Showing papers on "Submarine pipeline published in 1996"

Method for pipeline installation

Abstract: A method for installing an offshore pipeline is disclosed in which the inner and outer pipes are structurally connected at a terminal end of a pipe-in-pipe flowline and centralizers are placed in the annulus to provide lateral support and maintain concentricity between the two pipes and to prevent buckling of the inner pipe. The working end of the pipeline is suspended under construction in a substantially vertical position within slips at the weld floor of a J-lay installation barge and sections of inner and outer pipe are added. Inner pipe is added by sections by grasping and orienting the section of inner pipe to a vertical position and the section is brought into abutting position with the inner pipe at the working end of the pipeline under construction, welded in place, and the weld is coated with an arc resistant material. Sections of outer pipe are added by grasping and reorienting to a vertical orientation, sliding the section down over the section of inner pipe just welded in place, bringing the section of outer pipe into abutting position with the working end of the pipeline under construction and welding it into place. The working end of the pipeline is then advanced through the slips to bring the end of the section of outer pipe added adjacent the weld floor and the foregoing steps are repeated as necessary to add additional sections of inner and outer pipe to complete the pipeline.

Imaging approach to real-time tracking of submarine pipeline

Abstract: The work presents a real-time underwater imaging system for identification and tracking of a submarine pipeline on a sequence of recorded images. The main novelty of this work relies on adopting an automatic approach that is entirely based on the analysis and interpretation of visual data, in spite of the various limitations upon the ability to image underwater objects. The analysis of the data is performed starting from image processing operations (like filtering, profile analysis, feature enhancement) implemented on a dedicated board. Then, the system employs an efficient dynamic process for recognizing the two contours of the pipeline. In each frame the system is able to determine the equations of the two straight lines corresponding to the pipeline contours. The system reaches satisfactory performances in real time operation: up to eight frames per second on a Pentium based PC. The results of this work are somewhat more meaningful as the input images were acquired by three cameras, mounted on a remotely operated vehicle travelling at one nautical mile an hour, without any attention either to illumination conditions or stability of cameras. This work is originated from the interest of Snamprogetti in enhancing the level of automation in submarine pipeline inspection.

Trawl board impacts on pipelines

Abstract: Extensive research on the effect on submarine pipelines was carried out some 15 years ago. Since then trawl board sizes and towing velocities have increased and increased pipeline protection could be required. This paper describes an accurate method for determination of the impact energy of the trawl board and, in particular, the part of the impact energy absorbed by the pipe shell. Thereby unnecessary conservatism can be avoided in the design of pipeline impact protection. The method accounts for: trawl board particulars; pipeline and soil parameters; angle of impact with the pipeline; and elevation of the pipeline. The resulting maximum local impact energies absorbed by the shell, the effective impact mass and velocity, including the hydrodynamic effects from the water, and methods to determine the pipeline response are included. Two levels of analysis are proposed, simplified and advanced.

Offshore North Sea Pipeline and Riser Loss of Containment Study (PARLOC)—Applications and Limitations in the Assessment of Operating Risks

Abstract: Since the Piper Alpha disaster in 1988, there has been an urgent requirement to prevent such tragedies occurring by the introduction of higher safety standards and by improving the confidence in the statistical information available for the assessment of the risks of loss of containment associated with operation of North Sea pipelines. In order to achieve the latter, two databases have been compiled: (1) a pipeline database containing details of pipelines and risers installed in the North Sea; (2) an incident database containing details of reported occurrences (covering the period from 1975 to end 1993), which directly resulted or threatened to result in loss of containment from a pipeline or riser, The data has been compiled from information obtained from: U.K., Norwegian, Dutch and Danish Regulatory Authorities; Operators in the U.K., Dutch and Danish Sectors; reports from previous studies made available to the study; published sources. The databases have been used to perform assessments of factors affecting the frequency of incidents, such as: incident cause; part of pipeline or riser affected; pipeline or riser diameter, length, contents, age, type; whether the line is trenched or buried, piggy-backed or not; hydrotest pressure; location of pipeline or riser in the North Sea.more » The PARLOC study identifies potential hazards and provides an indication of likely loss of containment frequency associated with the operation of North Sea pipelines and risers. Furthermore, PARLOC provides a continually updated key reference for comparative risk assessment and ultimately for the implementation of risk control as part of an overall risk management program.« less

