Showing papers on "Submarine pipeline published in 1986"

Submarine pipeline buckling—imperfection studies

Abstract: In-service buckling of submarine pipelines can occur due to the institution of axial compressive forces caused by the constrained expansions set up by thermal and internal pressure actions. Previous attempts at modelling the appropriate behaviour have been based on idealised or perfect pipelines; further, such analyses have also employed fully mobilised friction forces. Herein presented is a set of analyses which incorporate structural imperfections and deformation-dependent axial friction resistance. Not only do these features enable a more rational interpretation of submarine pipeline buckling behaviour to be established, but, in addition, an inherent limitation existing in the previous mathematical modelling of the vertical buckling mode is elucidated and overcome.

Unsteady compressible flow in long pipelines following a rupture

Abstract: SUMMARY The unsteady frictional flow of a compressible fluid generated in a long pipeline after an accidental rupture is ofconsiderable interest to the offshore gas industry. It answers several important questions concerning safety and pollution, e.g. the flow rate at the broken pipe end. Laboratory tests cannot simulate the rather complex phenomenon satisfactorily. The problem is highly non-linear and no general analytical solution is yet known. In this study, based on computational fluid dynamics, the simplifying assumptions of isothermal and low Mach number flow often applied in the case of unsteady compressible flows in pipelines, have not been used. Owing to the choking condition (Ma = 1) which prevails for some time at the broken end, and the cumulative effect of friction over the 145 km long pipeline, we obtain (;p/?.~),+ - 7". This analytically established singularity leads to numerical difficulties which seriously affect the accuracy. For short tubes (such as shock tubes) this negative feature is much less severe. Special procedures were necessary to keep the accuracy within the chosen limit of I per cent. KEY WOKUS Flow Gas Numerical One-dimensional Pipeline Unsteady The amount of natural gas in a 145 km long offshore pipeline is about 7000 tons. This quantity is about one third of the crude lost during the famous BRAVO blowout in 1977 in the EKOFISK field in the North Sea. To obtain a more intuitive idea oFthis quantity we may think of it as a heat source delivering (after combustion) a heat power of 100 MW for 40 days (960 hours). Pollution and economic losses due to the spilling of fuel may therefore be equally high for a blowout in an offshore well as in a pipeline on the sea-bed. Various efforts have been made to control the former,'-2, but not much attention has yet been given to the latter. The mass-flow of gas escaping from a burst pipeline is several orders of magnitude larger than the mass-flow from a spilling well. The former case represents a much more severe hazard in several ways. It may for instance cause instability (due to a partial loss of buoyancy) of platforms or ships caught in the top of the resulting water-gas plume. The question arises how much the mass-flow released by a ruptured pipeline may amount to and how quickly it will diminish with time. From the fluid mechanics point of view this is a complicated problem, which is best dealt with by numerical integration procedures. An approximate analytical solution of the problem has been published by Fannelop and Ryhming3 The present article is based on Reference 4 where details may be found, in particular concerning the corresponding Fortran program 'PIPE 1'. The major difficulty is due to the singularity (established in the Appendix) which results from the combined effects of friction and choking, occurring at the broken end.

Method for launching from the mainland large-size submarine pipelines

Abstract: The method of laying an underwater pipeline which is assembled in sections at the shoreline and conveyed from the shoreline along the bottom of a waterway, said pipeline being divided by separation means into a plurality of cylindrical sections provided with regulating means for selectively introducing thereto or removing therefrom ballast water or compressed air, which comprises flooding at least a portion of the cylindrical sections in sequence as they are introduced into the waterway in order to achieve a desired residual weight, maintaining said desired residual weight by introducing compressed air into said cylindrical sections to displace excess ballast water contained therein, and continuing the layering of the pipeline along the bottom of the waterway by selectively supplying or discharging ballast water or compressed air to the cylindrical sections, and completely flooding the pipeline to complete its positioning at the bottom of the waterway and removing the cylindrical sections and the compressed air and ballast introducing and removing means from the pipeline.

