TM 402 - A New Operating Cable And Pipe Burying System

Free span assessment in watercourse crossings for the on-shore pipeline industry has become a more and more important part of pipeline integrity practice. One reason is that it has become increasingly well known that the dominant cause of pipeline failures in watercourse crossings is fatigue failure due to vortex induced vibrations at pipeline free spans. Recognition of this is now being identified in industry recommended practices and owners are incorporating this type of assessment into their pipeline integrity management practice. On shore pipelines are not designed with an allowable free span as is the practice with off-shore pipelines, but are buried. Design codes specify minimum depths of cover when constructed and indicate that pipelines should be maintained so that no excessive loads occur. In the past the no excessive loads requirement has been interpreted that the pipeline must remained buried. As experience from the off-shore environment and increasingly from experience on-shore has shown that most exposed and/or free spans do not fail. Due to various river erosion mechanisms; scour, bank erosion or avulsion, previously buried pipelines do develop free spans. Some of the free spans fail and release products directly into the watercourse. Failures, particularly for liquid products, are very expensive due to the economic loss, repair costs and environment clean-up of the watercourse and its banks. Similarly, costs associated with pipeline replacement for free spanning pipelines or repair of pipelines that might develop free spans are relatively high. It is important to develop an understanding of the probability of the pipeline failing due to a free span, or put another way, determine which free span is a threat to integrity. This paper discusses some of the challenges with assessing free spans in watercourse crossings as part of integrity programs and highlights experiences in assessing this threat to integrity. The objective of this paper is to discuss some of the key uncertainties related to the management of the threat due to free spans. These uncertainties are due to the reliability of information about the free span, water velocity and condition of the pipelines.

Cables and pipelines are buried in deepwater to provide thermal insulation, on-bottom stability and physical protection. In the soft soils associated with deepwater regions cable ploughs and ROV based jet trenchers are the tools of choice. The Offshore Engineering Division of the Coflexip Stena Offshore (CSO) Group and Perry Slingsby Systems have contributed significantly to the development of deepwater cable and pipeline burial systems. Significant resources continue to be allocated to geotechnical research programmes to support product developments. This paper discusses the key technical issues with respect to deepwater cable and pipeline burial. The state-of-the-art of geotechnical engineering and research, and it's application to new burial product developments, is also presented. Introduction It is now common for telecommunications cables to be buried across the world's continental shelves in water depths up to 1,500m. Such burial is primarily to provide physical protection, against fishing and shipping activity, and onbottom stability against environmental forces. Traditionally, burial of subsea cables has been achieved by simultaneous lay and trench using a cable plough pulled by the cable installation vessel. As such the installation speed of the cable is governed by the rate of burial, not the rate of cable lay. As a result there is a growing desire to de-couple cablelay from burial, i.e. use a separate vessel and/or tool to bury the product post-lay. This has led to technical issues for both subsea ploughing and jetting, which may be able to provide an alternative to ploughing in some circumstances. Proposed oil and gas developments, particularly in the Gulf of Mexico, offshore West Africa and Brazil, are now commonplace between 1,000 and 2,000 metres of water, with plans for 3,000 metres plus being discussed in the industry. It is well known that the requirements for pipeline burial change as water depth increases (3,5). Whilst physical protection and on-bottom stability issues still exist in deep water, as water depth increases their importance tends to diminish. As water depth increases flow assurance requirements becoming increasingly important and the potential benefits of flowline burial become clear (7). Thus the issues of pipeline burial in deepwater are focussed on achievable performance, e.g. burial depth, backfill parameters (particularly thermal conductivity and density) and mitigating issues associated with pipeline installation in deepwater soils, particularly floatation of light pipelines. This paper discusses the issues associated with burial of cables and pipelines in deepwater. The current state-of-the-art is reviewed, the knowledge gaps and technical risks are highlighted, and research programmes, which have been designed to address these issues, presented Deepwater Cable Burial Ever since the first two transatlantic telecommunication cables were installed by AT&T Submarine Systems in the late 1950's, the need for protection of subsea cables has been understood. It was quickly recognised that the sections of cable on the continental shelves were most at risk from fishing and shipping activity. It has been estimated that up to 95% of all subsea cables failures can be directly attributable to fishing activities (11).

