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SUMMARY: Experiments have been made in a laboratory flume to investigate the interaction of a mobile sand bed with a cylinder under currents and waves. The cylinder is free to move vertically under its own weight. Some general conclusions may be drawn from the results although some details could not be reproduced from one run to another with the same input conditions. The cylinder always caused incipient bed motion and ripple formation to occur at lower Shields numbers. The cylinder axis always dropped and forces were always reduced, sometimes substantially, as a result of bed motion. Hydrodynamic force was measured through the surface pressures by a novel device. INTRODUCTION The stability of pipelines on the sea bed when exposed to waves and currents has been the subject of much investigation. To assess instability, hydrodynamic forces are derived from wave/current kinematics with appropriate force coefficients and Coulomb friction has been assumed, again with an appropriate coefficient. However penetration of the pipeline into the bed is now realised to enhance stability. There has been considerable investigation of the lateral cylinder movement produced by wave loading causing the pipeline to "dig itself in" under its self weight, taking into account many factors, e.g. (1) and papers in OTC 87 and 89. Additional terms to represent the soil resistance force have been determined and understanding of stability criteria and associated hydrodynamic coefficients have been improved, for pipelines resting on sands and clays (2). There has also been considerable investigation of scour around pipelines (cylinders) in currents and waves where the cylinder is fixed in position (3), (4) and (5). There has also been some observation of the self-burial of piplines in the field, associated with tidal motion, and devices for enhancing self-burial have been proposed (6), (7).
ABSTRACT: A theoretical analysis of interactions between homogeneous masses of broken ice and structures in dynamic formulation is discussed. The problem is solved in the terms of soil mechanics. INTRODUCTION A most important task in designing engineering structures intended for offshore hydrocarbon exploration and production in freezing waters is to correctly establish external ice loads acting on these structures under various ice conditions. Numerous analytical and experimental studies have greatly enhanced our knowledge of the forces grouped under the first, the second and the fourth categories. The present level of research on the third group is, however, markedly lower. At the same time for many freezing sea areas, e.g. the Barents Sea, this very type of ice effects plays a decisive role. For other regions it is considered that interactions with ice fields are more characteristic for winter period while in spring/summer the structures are opposed by broken ice (Tunik at al, 1989). Numerous full-scale studies of ice interaction with engineering structures: lighthouses and drilling platforms (Mรครคttanen, 1986) indicate that a moving ice field most often transfers its force upon a face surface not directly, but through ice rubble which forms an "ice cusion" in front of the structure. Similar phenomena can be observed when there is a high compression of ice near flat ship sides, when icebreakers with flat fore or stern-lines move in brash ice or when an ice field or the broken ice interacts with a structure of considerable (compared to the ice thickness) cross-section. Neglect to studies on lcebreaker/brash ice interaction often leads to erroneous conclusions about advantages of this or that innovate shape of the bow. The bows which perform in an excellent way while in an ice field turn out to fail in channels with broken ice blocks or in brash ice.
- Europe > United Kingdom > North Sea > Central North Sea > Central Graben > Block 30/25 > Argyll Field > Zechstein Formation (0.99)
- Europe > United Kingdom > North Sea > Central North Sea > Central Graben > Block 30/25 > Argyll Field > Trias Group (0.99)
- Europe > United Kingdom > North Sea > Central North Sea > Central Graben > Block 30/25 > Argyll Field > Rotliegend Formation (0.99)
- (29 more...)
ABSTRACT: One of the peculiarities of ice cover development on the Northern Sakhalin Offshore is the presence of stamukhi, intensively affecting the Sea bottom in the field area. The main problems in the process of design and construction of subsea pipelines, which in harsh ice conditions of this region are the only means of all-year-round crude oil transportation from offshore fields to the coast, will be connected with the stamukha impact on the sea bottom. Field investigations on the Northern Sakhalin offshore showed that the discussed region in this paper is characterized by intensive ice cover dynamics, defining the appropriateness of sea ice morphological characteristics distribution. The total maximum vertical pressure ridge thickness for this region is defined equal to 35 m. Stamukha keels are formed by solid ice, which occupies up to 60โ85 percent of its total volume. Maximum stamukha penetriation depth into the Sea bottom is equal to 2.13 m according to the field investigations. INTRODUCTION The experience in the structure design and operation of subsea pipelines and template complexes in the Arctic sea condition shows that problems of providing their reliability and accident-free work are closely connected with the study of the stamukha impact on the sea bottom. In Arctic seas in the presence of hummocking ice and stamukhi, up to 100% of all subsea pipeline failures occur under the environmental influence [1]. In USSR we call pressure ridges as stamukhi, having contact with the sea bottom and also conglomerations of ice fragments in the form of pressure ridges, forming on the sloping shore [2] (Fig.2), Stamukha impact on subsea pipelines cause statistical and dynamic loads. These loads are especially large at the point of pipeline outlet on the shore. Ice conglomerations having large mass and dynamics may lead to pipeline deformation and failure.
