bluuebunny/crossref_metadata_2025 huggingface dataset:
Discontinuity Stress Decay in Offshore Platform Joints
Authors: Blackstone W.R. , DeHart R.C. , Maison J.R.
Published: October 2008

The literature contains little useful design information on discontinuity stress decay in cylindrical shells near intersecting axial plate or tubular members. A widely used rule -of-thumb is that the stress will become regular at about one and one -half to two cylinder diameters from the discontinuity, but neither the validity nor the range of application of this rule has been established. This study uses the computerized finite element technique to define the decay rate and pattern in a cylinder near an insert plate, and in a cylinder near the intersection of a small branch. Additionally, the feasibility of using ring stiffeners for stress redistribution near the cylinder intersection is explored.

INTRODUCTION

Today-'s fixed and semi submersible offshore drilling platforms are being designed for use in deeper water and stormier conditions than their forebears. As tubular member diameters and thicknesses are increased to withstand more severe loads, structural weight optimization becomes a necessity. One region that is often overweight, and should therefore receive care- ful investigation, is the tubular joint. Also, as the platforms grow in cost along with size, both owners and insurers are requiring more accurate and comprehensive stress and fatigue analyses in assessing the reliability of the rig.

In recent years, the computerized finite element method has crone to the fore as a powerful and cost-effective numerical analysis technique for platform design in general and for tubular joint design in particular. (1) The soundness of the method has become widely accepted, and it has been used extensively in stress analyses of tubular joints in platforms currently under construction. Inmost of these analyses, the joint design and construction was already complete, including the reinforcements at anticipated critical stress regions; the finite element method was used primarily to validate the design and to locate areas where additional reinforcement was required, i. e., t'hot spots".

The above use of the finite element method is often the only alternative, sinceconstruction deadlines can force fabrication and stress analyses to proceed concurrently. There is a built-in inefficiency in this approach, however. One invariably finds regions of low stress in those designs wherein metal could be deleted without significant effect on strength. Unfortunately, such weight optimization is often uneconomical at an advanced stage of design and/or fabrication. Clearly, the finite element method must be implemented at an early design stage, e. g., before selection of reinforcements such as rings, gussets, and longitudinal stiffeners is complete, if weight is to be optimized. one current program at Southwest Research Institute (SwRI) involving components of a pipe lay barge pontoon.
Sedimentary Provinces, Lithologic Parameters And Direct Hydrocarbon Finding Technique
Authors: Zoerb Richard M.
Published: October 2008

INTRODUCTION

Nothing in the past few years has so beguiled the exploration side of the petroleum industry a. she bright spot. The ultimate tool in oil finding, a direct means of identifying hydrocarbons, has been around as a dream for a long time, but in spite of much research has never really materialized in fact. Now, however, things may be changing. A particular blend of data acquisition techniques and advanced processing methods has given form to a remarkable new discipline in which bright spots and related seismic phenomena serve as interpretive leads, pointing to the occurrence of oil and gas in the subsurface.

It is perhaps significant that there is as yet little uniformity among geophysicists in matters of terminology or even in details of procedure and display. A strong consensus exists, however, in regard to directions research is going, and the goals such efforts should achieve. Study has thus far been concerned with seismic wave characteristics, principally amplitude, velocity and frequency. The end being sought is a means of positive detection of hydrocarbons at depth, in advance of the actual drilling stage in exploration.

While direct oil-finding techniques are of a distinctly geophysical nature, they can neither be ignored by the geologist nor discounted by him in his own efforts to find petroleum. The geologist's first concern may have to do with the universal applicability of the new methods. Are they as "direct" as their name implies? If "direct" is to mean avoidance of intermediate steps in exploration, then they plainly fall short of their mark. However, the methods have been given credit for improved success ratios in some areas, and this should be reason enough for further use on a much broader geographic scale than is the case today. Refinements also are a certainty, and should not only lead to higher levels of reliability, but permit adaptation to areas which at present are too problem-ridden to yield very acceptable results.

But the geologist's interests differ from those of the geophysicist since he is interested in where the techniques can be used rather than how or why they work. He must ask: Are direct hydrocarbon-finding methods, in the present or predictable state of their development, so impeccable an exploration tool that they can be used without challenge to their validity in any petroliferous province in the world? To find an answer it is necessary first to define a set of parameters wh1ch will dictate the viability of the technique, then test these limits against the geological qualities of differing areas of sediment occurrence.
A Review of Current European Research into the Effects of Offshore Mining on the Fisheries
Authors: Dickson Robert R.
Published: October 2008

This paper describes the present status and expected growth of offshore sand and gravel dredging on the European Shelf, the effects on fisheries and a review of the adequacy of current research into these problems. In order to minimize conflicts of interest between the fishing industry and the rapidly expanding offshore mining industry, the paper advocates cooperative fisheries research into specified problems and recommends the establishment of a common European code of practice for dredging regulation.

