Showing papers on "Submarine pipeline published in 1995"

Offshore transport of dense shelf water in the presence of a submarine canyon

Abstract: The formation and offshore transport of dense water over a uniformly sloping shelf crosscut by a submarine canyon is examined using a three-dimensional primitive-equation numerical model. A constant negative buoyancy flux is applied in a limited region adjacent to a straight coast to represent brine rejection from ice production in an idealized coastal polynya. A sharp density front forms at the edge of the forcing region, with surface and bottom intensified jets along the front. The flow around the head of the submarine canyon triggers a frontal instability that initially grows only on one side of the canyon. The unstable waves on the other side of the canyon are blocked by a localized barotropic flow that develops near the canyon head. Unstable waves also grow where the forcing region intersects the coast. The frontal waves grow rapidly (with O(1 day) e-folding timescales) and form eddies with horizontal scales of O(15 km) which extract the densest water from the forcing region and carry it offshore, directly across isobaths. In this way the eddies limit the maximum water density that appears in the model despite continued negative buoyancy forcing. Some dense water descends into the canyon, forming a bottom-trapped plume that transports the dense water offshore ahead of the eddies. The plume moves relatively slowly (i.e., small Froude number), with little turbulent entrainment, so the advancement and structure of the plume nose can be described successfully as a simple gravity current with an advective-diffusive heat balance. Eddies may slump into the canyon from the side, altering both the density anomaly and speed of the canyon plume, suggesting that canyon plumes are likely to be highly variable in both space and time.

An offshore pipeline with waterproof thermal insulation

Abstract: An improved, cost-effective, insulated pipeline (10) or assembly of pipelines suitable for use in water or below grade, that is insulated with a bituminous composition (20).

Pipeline seabed interaction, free span development

Abstract: As part of a Joint Industry Project ``Pipe/Cable Burial`` physical model tests were performed to study the two and three-dimensional scour development under combined current and waves. From the results of the tests it was possible to establish empirical relations for the onset of scour and the two-dimensional scour depth as function of Keulegan-Carpenter number and initial embedment. Also for the onset and development of the scour along the pipeline experimental relations were established. The results of this study have been incorporated in a three-dimensional model for the prediction of the self-lowering and free span development by submarine pipelines.

Shoreline erosion due to offshore tin mining

Abstract: Phuket is a well-known island resort on the west coast of the peninsula of Thailand and it is rich in tin deposits. Tourist and tin mining are conflicting especially in Bang Tao Bay. Before offshore tin mining in the bay, the bathymetry is quite simple/natural and the bay is almost in equilibrium with offshore sand movement by storm waves and onshore sand movement by swell. After tin mining in 1987, people in Villages 4 and 5 sent a petition to district and city officers from May to June 1988 to the effect that offshore tin mining in the bay had caused beach erosion and road damage, and that the dredger owner should be responsible for the cost of repairs. The sounding map makes in this study reveals that deep holes are created by dredgers, those nearshore are found to interrupt the cyclic changes and sand movement on the beach that results in a permanent loss of sand into the dredged holes and causes shoreline erosion; the maximum erosion in the middle of the bay is 40 meters in the 3 years from 1987 to 1990. A field test during May to June 1991 confirms that the high rate of shoreline erosion is consistent with that found in large wave tank experiments. Offshore tin or sand mining should not be made in shallow water where sand is mobile. If offshore mining were allowed nearshore, conditions should be imposed so that the bathymetry in the vicinity of the offshore mining should not change significantly.

Application of low density foam pigs offshore Brazil

Abstract: In complex offshore installations, such as in the Campos Basin, it is relatively common to encounter pipeline systems where conventional pigs can not be run due to several factors. Changing pipe diameters, and presence of wet X-mas trees and manifolds are the most troublesome ones. In this work a new successful concept of using low cost and low density foam pigs for both liquid removal in wet-gas pipelines, and paraffin removal in oil and multiphase flow pipelines, is presented. Experimental work conducted in a 4 in laboratory facility, including a small scale glass manifold and a 6 in steel manifold, proved these pigs to be very effective. The performance of almost all kind of flexible polyurethane foams manufactured in Brazil is evaluated. Three field tests are also reported. The first low density foam pig operation was performed on a 127 mile long, 16 in diameter wet-gas offshore pipeline where the foam pig showed even higher liquid removal efficiency than the conventional inflatable spheres. The second operation was performed on a 6 mile long, 12 in diameter multiphase production offshore pipeline, which has never been pigged during its 9 year operation, and resulted in the removal of approximately 200 tons ofmore » paraffin. Finally, the third successful case is the cleaning of a 2 mile long flexible flow line of a subsea completed satellite well, in which the foam pigs were sent through a 2.5 in gas lift line, through a wet x-mas tree, not designed to be pigged, and then back through the 4 in production flow line. In spite of the fact that this paper is focusing on condensate and paraffin removal in pipeline, the basic principles can be applied to several kinds of operations: general pipeline cleaning; products separation in pipeline; corrosion evaluation; chemical product application.« less

Settlement of Breakwater On Submarine Soil Due to Wave-Induced Liquefaction

Abstract: The stability and deformation of the seabed in response to ocean wave loading is an important consideration in the design of offshore structures such as breakwaters, anchors, platforms, and pipelines. In this study, the instability of the sandy seabed due to the wave-induced liquefaction is investigated based on intensive field observations and computational studies. A large settlement of the breakwater on loosely deposited sand bed was observed at a small fishery port in Hokkaido, Japan. To determine the appropriate countermeasure against this large settlement, intensive field observations and computational studies were carried out. It was found that the earthquake-type liquefaction phenomenon of the foundation sandy soil brought a significant settlement of the breakwater.

