Showing papers on "Submarine pipeline published in 1976"

Currents in Submarine Canyons: An Air-Sea-Land Interaction

Abstract: x8090 Submarine canyons serve as active conduits joining the shallow waters of the shelf to the deeper waters offshore. Canyon currents are generated by many forces, including those related to wind, surface waves, internal waves, tides, and suspended sediment. Studies of canyon currents indicate that submarine canyons can generally be divided into deep- and shallow-water regimes that are dominated by specific driving forces. The deep-water regime is generally exposed to energy from tides, intern al waves, and spin-off eddies from large-scale current systems, whereas the shallow-water areas are dominated by currents related to surface waves and wind. Strong down-canyon currents appear to be caused by a unique combination of air-sea-Iand interactions consisting of 1. a pile-up of water along the shoreline caused by strong onshore winds; 2. down-canyon pulses of water associated with groups of high incident waves; 3. excitation of standing edge waves that produce longer-period up-and down-canyon oscillations; and finally, 4. the formation of discrete pulses of down-canyon motion, which become more intense and lead to sustained down-canyon currents, as the weight of the sediment suspended by the currents overcomes the density stratification of the deeper water. Simultaneous measurements of currents and pressure in Scripps Submarine Canyon, and of winds, waves, and pressure over the adjacent shelf have been made for several years, with the strongest down-canyon current measured, 1.9 m sec-1 at a depth of 44 m, being recorded during the

Laying of submarine pipes

Abstract: The invention relates to a method of laying submarine pipelines by submergence from the surface or from an adjacent level with one point of the pipeline being secured near to the surface so that the pipeline on being submerged comprises a section descending from this point towards the bed and connected by a curved section to the part of the pipeline already laid on the bed, in which weights are suspended from the pipeline at intervals thereon, at least at the time of its submergence, such that the assembly has a slightly negative buoyancy and the pipeline sinks slowly in the water until it is slowed down and stopped when the weights contact the bed, the weights thus acting as a guide rope. The invention is applicable both to the case in which the sections of the pipeline are assembled on a floating device and the pipeline is lowered into the water as assembly proceeds while the floating device is moved along the laying course, and to the case in which the pipeline, previously constructed by the assembly of a certain number of sections, is towed along the laying course and is associated with floats which maintain the pipeline on the surface of the water or a short distance therebeneath and which can be put out of action to allow the pipeline to sink.

Offshore structure and method

Abstract: Method of joining two pipelines underwater by, for example, flanges, involves supporting a first of the pipelines in a frame having supports for holding a second pipeline in alignment with the first pipeline and moving the end of the first pipeline (which is conveniently near an elbow in the pipeline) longitudinally into contact with the second pipeline and joining together.

Offshore drilling platform - vertically floatable to site with foundation (legs), tanks and platform

Abstract: An offshore platform for oil and natural gas wells is completely assembled in a dry dock. It consists of three steel or reinforced concrete parts, the foundation with the legs, the floating receiver tank, and the working platform with the derrick which can slide on each other. The whole assembly is floated to the site in a vertical position and is erected by floating and flooding the respective buoyancy tanks. This saves much time in erection and requires no heavy lifting tackle on the high seas. During sea transport the platform is seaworthy enough to eliminate all risk by inclement weather. The rig can be towed over shallow waters.

Process and device for laying submarine pipelines

Abstract: For laying a submarine pipeline, hauling of the same is exerted by means of a force distribution cable which extends over the full length of the submerged part of the pipeline and which is attached to it by hangers, preferably in conjunction with heavy chains acting as guide ropes and anchoring blocks. A further cable attached to the head of the pipeline transmits directly thereto a part of the haulage force.

Prediction of wave-induced seafloor movements

Abstract: Foundation design for offshore structures in areas where wave-induced bottom pressures cause submarine mud slides requires a knowledge of the potential depth of slide and of the magnitude and distribution of soil movements below the slide. Several methods have been developed to evaluate the stability of the seafloor due to wave-induced bottom pressures. These methods are reviewed and an improved procedure is presented. This procedure makes use of finite element analysis and combines in a rational manner oceanographic information on wave statistics with stress-strain behavior of soils under cyclic load conditions in order to evaluate the effects of a given storm history on the behavior of submarine sediments.

