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ABSTRACT TWI has been processing materials with high power (4kW and above) Nd:YAG lasers since 1997 and has a history of welding structures with lasers extending back some thirty years. The work carried out at TWI for the pipeline industry using lasers has moved from early autogenous work with high power (9kW) fibre delivered Nd:YAG laser to hybrid procedures with Nd:YAG and MAG through to recent work carried out with a 7kW Yb fibre/MAG procedure capable of delivering deep penetration girth welding procedures at 1.8m/min travel speed. The paper describes the technical progress made throughout this work in terms of process developments to meet the exacting productivity requirements along with those necessary to meet technical requirements such as impact toughness and other pipeline code acceptance criteria. INTRODUCTION There is continual emphasis on reducing the costs associated with new pipeline development, particularly for large diameter gas transmission lines. In particular, Markland (2000) noted that BP expects to be involved in building over 10,000km of onshore pipelines for transporting oil and gas with capital expenditure estimated as exceeding £11 billion. Over half of the world's undeveloped hydrocarbon reserves are remote from potential users and very large pipelines, up to 1.42m (56") diameter are required to transport the fuel to market. The welding process used to make the site girth welds has a significant bearing on the total cost per kilometre of pipeline and is one of the areas that TWI has been involved with over the last few years. Current practice is to use either mechanised or automated MAG and in the short term there are probably further cost reduction opportunities offered by incremental improvements to this operation. The multipass MAG process, however, requires a high manning level and the costs of providing this and the necessary support in fairly remote regions
ABSTRACT In the Arctic pipelines for the transportation of oil and gas are buried into the sea floor. In some areas, however, the estimation of a safe burial depth is hampered by the possibility that ice masses can make trenches in the sea floor. In order to make a safe design, knowledge is required about the soil deformation when an ice keel is scouring over the sea floor. The burial depth is often deduced from the maximum gouge depth from ice keels, which have been scoured over the sea floor in the past. However, an unknown parameter is still the magnitude of the subgouge deformation. A more practical method to determine the burial depth of a pipeline could be to estimate the depth of subgouge deformation by parameters that are often available from soil investigation prior to pipeline trenching such as the undrained shear strength. Since it is difficult to examine ice scouring in a field test, some tests have been carried out in the geotechnical centrifuge of the University of Delft. Several parameters have been varied, such as: speed, undrained shear strength, scour depth and multiple scouring. The soil deformation was measured by means of image processing and the horizontal and vertical load was measured. The tests have shown interesting relations between these parameters and the subgouge deformation. To visualize the complex deformation pattern a grid was placed on the clay surface. Under some circumstances shear bands and deep cracks could be observed. INTRODUCTION Scouring ice keels is a class of soil-structure interaction problems associated with large soil deformations. These problems do not lend themselves to simulation by finite element calculations, and the only way of understanding them better is through experimental research.
Experimental Study And Numerical Analysis On Free Spanning Submarine Pipeline Under Dynamic Excitation
Zhou, Jing (State Key Laboratory of Coastal and Offshore Engineering, Dalian University of Technology) | Li, Xin (State Key Laboratory of Coastal and Offshore Engineering, Dalian University of Technology) | Dong, Rubo (State Key Laboratory of Coastal and Offshore Engineering, Dalian University of Technology)
ABSTRACT To investigate the dynamic response and seismic failure of the offshore oil/gas pipelines, a series of model experiment of free spanning submarine pipeline were carried out on an underwater shaking table in the Sate Key Laboratory of Coastal and Offshore Engineering, Dalian University of Technology. The factors to affect the dynamic response of pipeline, including the fixed condition, distance from the seabed, span length, and, the oil level inside the pipeline were researched in the dynamic experiments. Meanwhile, numerical analysis by FEM was achieved based on the equation of motion with force derived from Morison empirical equation. The numerical results are in good agreement with experimental ones. INTRODUCTION The construction of submarine pipelines for delivering gas and oil is increasing with the development of the offshore oil/gas industry in China. Many submarine pipelines were constructed in the seismically active region. Bohai oil field, the biggest offshore oil field in China locates in the seismically active region. The design ground acceleration is between 0.2 g and 0.25 g in this area. Therefore, the seismic load can not be omitted in the design of pipelines (Wang and Zhao, 1992). In many cases, the pipelines initially resting on the seabed may become suspended due to the pipeline be settled on uneven seabed or the movement of the seabed by environmental loadings. The damage is usually more serious for the free spanning pipelines than the embedded pipelines during earthquakes. However, it is still lack of the earthquake design code for the free spanning pipelines in China. However, a substantial volume of literature is currently available on the seismic response analysis and design of terrestrial pipelines (Anderson and Johnson, 1975; Datta and Mashaly, 1986; Hindy and Novak, 1980; Powell, 1978; Wong, Shah and Datta, 1986).
