installation and operational stages is evaluated. 3D finite element model of the DSA, including time intervals between installation phases, was created. The results showed the feasibility of DSA as the foundation structure of heavy subsea structures on very soft clays. It was observed that the maximum lateral deformations in the soil develop at shallow depths adjacent to the outside of the skirts, and the maximum vertical displacements occur in the soil plug inside the DSA and adjacent to the skirts. Concentration excess pore pressure was observed around at the tip of the skirts and adjacent to the stiffeners. In addition, it was found that the presence of post-lay rock at the vicinity of DSA considerably affects the settlement of DSA. INTRODUCTION Troll is a gas and oil field in the northern part of the North Sea, about 80 kilometers north-west of Bergen. The field is situated in the blocks 31/2, 31/3, 31/5 and 31/6 and the water depth in the area is 300 to 335 meters. The gas in Troll East is recovered by pressure depletion through 39 wells drilled from Troll A. The gas compression capacity at Troll A was increased in 2004/2005, and again in 2015. In addition to gas from Troll East, gas from the Troll B and C platforms is exported via the Troll A platform. The gas and natural gas liquids are transported from Troll A to Kollsnes Gas Processing Plant in Øygarden via three 36″ pipelines. The oil is transported from Troll B and C in pipelines to Mongstad. The Troll Phase 3 development (stage 1) is a 36’ subsea pipeline tie-back of two templates (W1 and W2) to the Troll A platform (see Fig. 1). Out of three initially proposed foundation structure (FST) alternatives, i.e. a rectangular foundation with peripheral skirts (Størkersen, 2016), a fourbucket suction anchor (Bertrane, 2010) and a dual suction anchor (DSA), the DSA was selected as the best foundation alternative for a pipeline end manifold (PLEM) on a soft clayey seabed. It was found that the DSA has advantages, such as providing a stiffer mainframe structure, keeping the periphery of the suction anchors within the frame extents and providing simple suction system arrangements compared with the four bucket solution, and a better control of installation and leveling process compared to the rectangular skirt solution. TrollWest DSA was installed successfully in July 2019 (see Fig. 2).

The J-lay and S-lay are two common methods for SCR (steel catenary riser) and pipeline installation. When using the S-lay installation method, onboard welded pipe joints leave the vessel horizontally and are guided to the seabed over a stinger. The pipe is lowered using tensioners. With the advantage of high production rate, S-lay can be a cost-effective solution for deepwater riser and pipeline installation. This paper investigates feasibility of using CNOOC’s HYSY 201 S-lay installation vessel to install Lingshui 17-2's SCRs and pipelines. This paper investigates feasibility of using CNOOC's HYSY 201 S-lay installation vessel to install Lingshui 17-2's SCRs and pipelines. This paper first introduces the S-lay installation vessel HYSY 201 and S-lay configuration. The hydrodynamic motion analysis for a Response Amplitude Operator (RAO) was computed for HYSY 201 in different environmental headings. It then presents the layout and description of SCRs and pipeline for LS17-2 project. With the site-specific metocean design basis, this paper presents an installation procedure, analysis methodology, and acceptance criteria. The study covers different sizes of SCRs and pipelines to investigate the feasibility of S-lay installation. The study starts from the static installation analysis of SCRs and pipelines and includes different installation steps. The acceptance criteria are examined for the pipes at over bend and sag bend regions. The support reactions load on the stinger structure are reported at each step. The dynamic analysis is selectively performed to evaluate Dynamic Amplification Factors (DAFs) of support reaction loads especially for roller box supports on the stinger structure. The sensitivity of DAFs to wave parameters such as wave height and peak period is analyzed as well. The maximum top tension and the stinger's roller reactions are also computed and post processed for installation team to check against HYSY 201's tensioners and stinger's load capacity. This paper finds the feasibility of S-lay installation of deepwater SCRs and pipelines for Lingshui 17-2 project using the installation vessel of HYSY 201.