INTRODUCTION

In view of the expansion of marine sand and gravel production throughout the European Shelf, the International Council for the Exploration of the Sea (ICES) has recently established a Working Group to identify the effects (direct and indirect) and international implications of different methods of marine sand and gravel extraction on the fisheries, to review techniques for studying these effects and to compare national codes of practice for the control of dredging activities. This working group of delegates from 11 member nations met at the Fisheries Laboratory Lowestoft on April 2-4, 1974, and its principal findings form the subject of this paper.

THE PRESENT AND PROJECTED STATUS OF EUROPEAN OFFSHORE MINING

In most European countries, the development of offshore sand and gravel extraction has been relatively slow, despite the expanding demand for material for concrete, roads and "fill" in engineering works. Until recently, land-based resources were adequate to provide an economical supply of both sand and gravel within a short distance of the major markets. However, as the pressure on land use for agriculture, housing and other environmental and social needs has become greater, extraction has been forced away from the vicinity of large towns; coupled with this, rising transport costs and increasing road congestion have caused a switch to marine sand and gravel production and have provided the impetus for rapid developments in marine mining technology. For example, Fig. 1 shows that, between 1960 and 1970, U.K. production of sand and gravel from marine sources increased from 4 to 13 million tons/a and the marine percentage of total production (land + sea) doubled to 12 percent.

Initially the dredgers were of small capacity; for example, as late as 1968, the average gross tonnage of British dredgers was 800 tons, but as Hill8 has pointed out, the average size of newly built British vessels in 1970-71 was 3,500 tons and vessels of up to10,000 tons are now in operation. These ships are now capable of working in water depths greater than 35 m and of unloading on a 24-hour cycle so as to make use of cheap tidal docking facilities. Where the industry requires the provision of a specified grade of material, the development of onboard methods of screening, separating and washing different size fractions has allowed the working of hitherto unsuitable or low-grade deposits.
The Ryan Ramp-A Unique Stabilizing Design for a Dynamic Situation
Authors: Ryan William J.
Published: October 2008

The Ryan Ramp (Patent pending) is a unique structural design which affords safe transfer of personnel and equipment between vessels and offshore structures.

A study conducted on the prototype ramp under actual field conditions is presented in this paper. The tests relate the forces involved in the system and the stability imparted to the vessel. The swing rope and personnel basket are also compared with this new technique. Design details are discussed.

INTRODUCTION

Problems in the transfer of personnel and equipment at sea have been in existence since the invention of boats. Although many devices have been designed to solve this problem, the offshore industries generally use two basic methods: the personnel basket and the swing rope. These techniques have managed to keep the industry operating, but not without problems.

The purpose of the Ryan Ramp is to increase safety and accessibility to offshore structures. This new design has been in active use for over a year and was used in all operational sea conditions without a malfunction. It weathered Hurricane Carmen, which had 180 mile per hour winds, without damage to the platform or the ramp.

DISCUSSIONS

Swing Rope

The swing rope is the least expensive and the most used method. It operates satisfactorily in light seas with no outside assistance. However, many accidents have resulted from this technique. A person using the swing rope successfully must possess the following physical dexterity:Confidence in his ability to negotiate the transfer.Timing in order to grab the rope when the boat is on the top of the swell.Judgment as to when to release from the rope. Otherwise, he may swing back between the boat and the structure.Strength to hold his body weight by his hands alone while swinging.Agility to adjust to the impact when he hits the deck while maintaining balance on a moving boat.

In using the swing rope, the boat operator must position the boat close to the structure and the man preparing to use the swing rope must get close to the side or stern of the boat. If a swell surges the vessel into the platform, the impact can cause damage and send him over the side.

Personnel Basket

The personnel basket requires a crane on the structure which has as its primary function: the handling of heavy equipment. It is relatively inexpensive and is more effective in rougher seas than the swing rope.

This method requires the structure be manned in order to operate the crane. It is limited by the skill and ability of the crane and boat operators, as well as the ability of the passengers on the basket. Also, the loose construction of the basket tends to give the passenger a feeling of insecurity, particularly when he is hanging on the outside high above the water. Since the crane operator is located well above the boat deck, many accidents have resulted from misjudgments.
An Advanced Two Axis Acoustic Current Meter
Authors: Hardies Charles E.
Published: October 2008

A Current Meter for long "in situ" performance in the ocean environment is described. The problems solved in applying acoustic techniques to current measurements in open flow channels, the limitations of these techniques, and test results are presented. The meter has good accuracy, it has no moving parts, and it consumes very little power. Its short and long term stability are both excellent. These features together result in an instrument uniquely suited for long unattended use in the ocean environment.

