bluuebunny/crossref_metadata_2025_split huggingface dataset:
A Comparison of Methods for Predicting Extreme TLP Tendon Tensions
Authors: Hodges S.B. , Chiu Hin , Kan W.C. 
Published: October 2008

ABSTRACT
In this work, three companies undertook analyses of a given tension leg platform (TLP) configuration to predict maximum and minimum tendon tensions in an extreme design storm in the Gulf of Mexico. Each participant used its own analytical methods and experience to analyze the subject TLP. The results of this exercise are presented along with a discussion of the different analytical methods used to arrive at the results. The variability in the results can be attributed to a variety of reasons which can be divided into three general categories: items for which Widely accepted analytical procedures were used by all participants, items for which a combination of analytical and empirical evidence was used, and items for which the participants relied on empirical evidence, past experience and engineering judgement. In general, the magnitude of the variability in the results increased from the first to the third category.
The study also pointed out the relative importance of the various contributions to the tendon tension predictions. In some instances, items with a great deal of uncertainty in their estimated effect turned out to have minimal impact on the final result. The results of this study give some indication of the variability and uncertainty in the available analytical methods which may be useful for the calibration of reliability based design codes.

INTRODUCTION
In the design of a tension leg platform (TLP) the prediction of the extreme maximum and minimum tendon tensions is of the utmost importance. The tendons must be large enough to withstand the most extreme maximum tension and the amount of pretension (or excess of displacement over weight) of the TLP must be large enough that the tendons do not go slack. Since the cost of a TLP is quite sensitive to hull and tendon size (and hence pretension levels as well as maximum tension levels) it is important to accurately predict the tensions.
The results presented in this paper arise from a study conducted by three major oil companies in the context of preparation for a possible joint venture involving a deep water TLP. To come to a better understanding of the companies' analytical methods and design practices, a small study was conducted whereby each participant was provided with the particulars of the same TLP subjected to the same environmental conditions and given the task of predicting maximum and minimum tendon tensions.
The immediate purpose of this exercise was to identify areas in which the participants agreed and disagreed on analytical methods and the selection of design values. However, the results are somewhat more far-reaching when viewed from the point of view of an outside observer interested in TLP design. The study provides three "stateof- the-art", or perhaps more accurately, "state-of-practice", analyses by three different organizations, all well versed in the specific problems of TLP design. Each participant followed rational and Widely accepted design and analysis practices.
A Method for Estimating the Fatigue life of a Conductor Pipe
Authors: Samier Pierre , Lebas Genevieve 
Published: October 2008

ABSTRACT
The purpose of this new method is to calculate the probability of failure by fatigue of a free standing conductor pipe subjected to waves.
This combines two approached;stochastic approach using statistical distribution of sea wave conditions and of fatigue crack initiation time.deterministic approach using standard nonlinear finite element analyses to compute the nonlinear transient response of a conductor pipe to a given set of irregular waves.
Two types of nonlinearity are of importance:soil rheology leading to a nonlinear stiffness matrix,wave loading due to the nonlinear term in the Morison equation which is proportional to the square of the relative velocity between the flexible structure and the water particles.
Experimental data on fatigue measurements (S-N curve) and sea conditions display a high degree of scatter. A deterministic approach adopting a safety margin at every stage may therefore lead to unrealistic design.
The method described below takes into account the sources of randomness, the uncertainties and the nonlinearities. To characterize the scatter in the data, the probability density functions are used.
A fatigue analysis using this method has been carried out for a typical conductor pipe 'in the Guff of Guinea.
A dozen dynamic analyses using generated waves described by different wave heights and associated periods are needed because of nonlinearity and since the stochastic approach requires computing the response of the structure to any irregular wave.
For this study, results show that the conductor pipe is still sfee while the usual deterministic approach leads to a damaged structure.
The end result is no longer an overconservative lifetime but a distribution for the lifetime of the structure.