The pipe-in-pipe (PIP) offshore flowline is gaining popularities in ultra deep water developments due to its better characteristics in thermal insulation, thermal expansion, seabed stability, free span and maintenance. So far most of the larger size PIP flowline are installed using J-lay method. During the pipe welding and lowering process, the vessel tensioner grabs the outer pipe with the inner pipe free-standing inside the outer pipe. Therefore a large top lay tension is applied to the outer pipe while the inner pipe is under a sizable compression due to its own weight. A bulkhead is welded to the both inner and outer pipes with a predetermined spacing. As the PIP is being lowered toward the sea floor, the large lay tension on the outer pipe is gradually released, and the outer pipe tends to go back to its original length. This results in a push to the inner pipe from the outer pipe and develops a locked-in compression in the inner pipe and a locked-in tension in the outer pipe. In the ultra deep water PIP case, the locked-in loads and locked-in stresses could be critical if they are not well addressed. The solution to limit the locked-in effects to the inner and outer pipes is to apply a predetermined pretension to the inner pipe before both the pipes are welded together through the bulkhead. The pretension is a function of water depth, pipe length, lay angle, bottom lay tension, soil friction, pipe wall thickness, content density, content temperature, content pressure and bulkhead spacing, installation sea state and vessel motion. The accurate prediction of the pretension demands significant resources and time through utilizing the advanced nonlinear finite element analysis (NLFEA) tools such as ABAQUS. This paper proposes analytical formulations to estimate the pretension requirement to the inner pipe. The formulations are validated using ABAQUS modeling. The proposed formulations can be used as a cost effective alternative to the more time consuming and cost driven FEA method, especially when only a high level analysis is needed such as in the FEED stage or as a starting point for the detailed design stage. Introduction With the ever increasing demand for oil and gas and the fast depleting surface reservoirs, oil and gas companies are forced to search for new oil reservoirs, and hence the project requirements for pipeline systems are intensifying. Currently, subsea systems are being designed for water depths to 10,000 feet, high product temperatures and high pressures. Designing pipelines to transport high pressure and high temperature (HPHT) oil and gas from these deepwater locations is challenging. Pipe-in-pipe (PIP) flowlines are widely used to address this challenge because of their superior insulation capacity [Ref. 1, 2, and 3]. With PIP flowlines, the pipe carrying the hot oil or gas is placed inside another pipe; thermal insulation in the ringshaped space between the two pipes minimizes blockages or hydrates that can form in the pipeline by providing an adequate thermal barrier to reduce heat loss [Ref. 1]. Further, PIP flowlines are gaining popularity due to their good characteristics in thermal expansion, seabed stability, free span and maintenance.

Wave action on a vertical wall with a submerged horizontal plate: Analysis of phase variation of forces and probability of exceedance

Traditionally power cables, during installation or maintenance, are tested with a dc high voltage for its electrical strength as prescribed in IS 1255-1983, reaffirmed 1996. Modern extruded dielectric power cables such as Cross Linked Poly Ethylene (XLPE) have inherent space charge accumulation tendencies when subjected to a high voltage dc. The accumulated space charge leads to over stressing of insulation resulting in cable breakdown with a high downtime and repair costs. As IS 1255-1983 is silent on the harmful effect of dc on XLPE cables, power companies in India are facing revenue losses as well as the quality of service to the consumer is affected.This paper analyses the demerits of IS 1255 and compares it with the other available test methods such as Very Low Frequency (VLF) and Damped Alternating Current (DAC) test, as well as condition assessment methods, such as Dissipation Factor and Partial Discharge. A case study highlighting the advantages of newer test methods has been presented and a cost to benefit analysis is undertaken.