1 INTRODUCTION

The Oceanic Division of Westinghouse is a manufacturer of acoustic flowmeters. (1, 2) We also supplied the sensor system for the engineering experimental phase of the National Data Buoy Development Project. (3, 4) As a continuation of these programs, we have a development program on a new acoustic current meter. The purpose is to provide users with a reasonably accurate and reliable meter that is capable of long "in situ" operation. (5) We are using an extension of the principle used on our Westinghouse flowmeter, namely the difference between acoustic pulse travel times in opposite directions thru the same path. Flowmeters using this basic principle have been field proven to be both accurate and reliable. Systems are presently achieving approximately 0.1% accuracy.

Our interest in current meters resulted from the difficulty we experienced with the water current sensors on the Engineering Experimental Phase of the National Data Buoy (NDB) program. As sensor system supplier, we had to identify sensors for the various measurands. We were able to identify sensors that offered a high probability of successful performance over the target one year deployment for all of the parameters except current. (4) The requirement for long deployments eliminated current meters with moving parts. Figure 1 shows one of the oceanographic sensors after 6 months dep10yment.which has been antifoulant coated with tetratributyl tin oxide prior to its deployment. The two types of meters that we concluded could function for a year, and had reasonable accuracy and power consumption were the electromagnetic and the doppler acoustic types. The problem with the electromagnetic sensor is that its response to currents other than in line with the probes is nonlinear. Cosine response is required for a sensor in order to output the two orthogonal components of the current. We saw no way to improve the EM meter and chose to use the acoustic doppler. Several of these sensors were procured and tested. We found them unacceptable in water where the concentration of particles for the sound to backscatter from was low. This problem was encountered in tests at the David Taylor Model Basin tow tank, and later in at-sea tests in the Gulf of Mexico.

The Westinghouse flowmeter is specifically designed to measure volumetric flow in closed conduits such as pipes or rivers. It was included in the evaluation of transducers for the oceanographic sensors, but the development effort required to change it to a current sensor was not compatible with the NOB program schedule.
Display Parameters of Marine Geophysical Data
Authors: Sheriff R.E. , Farrell Judy E.
Published: October 2008

The display of marine geophysical data has an important influence on the ability of an interpreter to recognize and understand interrelationships among data elements. For seismic record sections, the proper choice of such parameters as horizontal and vertical scales, the number of traces per horizontal unit, the trace amplitude color, and black/white bias may aid the interpreter in his search for significant structural and stratigraphic features.

Continuity of events can be emphasized with variable area displays. Superimposing a wiggle plot on the variable area aids the interpreter in detailed work. Vertical exaggeration also emphasizes reflection alignment but loses some details of wave shape.

Apparent information content is altered by varying display parameters. The choice of these parameters, therefore, has a critical effect on the ability of the display to communicate information to the interpreter.

INTRODUCTION

The volume of geophysical data which an interpreter must comprehend and interrelate is vast. The output of a marine seismic crew can be in the order of 100 reels of magnetic tape per day. The interpreter must be able to search through these data for significant features for mapping of earth structure. He must attempt to determine the nature of the rocks and the fluids which they contain and he must be able to interrelate data elements to check the internal consistency of his interpretation hypotheses. If oil is found in the minds of men, as it is often said, then the problem we have to face is how to get our geophysical information into the mind of the interpreter in a form that he can comprehend.

Marine seismic data are usually acquired along lines of traverse and displayed in record section form. The abscissa of a seismic record section is location along the seismic line and the ordinant is the travel time of reflections. The travel time, in a crude way, indicates the depth of the reflectors (when allowing for velocity and reflector dip) so that the seismic section is sort of a pseudocross-section of the earth indicating reflecting interfaces.

DISPLAY MODES

Seismic data are ordinarily displayed in wiggle, variable area or variable density form, or a superposition of these forms. Display parameters include choice of horizontal and vertical scale, the number of traces per horizontal unit, the trace amplitude, the degree of overlap between adjacent traces, and the zero-line bias.

The term "wiggle" describes the appearance of the individual trace on the record section, where displacement from a zero line indicates data values. It is simply a conventional graph display. This display is generated by pen plotters, raster-scan plotters and analog plotters commonly in use today. One significant quality of this display mode is that it allows the interpreter to see details of waveshape.
New York Bight- An Environmental Baseline Study
Authors: Cox Geraldine V. , Wastler T.A
Published: October 2008

1.0 Abstract

This paper summarizes the field data collection effort associated with the first comprehensive baseline survey of a proposed ocean disposal site under the Marine Protection and Sanctuaries Act of 1972, PL 92–532.