Method and apparatus for the laying of a submerged pipeline such as a submarine pipeline

Abstract: A method and apparatus for laying a submerged pipeline, such as a submarine pipeline, on the bed of a body of water along a path which crosses a ditch in said bed in which there is a current transverse to the pipeline, the depth of the body of water being at a maximum in said ditch and said pipeline being drawn along said bed from a shore towards open water, wherein at least one ballast tube is integrally associated with the pipeline so that a portion of said pipeline with the associated ballast tube takes up a position within said ditch in substantially U-form, the ballast tube being filled partly with air and partly with water which collects in the portion of the ballast tube of substantially U-form whereby the apparent weight of the pipeline is increased solely with respect to the portion thereof located in said ditch, the water remaining in position in the portion of the ballast tube temporarily located within said ditch as the pipeline and the associated ballast tube move forward during the laying operation. An air circulation pipe may be associated with said ballast tube, being preferably located inside the ballast tube, said pipe placing the part of the space within said ballast tube near the front end thereof into communication with a source of air located on land.

Scour around model pipelines due to wave action

Abstract: The size, number and application of offshore pipelines are steadily increasing. At the same time, the incidence of reported pipeline failures is also increasing. There appear to be several reasons for these failures, and they can be placed in two basic categories: 1. inadequate cover, and 2. low "specific gravity" of the pipeline. Under the first category the depth of burial may be insufficient, the type of burial material may be inferior to the material alongside the trench, or the compaction of cover material may be inadequate. Under the second category the pipe may actually float up to the surface from the ocean bottom as material around the buried pipe liquifies. An extensive literature search revealed that many studies were conducted by Meyers (1936), Waters (1939), Johnson (1940), W.E.S. (1940), Rector (1954), Wiegel, et al (1954), Saville (1957), Iwagaki and Noda (1962), Nayak (1972), Noda (1972), and Earattupuzha (1974). In general, two types of "equilibrium profiles" were developed in the laboratory flumes, the "ordinary" and the "storm" (sometimes referred to as summer and winter profiles). Despite numerous previous investigations, knowledge of the "scale effects" involved in equilibrium beach profiles is inadequate. Many authors have analyzed model data without stating the relation between model and prototype dimensions. In addition, many have claimed certain phenomena observed in the model to be independent of initial slope. An extensive laboratory study was conducted to evaluate the development of underwater bars and scour patterns with the pipeline buried at various depths below the ocean bottom. Pictures of the beach profile were taken at specific time intervals through the glass wall of the wave tank. Attempts were made to correlate equilibrium profile geometric quantities, such as depth of offshore bar, scour depth and berm height with the wave characteristics. Qualitative agreement between laboratory and natural beach profiles were demonstrated by trial and error fitting of one to the other.

Apparatus and method for connecting an offshore platform riser to a pipeline

Abstract: Connection of an offshore platform riser conduit is made to a submerged pipeline by initially providing the riser with an elongated, pivotally connected extension which is operably engaged to the platform. The extension is connected to the pipeline at a point above the water's surface, and then gradually lowered to the ocean floor as additional pipe lengths are added.

Development of an unmanned deepwater pipeline repair system

Abstract: A pipeline repair system has been designed for performing all tasks required to locate, assess, and repair damage to pipelines in water depths beyond diver capability. Trade-off studies indicate that the system is also applicable for water depths within diver capability. A cooperative industry development program sponsored both the detailed preliminary design for the entire system and detailed fabrication level design of critical components. Critical components have or will undergo model and prototype testing. The system is designed to be able to perform such activities as soil excavation, pipe-coating removal, pipe cutting, end preparation, and transport and positioning of replacement sections. The technology to implement these activities constitutes a significant advance in offshore pipeline repair technology when combined into a single system.

Statfjord-to-Norway pipeline poses design, laying challenge. [Norwegian-trench crossing, about 300-350 m deep]

Abstract: A pipeline is discussed as a possible solution for transportation of crude oil from the Statfjord field in the Norwegian North Sea to Norway. A typical pipeline route profile is described across the Norwegian Trench which has a maximum depth of about 330m. Feasibility and problems in design, installation and underwater operations are considered. A discussion of deep water pipeline technology includes the following topics: pipe strength, submerged weight, weight design, pipe-laying equipment, laying stress control, position control, wet-buckle repair, and shore approach. (DDA)