This paper proposes a direct metal patterning method on three-dimensional structures with vertical side walls. It uses a 3-D multi-height silicon shadow mask made by double-side Deep Reactive Ion Etching (DRIE). Aluminum has been successfully patterned on the top, bottom and vertical side walls of 280mum wide trench with a depth of 250mum by sequentially tilting the wafer at three different angles during evaporation. The resulting tracks exhibited good isolation between adjacent metal patterns and with the resistance of the track between top and bottom of trench measured at 3.4Omega.

Many physical aspects of the depositional environment in which some rocks are formed may be reconstructed with the aid of trace fossils such as tracks, trails, borings, or other evidences of organism activity. Trace fossils are extremely abundant in sedimentary rocks of all ages, but commonly have not been used by geologists as an aid in paleoecologic interpretation. Water depth, salinity, current action, relative acidity, kinetic energy of the depositional environment, rate of sedimentation, and mode of life of the organisms may be deduced by using trace fossils as an interpretation tool. Orientation of trace fossils in beds may indicate approximate directions of current action, whereas the type of trace preserved connotes the habitat preferred by the organism. Vagile, benthonic, filter-feeding organisms commonly build nearly vertical burrows; detritus-feeding organisms tend to burrow horizontally. Filter-feeders live in an environment where the current velocity is sufficient to winnow fine particles; detritus-feeders live where fine-grained sediments and finely divided organic matter slowly settle from the water. Delicate tracks and trails preserved in rocks are indicators of a calm environment and slow sedimentation rate, whereas tubes, burrows, and borings are built and preserved in current-activated waters. In sedimentary rocks that are lacking skeletal or body fossils, trace fossils are valuable aids for use in reconstructing the physical history of the depositional environment. End_of_Article - Last_Page 730------------

The BM-C-33 gas export pipeline, with its dimension of 22/24"OD, is one of the deepest large-OD pipelines under development. The pipeline design at such water depth is pushing the boundaries of current design codes, line pipe manufacturing capabilities and available installation vessels in the market. The purpose of this paper is to mainly focus on the key challenges and opportunities related to design, installation, and commissioning of the ultra-deep section of the BM-C-33 gas export pipeline route. Furthermore, it will outline associated mitigations that will be captured in the project development and execution phases. Key challenges to be discussed in this paper are related to the ultra-deep end of the pipeline route includes high installation loads; wall thickness design considerations for high external pressure; large and complex pre-commissioning scope involving exploring using the REPLACE JIP methodology; PLEM design considerations; free span and thermal buckling mitigation strategies and route challenges.

Queueing theory is generally known as the theory to study the performance of queues. In this paper, we are interested in another aspect of queueing theory, the theory to construct queues via switched delay lines. We consider three types of discrete-time queues: linear compressors, non-overtaking delay lines and flexible delay lines. These three types of queues correspond to certain conditional nonblocking switches and (strict sense) nonblocking switches in switching theory. Analogous to their counterparts in switching theory, there exist multistage constructions for these three types of queues. Specifically, we develop a two-stage construction of a linear compressor and a three-stage construction of a non-overtaking delay line. Similarly, there is a three-stage construction of a flexible delay line. Moreover, a flexible delay line can also be constructed by a layered Cantor network.

This paper describes an operational subsea wireline system that is self-contained and flexible and offers a safe, economical, and proven method for riserless re-entry into any subsea well. The system discussed here was developed over a number of years and has been used to carry out a comprehensive range of wireline tasks from floating vessels in the North Sea. Although generally deployed from a diving support vessel (DSV), the system has been successfully used from a drilling rig to conduct wireline operations in a well, simultaneously with workover operations in an adjacent well, on a subsea template.