This study included data collection of every environmental element associated with the proposed ocean disposal site. It resulted in 45,000 discrete data points relating to over 2,000 species and approximately 45 different types of environmental measurements. Three cruises were conducted within a one-year period, and the data collection effort was as synoptic as logistics would allow.

The results of the study are used to characterize conditions prior to sludge disposal as well as to form a data base against which a monitoring program will be developed. Accurate baseline documentation is essential to generation of a statistically-based monitoring program capable of defining environmental changes which result from sewage sludge disposal at the site.

2.0 Background

Barged Ocean disposal of waste materials was first regulated under the 1888 Rivers and Harbor Act. Under this act, areas for the disposal of mud, cellar dirt, stone and wrecks were established in areas where they would not be considered hazardous to navigation. A site for the disposal of sewage sludge was selected in 1924, and it has been in continuous use since that time. The acid waste site was established in 1948 and has been used since that time. Figure 1 illustrates the dispersal pattern of acid wastes in the New York Bight Apex.

In 1965 a toxic wastes site was established about 120 miles southeast of New York.. The locations of these sites and a use summary are presented in Table 1. Roughly 27% of all wastes discharged in this period from 1960–1974 were sewage sludge solids.

In 1974, for example, 3.7 × 10 6m3 of sludge (4.9 × l06yd3) were released at the New York Bight sewage sludge disposal site.

Since 1971, considerable concern about sewage sludge movement and impact has encouraged many studies in the New York Bight apex. Most of these studies were conducted under the auspices of the MESA program of NOM. Charnell3 reviews these data; and MESA4 released a recent review. Cox5 presents a summary of ocean disposal in the United States.

Public pressure against sewage sludge release 12 miles from area branches caused the Environmental Protection Agency to seek an alternative sewage sludge disposal site. They asked NOAA to designate candidate sites, and the study site, Figure 2, was one of the two NOAA nominations. EPA issued contract 68-01-2770 to Raytheon Oceanographic & Environmental. Services to perform the first comprehensive environmental baseline study conducted under PL 92–532, The Marine Protection and Sanctuaries Act of 1972.
On-Bottom Pipe line Stability In Steady Water Currents
Authors: Jones Warren T.
Published: October 2008

A recommended practical is established for the on-bottom stability design of a pipeline subjected to steady water currents. The analysis leading to the recommended design procedure recognizes that, the water velocity decreases as the bottom is approached due to the boundary layer effect and that the magnitude of the hydrodynamic forces on the pipe will be a function of the shape of this velocity profile. The analysis also assumes that the lateral resistance to movement provided by the bottom soil is proportional to the net vertical resultant force acting on the bottom. Equilibrium, or stability, occurs when the lateral resistance is just equal to the forces exerted on the pipeline by the steady current. The resulting design equation (or the required pipeline weight contains several parameters whose numerical value depends on the pipe, seawater, and soil properties. A nominal see of these values is chosen and a parametric study is made of their effect on the required pipeline weight. Design curves are generated based on the chosen parameter values, and procedures for their user are recommended. The parametric study demonstrates that the minimum specific gravity required for equilibrium is relatively insensitive to large variations in the value of most of the parameters in the design equation. It also demonstrates that the selection of the design current velocity is the most significant factor in the stability analysis. Hence, further research on stability can most profitably be aimed at developing better methods of determining the design velocity for a particular location in the ocean.

INTRODUCTION

The design of an offshore pipeline system must give due consideration to each of the following factors. The operating requirements internal pressure, throughput, etc. have a large influence on the design. At the same time the design must provide for the safety and integrity of the line in the face of external and environmental factors over the expected lifetime of the system. Factors influencing the selection, design, and efficiency of the construction system must also be included in the overall consideration of the design.

The specifications for the line pipe and the pipe coating system must not exceed those required to ensure adequate operating performance and long-term safety of the line. Unnecessary pipe weight and too stringent pipe handling criteria impose undue operating limits on present construction systems even in moderate water depths. In deeper water they may impose impractical requirements on the construction system. The selection of the pipe and specifications for the coating system are directly affected by the criteria established for the maximum environmental conditions expected over the life of the pipeline. Therefore, the environment of the operating pipeline is the basic starting point for the design.

A complete discussion of the environment near the seawater soil interface is beyond the scope of this paper.
Evaluation of Fatigue Considerations in the Design of Framed Offshore Structures
Authors: Kallaby Joseph , Price James B.
Published: October 2008

Fatigue is an important consideration for deep water platforms in hostile environments such as the North Sea and the Tasman Sea. This paper evaluates the implications of the fatigue criteria on platform design using recent experiences with the Maui Platform A offshore New Zealand. It underlines the importance of realistic fatigue criteria and examines various methods for analysis. The need for estimating appropriate stress concentration factors is illustrated. The impact of fatigue on the weight and cost of the platform is discussed.

