Showing papers on "Submarine pipeline published in 1984"

In‐Service Buckling of Heated Pipelines

Abstract: Compressive forces may be induced in pipelines by the restraint of axial extensions due to temperature changes or other causes. These forces may cause vertical or lateral buckling of the pipeline. These two buckling modes, which both involve an overall column-type response without gross distortion of the pipeline cross-section, are analyzed on the basis of related work on railroad track. For normal coefficients of friction, the lateral mode occurs at a lower axial load than the vertical mode and is dominant in pipelines unless the line is trenched or buried. The theoretical solutions are illustrated by numerical results for a typical pipeline and some design implications reviewed.

Interaction Between Pipelines and the Seabed Under the Influence of Waves and Currents

Abstract: The prediction of the behaviour of submarine pipelines on an erodable seabed is made based upon a series of small scale flume tests with currents and waves. In these tests the influence of the basic parameters, such as pipe diameter, approach velocity and height of the pipe relative to the original seabed, have been studied. Results of measurements of velocities and bottom changes have proven to be enlightening, both for the understanding of the mutual interactions between the disturbed flow field around the pipe and the seabed morphology as well as to make a first prediction of scour depths near prototype pipelines by using the tests as a scale series of the prototype.

The computation of bed shear in a numerical model

Abstract: Obstructions located in coastal and offshore waters usually disturb the natural flow pattern. This disturbed flow will, in general, cause local morphological changes in the position of the erodable boundary. Often these changes should not be allowed to exceed certain limits, for example, when local scour around an offshore construction may endanger foundations. Local morphological changes result from changes in the local sediment balance, brought about by the flow disturbance. In the present paper a mathematical model is described which gives the bottom shear stresses and the configuration of the seabed around an obstruction using a computation of the two dimensional turbulent flow field. The obstruction considered is a submarine pipeline laid uncovered on a seabed consisting of non-cohesive sediment. A research project on the local scour near submarine pipelines is being carried out at the Delft University of Technology. Part of the project is the application and extension of an advanced numerical flow model for scour development near pipelines on the seabed exposed to current action. This work is being carried out in cooperation with the Delft Hydraulics Laboratory. The code of the flow model has been developed in a joint venture between the Delft Hydraulics Laboratory and the Laboratoire National d"Hydraulique in France. The turbulent flow field is computed taking into account the influence of turbulence generated at the bed and by the pipe. The bed shear stresses are assumed to play the key role in the interaction between the flow and the seabed. In the computer model the bed shear is related to the flow through the "law of the wall". The model operation is schematized in the diagram below in which the first loop represents the evolution of the velocity field through a series of hydraulic time steps. After the velocity field is stabilized, in the second loop one morphological time step can be used for the computation of the local seabed changes. In this second loop the computed bed shear is applied together with a sediment transport formula. After the morphological time step a new bed topography is obtained and a new grid is generated for the next flow computation.

Pockmark-like structures on the Poverty Bay sea bed — possible evidence for submarine mud volcanism

Abstract: Side-scan sonographs of the shallow (2–22 m) sea floor off Gisborne Harbour, northern Poverty Bay, New Zealand, include areas of scattered to locally prominent, subcircular, flat-floored depressions, resembling pockmarks, typically 5–20 m across and 0.3–0.5 m deep, in muddy very fine sands. Because of their geologic setting, it is speculated that the structures are exhalative pits for ascending streamers of mud, water, and/or natural gas from underlying diapiric intrusions of predominantly Paleogene shale, and that they may be submarine equivalents of the subaerial quiescent mud volcanoes occurring in the Gisborne district. Because of their possible significance in hydrocarbon prospecting, tsunami generation, and siting of subsea cables, pipelines, and offshore structures, they require further research.

Pipelaying in artic offshore waters

Abstract: The present invention provides a method and apparatus for constructing pipelines in Arctic offshore waters by a directional drilling technique, thereby minimizing exposure to ice gouging and eliminating the hazards associated with unstable permafrost. A special drilling-pipeline construction vessel is also provided which has a conical shape with reinforced outer walls to resist ice forces, which vessel includes means to install deep underground pipeline segments and means to connect and protect the pipe ends.

Offshore oil production method

Abstract: Method of oil production comprising drilling at least one seabed well by means of a drilling platform (1, 15) attached to the seabed (2) substantially directly over the well head (3), connecting the well head by means of pipeline (5) to a floating production platform (7) spaced laterally from the well head, and producing and storing oil by way of the floating production platform, the respective functions of the drilling and the production platforms being substantially discrete.