Acoustic environment and physico‐mechanical properties of the shelf seabed off the pearl river mouth

Abstract: The vast shallow sea off the Pearl River mouth in the northern South China Sea is an important prospecting area for offshore oil development. In recent years, the authors have investigated acoustic and geotechnical characteristics of marine sediments in this area. An intercalated layer of low sound velocity and low compressive strength has been found within the seabed, in which the median diameter of sediment grains is fine and the sound velocity is 100–200 m/s lower than that of the overlying and underlying layers. The minimum unconfined compressive strength of this layer is 0.075 kg/cm2, which is lower than that of the over‐ and underlying layers by an order of magnitude. Such an intercalation often constitutes a threat to the stability of shallow foundation soil. In case of overloading, the layer may be weakened, and seafloor sliding between different sediment layers may occur. The regional distribution of these kinds of weak intercalations of low sound velocity may be traced by a subbottom pr...

A method of supplying offshore oil fields with gases for enhanced oil recovery

Abstract: The invention relates to a method of supplying gases to offshore oil fields for the purpose of enhanced oil recovery, characterised in that the gas [e.g. carbon dioxide or nitrogen] is compressed on shore to such a level that it is delivered to the production facility of the offshore oil field by high pressure pipeline at a pressure higher than the minimum needed for direct injection into the reservoir to produce a miscible flood. The method may employ a pipeline made up of pipe lengths and mechanical couplings of the type and material coded by API for oil field tubing and casing. The pipeline may have an external diameter of up to about 133 DIVIDED 8" [0.34 m].

Trenching and Burial of Submarine Pipelines

Abstract: There have been two kinds of requirement for pipeline trenching. In shallow water, on beaches and on tidal flats, usually within a few hundred metres of the shore line, there is a need for relatively deep trenches, so that the pipeline does not become exposed if storm action changes the level of the sea bed. In deeper water, pipelines need to be protected against trawl gear and anchors, and to be safe against changes in the bottom, as a result of local scour or of large-scale sediment transport phenomena such as sandwave migration. It may also be desirable to reduce wave and current forces by sheltering the pipeline in a trench.

Setting of coast-fixing type wave power generator

Abstract: PURPOSE:To reduce the cost of construction work by a method in which an artificial slope leading to deep seabed where no abrupt damping of progressing waves occurs is formed in the coastal sea area, and an air chamber for wave power generator is set near a place where the tidal height becomes highest CONSTITUTION:A datum point 10 at which water depth (d) on sloped seabed is equalized with an offshore minimum water depth (d2) or a water depth immediately before the tidal height begins to reduce abruptly is obtained The seabed on the beach line side from the seabed 2 of the datum point 10 is formed into an artificial seabed 3 of a comparatively steep slope of 1/5 The air chamber 7 for a wave power generator is set on the coastal rocky area 11, and a turbine and a power generator are set in the chamber 7

Tests prove two-phase efficiency for offshore pipeline

Abstract: Tests prior to the conversion of the Matagorda Offshore Pipeline System (MOPS) from single-phase flow to two-phase flow revealed the weakness of many generalized theories and correlations when applied to large (20-30 in.) pipelines. Northern Natural Gas (NNG) Co., operator of the south Texas line, set up the procedures and conducted the tests that led to this observation.