INTRODUCTION

Offshore structures installed in the hostile North Sea can be subjected to fatigue loading far exceeding that experienced in the Gulf of Mexico. The China Sea and offshore Australia and New Zealand are examples of other areas imposing a fatigue premium. Several papers have dealt with various elements of the analysis and design for fatigue with attention focused on estimating the stress concentration factors at the nodes of frame structures.

This paper evaluates the significant elements of fatigue design using recent experiences with the Maui Platform A, installed offshore New Zealand. It evaluates the importance of realistic fatigue criteria and examines various methods for analysis. A comparison of stress concentration factors determined with several proposed equations and a finite element analysis is presented. The weight and cost implications are discussed.

MAUl PLATFORM A

The Maui Platform A, Fig. 1, presently being installed in 354 feet of water some 23 miles offshore Taranaki, North Island, New Zealand, consists of a 432 foot tower topped by three deck levels for development drilling, production and processing of 660 MMscfd of gas and 20,000 bpd of condensate through 12 wells.

The four legged tower is 70x 160 feet at the top and 160 × 160 feet at the base with the broad sides battered and the narrow sides vertical (Fig. 2). Two of the legs are 22 feet in diameter necking down to 6 ft. at the top. The legs served as pontoons to float the tower on a 5200 mile journey from the fabrication site in Japan to New Zealand. The other two legs are 6 feet in diameter increasing to 16 feet in the bottom panel. The tower is anchored to the seabed with twenty-eight 48 inch diameter steel piles driven to 240 feet penetration.

The tower float out weight is 14020 kips. Maximum deck loading is 24000 kips. The mass for calculations of the dynamic properties of the platform is 100,000 kips, which includes added mass. Steel specifications called for normal DIN steel with 50 ksi yield strength. To enhance the resistance of the structure to fatigue, improved DIN steel, with special impact and through-thickness properties, was specified at the joints. Approximately 2500 kips of this special steel was required. Further discussions of the tower is given in Ref. 1 and 2.
A Deep-Tow Multi-Purpose Sparker System
Authors: Harrington Patrick K. , Moody C. Douglas
Published: October 2008

Sea trials were conducted on deep tow Sparker profiling equipment. Preliminary results indicate that data can be obtained of higher quality and in significantly worse sea conditions compared with equivalent surface towed systems. The addition of a tape recording facility should partly eliminate the problem of combining high resolution with good penetration. Cost will be comparable to existing surface towed systems, with mobility and operational flexibility only slightly reduced.

1. INTRODUCTION

For many years, engineering seismic profiling surveys have been conducted under a number of limitations. Foremost amongst these is the problem of obtaining consistently good records in sea conditions resulting from wind forces greater than about force 3. In the North Sea this problem has become progressively more important as oil activity has flowed northwards into rougher, more exposed waters. At the latitude of the Shetlands in winter, successful profiling work is normally restricted to a very few short lulls of seldom more than a few hours duration and, as often as not, at times when accurate navigational systems cannot be used. Ship's propeller noise can be an allied problem. This varies markedly from ship to ship, is difficult to predict and requires skill and experience to eliminate. Some vessels are virtually unusable. A third problem is that increasing resolution tends towards decreasing penetration. Inevitably same compromise is necessary between the power and the frequency of the seismic source.

With such limitations in mind targets were set to increase the usefulness of the profiling system. These targets are:-SEA NOISETo obtain good quality records in sea states corresponding to winds up to at least force 6.ENGINE NOISETo be able to use any vessel without interference from engine noise.PENETRATION AND RESOLUTIONTo be able to obtain records combining good penetration with high resolution from a single system. (Specifically 300 feet of penetration through sediment, with an ability to resolve down to 1 foot in the uppermost 30 feet).COSTCosts should not differ markedly from conventional surface towed equipment.PORTABILITYThe system should be fully portable and capable of operating from boats down to about 30 feet in length.

Targets 1 and 2 (sea and engine noise) can be overcome by the use of deep-tow equipment. However to satisfy 4 and 5 (cost and portability) it was necessary to use existing equipment wherever possible. Target 3 (penetration and resolution) is more difficult. A Multielectrode Sparker has the necessary frequency content and power handling capability, but like all other sources cannot normally achieve both aspects of the target on a single-pass. A partial way round this is to tape input. To keep within the cost target an analogue or very simple digital system is required and, it must be confessed here, this target has not yet been satisfactorily achieved.
An Advanced Sonar for Hydrographic Survey
Authors: Colvin Douglas W.
Published: October 2008

Admiralty charts published by Hydrographer, Royal Navy, are used world-wide, but many relating to British coastal waters have not been up-dated since the last century. The United Kingdom is surrounded by some of the busiest shipping routes in the world. Many vessels are of a draught undreamed of 20 years ago. Offshore exploration and exploitation is taking place throughout the Continental Shelf at an accelerated pace. To keep up with these developments, the marine surveyor is now required to work faster, more accurately, and to greater depths, over very large areas of the seabed. The present paper summarizes the evidence available on the inadequacy of hydrographic charts, describes detailed field trials of research sonar equipment, presents parameters and design criteria for new survey equipment, describes pre-production equipment now under manufacture and summarizes its proposed method of deployment in the field.