Effects of Internal Flow on Vortex-Induced Vibration and Fatigue Life of Submarine Pipelines

Abstract: With the rapid development of the offshore oil industries, submarine oil / gas pipelines have been widely used. Under the complicated submarine environmental conditions, the dynamic characteristics of pipelines show some new features due to the existence of both internal and external flows. The paper is intended to investigate the vortex-induced vibration of the suspended pipeline span exposed to submarine steady flow. Especially, the effects of the flow inside the pipeline are taken into account. Its influences on the amplitude of pipeline response, and then on the fatigue life, are given in terms of the velocity of the internal flow.

Simulation of Thick-walled Submarine Pipeline Collapse Under Bending and Hydrostatic Pressure

Abstract: The problem of submarine pipeline buckling or collapse as a result of bending and external pressure is investigated by numerical modeling using finite element analysis. The model takes into account the initial variability of material properties, the effect of cold-work on the pipe material properties and initial geometric imperfections. It is capable of simulating the nonlinear behavior, and structural instability due to the combined effects of bending and pressure. The solution algorithm and verification against experimental results are presented. In addition, a deterministic model for collapse under combined pressure and bending based on measured stress-strain behavior and pipe geometry is derived. Results from both finite element and deterministic models for different parameter sensitivities are examined.

Lateral snaking of hot pressurized pipelines mitigation for Troll oil pipeline

Abstract: The Troll Oil Pipeline operates at high temperature and pressure. Bar buckling is a potential hazard for the structural integrity due to the potential development of excessive bending, in particular in the proximity of the offshore tie-in point and in the first section of the route across the Norwegian Trench. The axial compressive force caused by operating loads, may be released in one location and give rise to large lateral deflections in a single buckle. Bending strains may reach unacceptable levels if the axial friction for sections adjacent to the buckled length is low, such that significant feed-in to the buckle occurs. At present, design guidelines and international codes do not cover these aspects satisfactorily. In this paper the susceptibility of the Troll Oil Pipeline to bar buckling is analyzed and discussed. A new mitigation method based on the concept of controlled feed-in, is presented. The worthiness of the proposed mitigation for the Troll Oil Pipeline to comply with the required structural integrity, is demonstrated through a series of analyses using analytical tools as well as finite element methods. The main findings, and particularly the calibration of analytical tools against finite element methods, are described and commented.

Offshore risers must be designed to resist pipeline movement

Abstract: Design methods are available to counter effects of pipeline movement on subsea riser systems. Their application depends on environmental conditions, platform structure/constraints, in-service conditions, pipeline approach to the platform, and economics. Factors for selecting among the methods are discussed here. A hypothetical project, a 24-in. OD pipeline, is presented as an example. In this example, the seabed is prone to scouring, necessitating seabed preparation around the platform to ensure structural integrity of the riser system. Additionally, it is assumed that the system will be operated at high pressure (150 barg) and temperature (80 C) in 50 m of water.

Deepwater pipelay prospects prompt study of mechanical connectors

Abstract: A joint industry project to study mechanical connectors for pipeline construction will issue results to its participants next month. Although the study addresses mechanical connector`s use in any environment, connectors are being looked at by offshore operators as a means to minimize pipeline-installation costs, especially in deepwater. The joint industry project, dubbed Low Cost Pipeline Connection Systems, does not compare available connectors but was initiated to specify criteria that operators can use to qualify connectors for use. The project was organized and is now being managed by Hunting Oilfield Services, Aberdeen. Secondarily, the project aims for the following: to develop a clear design premise; to address relevant installation and service issues such as corrosion protection, installation methods, and repair methods, and costing models; to develop specifications and acceptance criteria for the testing of pipeline connectors, this will parallel the ISO specifications and API recommended practices for the testing of downhole connectors; to prove the adequacy of the specifications and criteria by analytical validation methods and in particular by testing programs that simulate, with adequate margins of safety, the installation and service loads on pipeline connectors; to establish and prove, as far as possible, a standardized approach to the testing ofmore » pipeline connector systems. That the study is being carried out at all indicates the growth in nonwelded approaches to pipeline construction and reflects industry`s efforts to hold down construction costs, especially for offshore. Yearly, labor costs exceed 45% of pipeline construction costs, as reported in Oil and Gas Journal`s annual Pipeline Economic Reports. This paper reviews the project goals and progress in the areas of research.« less