Submarine-pipeline developments are moving into deeper waters. As a result, thicker pipe walls are needed and hence the quotient of the pipe diameter and its wall thickness (i.e., D/t ) reduces. On the other hand, there is a push to optimise properties and requirements for moderate water depths of several hundred metres. Design criteria in the prevailing submarine-pipeline design standard DNVGL-ST-F101 (2017) were developed for straight pipes with 15 ≤ D/t ≤ 60 but applicability is limited to D/t ≤ 45. There can be a desire to go beyond this limit when designing for moderate depths. When pipe walls are becoming thinner, this makes the pipeline more susceptible to collapse. It has been found that, in some cases, the DNVGL-ST-F101 formulations that aim at predicting the collapse pressure of relatively thin-walled pipelines can lead to nonconservative results. This is a concern when the line-pipe manufacturing technique employs cold forming—such as the cross-section expansion step in the UOE and JCOE methods—and the adverse contribution of the Bauschinger effect is not mitigated in a suitable manner. INTRODUCTION The UOE and JCOE methods are used for manufacturing largediameter seam-welded line pipe. Both methods include a coldexpansion step, which can promote the Bauschinger effect. The pipe's compressive stress–strain curve can be affected in two different ways: (1) the plasticity plateau can be lowered (i.e., a reduction of the yield stress), and (2) the curve can become more rounded near its transition from linear-elastic to plastic behaviour. Current design formulations were derived after assuming bilinear (elastic-perfectly plastic) relations between stress and strain, and deal with only the first effect, via the fabrication factor. The second effect can cause significant narrowing of the range in which the material behaves linearly and is particularly pronounced for steels that are not subjected to (light) heat treatment after cold forming. The collapse mechanism is a typical design driver for pipelines in deep and ultra-deep water. However, it can also be important for pipelines in intermediate water depths. Collapse is the failure mode where the pipe cross section becomes unstable due to excessive external pressure acting on the pipe wall. It is typically viewed as buckling or bifurcation behaviour because the cross section will deform significantly only when the acting pressure is very close to the limit capacity. In this range of pressure, a very small pressure increase will result in a relatively large growth of deformations. When the cross section cannot sustain any more pressure increase, it will ovalize excessively and ultimately flatten: this is called collapse.

The primary goal of this research is to investigate the effect of defect on the fatigue-induced magnetic behavior of a ferromagnetic steel. Uniaxial cyclic loading tests on X70 pipeline steel were carried out with various stress levels. The variation of the magnetic signals surrounding the specimen was detected by two fluxgate magnetometers. The results indicated that the evolution of the magnetic field at defect shows significant differences compared to the smooth area. The evolutions of the magnetic fields similar in the first two stages, however, in the third stage, the magnetic field at defect changed both in the amplitude of magnetic field and the shape of the hysteresis loops. The experiment results proposed a feasible non-destructive testing method for pipeline steels. INTRODUCTION With the development of the world offshore oil industry, submarine pipelines are widely used in deep-sea oil and natural gas exploitation. Yet corrosion defects are often found in pipelines. Corrosion is one of the main causes of accidents in the oil and gas industry. Corrosion can lead to local damage to the pipeline and result in stress concentrations. Additionally, due to the existence of vortex-induced vibration (VIV) (Williamson and Govardhan, 2004) and suspended span (Zakeri, 2009), submarine pipelines are prone to fatigue damage, especially in the defect areas. Hence, it is important to detect these defects timely with non-destructive testing methods. Structural Health Monitoring (SHM) technology can sense and predict a series of factors detrimental to structure such as structural defects, damage, deformation, and corrosion. The main purpose of pipeline monitoring is to identify the location of corrosion defects, assess defects accurately and predict the residual life of the pipeline. Common NDE techniques are magnetostrictive sensors (MSSs) technique (Cheong, Jung and Kim, 2006; Luo, Rose and Kwun, 2004; Jia, Liu, Wang, Liu and Ge, 2011), distributed fiber sensors technique (Rajeev, Kodikara, Chiu and Kuen, 2013; Thien, Chiamori, Ching, Wait and Park, 2008), electromagnetic acoustic transducers (EMATs) technique (Hirao and Ogi, 1999; Zhao, Varma, Mei, Ayhan and Kwan, 2005), guided waves method (Cawley, Cegla and Galvagni, 2012 ; Harley, Ying, Moura, Oppenheim, Sobelman and Garrett, 2012), ultrasonic sensors technique (Ying et al., 2013 ; Michaels, Cobb and Michaels, 2004) and so on.