Laybarge inspection of submarine pipelines

Abstract: Over the past four years, the Authors have been involved in the installation of five submarine pipelines, laid with the use of conventional laybarge installation procedures; the welding was done by the manual metal arc process in the vertical down position , and the welding standard BS 4515:1969 was applied. From an analysis of this experience, certain factors have emerged that have a significant influence on pipeline quality. These factors are discussed in detail under the headings:- Pipeline Installation Programme . Pipeline Quality Control . Acceptance Criteria . Summary (of conclusions and recommendations)

Transporting Arctic petroleum: a role for commercial submarines

Abstract: Following a review of commercially-viable offshore oil deposits in northern Canada, Alaska and Greenland, the author explores alternative possibilities currently under consideration for transporting the oil to centres where it will be used.Hazards of pipeline construction, particularly under water, and the problems and dangers associated with giant surface tankers and projected giant submarines are discussed. The author concludes that conventional submarines towing oil-filled plastic drogue tanks offer the safest and most expeditious method of solving the problem. This is the second of two articles (see Polar Record, 21 (133): 369–81 (1983)).

Method and apparatus for connecting a flowline to a subsea structure and laying the flowline from the subsea structure

Abstract: A method and apparatus are provided for connecting an offshore pipeline or flowline bundle (10) to a deepwater subsea structure (11) and then laying the pipeline or flowline bundle (10) away from said structure (11). The pipeline or flowline bundle (10) is lowered vertically from a pipelaying vessel (13) to make a hinged connection with the subsea structure (11). The connection operation is facilitated by a flowline connection tool (14) attached to the pipeline or flowline bundle (10) and designed to be inserted into a funnel located either centrally or on one side of the subsea structure (11). The connection procedure comprises landing and securing the flowline connection tool (14) onto the subsea structure (11),then hinging over and connecting the pipeline or flowline bundle (10) to the subsea structure (11) as the pipeline or flowline bundle (10) is laid on the sea floor (12) beginning at the subsea structure (11).

Design And Installation Of The North Rankin Trunkline And Slugcatcher

Abstract: Design studies for the offshore pipeline system for the North West Shelf project in Australia commenced in the early 1970's. Flow mode selection resulting in a two-phase flow system for gas and condensate was completed in 1978. A diameter of 1016 mm was selected for the 134 km trunkline from the North Rankin platform to shore. During 1978 and 1979 detailed route surveys, oceanographic investigations and cyclone hindcast studies were completed, allowing detailed engineering to commence. Pipe was ordered from Japan in December 1980 and deliveries were made between April and August 1981. Pipe coating was carried out in Western Australia between August 1981 and March 1982. Pretrenching of portions of the pipeline route was completed between December 1981 and September 1982. Pipeline installation commenced in May 1982 and was completed, including post-trenching, by December 1982. Backfilling over the pipe was carried out between August 1982 and June 1983. The tie-in to the platform and final hydrostatic test on the pipeline were completed by May 1983. Dewatering, drying and inerting is planned for October and November 1983. The slugcatcher associated with the two-phase system will be completed by December 1983. The line is expected to be commissioned in June 1984.

Geotechnical modelling of iceberg-seabed interaction

Abstract: Exploratory drilling on the eastern Canadian continental shelf has proven the presence of commercially viable quantities of hydrocarbons. Any process to extract the resources from beneath the seafloor offshore Newfoundland and Labrador has to take into account the severe environmental condition some of which are unique to this geographic region. Damage to seafloor installations such as pipelines of wellheads by bottom dragging or scouring icebergs is one of the potential problems. This has been recognized since the early 1970’s. However, methods of estimating the maximum iceberg scour depths and methods of protecting seabed installations are still topics of research. -- In this thesis an experimental approach was taken to physically model the iceberg scour process in a 14 m x 3 m x 1 m towing tank. Cohesionless soil at a uniform slope and with controlled properties was used as the representative seafloor material. Iceberg models 500 mm wide and a pipeline model 122 mm diameter were instrumented and used in a text programme aimed primarily at examining the interaction of the iceberg model and the soil and delineating the influence of the scour process below the incision depth. -- For a horizontally scouring iceberg the frontal soil resistance was found to be the major affecting the scour size. The shape of the iceberg keel in contact with the soil was also found to be an important parameter in the scour process. The tests indicate that the zone of soil disturbance extends below the keel of the scouring iceberg. This zone of influence should be accounted for in the design of all buried installations in the Newfoundland and Labrador offshore region.

Connecting device for submarine pipeline

Abstract: PURPOSE:To prevent a submarine pipeline from being cut, by a method wherein a submarine pipeline and a submarine bottomed oil-storing tank are connected to each other by two pipes jointed to each other by a flexible pipe joint, and a buoyancy body is fitted to the joint part of the two pipes. CONSTITUTION:A connecting end part 3A of the submarine pipeline 3 and a connecting end part 2A of the submarine bottomed oil-storing tank 2 are connected to each other by the two pipes 5A, 5B jointed to each other by the flexible pipe joint 4A, and the buoyancy body 6 is fitted to the pipe joint 4A. Accordingly, even when the position of the tank 2 is fluctuated, the displacement can be absorbed by the connecting device, so that the pipeline 3 can be prevented from being cut.