Seismic Assessment for Offshore Pipelines

Abstract: An international consensus on seismic design criteria for onshore pipelines has been established during the last 30 years. The need to assess seismic design for offshore pipelines has not been similarly recognized. The geotechnical hazard for a pipeline routed across steep slopes and irregular terrains affected by earthquakes are discussed in this paper. The integrity of both natural and artificial load-bearing supports are assessed. The response of the pipeline to direct excitation from soil or through discontinuous, sparsely distributed natural or artificial supports are commented on. Some applications are given in order to point out topical aspects and major design issues for currently operating offshore pipelines crossing seismic active seabeds.

Tunneling Under Pressure

Abstract: Work will begin this month on the South Bay Ocean Outfall (SBOO) project, a $140 million undertaking to build 3.6 mi of tunneling through the saturated ground of the Pacific Ocean. When completed in 1998, the SBOO, combined with the new South Bay International Wastewater Treatment Plant (SBIWTP) and the existing South Bay Land Outfall (SBLO), will stop the 60 years of sewage discharge into the Tijuana River Valley and the South Bay beaches of San Diego. The finished project will deliver raw sewage originating in Tijuana, Mexico to the SBIWTP, the design of which proceeds in parallel with the design of the SBOO. From there the treated effluent will pass through a distribution structure and an energy-dissipation structure before entering the existing SBLO, a 144 in. diameter, 12,300 ft pipeline. An anti-instrusion structure will be constructed at the end of the SBLO and a drop shaft will convey effluent from the SBLO to an elevation of about 165 ft below sea level. At that point, a tunnel will be constructed with an internal diameter of 121 in. and an overall length of about 19,000 ft. The tunnel will cross under land (onshore) for 5,000 ft and will terminate about 14,000 ft offshore. There it will connect to a 108 in. diameter, 147 ft long riser, which will convey effluent vertically to a 120 in. pipeline on the seabed. This 5,000 ft long sea floor pipeline will convey the effluent to a wye, where it will be discharged at 25 ft canters along two 2,000 ft diffuser legs on the seabed. Because of the unique geological conditions of the site, the tunnel will have to carry effluent under internal differential operating heads of 16-39 psi, and it will be constructed under the ocean with potential for high external ground-water pressure up to 100 psi, averaging 86 psi. Consequently, the liner design criteria must consider the internal and high external heads and soil cover, while the tunnel boring machine (TBM) must be designed to withstand the high external head.

East spar field—from discovery to sales

Abstract: The East Spar field is located 40 km west of Barrow Island on the North West Shelf, offshore WA, and con­tains 23.6 G.m3 (834 Bscf) of proven and probable wet gas in-place in the Early Cretaceous Barrow Group. The trap is structural, but with negligible time closure. At the time of the discovery and early appraisal of East Spar in late 1993, a rapid deregulation of the gas market was taking place. In combination with the concept of a gas pipeline to the central WA Goldfields region, a marketing 'window of opportunity' was created for the East Spar field, if the development could be crystallised in the available period of 9 months. This required ap­praisal drilling, geotechnical studies, reservoir engineer­ing and facilities engineering to be advanced on parallel fronts, with close co-ordination and communication be tween all disciplines. The concept of an alliance between the East Spar Joint Venture and the engineering/construction contractors was identified as a way of retaining flexibility to alter the development concept during this period, and provide other benefits during the subsequent construction phase. This alliance was ultimately formed to include represen­tatives from WMC (on behalf of the East Spar Joint Venture (ESJV)), Kvaerner-R J Brown and dough Engi­neering. The East Spar facilities will comprise a subsea comple­tion and gathering system, with all produced fluids being piped to processing facilities on Varanus Island. The treated gas will then be transported to the mainland via the existing sales gas pipeline to the onshore Dampier to Bunbury pipeline, which connects with the Goldfields Gas pipeline. The condensate will be exported from Varanus Island by tanker. First sales are expected in October 1996