The ability to predict offshore pipeline plough performance (e.g. tow forces and progress rates) in a variety of ground conditions is an important part of project planning. This may be estimated based upon experience from nearby locations or similar ground conditions, but existing empirical plough force prediction models are available and recent updates have been made. With the increasing use of digital data, it is hoped that greater reliance can be placed on these models and this process can be automated and integrated into Geographic Information System type applications. This paper uses real offshore plough data from three trenching projects in sand to compare plough performance prediction models. INTRODUCTION To allow appropriate planning for offshore pipeline ploughing installation campaigns it is necessary to reliably predict tow forces and advance rates prior to undertaking works, or at the tendering stage. This is not only important for planning, but also in selecting appropriate tow vessel support and deciding the approach to ploughing i.e. can the ploughing be undertaken in a single pass whilst minimising tow forces and maintaining adequate progress rates, or are further passes required. A multi-pass approach may be adopted where although the design trench depth could be achieved in a single pass, trenching is undertaken in two or more passes with an initial shallow trench depth followed by trenching to the final design depth (Machin, 1995). A multipassing approach may seem counterintuitive because of the associated additional plough handling time and the requirement of pulling the plough across the seabed more than once, but this can be more efficient and save time when compared to a single pass. The potential benefits of a multipass approach are demonstrated by Eq. 1 (Cathie and Wintgens 2001) where the passive pressure component of tow force ( F ) is shown to increase with depth ( D ) cubed and there is a rate dependent term or potential for tow forces to increase with increasing plough velocity ( v ). This latter term is dependent again on the depth of the plough share but also on the soil permeability and its potential to dilate (relative density, or unit weight γ and depth of ploughing) during shearing, resulting in low pore pressures and increased effective stress (Lauder et al., 2012).

Market demand pushes subsea developments into ultra-deep water. Pipelines installed in such environment require very thick walls to cope with the extreme hydrostatic pressure. However, the design criteria for local buckling under combined loading in one of the prevailing submarine-pipeline design standards, DNVGL-ST-F101 (2017), are stated to be valid only for pipelines with a diameter-to-wall-thickness ratio ( D/t ) between 15 and 45. The European Pipeline Research Group (EPRG) evaluated whether the existing design equations can be used for very thick-walled pipelines with D/t below 15 that are subject to external pressure and bending, without affecting the level of conservatism underlying the code framework. The limit-state formulation for load-controlled behaviour is found to be increasingly conservative for thicker pipe walls. INTRODUCTION Background Intecsea reviewed the status of deep-water pipeline technology for the EPRG Design Committee as part of EPRG Project 178/2015. This study covers a gap analysis and was concluded in 2016. Areas that require further research were identified and subsequently included in EPRG's research roadmap. An important gap is the absence of a reliable and valid limit-state formulation for local buckling of thickwalled pipe when loaded by a combination of bending, axial force and pressure. The limit-state formulations for local buckling included in DNVGL-ST-F101, which is widely used for design of subsea pipelines, are stated not to be valid when D/t is less than 15. Deep-water pipelines installed to date require D/t in the order of 20 for external pressure design. This is the case in maximum water depths in the range of 2000–2500 m. When moving to ultra-deep water, the required D/t can be even lower than 15. This asks for technological advancements, which should also be sought in a fundamental review and a potential reformulation of the existing design equations. In addition to the lack of adequate design equations, manufacturability of line pipe with an extremely thick wall, meaning very low D/t , may be beyond the capabilities of the leading pipe mills. This depends on the selected manufacturing method; this paper considers seamless (SMLS) and longitudinally arc-welded (SAWL) pipe. The design of pipelines with D/t below 15 needs documented information on what can be produced, and according to which specification.