INTRODUCTION

The Hydrographer of the Royal Navy runs an organization responsible for carrying out depth soundings and producing Admiralty Charts used by mariners world-wide. For some years now he has inserted cautions in the Mariners' Handbook (1) and issued regular Notices to Mariners (2) drawing attention to the dangers involved in reading false security into his charts.

It is necessary to look more closely at the background to the general concern and at what has led Hydrographer to issue such serious warnings about the inadequacy of his own products.

SHIPPING STATISTICS.

We begin by looking at trends in accident statistics, the increase in world shipping, its change of character and the causes of accidents.

Annual total loss figures have risen fairly steadily for many years (3): from just under 3 × 105 ft (87 ships) in 1958 to record levels over 1 × 106 gt in 1972-74 (195 ships in 1974). Tanker losses were 7 (8%) in 1968 and 25 (13%) in 1974. This latter figure, however, constituted more than 20% of all total losses (the 1972 figure was 44%). In this time the world fleet tonnage had risen by a factor of 3 to more than 3 × 108 gt and its composition changed. In 1958 VLCCs constituted 1/3 of the world fleet. By 1973 they accounted for almost 3/5 (4), oil tankers alone equating to the total world fleet in 1958, and representing, as a single category, almost 40% of the 1973 world fleet. 1973 was an outstanding year for world ship building, but the world order book itself rose to the phenomenal total of 1.3 × 108 tons at the end of December. The world tanker order book constituted 75% of this, almost equaling the then world tanker fleet. A year later the world economic crisis had begun to take effect and the decrease in world trade, especially in oil, reduced demand.
Underwater Welding of Mild Steel a Metallurgical Investigation of Critical Factors
Authors: Nagarajan Yedapurisan , Loper Carl R.
Published: October 2008

Underwater welding of mild steel (without" mechanical shielding of the arc) was performed in the laboratory using a tank with continually circulating water. U groove welds (A.W.S.BU6) and square groove butt welds (A.W.S.BPlb) were made (E60l3 electrodes): In the first case, the welds were cleaned by wire brushing and shot blasting between passes, while in the latter case the back side was additionally ground. When thoroughly cleaned, the welds showed an improvement in ductility from the original 15% R.A. to 30% R.A. Bead on plate tests were used to compare E6013, E6020, and E7024 electrodes. Crack free welds were obtained only with E7024, with the crack susceptibility of E6020 intermediate.

INTRODUCTION

Though it has been recognized that the properties of the welds produced under water are inferior to those of surface welds, the actual effects of the water medium are still not clearly understood. With a growing interest in offshore construction, interest in the area of underwater welding has been revived in recent years (l,2,3,4).

In addition to faster cooling rates experienced in underwater welding, the introduction of harmful hydrogen in the weld metal and structural inhomogeneities, e.g., incomplete fusion and slag inclusions, are inevitable. Further due to the production of gases from the electrode covering, and the dissociation of steam into hydrogen and oxygen, a fair amount of porosity is also present in the structure. It is known that when the cooling rate of the weld metal exceeds a certain critical rate in the presence of hydrogen, microfissuring occurs, however, an investigation that considers all pertinent factors is still required.

The research study briefly reported here is the result of preliminary investigations of the critical factors that affect the mechanical properties of the mild steel welds made under water. This study was carried out in three phases:Phase I - Preliminary studies on U groove welds.Phase II - Cleaning procedure modifications and studies on butt welds.Phase III - Bead on plate welds to study the conditions under which micro cracking could be controlled.

EQUIPMENT AND MATERIALS

Tank and Accessories

The welding reported in this study was performed in a p1exig1ass tank 18"×18"×15" in size. The water depth at the work table was 9 inches. Continuous circulation of water was used to avoid turbidity, thereby improving the visibility.

A periscope was constructed and attached to the outside of the tank and provided the welder with a clear view of the arc despite the turbulence of the boiling water. Welding guides were used to aid the welder in laying a straight bead. A schematic arrangement of the tank and accessories is shown in figure 1.

The welding power source was a 300A capacity motor generator with an open circuit voltage of 40V.
Development of an Unmanned Deepwater Pipeline Repair System
Authors: Bline Donald B. , McDonald Wm. M.
Published: October 2008

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.