In June of 1976, the sedimentary structures of bottom deposits were surveyed by the seismic profiler “UNIBOOM” in Lake Abashiri. The profilings were a first trial in Japanese lakes. Lake Abashiri is situated in the Eastern part of Hokkaido Island, 7.2km upstream from the estuary of River Abashiri which discharges to the Ohotsk Sea. It is a maritime coastal lake with mean altitude of 0.35m above sea level, and the morphometric features are as follows : area, 32.8km2, maximum depth 16.1m : mean depth, 6.1m : length, 12km : maximum breadth, 4km : and shore development, 2.18. Continuous seismic reflection profilings were made along five lines traversing the lake as shown by Fig. 1. As a result of the seismic profilings (Fig. 3), two peculiar evidences were observed in the features of strata. One was the disturbances in the strata which appeared at a water depth of about 10m, off both the shores on the each of the lines except for E-E' line, which is shallower than 10m. Another was the presence of strong reflection strata in the level of 12m below the water surface under the trench bottom. The trench (the so called fairway) is carved on the lake floor from the outlet to the point of 300m up D-D' line at the depth of 12.5m, on D-D' line the maximum water depth of trench is 12m, the floor depression is 1.2m in depth, 40m in width, while on E-E' line, the respective measurements are 8.8m, 2.6m and 100m. The trench cannot be carved by the present tidal actions because the water depth is too large to erode the lake floor. If it is inferred from the above mentioned facts that the lake levels were lower about 10m than present lake levels at the ancient time, then the positions of disturbed strata may be situated at the ancient shore line of the lake reduced and the strong reflection strata under the trench of E-E' line may be corresponded to the past river bed.

Hydrodynamic characteristics of a vertical wall with an immersed horizontal plate subjected to regular and random waves

Impact pressure of dam-break waves on a vertical wall with various downstream conditions by an explicit mesh-free method

This paper presents an assessment of some of the results of an internationally funded joint industry project to measure the dynamic behaviour of a drilling conductor run from a large jack-up platform operating in deep water at the North Sea. Three different elevations spanning the conductor were instrumented using environmentally protected strain gauges while the rig was operating. The objective was to gather data for selected storms for subsequent spectral and statistical analyses and to validate finite element analysis of a drilling conductor system. The response amplitude operators (IWO) from the analysis showed good agreement with the measured RAOS. This agreement increases confidence in the validity of the loading and response calculation methods currently available for the design of drilling conductors. In the frequency analysis, the computed natural periods showed good agreement with those measured under different drilling conditions. Measurements showed that the natural frequency oscillation of the conductor was mainly in the first mode of vibration. In the time domain analysis, the computed bending loads were found in good agreement with measured values particularly at the middle and lower gauged levels. The analytical results showed that for small waves the dynamic amplification was substantial when comparing static and dynamic analytical techniques. However, for large design waves the dynamic amplification was found to be small and the static analytical technique was found to be accurate in predicting environmentally induced loads. INTRODUCTION Designed originally for shallow waters, jack-up platforms are increasingly used in harsher and deeper waters for exploration and exploitation of offshore oil and gas fields. A new generation of jack-up platforms can operate nowadays in water depths up to 360 feet. Conducting drilling activities in harsh environmental conditions at the North Sea pose challenging problems for the design of an adequate conductor system capable of withstanding the structural and extreme environmental loads. The conductor which represents an environmental barrier and structural support for the subsequent casings must withstand the environmentally imposed loads of waves, current and wind combined actions. Current practice of drilling from a jack-up platform uses a set of concentric casings known as the casing programme. The outer casing or conductor commonly of 30" diameter is followed by successively longer and smaller diameter casings until the pay zone of the well is reached. The tubing running inside the last casing and reaching the pay zone is usually referred to as the production tubing. The casings are cemented in the holes up to specified depths. Another feature of jack-up drilling practice is the mudline suspension system usually fitted a few feet below the mudline, where the weight of the casings below the mudline is supported and hence the weight supported at the surface is reduced. The mudline suspension system which consists of a set of casing hangers also provides a disconnect point at the mudline so that the conductor and casings extensions from the seabed to the surface can be removed when the platform moves off location.

Wave force variation due to burial of submarine pipelines in uniformly graded and low hydraulic conductivity soil