ABSTRACT: Dents in the walls of pipes or plates are caused by plastic deformation due to the action of external forces. Such dents result in a local redirectioning of the existing force flow, giving rise to notch stresses. These stresses can initiate cracks. Two types of cracks can be observed, diametral and circumferential cracks. Following an initial 2D-investigation into the different crack paths observed [1], the paper presents a 3D-Finite-Element analysis of spherical and cylindrical indentations in plates. The analysis is carried out for linear-elastic material response and investigates the influence of the dent geometry on possible crack growth. The shape of a dent determines wether the maximum stress peaks occur at the root or the rim of the dent. This suggests the existence of a "critical" dent geometry which determines the crack path followed. The paper presents part of a project concerned with the integrity assessment of pipelines containing flaws or defects. 1. INTRODUCTION Cross country and offshore pipelines provide one of the safest, most reliable and also economic means for the transportation of large quantities of liquids and gases. Extensive research is being carried out worldwide in order to further improve pipeline steels and welding procedures especially for offshore application. However some of the pipeline systems installed are reaching ages of twenty to thirty years or more. It is therefore of increasing importance, especially for the operators of such older installations, to be able to assess the true state of their pipes. Initially the possibilities of revalidation of hydrostatic testing (Fearnehough, 1990) were investigated. Such detection tools must ensure that flaws of defects in pipes which can possibly lead to failure resulting in loss of life, environmental or economic damage are detected before they reach a certain, material specific critical size.
Abstract : Pipeline construction in Arctic zones requires to use the special methods for the settlement such problems as a choice of pipe material, pipe shielding, welding technology, lowering-in of pipeline, anchoring of pipeline, bore cleaning and diagnostic. The following is the consideration of these problems and methods in application to the USSR. Introduction For intense development of USSR economy, substantial increase is required in efficiency of the fuel and power complex industries to provide capacities for basic national economy branches. This task can be accomplished only through building a vast network of transmission pipelines which are recognized to be indeed the transport of the scientific and engineering revolution epoch. The pipeline network in the USSR now totals more than 270 thous.kms and its share in the overall fuel transportation is the highest one: 80% as referred to a ton of equivalent fuel. In 1986 transportation through gas pipelines alone brought about more than 1551 bln mkm. By having become an important component of production in the infrastructure, pipeline systems furnish the national economy with oil and gas in quantities and with consistency not attainable by conventional transport means and allow more reasonable locations for productive forces and interregional and interprovincial industry specialization and cooperation. The scope and pace of pipeline construction in the USSR are far above those achieved in the developed countries. Enormous volumes of pipeline construction and extreme climatic conditions (Arctic, West Siberia, Central Asia) as determined by geography of oil and gas fields have made it necessity to develop essentially new resolutions and revolutionary approaches to cope with problems arising in construction of pipeline systems. The All-Union Pipeline Construction Research Institute (VNIIST) is the chief research group responsible for conducting scientific studies and establishing construction procedures and specifications in accomploshing grand tasks set before the pipeline industry.