A pipeline inspection gauge (PIG) has been a versatile tool for the maintenance of a long pipeline. However, speed excursions in a low-pressure gas pipeline may damage the pig or the pipe. Due to the gas compressibility, significant speed excursions may occur during the start of the pig inflow pressure gas pipeline. This work presents the numerical model to simulate the behavior of the pig in a low pressure gas pipeline. In this model, the transient gas flow equations are solved by method of characteristics (MOC), and then the Runge-Kuta method is used for solving the dynamic equation of the pig. A parametric study was conducted to investigate the influence of main variables on speed excursions. The obtained results were compared to those for the commercial simulation tool, OLGA. The results show the static friction and pressure has a significant impact on the speed excursion, while the flow rate has a slight impact on it. INTRODUCTION Pipeline pigging is considered as the common way to inspect and maintain an oil and gas pipeline system. In a high pressure pipeline, the pressure creates enough force for the PIG to run inside the pipeline, allowing the pig to perform the inspection mostly successfully. However, there is not enough force to push the pig in the low pressure pipeline, and cause a speed excursion which is repetitive movements that PIG stops and restart at high speed. This phenomenon is called "stick-slip motion", which often occurs in a certain pipeline configuration, such as pipe diameter changes, curved pipes, and PIG start locations (Hendrix et al 2018). The speed excursion of the pig can damage the pipe and pig, and can lead to dangers of pipe breakage. This especially likely when the fluid in a pipeline is gas, the speed excursion would occur more often due to the compressibility of the gas. Hence, the estimation and prevention of_ speed excursions is essential.

Ultra-deepwater hydrocarbon pipelines face a number of design challenges in the form of demanding geotechnical characteristics of the selected route, extreme slope, construction loads arising from suspended catenary and loads introduced during conventional hydrotesting of the installed pipeline. The paper details the design, manufacturing and construction approach adopted by the Turkstream project to eliminate hydrotest requirements. Following completion of pipelay, both pipelines were pre-commissioned with multiple cleaning pigs propelled by compressed Nitrogen and batches of mono-ethylene glycol (MEG) as desiccant for the moisture entrapped in the pipeline during construction. INTRODUCTION South Stream Transport BV (SSTTBV) has constructed and commissioned an ultra-deepwater major gas transmission system in the Black Sea comprising of two (2) offshore pipelines installed in water depth up to 2200 m (Fig. 1). Each pipeline is designed for transportation of 15.75 billion cubic metres of natural gas per year over a seabed distance of some 940 km from Russia to Turkey at maximum operating pressure of 284 barg. Key parameters of the pipeline system are detailed in Table 1. This project is widely considered as one of the most challenging pipeline projects to-date, stretching both pipe manufacturing and offshore construction capabilities of linepipe manufacturers and pipelay contractors. Ultra-deepwater hydrocarbon pipelines generally span across continental shelf and abyssal plain of the intervening ocean. Selection of the shortest technically feasible pipeline route between the pre-determined landfall locations demand thorough assessment of technical limitations set by geotechnical characteristics of the planned route, pipeline material properties and construction methodology. In most cases of ultra- deepwater gas pipeline design, the loads encountered during the construction phase far exceed in-situ pipeline operating loads; tending to dominate pipeline design parameters. Where governing regulatory environment does permit elimination of in-situ hydrotest of the installed pipeline, design optimisation can yield significant economic and environmental benefit to the pipeline operator. Pipeline certification authorities, e.g. DNV-GL, have developed design code (e.g. OS-F101) to enable pipeline designer to secure "hydrotest waiver" via implementing stringent design verification, linepipe material selection, manufacturing quality control, advanced construction quality surveillance and "dry" pre-commissioning of the installed pipeline.