INTRODUCTION
A free standing conductor pipe is a slender structure commonly used in shallow waters. It gives oil companies much concern in terms of repair, and needs specific dynamic and fatigue studies. For water depths beyond 30m, the structural behavior is critical since a lot of these structures suffer damage due to fatigue. Standard deterministic analyses based on Miner's rule generally confirm that the structural behavior is critical at this depth. However, they predict a much shorter lifetime than the actual one.
Miner's rule is almost universally used today to predict the lifetimes of parts subjected to random amplitudestresses. However, this universality is not immune to criticisms:the method uses an S-N cuNe, or in other words, it omits, by some means, the scatter of the experimental data obtained at constant amplitude cycles,the critical value of 1 for the accumulative damage is also subject to a high degree of uncertainty whichis confirmed by conductor pipe experience and by fatigue tests under variable amplitude stress. The aim of the paper is to provide a more realistic lifetime estimate.
Design Enhancements for Offshore Platform Fire Systems
Authors: Dailey R.E. , Mayhew R.E. 
Published: October 2008

ABSTRACT
Existing firewater/deluge systems on open Gulf of Mexico type offshore platforms were evaluated to improve their operation and reliability, and to reduce maintenance. Pumps, firewater systems and deluge systemswere upgraded to meet performance and reliability criteria developed from field and fire testing as well as survey data. Upgraded systems utilize bronze pumps and valving; fi berglass and alloy piping; and a central manifold design. Deluge nozzle placement changed from impingement spray similar to NFPA 15 requirements to area/density spray similar to NFPA 13 requirements and coverage was increased. Principles of material selection and nozzle placement are applicable to alloffshore facilities where reliable automatic fire control is desired.

INTRODUCTION
The size and nature of an offshore firewaterprotection system depends to a large extent on the operator's emergency response philosophy, but if a firewater system is employed, common prob1ems can be encountered. The author's company offshore fire response guideline states:
"Emp1oyees are expected to utilize provided equipment and training to protect themselves, their fellow employees and, if practical, the facility bycontrolling a fire in its incipient stage. The Company does n2i expect employees tofight severe or escalating fires or to use equipment for which they have not been trained."
The firewater systems provided are typicallyfed by auto-start diesel engine driven pumps and contain both manual fire equipment (hose reels and monitors) and automatic deluge (water spray) segments. The deluge is provided to both assist manual fire fighting and prevent escalation.

FIRE PUMPS
Dual, 100% capacity, fire pumps are providedexcept on gas platforms that can be shut down when a pump is out of service. In such cases, facility blowdown is an alternative means of preventing escalation and only one pump is installed. If possible, pumps are located on different deck levels to prevent a pool firefrom affecting both pumps. A1so, when possible, at least one of the pumps is located in or adjacent to the muster or safe area. Pumps are vertical turbine design driven through a right angle gear, and ratings areeither 1500 or 2500 gpm at 140 psi cellar deck level discharge pressure. Size is dependent on total deluge area, and head-capacity curves meet NFPA 20 requirements. This means that end-of-curve performance is 2250 or 3750 gpm at 90 psi which, without hose and monitor use, wi 11 cover several deluge zones as will beexplained later.
A review of test and maintenance recordsindicated that the average time between overhauls was 3 years for the coated cast iron pumps in general use. A smaller sampling of nickel aluminum bronze pumps was averaging 10 years between overhauls which coincides withmanufacturer's experience overseas. Nickel a1umi num bronze pump assemblies cost three times as much as the cast iron assemblies, butthe longer time between overhauls makes the investment attractive and the greater reliability is a safety bonus.
Dynamic Positioning System Evaluation
Authors: Shatto H.L. 
Published: October 2008

ABSTRACT
Evaluation of dynamic positioning systems consists principally of determining the holding capability against expected weather and the reliability of the DP system in operation. Efforts to quantify reliability, by estimating mean time between failure, now permit several useful risk analysis evaluations. The main considerations for DP evaluation are covered here.