Performance trials of two centrifugal compressor trains on an offshore platform

Abstract: Two centrifugal compressor trains on a North Sea oil production platform were apparently not achieving their predicted performance. The compressor trains will be used to pump the gas associated with the oil through a pipeline to the shore from 1986. Therefore the ability of the trains to handle all the available gas is vital to the project. This paper describes the successful tests conducted offshore to determine the actual performance characteristics and the measures taken to minimise the measurement errors.

Seabed mechanics : edited proceedings of a symposium

Abstract: I Sub-Seabed Characteristics.- Section 1 - Strength and Consolidation.- - Modelling and the Consolidation of Marine Soils.- 1 In situ Void Ratio, Strength and Overburden Pressure Anomalies in Seabed Clays.- 2 Undrained Shear Behaviour of Quasi-overconsolidated Seabed Clay Induced by Cyclic Loading.- 3 Consolidation Properties and Stress History of Some Deep Sea Sediments.- 4 Settlement and Consolidation in the Laboratory of Steadily-deposited Sediment.- Section 2 - Submarine Slopes and Sediment Testing.- - Submarine Slope Failures.- 5 Slope-stability Analysis and Creep Susceptibility of Quaternary Sediments on the Northeastern United States Continental Slope.- 6 Analysis of Slope Stability, Wilmington to Lindenkohl Canyons, US Mid-Atlantic Margin.- 7 A Device to Facilitate the Sampling and in situ Testing of Sediments.- 8 A New Technique to Identify Sea Sediments in Shallows.- II Sub-Seabed Site Investigation and Design.- Section 3 - Probes, Corers and Pore Pressure Measurement.- 9 Calculation of Stresses on Shallow Penetrometers and Footings.- 10 Measurements of Wave-induced Pore Pressure and Coefficients of Permeability of Submarine Sediments during Reversing Flow.- 11 Non-linear Finite Strain Consolidation of Soft Marine Sediments.- Section 4 - Cyclic Loading and Sub-seabed Stability.- - Liquefaction of Seabed Sediments: Triaxial Test Simulations.- 12 Wave-induced Liquefaction in Seabed Deposits of Sand.- 13 Liquefaction Prediction in the Marine Environment.- 14 Methods of Predicting the Deformation of the Seabed due to Cyclic Loading.- 15 Geotechnical Hazards Associated with Leg Penetration of Jack-up Rigs.- Appendix to Parts I and II Sub-seabed Studies Workshop.- III Sediment Transport.- Section 5 - Wave- and Current-induced Transport.- 16 Wave-induced Bed Load Transport.- 17 Resuspension of Clays Under Waves.- 18 Sediment Transport due to Waves and Tidal Currents.- 19 Sediment Transport by Tidal Residual Flow in Bays.- Section 6 - Storm Impact and Forecasting.- 20 Littoral Drift Caused by Storms.- 21 Climatic Variation in the North Sea Region.- IV Sediment-Structure Interaction.- Section 7 - Influence of Wave/Current and Fluid/Sediment.- 22 Interaction Between Pipelines and the Seabed Under the Influence of Waves and Currents.- 23 Local Erosion at Vertical Piles by Waves and Currents.- 24 Grain Shape Effects on Sediment Transport with Reference to Armouring.- 25 Potential Influence of Gas-induced Erosion on Seabed Installations.- Appendix to Parts III and IV Sediment Transport Studies Workshop.- Closing Address - Delayed Consolidation of Marine Clay (Soil Mechanics from Onshore to Offshore Seabed).- List of Delegates.

Time and Frequency Loading Analysis of Submarine Pipelines

Abstract: Fatigue damage to marine pipelines subjected to wave forces is evaluated using time-domain and frequency-domain methods. Spectral techniques are applied to North Sea, Gulf of Mexico and offshore Atlantic Canada wave conditions. Time-domain analysis is applied to wave conditions in the Canadian North Atlantic Ocean. The frequency-domain analysis is performed using spectral and probabilistic techniques suggested by L. Borgman {?.). The pipeline dynamic characteristics are described by classical analytical descriptions. The time-domain analysis computes time histories of wave force loading on the submerged pipeline from actual wave records. The traditional Morison wave force equation is used to obtain the time history of the loading on the pipeline. Empirically determined wave spectra are shown not to produce as good a correlation with the deterministic results as the actual wave spectra. Free spanning submarine pipelines subjected to cyclic surface wave loading accumulate strength reductions leading to failure from material fatigue. The Palmgren-Miner rule for the linear accumulation of fatigue damage is applied to evaluate the time to failure. The American Welding Society X-X stress accumulation curve is applied. The results of the deterministic analysis were compared with those of the more efficient spectral analysis. It is shown that comparable results can be obtained from the spectral analysis provided the actual spectra of the water surface elevation is employed in the spectral analysis.