In this research, the investigation on simulation of sloshing pressure based on SPH is mainly demonstrated. Two different boundary conditions, dynamic boundary conditions (DBC) and dummy particle conditions (DPC), are utilized in the SPH models. The benchmark test with respect to the traditional 2D rectangular tank is firstly conducted. Then, simulations based on two boundary conditions are performed for 3D spherical shape MOSS-Type tank. The corresponding model tests are carried out to verify the performance of numerical simulation. Smoothed boundary model (SBM) is used to better illustrate the 3D spherical shape and the predicted pressure based on DBC and DPC can be enhanced by SBM. Finally, the influence of particle shift algorithm on the prediction of surface pressure is discussed. INTRODUCTION With the increasing demand of Liquid Natural Gas (LNG) and growing LNG exportation from the United States, Australia and other countries, how to qualitatively and quantitatively evaluate the in-tank LNG sloshing influence on the LNG ship motion and structural strength is always a challenging concern. Conventional scale model test is the most straightforward approach to study the sloshing behavior. However, performing model test usually involves huge budget and large amount of time and scale effect can not be considered as well. To overcome the shortage of model test, as an alternative solution, Computational Fluid Dynamics (CFD) has been successfully utilized in sloshing research in recent decades. Many studies have demonstrated the accuracy of the Eulerian grid-based fluid model for sloshing simulations. Kishev et al. (2006) successfully used the constraint interpolation profile method to tackle the 2D violent sloshing problem. The popular finite volume method (FVM) solver OpenFOAM has been widely used to investigate sloshing behavior (Li et al., 2011; Moirod et al., 2010; Jiang et al., 2015). Lee et al. (2007) used the commercial FVM solver FLOW-3D to examine the parametric sensitivity of the sloshing force in liquefied natural gas (LNG). In the above FVM models, establishing how to obtain the free surface is usually the crucial problem. Although this problem can be solved by volume-of-fluid (VOF) theory or level-set (LS) theory, new problems may be introduced as VOF is essentially a step function, and the law of mass conservation is usually violated in LS models. Furthermore, numerically capturing the fluid surface and updating the fluid mesh make the numerical model more complex and more time consuming.

Experimental results of sloshing model test have been investigated by data mining in the database of Seoul National University. More than 540 terabytes experimental data have been accumulated for various cargo holds, vessels, environmental conditions, operational conditions, and experimental conditions. The database was organized, cleaned, and analyzed. Model tests related to the floating units larger than standard size LNG carriers or LNG fueled vessels were selected. Then, the selected target data had been used for the artificial neural network to predict the model test results from the test conditions. The network successfully predicted the experimental results considering the various parameters. INTRODUCTION Vessels carry many different liquids such as Liquefied Natural Gas (LNG), petroleum, and sea water in cargo tanks. When a vessel sails under the environmental loads, sloshing occurs in a tank containing partially filled liquid, which can cause serious damage to the structure. Therefore, when designing a ship, it is necessary to accurately estimate the sloshing loads (Faltinsen and Timokha, 2009; Malenica et al., 2017). Recently, many studies have been conducted to estimate sloshing load. One reason is the increase in LNG volume and the rapid expansion of the LNG carrier construction market (BP, 2018; Kuo et al., 2009). LNG carriers have been enlarged for efficient transport. Since larger sloshing impact loads may occur in larger cargo holds, studies have been actively conducted to estimate them. With the expansion of the LNG carrier market, LNG fueled vessels have recently become one of the main products in the shipbuilding market (Congressional Research Service, 2019). Environmental regulations for ship operations have been tightened and LNG has begun to be used as a propulsion fuel for the vessels. Fuel tanks used in the LNG fueled vessels have a different shape from the cargo holds; therefore, partial loading conditions must be considered unlike the LNG carriers.