INTRODUCTION

The capability to repair marine pipelines damaged by corrosion, storms, earth movement, third parties, etc. in water depths beyond the practical reach of divers is a near-term requirement for offshore oil and gas producing operations.

To meet this requirement, a cooperative industry program to develop an unmanned pipeline repair system was initiated in late 1973. The result of this program was a detailed preliminary design of equipment and procedures as well as prototype testing of selected critical components.

SYSTEM DESCRIPTION

The basic system consists of two separate vehicles for deployment of tools and pipe-repair components to the seafloor work site. The Work Vehicle (WV}, Fig. 1, is an unmanned, umbilically tethered, tool platform used for observation, excavation, pipe preparation, and light manipulative tasks. The Vertical Transport Vehicle (VTV), Fig. 2, is a buoyant, umbilically tethered, heavy load lowering platform for transporting the large, heavy pipe connection and replacement equipment. In areas where relatively calm seas persist, two large workboats could be used to deploy these vehicles. Other equipment includes a power and control cable to each of the two vehicles, plus the pipeline repair and replacement components.

A key feature of the repair system is that it can adapt to a wide variety of damage situations including damage to a buried pipeline. The design is based on a maximum diameter of 36-in for a concrete coated pipe. Equipment is designed for a depth of 4000 ft, but the system is relatively insensitive to water depth.(Equation available in full paper)

Structure.

Principal elements comprising the vehicle are two mirror image trussed hull structures joined at their top by six composite beams upon which are attached six buoyancy units. The hulls are completely floodable simple trusses having a light-weight sole plate and a sheet fairing on the outboard sides. All structural elements are of special alloy aluminium. The hulls carry the principal items of machinery including electric motors, hydraulic systems, switch gear, etc.
Block Erection Method of Maui "A" Tower
Authors: Kawakatsu Yasuo , Matsubara Hiroyoshi , Watabe Takashi , Shiroichi Akira
Published: October 2008

This paper introduces the block erection method used to assemble the Maul 'A' Tower an offshore platform located 21 miles off the Taranaki coast of New Zealand's North Island. Descriptions are given herein ofthe block erection concept applicable to the various components of an Offshore platform,the materials used in the main sections of the tower, andthe assembly procedures.

The principal characteristics of the tower and the shipyard where it was fabricated and assembled are also outlined, as are the tower flotation procedures and the benefits of the block erection method over the conventional panel erection method.

INTRODUCTION

Shell BP and Todd Oil Services Limited (SBPT) discovered the Maui field some 30 miles off the South Taranaki coast in early 1969 on a prospecting license area of 11, 030 square-miles. The field is being developed by Maui Development Limited, a joint venture company operating on behalf of the New Zealand Government (as Offshore Mining Co. Ltd.), 50%; Shell (Petroleum Mining) Co. Ltd., 18.75%; BP (Oil Exploration) Co. of New Zealand Ltd., 18.75%; and Todd Petroleum Mining Co. Ltd., 12.5%.

On behalf of Maui Development Limited, Shell BP and Todd Oil Services Limited is the operator responsible for design, procurement, construction and operation of the platforms, submarine pipelines, and onshore processing facilities.

Project plans called for a gas and oil drilling and production platform to be installed at the site in a water depth of 108 meters. In April 1974 our company was awarded the contract by SBPT to build the tower support structure for the platform. Seventeen months later, in September 1975, the tower was delivered to the client.

Besides being one of the world's largest structures of its kind, the Maui 'A' tower is also the world's first self-buoyant tower of this type and for this water depth ever erected. Further, delivery involved the world's longest tower tow, some 9,200 km. The principal particulars of the tower are: height, 131.674 m; breadth (leg center to leg center), 21.366 × 48.768 m (top), 47.854 × 48.768 m (bottom); leg diameters, 6.706, 4.877 and 1.829 m; maximum wall thickness, 95.3 mm; total weight, 6,400 metric tons (tower, 5,174 tons; accessory structures and systems, 831 tons; piping systems, electrical equipment and wiring supports, 395 tons).

High-strength steel produced to DIN specifications are used in the principal members of the tower, while a steel produced to satisfy DIN specifications for mechanical strength in the through thickness direction is used in the nodes.

The tower was assembled at our Tsu Shipyard (refer to Fig. 1) by the block erection method the first time this method has been used to assemble an offshore structure. This was the principal factor that permitted the completion of the tower in a record time of 17 months.
The Experimental and Theoretical Study of a Tension Leg Platform in Deep Water
Authors: Yashima Nobuyoshi
Published: October 2008

The offshore industry is going into deep water exceeding 3,000 ft.

The tension leg platform Js available for exploratory drilling, supporting production equipment, and work over operations in such deep water.