- Production and Well Operations > Production Chemistry, Metallurgy and Biology > Corrosion inhibition and management (including H2S and CO2) (0.47)
- Facilities Design, Construction and Operation > Pipelines, Flowlines and Risers > Offshore pipelines (0.47)
- Facilities Design, Construction and Operation > Pipelines, Flowlines and Risers > Materials and corrosion (0.47)
ABSTRACT: The risk analysis technique is applied toยท those accidental scenarios associated with the external human offshore activities in the areas, outside platform safety zone, crossed by a pipeline. The interaction with ship anchors, dropped objects, sinking ships and fishing gears are discussed. Basic data and methodology for the frequency assessments are presented as well as Some consideration on the consequence assessment. INTRODUCTION The term "Risk" encompasses considerations relevant to both expected frequency of accidental events and the relevant consequences. Design solutions and protection means can cope with most, but not all, of the possible negative occurrences during the life time of a pipeline. After the application of safety standards and rules, the residual possibility of accidental events needs to be assessed. The application of risk analysis techniques to the offshore pipeline design, and cost/benefit analysis, help the project team in the decision making relevant to the optimum design solutions. This paper deals with possible methods and means to be adopted for the identification of risks associated to offshore pipelines in operation, with particular concern to those risks induced by human activities along the pipeline route. RISK ANALYSIS - HUMAN RELATED RISKS The risk analysis technique has been largely applied in offshore engineering. Potential Hazards: the hazardous conditions which could cause pipelines to fail can be schematically separated into two categories: natural and man- made. Natural are those caused by environmental and/or natural occurrences and disasters such as severe sea states, hurricanes, earthquake, bottom instability, etc. Mart-made hazards are those related to offshore activities, erroneous pipeline operating conditions and material deficiencies. In this paper, the attention is focused to man-made hazards relevant to third party offshore activities. These accidental scenarios are discussed in the following and the major aspects, relevant toยท the frequency and consequence assessment, are identified.
ABSTRACT: Safety and integrity of submarine pipelines/flowlines under interaction of fishing trawl doors are investigated for the 16" and 36" pipe. The trawl door pull-over loads are based on experimental results. Global responses are calculated with respect to normal stresses and lateral displacements for different pipeline conditions, using time-domain simulations. Local response analysis is performed with respect to indentation considering both elastic and plastic deformation. Serviceability, fatigue and ultimate limit states are established considering pigging requirement, low cycle fatigue, yielding, excessive lateral displacement and local deformation. Safety is assessed based on the results from global and local response analyses and realistic uncertainty measures. 1 INTRODUCTION Submarine pipelines and flowlines play an important role in offshore oil and gas transportation. Structural failure of steel pipes will result in serious consequences, such as release of transported hydrocarbons, pollution to the environment, and heavy costs due to repair and even shut down of the transportation system. Previous submarine pipeline/flowline in-service records indicate that a major cause of pipe failure is due to interference of the third party activities (Andersen and Misund, 1983, Cannon et al., 1985, Mandke, 1990). For relatively small diameter pipes laid cross the areas with dense fishing traffic, impacts from fishing trawl doors may be critical to the pipe integrity. To avoid external interference, it is possible to protect pipelines or flowlines from external impacts by simply trenching or burying the exposed pipes, which may often lead to an unacceptable increase in costs. A careful global and local pipe response analysis together with an appropriate safety evaluation, however, may avoid such expensive actions and result in a cost benefit design. In this paper, time domain dynamic global response analysis and static local response analysis are performed. Sensitivity analysis is made to identify the important parameters governing the response characteristics.
- Europe > United Kingdom (0.28)
- Europe > Norway (0.28)
ABSTRACT: Engineering Systems Analyses of new and existing pipelines are proving to be useful to develop codified specifications and evaluate the economics of construction, commissioning, operating, monitoring and maintenance intervention of aging or damaged systems; and to objectively evaluate failure consequences due to combined environmental loads including environmental loads, geotechnical loads and normal operating loads using current measurementยท of pipeline limiting strengths and response characteristics. Surveillance, environmental and geotechnical load monitoring; pipe1ine structural integrity monitoring and safety analysis, and intervention plans to prevent failures or control consequences are necessary components for reliable operation and maintenance planning. This paper proposes a general classification for monitoring and surveillance systems postulated from statistical failure experience in North America and proposes a structural reliability criteria basis for integrated design, monitoring and maintenance intervention planning. Complementary pipeline integrity monitoring methods and some development needs are also outlined. INTRODUCTION Pipeline operation in areas with soil instability or offshore require structural integrity monitoring and surveillance to ensure reliable operation with intervention whenever and wherever trends to structural safety limits are detected, or sudden extreme load events may cause a failure (Price, 1984; Simmons and Ferrell, 1986; Pipes and Pipelines International, 1986 and 1987; Nyman and Lara, 1986; Lara, 1987; Masterson and Price, 1989 and 1990). Several corrosion and material quality pig monitoring and nondestructive inspection services are commercially available. These are now capable of surveying the centerline axis, dents, internal diameter, girth weld and preformed bend detection and location, pipe joint length between girth welds. In addition systems for periodic and real time local areas monitoring have been developed (Price, 1985; Stevens et AI., 1989). Promising encroachment and surveillance monitoring systems using multi-spectral scanner imagery with integrated global position satellite and inertial interpolation technology are in the feasibility and development stages for periodic airborne surveillance activities.