Coupling device for submarine pipeline system

Abstract: A demountable coupling device for submarine pipeline sections (33,34,35) where one or a plurality of conduits can be connected together on the seabed by a remotely controlled operation without the use of divers or guidewires. The connection of the pipeline sections, which are provided with square flanges (2), takes place by a vertical movement of the coupling unit (1) of the coupling device, which is provided with a groove (1') at each of its ends, the grooves being adapted for reception of the largely vertical portions of the pipeline flanges (2) when in an operating position on the seabed. The casing (1) of the coupling unit contains all components which are necessary for the connections. Once the C-shaped groove of the coupling unit are engaged by the pipeline flanges (2), connection takes place by moving the telescopically displaceable connecting tubes of the casing into corresponding bushings in the respective conduits of the pipeline flanges (2), in that a sealing system ensures effective seal tightening. The coupling operation is reversible, and mounting can take place independent of the order of the demounting. To achieve a prestressing of the respective pipeline flanges against the coupling unit, prestressing devices are placed in the casing of the coupling (1). The coupling is secured by means of a locking mechanism.

Inspection pig system for offshore pipeline (2nd report)

Abstract: Developpement d'un systeme de controle permettant de detecter la corrosion de la surface interieure des pipelines offshore. Cette technique met en œuvre une methode ultrason et de courant de Foucault

Statpipe experience reveals techniques for seabed problems

Abstract: Design and construction problems posed by severe permanent seabed irregularities along the Statpipe route in the North Sea required careful route planning to avoid pipeline damage and extensive intervention work later. Experiences from the Statpipe project will prove useful for future pipeline construction on the Norwegian Shelf where even more severe seabed irregularities lie north of 62/sup 0/ N. This first of two articles categorizes the major seabed irregularities encountered and recounts design approaches to solving consequent pipelay problems. The Statpipe pipeline system consists of four pipeline legs and totals 842-km subsea and 40-km onshore lines. Two pipelines cross the Norwegian Trench at about 300 m water depth: a 289-km, 30-in. line from Statfjord to the landfall at Kalsto, and a 208-km, 28-in. line from Kalsto to riser platform 16/11S in block 16/11. One 155-km, 36-in. pipeline goes from Heimdal field to 16/11S, and another 191-km, 36-in. line links 16/11S to riser platform 2/4S which is bridge-connected to the Ekofisk field complex. The two 36-in. lines and parts of the 30-in. and 28-in. lines are laid on the North Sea Plateau, west of the Norwegian Trench, in relatively shallow water (70-150 m) on a regular seabed. These represent traditional Northmore » Sea pipeline problems only. On the other hand, the two lines crossing the Norwegian Trench have been a challenge both because of the water depth and because of the wide areas of severe seabed irregularities.« less

Operational Experience with the Cold Water Pipe at the Natural Energy Laboratory of Hawaii

Abstract: The 2000-ft. deep, 5500-ft. long, 12-in. diameter polyethylene cold water pipe and pumping system which the State of Hawaii installed at NELH in December 1981, has operated nearly continuously since August of 1982. Following an initial review of the system design, this paper discusses some of the problems encountered in its maintenance and operation. These include 1) pump specification and performance problems, 2) electrical supply cable failures, 3) submersible pump motor corrosion and resultant failures, 4) nearshore pipeline mounting failures caused by both routine motions and by large waves, and 5) onshore pipeline protection system failures. The offshore location of the pumps exacerbates these operational problems by making maintenance and repair extremely dangerous if not impossible when the waves are large. Specific design constraints suggested for future deep water pipelines include: 1) locate the pumps as far onshore as possible; 2) consider previous manufacturer experience in sizing and selecting pumps and motors; 3) avoid submersible motors for long term operation in seawater; 4) specify stainless steel metallurgy sparingly and carefully, and ensure that the specifications are followed; 5) design electrical cables and conduits for permanence, but include provisions for cable changeouts; 6) avoid pipeline or cable runs parallel to shore; and 7) overdesign all onshore and nearshore components.

Pipeline Inspections:An Overview

Abstract: The number of submarine pipelines in the North Sea continues to grow and with it comes the need to monitor and service such systems. In most areas of the North Sea, pipeline inspections are required annually by government inspectorates. These twelve-monthly inspections must be capable of detennining, as far as reasonably practical, the following: movement of the pipe; unsupported spans; loss of cover in buried lengths; damage to the pipe; debris adjacent to the pipe.