INTRODUCTION
Dynamically positioned vessels have been in operation since 1961, and they have allowed us to do many things that anchored vessels are not able to do. Core holes have been drilled and reentered in over 18,000 ft of water, and oil exploration wells have been drilled in 7500 ft of water. Within anchor depths DP has eliminated the risk of anchor damage to subsea pipelines and facilities. A tracking mode allows a pipe or cable laying vessel to move along a pre-set corridor.
Since its first use in core drilling and then exploration drilling its use has grown to include vessels for pipe laying and cable laying, diving support, heavy lift construction, and search and salvage. Most recently it has found its way to small supply and anchor handling boats which are also useful for light maintenance work on subsea facilities.
For all its virtues, its record has not been unblemished. Failure to hold position in bad weather has been an occasional problem. This is not necessarily because of inadequately designed thrust capacity. More often it is lack of redundancy.
Reliability, or the lack of it, is the most frequent cause of position failure. The mean time between failure (MTBF) of DP systems has ranged from less than one month to well over three years, depending very largely on the level of redundancy provided and the elimination of single point failures. Reliability cannot be measured or calculated with much accuracy, but past experience with many systems, some reasonable estimates of component failure rates, and an understanding of the role of redundancy allow useful estimates to be made. Depending on the job to be done it can be very important to know where in the broad range of MTBFs a particular system falls. Although weather plays an important role in determining DP system reliability, the ability to include weather in estimating system MTBF is fairly recent.
Evaluation of holding capability and reliability along with expected weather exceedance and probable cost to the job for a DP system failure permit a fairly straightforward risk analysis to be made. This provides a rational and reasonably quantitative basis for judging the suitability of an existing DP system or the design of a new one for the particular work that will be required of it. This approach can also be used to quantify justification for additions to redundancy for either new or existing vessels.
This paper does not address the suitability of a vessel regarding seaworthiness, motion characteristics, load carrying, deck space, or the many other things that must be evaluated for a particular job to be done.
Failure Probability Analysis Techniques for Long Mooring Lines
Authors: Flory J.F. , Hearle J.W.S. , Stonor Richard , Luo Yong 
Published: October 2008

ABSTRACT
This paper describes statistical techniques for analyzing failure probabilities of long mooring lines. The long line is treated as a series of segments, each as long as the break or fatigue test specimens. Termination failure statistics are treated separately.
The analysis techniques are applicable to mooring lines comprised of chain, Wire, or fiber rope. They are also appropriate for long electrical and control cables, hoses, and umbilicals. Examples are given to illustrate the techniques.

INTRODUCTION
There is much interest in assessing the reliability of deepwater mooring systems.! Mooring lines are typically much longer than the short test specimens used in determining breakmg strength and fatigue life statistics. For example, each ofseveral mooring lines used on a floating platform in deep water might be over 1000 m (3000 ft) long, but the specimens used m break and fatigue testing might only be 10 m (30 ft) long., This paper addresses problems in relating break and fatigue test .data obtained from tests on short specimens to the reliability of the same type of line in very long lengths. It includes the effects of terminations with different statisticalproperties than the body of the line.
. "A chain is. only as strong as it's weakest link". For simplicity chain will be used as a model in this paper. The technique s also apply to wire and fiber ropes, in which performance IS determined from tests on short specimens and the ropes used in service are much longer. "Short rope" can be substituted for 'link', and long rope" can be substituted for 'chain' throughout this paper. Here the word termination means any component or method used to connect parts of the mooring line together or to connect the entire mooring line to a vessel or an anchor. Examples include chain connector links shackles and splices in wire or fiber rope. "
The probability of failure at any given load increases as the total line length and the number of terminations increase. Of course. It also depends on the mean strength and the strength variability of these components. If sufficient statistical data for the components are available, the analysis techniques described m this paper can be used to design a system with an acceptable risk of failure.
The prediction of reliability for a length of chain based on the statistics of individual links is first considered. The effects of terminations on the reliability of this length of chain areintroduced later.

STATISTICAL CONCEPTS

The Chain Link Model
A theoretical chain comprised of individual links is shown in Figure la. It is analogous to a long length of chain made upof shorter lengths equivalent to the test specimen length, as shown in Figure lb. It is also analogous to a long length of rope, again made up of shorter lengths equivalent to the test" specimen length, as shown in Figure lc.
The breaking strength of the long chain can be determined from the strengths of individual links.
Calculating Remaining Useful Life of Ships
Authors: Egan G.A. , Andrews B.V. 
Published: October 2008

ABSTRACT
Recent developments of engineering analysis methods enable useful forecasts of physical life of ship hull structures, piping, and machinery. Economic analyses of the costs of rehabilitation and increasing maintenance costs can demonstrate that the useful life of tankers can be extended many years at significant savings over replacing 15- to 20year old vessels.