In order to test the localized Skin Effect Current Tracing technology, which will be large-scale applied in offshore oilfields. A large-sized experimental apparatus is set up in the dock of a port in Bohai Bay of China. The results showed that when the SECT is turned on, the temperature along the pipeline increase and reach the target value in 12 hours. Nearly two years passed, the apparatus and the heating and insulation effect in the test pipeline section is keeping in good condition. The results have verified the functional feasibility and physical performance reliability of the localized SECT. INTRODUCTION After the Chinese government propose a requirement for no less than 200 million tons of domestic oil production per year recently years, all the oil & gas companies in China strive for production increasing. According to the state planning, the vast majority of the yield increase will be produced from offshore oilfields. High viscosity crude oil which accounts for 68% of the total reserves of Bohai Bay, and high pour point crude oil which is abundant in the less developed South China Sea and East China Sea, will become the focus of offshore oil development in the future. At present, the measures of blending heat water or heating normally are adopted to improve the heat capacity in system, and reduce the fluid viscosity when pipelining the oil-gas-water mixtures. However, with the further increase of crude viscosity, water depth, transportation distance and operating pressure, the method of blending water or heating cannot meet the requirements of economic and safe transportation. Due to its strong safety performance, high heat tracing efficiency and uniform temperature distribution along the subsea pipeline, the skin effect current tracing technology, SECT for short, will be large-scale applied in the development of offshore high viscosity, low pour-point oil and deep-water oil & gas in China (Wan, Liu and Qian, 2019). In 2009, the first SECT cable and devices are introduced from Japan and laid in Bozhong 13-1 offshore oilfield to increase the heat capacity of produced fluids to overcome the risk of cooling, solidification and waxing during transportation. According to the on-site feedback, the temperature at the outlet of the 13km-pipeline has a rise of 5°C after the skin-effect electric heat tracing apparatus is turned on in winter.

In this work, computational fluid dynamics (CFD) simulations have been conducted on leaked LNG vapor diffusion in which the gas is discharged from the vent post of a LNG powered RORO ship. A numerical model is proposed based on an open source Computational Fluid Dynamics (CFD) tool called OpenFOAM® for numerical simulation of the turbulent gas diffusion. The numerical method is first validated against a benchmark case and an experimental case. Two turbulence models, k-ε and LES, are applied and the numerical results are compared and discussed. By using the proposed numerical model, a series of LES simulations have been conducted on the LNG vapor diffusion of the RORO ship under several wind speeds and air temperatures. INTRODUCTION In recent years, a number of LNG powered merchant ships have been or are being built for the advantage of cleaner emissions over conventional oil engines. However, since LNG is of extremely low temperatures, using it as fuel for merchant ships introduces new systems on board together with their associated risks. One of the major risks is the LNG vapor (natural gas) leakage which should be thoroughly investigated. Due to the very low boiling point (111.7 K), once LNG is leaked it vaporizes very quickly. At atmospheric conditions, the cold LNG vapor is about 1.5 times heavier than the ambient air (Koopman & Ermak, 2007), and therefore is called as a dense or a heavy gas. The leaked LNG vapor, mainly in the engine room, will be collected and discharged from the vent post of the ship into the air. Then the gas will be diffused by the surrounding turbulence air flow. To design such ships, it is needed to ensure that the concentration of the leaked gas on designated areas of the ship does not exceed a safety value. Prediction of the gas diffusion needs to consider ship speed, superstructures of the ship, and surrounding air conditions such as the wind and temperature.