Environmental impact of submarine pipeline installation

Abstract: As offshore pipelines are being increasingly laid, the subject of environmental effect of pipelay construction is being raised more frequently. It is an arguable yet reasonable point of view that environmental impact of offshore pipelay construction is more disruptive rather than destructive. Some of the main impacts are described in the article.

Directional Wind Wave Characteristics at Harvest Platform.

Abstract: : Long-term observations of well-resolved, deep-ocean, wind wave frequency-direction energy spectra are essential for advancing knowledge in ocean surface dynamics. This knowledge is required for such things as providing ground truth to help interpret satellite imagery of the ocean surface, testing evolution and propagation models of open-ocean wind waves, and establishing seaward boundary conditions for models of wave propagation and transformation from deep water to coastal regions. The latter problem is of considerable interest in coastal engineering because wind waves generated offshore are among the dominant forcing mechanisms for coastal dynamic processes. This problem is particularly pronounced in the region of the Southern California Bight where waves generated in the deep ocean must propagate past a number of offshore islands to reach the coast. Refractive, diffractive, and dissipative effects of the bathymetry around the islands have strong local effects on the amount of wave energy reaching the shore, and these effects are quite sensitive to the directions of incident wave propagation. To gain insight into the nature of directionally distributed wind wave energy from the open ocean in the vicinity of the Southern California Bight, a high-resolution directional wave gauge has been installed on a deepwater oil production platform near the north end of the bight. (MM)

Advanced Offshore Pipelaying Analysis Techniques Part 2 : Laybarge Methods

Abstract: Various laybarge methods for offshore pipeline installation are introduced. Pipe stresses and strains during the installation are discussed with linear and nonlinear analysis methods. Several operational modes of offshore pipeline installation are described. Computer modelling techniques of the pipeline installation analyses are suggested.

Foam pigs solve pipe cleaning problems offshore Brazil

Abstract: Pipeline systems in which conventional pigs cannot be run are common in such complex offshore installations as are found in Brazil`s Campos basin. These systems may contain changing pipe diameters or wet christmas trees and manifolds. A new concept for using low cost, low-density foam pigs for both liquid removal in wet-gas pipelines and paraffin removal in oil and multiphase pipelines has been successfully tested offshore Brazil. Although the present discussion focuses on condensate and paraffin removal in pipelines, the principles can be applied to several kinds of operations including general pipeline cleaning, product removal or separation in pipeline, corrosion evaluation, and chemical product application.

Offshore pipeline installation

Abstract: The pipeline requirements for offshore developments depend on a variety of factors ranging from the overall configuration of the development to the type and nature of the products to be transported. The combination of lengths, diameters, and materials are, consequently, endless. Methods available for the construction of pipelines, on the other hand, are limited to proven techniques that have developed over the last 30 or so years. They have been designed to cope with pipeline requirements, whilst at the same time generating a reasonable rate of return for the contractors that employ them. The decisions surrounding the developments of methods, and how they are chosen to suit the particular requirements of a project, are described in the following paper.

Free span development and self-lowering of pipelines

Abstract: The paper describes the numerical program, PIPESIN, that simulates the behavior of a pipeline placed on an erodible seabed. PIPEline Seabed INteraction from installation until a stable pipeline seabed configuration has occurred is simulated in the time domain including all important physical processes. The program is the result of the joint research project, ``Free Span Development and Self-lowering of Offshore Pipelines`` sponsored by EU and a group of companies and carried out by the Danish Hydraulic Institute and Delft Hydraulics. The basic modules of PIPESIN are described. The description of the scouring processes has been based on and verified through physical model tests carried out as part of the research project. The program simulates a section of the pipeline (typically 500 m) in the time domain, the main input being time series of the waves and current. The main results include predictions of the onset of free spans, their length distribution, their variation in time, and the lowering of the pipeline as function of time.

Reliability based calibration of partial safety factors for design of free pipeline spans

Abstract: This paper demonstrates how a structural reliability method can be applied as a rational means to analyze free spans of submarine pipelines with respect to failure in ultimate loading, and to establish partial safety factors for design of such free spans against this failure mode. It is important to note that the described procedure shall be considered as an illustration of a structural reliability methodology, and that the results do not represent a set of final design recommendations. A scope of design cases, consisting of a number of available site-specific pipeline spans, is established and is assumed representative for the future occurrence of submarine pipeline spans. Probabilistic models for the wave and current loading and its transfer to stresses in the pipe wall of a pipeline span is established together with a stochastic representation of the material resistance. The event of failure in ultimate loading is considered as based on a limit state which is reached when the maximum stress over the design life of the pipeline exceeds the yield strength of the pipe material. The yielding limit state is considered an ultimate limit state (ULS).

Estimation of burial depths for pipelines in arctic regions

Abstract: Ice scouring poses a significant threat to underwater pipelines for offshore oil production facilities in ice-infested waters. For most locations, the only options against this hazard are to protect the pipeline by trenching, burial, or creative alignment. The optimal burial depths along the length of a pipeline are usually selected on the basis of a hazard model that describes the recurrence rate and severity of scouring along its length. Although sufficient data at a specific site are rarely available to accurately estimate the hazard model, several thousand scours have been documented over extended regions and can provide an estimate of scouring hazards at preliminary stages of design. The main features of the proposed model are a parametrization of the scouring hazard model as a function of water depth and exposure to the ice environment, and the propagation of uncertainties due to model incompleteness and sample size. The proposed model can be validated or readjusted at later stages of the project as more site-specific data become available. The application of the proposed model is demonstrated for the determination of the optimal burial depth for a hypothetical pipeline route.