- North America > United States (1.00)
- North America > Canada (1.00)
- Europe (0.93)
ABSTRACT: In the past investigations of the optimum marine pipeline construction technologies in the Arctic Seas have been made and specialized; construction equipment and technique have been developed. This paper presents the results of the investigations of the marine crossing construction for the transmission gas pipeline system which routed across the Baydaratskaya inlet in the Kara Sea. Natural and climatic conditions of this region are presented. Characteristics of the marine pipeline structure are given. The procedures of the pipelaying on the sea bottom from the ice surface are described. Technical data of the lay vessel under the conditions of the Baydaratskaya inlet are set. INTRODUCTION The development of the oil and gas fields was spread to the North marine regions, where increased investigation work has resulted. Far going production perspectives are connected With the development of fields in the Barents and Kara Seas. Vast natural gas fields have been discovered in the Yamal peninsula and nearby regions. However, one of the factors delaying the development of hydrocarbon production in the Arctic is a lack of pipelines for transportation to the industrial regions. Technical and economic analysis of the on-shore and off-shore variants of transmission pipelines for gas transportation from the Yamal fields to the USSR central regions are as follows. The marine multiline option including the Baydaratskaya inlet crossing decreases the length of the route by more than 200 km in comparison With the on-shore option and reduces the material and labor necessary for gas pipeline construction. The Baydaratskaya inlet and the Kara Sea are a part of" the described Arctic regions which have become the subject of the investigations. The choice is explained by the possibility, on the one hand, defining the technique of marine pipeline construction under extreme conditions.
- Europe > Russia > Kara Sea (1.00)
- Asia > Russia > Kara Sea (1.00)
- Asia > Russia > Ural Federal District > Tyumen Oblast > Yamalo-Nenets Autonomous Okrug (0.24)
ABSTRACT: Hydrocarbon reservoirs on the shelf off the west Indian coast require multiple platforms. Phased field development, modified to cater for increased production congests the pipeline network. Design and engineering problems in this scenario, are assessed and solutions presented including high resolution surveys, reassessment of environmental parameters, marine growth, and conceptualized structural model at platform vicinity, for pipeline-riser system. Appropriate installation procedures formulated. A model flexible complex optimizing various requirements presented. It is concluded that if all required issues are considered and assessed at the outset, appropriate engineering solutions for various design issues are possible, reducing congestion. INTRODUCTION Extraction of hydrocarbon from offshore reservoirs off the west coast of Indian peninsula (Bombay High) located on shelf (Figure 1), require multiple extraction platforms with process platform unit serving as nuclei. The field development is generally planed in a phased manner. Often accelerated production requires to increase the number of platforms and submarine pipelines. This catches the pipeline engineer on the wrong foot, as planned riser locations, size of riser clamps and pipeline corridors at the vicinity of platform are found to be unsuitable. Added to this, increase in marine growth is observed. Various on-going projects presented the opportunity to synthesize the divergent problems with interfaces. The problems were analysed to obtain acceptable solutions, which have been integrated to develop a comprehensive approach to collect job specific data for engineering application. PLATFORM FACE AND APPROACH SURVEY Designing of risers, location of riser bottom bends and routing of pipelines in this intricate zone of platform approach, requires high precision survey with specific equipment, instrumentation of defined capacity and procedure to obtain high resolution feedback. PLATFORM APPROACH SURVEY This zone is defined by the area covered from face of platform up to 250 m of a pipeline corridor.
- Asia > India > Maharashtra > Arabian Sea > Bombay Offshore Basin > Mumbai High Field > L-V Formation (0.98)
- Asia > India > Maharashtra > Arabian Sea > Bombay Offshore Basin > Mumbai High Field > L-IV Formation (0.98)
- Asia > India > Maharashtra > Arabian Sea > Bombay Offshore Basin > Mumbai High Field > L-III Formation (0.98)
- (2 more...)