Reel-laying rigid pipelines induce cyclic deformation that affect the section. Among other, excessive ovality may jeopardize pipe strength during installation & in-service. Previous works shown that conventional material stress-strain relation is no longer suitable for pipeline reel-lay simulations. This paper introduces an advanced model for material behaviour. The evolution of the material behavior and its variations on the cyclic loads paths is detailed. The model uses stressstrain relations and yield surface evolution from the first load curve, with Lüders plateau leading to stabilized cycle with material property variations in cycles. The model has been implemented in finite element software. This model calibration and validation are discussed in this paper. Simulation accuracy is improved compared to published results. INTRODUCTION The pipeline reeling installation process can be a cost-effective installation method for infield flowlines/risers and smaller diameter export lines under certain economical, logistical and technical circumstances. Saipem has acquired a recent pipeline construction vessel, Constellation, which has been designed as a high-performance construction and lay vessel, capable of performing in the world's hardest environments and designed to meet the requirements of current deep and ultra-deep-water projects. During offshore reeling installation, and possibly later pipeline recovery and re-reeling installation, the pipe is reeled, unreeled and straightened. During the process, part of the pipe cross-section has experienced varying levels of plastic deformation in compression and tension, in a cyclic manner. Throughout these steps, the plasticity deformation has modified the pipe material properties, while the other part remains in the elastic domain. Materials under cyclic loading can harden both kinematically and isotropically (or anisotropically). For applications where cyclic loads stay within a single cycle, hardening process comes mainly from kinematic hardening while yield domain surface evolution is negligible. Within a single cycle, Bauschinger effect drive the model behavior, while variation of this behavior through cycles comes from isotropic hardening. The Bauschinger effect refers to a property of materials where the material's stress/strain characteristics change as a result of the microscopic stress distribution of the material. An increase in tensile yield strength occurs at the expense of compressive yield strength. After increasing the tensile yield strength, the local initial compressive yield strength is actually reduced. The greater the tensile strengthening, the lower the compressive yield strength.

ABSTRACT To quantify and set up the LNG carrier's Moving Safety Zone is the precondition for ensuring the safety of the LNG carrier in the Yangtze River downstream. Based on the car-following model of traffic flow and the control characteristics of the LNG carrier, the mathematical model of the LNG carrier's braking maneuver is constructed. Applying the theory of ship domain to construct the ship domain of inland LNG carrier, then adapted to the characteristics of the channel in the downstream of the Yangtze River, so that the scale of LNG carrier's Moving Safety Zone is quantificationally defined and the longitudinal scale of LNG carrier's Moving Safety Zone is further obtained INTRODUCTION For a long time, China's energy structure system, with coal as its main energy source, has been challenged by air pollution, acid rain and declining atmospheric quality. Therefore, it is imperative to adjust the energy structure. Liquefied Natural Gas (LNG) has attracted more and more attention due to its advantages of easy transportation, high storage efficiency and environmental protection. Although LNG reserves are abundant in China, most of its producing areas are far away from industrial and population-intensive areas, especially in offshore gas development. Therefore, transportation and storage problems must be solved. LNG itself has the characteristics of low temperature, explosiveness and evaporation, which lead to high cost and high risk of LNG carrier, so it is particularly important to ensure the safety of LNG ship in the process of transportation. Especially in the areas near the port where the traffic flow density of LNG ships is high, it needs more attention from operators, ship pilots and port managers. In order to ensure the safety of LNG ships entering and leaving the port, the concept of safety zone is put forward. But up to now, there is no unified standard for the definition of safety zone. The size of safety zone varies with the size of LNG ships, the navigation environment of port waters, the meteorology during the process of ships entering and leaving the port, the sea conditions and the navigation density of local ports. If the scope of the safety zone is too large, not only can not effectively restrict the surrounding ships, but also waste the manpower and material resources of the port, waterway and other management departments, prolonging the impact on the normal navigation of the waterway; if it is too small, it can not limit the interception of surrounding ships to ensure the safety of ships. Therefore, the study on the safety zone of LNG ships in inland navigation process not only provides a reliable barrier for the safety of LNG ships, but also reduces the impact on inland navigation, which has important practical significance for the implementation of safety protection measures for waterways.