The moored stable platform with a buoyancy exceeding the weight has tensioned vertical anchor cables. The tension leg generally consists of wire ropes with elasticity that cannot be ignored in deep water.

The elongation of the anchor cables results in roll, pitch, and heave motions of the structure. These three motions are small and, therefore, have no significant effect on the actual field operations; however, in extremely deep water the vertical motions are not negligible.

In order to evaluate the effect of elasticity of the anchor lines in deep water, we made a 1/50 scale model of a tension leg platform that has four vertical cylinders and four anchor lines. Hydrodynamic forces acting on the cylinders were calculated by considering the radiation and wave exciting forces vertically and the drag and inertia forces horizontally. We recognized through the theoretical study and model experiments that more elasticity in the tension cables would result in less tension variation of the cables in motion response by waves, and investigated the nonlinearity of motion response to regular waves under steady state forces such as wind, current and wave drift.

INTRODUCTION

Floating vessels, such as a drill ship and a semisubmersible drilling rig, experience more heave, pitch, and roll motions as sea conditions become rougher and water depths greater, resulting in costly downtime. However, the tension leg platform, which is held firmly in place by vertical anchor cables, results in less motion response to heave, pitch, and roll even in deep water.

This is because the cable tension prevents vertical motions, and acts to lessen horizontal motions. The tension leg-platform concept is adaptable to several specialized types of offshore oil structures such as a production platform and a workover unit for servicing subsea wells.

Similarly, the amplitude of the tension Variations between the maximum end the minimum cable tension by a regular wave could change, depending upon the magnitude of the steady state forces. Fig. 7 shows the tension variations of Cables 1, 2, 3, and 4 in Case B, in which the external forces ere horizontal force components of a wave with a period and height of 1.5 seconds and 10 cm, respectively, end steady-state forces.

The natural periods of heave, pitch, and surge of the 1/50 size model me shown in Table 1. Cases A, B, C, and D indicate the different property characteristics of the cables as shown in Fig. 5. (There are no legs in Case D).

Nevertheless natural periods of surging in Case: A, B, and C are not very different; that is, these periods. not significantly dependent upon the elasticity of the tension cables.
Performance Tests of Off-The-Shelf Oil Skimmers
Authors: Griffiths Richard A.
Published: October 2008

Five advancing-type commercially available oil skimmers were tested at the EPA's OHMSETT facility. Four were found to be low speed devices, with very low thruput efficiency at speeds greater than 1.25 kt to 1.5 kt.

One device, the Cyclonet, recovered oil best at speeds of 4 kt to 6 kt. Typical oil recovery rates were 10 gpm to 20 gpm. Improvements in the design, use, and testing procedures for these types of skimmers are suggested.

INTRODUCTION

During July 1975 the U. S. Coast Guard Office-of Research and Development sponsored tests of five off-the-shelf oil- recovery devices at the EPA's OHMSETT facility. The tests had four objectives:to develop a standard test procedure for testing oil recovery devices,to familiarize Coast Guard Strike Teams with the devices tested,to assist in the evaluation of these skimmers for purchase as operational equipment, andto evaluate these skimmers for use in fast currents.

The oil skimmers tested are considered representative not only of each manufacturer's products but of different generic types of skimmers. Interpretation of the test results, then, enables one to evaluate each particular device, to consider design advantages or disadvantages (or possible improvements) of each type, and to criticize and improve the test procedures.

A complete evaluation of a device must involve additional considerations besides oil recovery performance. Testing the full scale, prototype devices in a large-tank such as OHMSETT also allows a qualitative evaluation of practical problems encountered when using a skimmer, such as set-up time, ease of operating, demobilization and cleaning problems, and support equipment, manpower, storage, and maintenance requirements.

A comprehensive report with test details will be released soon by the Coast Guard and will be available through NTIS.

TEST PROCEDURE AND RATIONALE

The test plan was basically the same for each device, with oil distribution rate, tow speed, etc. adjusted to suitable values. Each plan began with an investigation of the effects of speed on performance and determination of the "optimum speed" followed by investigation of the effects of encounter rate, waves, and oil type. In each test an attempt was made to achieve "steady state" conditions, defined as the average operating conditions during several hours of continuous skimming. In general this meant establishing a stable slick in front of the device and filling basins, sumps, pumps, and hoses with fluid recovered under such conditions.

Three measures of-performance were of general concern: (oil) recovery rate; recovery efficiency, defined as that percent of the recovered fluid which is oil; and thruput efficiency, defined as that percent of the oil encountered which is recovered.

A lube oil and ½ fuel oil were selected for testing. The oils were reused repeatedly during the four week test period with gravity separation of the water between uses. The following were the average properties over the period:(Available in full paper)