- Research Report > New Finding (0.50)
- Research Report > Experimental Study (0.50)
Vortex-induced Vibration Model of Span Segment of Buried Submarine Pipeline
Xing, Jing-Zhong (Institute of Mechanics, Chinese Academy of Sciences & School of Sciences, Lanzhou University of Science and Technology) | LIU, Chun-Tu (Institute of Mechanics, Chinese Academy of Sciences) | Duan, Meng-Lan (Dept. of Mechanical Engineering, Yangtze University & China Classification Society)
ABSTRACT Static deflections of submarine pipeline with span segment under self-weight and thermal expansion are analyzed in condition of elastic soil. The closed-form deflection and internal forces functions of both segments are yielded. Taken the static deflection of the span segment for mode shape function, mode shape factor and the first order frequency are calculated by energy balance method. Then, the VIV response at any current velocity can be determined according to DnV codes. INTRODUCTION The flow around structures, ranging from clarinet reeds to skyscrapers, always causes destructive vibrations. Such nature phenomena is called flow-induced vibration. Currents also bring offshore platforms crashing into the ocean (Blevins,1977). The interaction of flow and structures forms a coupled nonlinear vibration system. Among flow-induced vibration, VIV is of importance in ocean engineering. Free spanning of pipelines results from unevenness of sea bed or current scouring. Det Norske Veritas (DnV) issued a special code for free spanning pipeline (DnV, 2002). A lot of researches about free spanning have been carried out (Choi et al., 2001, Reid et al., 2000, Mork et al. 1999,1997, Fyrileiv et al.,1998, Park et al., 1997, and Bryndum et al., 1989), and some regulations are developed (DnV 2000a, 2000b). Park et al.(1997) analyzed static and dynamic free spans of pipelines, and proposed an allowable length of free span. The variation of allowable lengths is examined for specialized boundary conditions, where free spanning is modeled as a beam with transversal and rotational springs at each end. Considering tension and compressive force, Choi (2001) derived a closed form solutions of the beam-column equation for the various possible boundary conditions. The natural frequency is calculated by energy balance method. Some calculations are to present the sensitivity of the axial forces on the allowable free spanning lengths.
ABSTRACT An advanced finite element analysis of liquefaction process is carried out in order to simulate geotechnical centrifuge test of horizontal cyclic loading of pipeline. The displacement behavior of pipeline, the effective stress path, the shear stress-strain relationship and the pore pressure build up in seabed around the pipeline are numerically investigated through some simulations by this numerical analysis. The movement of pipeline during horizontal cyclic loading strongly depends on the ratio of horizontal to vertical load and the horizontal cyclic frequency. INTRODUCTION It is very important in pipeline design to make an accurate evaluation of pore pressure build up in the soil around a pipeline on the seabed due to direct wave action and induced currents. The pore pressure accumulation will reduce the effective strength of the soil and degrade the bearing response of a pipeline. The reduction of bearing capacity can lead to large vertical and horizontal displacements of a pipeline. In particular, an increase of horizontal displacement of the pipeline may lead to sudden break-out, which has a serious influence on the safe operation of the pipeline. It is therefore very important for design engineers to be able to evaluate the pore pressure accumulation in the soil around a pipeline under horizontal cyclic loading conditions. This can be achieved by carrying out numerical analyses (Taiebat and Carter, 2000; Zhang et al., 2001a; Takatani and Ogawa, 2004) and simulations (Zhang et al., 2002; Takatani and Randolph, 2003) based on experimental data of pore pressure build up. In this paper, an advanced finite element analysis of liquefaction process for the pipeline-seabed interaction problem is carried out in order to simulate some pore pressure build up response and pipeline movement in geotechnical centrifuge tests (Zhang and Randolph, 2001b).