THE TANK SHIP OWNERS' OUESTION: VESSEL USEFUL LIFE?
The last two decades have been hectic for tank ship owners and their builders. Business and revenue boomed in the early 1970s, faltered in the mid-1970s, and rose again at thestart of the 1980s. Prospects crashed to depression by the mid-1980s and only now are returning to normal. Theproximate cause for these demand fluctuations were the double OPEC oil price shocks of 1973 and 1979 that caused worldwide economic disruptions.
Crude oil tankers, and especially the very large crude carriers (VLCC) and even larger tankers were being over orderedand over-built from 1968 to 1975. Then in 1973, the Persian Gulf OPEC countries raised prices from $3 to $13 per barrel for crude oil cutting oil transport demand quite sharply. Even though tanker capacity supply was suddenly about 35% excess over demand, more tankers were ordered later. As shown in Figure I, most of the VLCC/ULCCs (that represent about two-thirds of all tanker capacity) were delivered between 1973 to 1978(1).
Over 100 million deadweight tons (dwt) of tank ships were scrapped in the early 1980s to reduce the excess fleet. Crude oil prices have plummeted since 1986; therefore, demand has escalated and the gap between excess tanker supply and demand has narrowed. Ship charter hire rates have at last escalated to profitable levels for existing tankers for the first time in 20 years.
Since the last major ship orders in the late 1970s, extensive cuts have been made in the world shipbuilding industrycapacity. Few shipyards are now able to build large ships and are quoting increasingly high prices. (These prices should go up even more when state subsidies are discontinued by international agreement.) For example, a 1971 vintage VLCC that originally cost $15 to $20 million will now cost nearly $100 million to replace. If a double hull is required, the new building cost is over $110 million. Therefore, charter rates must increase even more to make profitable investment in expensive new tankers.
In summary, ship charter rates now are not adequate to pay for building and operating new tankers. In addition, not enough ships of each kind have been built in the last decade. As a result, economics forces most owners to keep using their existing ships longer than their typical 16- to 20-year life span.

BASIS FOR LIFE EXTENSION
During the last two decades, many tank ships and other vessels have been laid up or slow-steaming and extended porttimes, some for several years and in varying degrees of care. As a result, they have not been worked hard nor overstressed.
A Vertical Connection System To Attach Flexible Pipeline to a Subsea Manifold
Authors: Brandao Maxwell , Couto Paulo 
Published: October 2008

ABSTRACT
This paper presents a vertical guidelineless system for connecting flexible pipelines to a subsea manifold. The system uses only field proven components and allows the operator to test many different installation methods. The installation tool may be run by cable or drill pipe. Hydraulic control is supplied by umbilical or through a ROV hot stab. Field test results will be used to determine the optimum installation methods and to optimize the equipment design that will establish a new generation of subsea connection system that is simpler, more reliable and cost effective.

INTRODUCTION
The vertical guidelineless connection system to attach flexible pipeline to subsea manifold has been developed as alternative to existingsystems which use horizontal connection and pull-in system.
The project was based on the deepwater guidelineless drilling and completion experience in Brazil, resulting an equipment fullycompatible with operational requirements for a dynamically positioned drilling vessel. The main system components are:Temporary Abandonment Base (TAB)Vertical Connection Module (VCM)Running and Connection Tool (RCT)
A prototype is being developed to simulate, in a field test, the actual conditions of thevarious installation methods, in order to obtain enough data feedback for future improvement.

INSTALLATION METHODS
For better understanding, the operation can be divided in two phases:(AVAILABLE IN FULL PAPER)

ABANDONMENT METHODS
Two temporary abandonment methods of the VCM and TAB were established. These methods depend onthe type of vessel involved in the abandonment operation, as described below:

Abandonment with DP drilling vessel
This method, illustrated in fig. 1, requires the VCM to run connected to the TAB. The running operation of the VCM!TAB is made by means of a cable passed over a side of the drilling vessel while the guidelineless Christmas Tree runs through the moon pool. This method is only applicable in the case that requires the use of a short flexible jumper between the satellite Christmas Tree and the manifold (less than 100 meters). The great advantage of this method is that there is no need to use the pipe lay vessel to accomplish a layaway operation. The use of short jumper can also introduce a new concept of subsea layout with the satellite wells very close to the manifold.

Abandonment with the pipelay vessel
This method of abandonment using a pipe lay vessel, illustrated in fig. 2, also requires the VCM to run connected to the TAB. The running operation of VCO/TAB is made by means of a cable operated by the vessel while the GLL Christmas Tree runs through the moon pool of the DP drilling vessel using the layaway methods. Therefore the VCM/TAB should be fully compatible with the handling conditions of the pipe lay vessels. This method is necessary for longer distances between the satellite Christmas Tree and the manifold but may be applicable to any distance.