Wave-Induced Pipeline On-bottom Stability: Comparisons Between Pipe -Soil And Wave-Pipe –Soil Interaction Models
Gao, Fuping (Institute of Mechanics, Chinese Academy of Sciences) | Wu, Yingxiang (Institute of Mechanics, Chinese Academy of Sciences) | Jeng, Dong-Sheng (Department of Civil Engineering, The University of Sydney) | Jia, Xu (China Offshore Oil Research Center, China National Offshore Oil Company)
ABSTRACT To have a better insight into the mechanism of wave-induced pipeline on-bottom stability, the pipe-soil interaction model (Wagner et al., 1987) and the wave-pipe-soil interaction model (Gao et al., 2003) are compared intensively in this paper. This includes the comparisons of their experimental setups, procedure of tests, phenomena of pipe losing stability etc. The comparison indicates that the critical lines for the instability of anti-rolling pipeline and freely-laid pipeline in the empirical wave-pipe-soil interaction model overall agree with the design values, based on both simplified and generalized methods in DnV standard, respectively. However, with the increase of Froude number, the generalized method in DnV standard becomes more conservative than the wave-pipe-soil interaction model for the on-bottom stability design of pipeline. Therefore, wave-pipe-soil coupling effects should be taken into account when we analyze the on-bottom stability pipeline under wave loading. INTRODUCTION One of the main problems encountered with the use of the pipeline in offshore engineering is the wave-induced pipeline instability (Herbich, 1985). When a pipeline is installed upon seabed and subjected to wave loading, there exits a complex interaction between wave, pipeline and soil. To avoid the occurrence of pipeline on-bottom instability, the pipeline has to be given a heavy weight of concrete coating or alternatively be anchored/trenched. Both methodologies are expensive and complicated from the aspects of design and construction. Recently, considerable efforts have been devoted into the interaction between pipeline and seabed. The state-of-the-art in pipeline stability design has been changing very rapidly recently. Three major investigations have addressed the problem of pipeline-seabed interaction, which include PIPESTAB project (Wagner et al., 1987), the American Gas Association (AGA) project (Brennodden et al., 1989) and a project at Danish Hydraulic Institute (DHI) (Palmer et al., 1988).
ABSTRACT This paper is concerned with a numerical simulation of laying a pipeline for intake of deep ocean water. An implicit finite difference algorithm is employed for three-dimensional dynamic equations of a pipe. Geometric nonlinearity and bending stiffness are considered and the equation is solved by Newton-Raphson iteration technique. The dynamic behavior of the laying pipeline is analyzed including pretension, pay-out rate, and seabed slope. In the case of a flat seabed, a touch down velocity is fast at the initial laying stage due to pretension loss and then gradually approaches to a steady-state condition. For the flat seabed, the top tension also greatly decreases when the pipe touches down the sea bottom and then gradually approaches to a steady-state condition. Meanwhile, when the seabed has a slope, the variation of the touch down velocity is nearly regular because the pretension effect is not large. The result shows that some attention needs to be paid when a laying pipeline touches down on a flat seabed INTRODUCTION Deep ocean water (DOW) is one of important marine resources and has the characteristics of low temperature, purity, stability, eutrophication and maturity. It is known that DOW is generally found at deeper than a depth of 200m. Around the Korean Peninsula, the depth is limited to the East Sea which has a favorable condition to develop DOW. There are two types of DOW development systems. The one is a land-based DOW production system. In this case, DOW within 5 km from a coastline is transported through a subsea pipeline on or under the seabed into the facilities located on land. The other is a floating platform system where a vertical riser pipe is attached and functions as a main device for pumping up DOW.
ABSTRACT This paper gives a definition of a "short" pipeline and derives the analytical linear elastic equations governing the lateral buckling problem for "short" perfectly straight pipelines exposed to high temperature and pressure loading. The use of the equations is illustrated through an example. INTRODUCTION Prior to carrying out non-linear finite element analysis it is common industry practice first to assess the criticality of lateral buckling of pipelines subjected to high temperatures and pressures using linear elastic analytical equations. The equations commonly used are those developed by Hobbs (1984) who built on work by Martinet (1936) and Kerr (1978) for rail tracks. The equations were derived for "very long" straight pipelines with no imperfections using linear elastic material behavior. Several investigators have investigated the effects of initial imperfections (Tvergaard and Needleman, 1980 and 1981; Taylor and Gan, 1986; Spinazze, Vitali and Verley, 1999 and others). Tvergaard and Needleman (1980) studied the effects of initial imperfections and found that if imperfections exist, buckling can initiate before the axial force reaches the critical force derived analytically for straight pipelines. In the post buckled condition the behavior is similar to that expressed using the analytical expressions for straight pipelines. For submarine pipelines the localized post-buckling behavior is more important than the actual force under which the pipe buckles which justifies using the analytical expressions for straight pipelines without imperfections. When the linear elastic analytical methods are insufficient to prove the structural integrity of the pipeline, non-linear analytical methods (Bruschi, Curti, Dumitrescu, Vitali and Leira, 1994), non-linear finite element analysis (FEA) (Bruschi, Spinazze, and Vitali, 1999; Mork, Collberg, Levold, and Bruschi, 1999; Torselleti, Luigino and Levold, 1999; Nystrom, Tornes, Bai and Damsleth, 1997; Bai, Nielsen and Damsleth, 1999 and others) or mitigation methods (Spinazze, Vitali, and Levold, 1999) have been used instead.
- North America > United States (0.28)
- Asia (0.28)
ABSTRACT It is well known that lateral buckling of submarine pipelines is a partially displacement and load controlled phenomenon due to the restraint provided by the lateral friction on the seabed. In this paper, the proportion of displacement versus load control in terms of a percentage displacement control is quantified for various cases for a "short" pipeline. The method used to define the proportion of displacement control is the one developed by Collberg, Palmer, Aronsen and Hahn (2003) for a J-lay configuration. The definition of a "short" pipeline is given by Christensen (2005). It is shown that using this new method the example pipeline in the post buckled condition is in fact within acceptable limits in accordance with the DNV-OS-F101 local buckling check. Had the conventional method assuming 100% load control or the HOTPIPE method (Mork, Collberg, Levold, and Bruschi, 1999) been used, it is shown that the pipeline would have instead failed the local buckling check. INTRODUCTION Buckling of a pipeline due to temperature and/or pressure loading is different from "normal" column buckling in the sense that the buckling force reduces (releases) as the pipe feeds into the buckling region. The maximum bending moment is limited by the amount of feed-in into the buckling region and whereas buckling under constant force may lead to structural collapse this often does not happen for a buckling pipeline. The amount of feed-in is well predicted and can be calculated as the axial displacement due expansion of the pipeline into the buckling region less the resistance provided by the friction on the seabed. For a given axial friction force determined by the axial friction coefficient, μa, and pipeline submerged weight, w, the feed-in therefore is determined regardless of lateral friction or pipeline stiffness.
Problems of Probabilistic Simulation of an Underwater Pipeline Track Under Impact of Drifting Hummocks Offshore Sakhalin Island
Bekker, Alexander T. (Far-Eastern State Technical Univ.) | Sabodash, Olga A. (Far-Eastern State Technical Univ.) | Truskov, Pavel A. (Sakhalin Energy Investment Company Ltd.)
ABSTRACT Drifting hummocks are the major problem in achievement of sufficient reliability of pipelines in freezing seas because such hummocks may contact the sea bottom, as well as pipelines, during their movement. In this paper, the authors have considered the problems of track choice for an underwater pipeline offshore Sakhalin Island. For such purpose, there was applied a probabilistic approach to determination of spatial position (including bottom configuration) of the underwater pipeline track. INTRODUCTION As a rule, pipeline transportation is the most economic kind of transportation for oil&gas during development of sea fields, including those within the offshore of the Sea of Okhotsk. The Sakhalin offshore, which total area is almost 20 thou sq. km, is the most examined and promising part of the Russian Far-Eastern region concerning oil&gas. According to experts' estimations, conditions of resources development on the Sakhalin offshore are very complicated. The sea within Piltun- Astokhskoe field, where "Molikpaq" platform was installed in 1998, is 30-meters deep with ice cover for more than 6 months during a year. Thereby, we should take into consideration influence of the ice features, when designing or constructing the underwater pipelines or other structures on the Sakhalin offshore. In the freezing seas, drifting hummocks are the main problem in achieving sufficient reliability of pipelines, because they may touch the sea bottom or the pipelines during movement. Such contact, if any, may destroy the pipeline that is confirmed by statistics data of averages on available pipelines. At the same time, deepening pipelines into soils is the main and the most applicable way of pipeline protection from external impacts. It is generally known that natural factors, which define strength and frequency of the drifting hummocks' impacts on the sea bottom, possess spatial variability and inhomogeneity, and are subject to considerable seasonal-temporal variability, as well.
- Asia > Russia > Far Eastern Federal District > Sakhalin Oblast (1.00)
- Asia > Russia > Far Eastern Federal District > Sakhalin Island > Sea of Okhotsk (1.00)
- Asia > Russia > Far Eastern Federal District > Sakhalin Island > Sea of Okhotsk > North Sakhalin Basin > Piltun-Astokhskoye Field (0.94)
- Asia > Russia > Far Eastern Federal District > Sakhalin Island > Sea of Okhotsk > East Sakhalin - Central Sea of Okhotsk Basin > North Sakhalin Basin > Chayvo License Block > Chayvo License Block > Chayvo Field > Zone XVII/XVIII Formation (0.94)