bluuebunny/crossref_metadata_2025_split huggingface dataset:
Offshore Pipeline Welding For Cats Project
Authors: Ibarra S. , Pronko M. , Grass G.D. , Hostler F. , Hutchens E.J. 
Published: October 2008

ABSTRACT
This paper presents some of the challenges encountered during the welding of the Amoco CATS pipeline. The 36-in. diameter high pressure gas pipeline was installed from an onshore terminal at Teesside, England to the North Everest Riser Platform located in the Central Graben Development Area in the North Sea. The off- shore pipeline was installed by McDermott/ETPM using the lay barge LB200. Submerged arc welding (SAW.) was used for the double joints and ETPM's proprietary Saturne 8T gas metal-arc welding (GMA W) system for both the mainline welds and the root pass of the double-joint welds. The CATS pipeline has undergone rigorous testing, not only when the line pipe was being fabricated, but also when establishing welding procedures and throughout the pipelaying process. This rigorous testing and monitoring has resulted in a pipeline of very high quality.

INTRODUCTION
A two-year pipelaying program has been completed in the North Sea, using primarily automatic GMAW techniques. The CATS Pipeline and Riser Platform was installed to join the gas fields in the North Sea to the industrial area of Teesside, England as shown in Fig. 1. A power generating plant is being completed, and other industries in the Northern sector of England will benefit from this gas. The total length of the pipeline is 404.5 km (251,3 miles) and the riser length is 115 meters. The pipeline is 36 in. in diameter, API 5L Grade X65 fabricated with double submerged arc welds to form the longitudinal seams. The wall thickness was 28.4 mm (1 .12 in.) with a small portion 33.9 mm (1 .33 in,) wall thickness at onshore and shore approach sections. The line was designed for dry sour service. The design pressure is 2600 psig with a 1500 ppm/4 psi max. hydrogen sulfide. The design oxygen content was 10 ppm/0.03 psia max. and the carbon dioxide was 25 mol%A/654 psia max.

LINE PIPE MATERIAL
The line pipe was fabricated by Mannesmann to conform to sour service performance requirements. The CATS pipeline represented an order for 260,000 tons of steel. The technical requirements for the line pipe were based on the API 5L specification for line pipe1 with certain additions, deletions, and modification made to conform to Amoco requirements with mutually agreed manufacturing Iimits2. For example, the product analysis chemistry of the pipe material was subject to the limits shown in Table 1. The two carbon equivalent measurements specified were the IIW and Pcm suchthat:(Mathematical equation available in full paper)
Charpy V-notch impact testing was also modified from API 5L requirements to state that a set of three specimens would be taken from a pipe from each heat, transverse to the weld, from each of the following locations:Weld Metal - Notched on weld centerlineHeat Affected Zone - Fusion line centered on(HAZ) notchBase Metal - Notch on base metal
It was also stated that the top of the Charpy V-notch specimen would be taken 2 mm from the outside pipe surface. The acceptance criteria for the toughness are shown in Table 2.
Troll Oil Development Concept
Authors: Prydz Rolf 
Published: October 2008

ABSTRACT
Underneath the large gas accumulation of the Troll field lies a considerable volume of oil. However, its development requires an innovative approach because it is located in thin layers sandwiched between a large gas cap and an active aquifer. During the past 4 years Norsk Hydro has carried out extensive technical studies and an ambitious seismic acquisition and appraisal well programme to identify an economic development concept for the oil resource. This has resulted in the submission of a development plan for an extensive subsea development based on horizontally completed wells which will be manifolded on the seabed and tied back to a concrete semi-submersible production platform.

INTRODUCTION
The Troll field is located on the Norwegian Continental Shelf in 315-340m of water 100 km NW of Bergen as shown in Figure 1. It is covered by production Iicences PL054 and PL085 which are unitized. The owners of the field and their individual percentages are shown in Table 1.
In December 1991 the Troll Licensees submitted a Plan For Development and Operation (PDO) for the oil resources of the Troll Field. The plan marked a successful milestone in the extensive development study and appraisal well activities carried out by the operator, Norsk Hydro since 1988. The proposed development concept consisted of 17 horizontal subsea wells tied back in groups to a concrete floating production platform. A schematic of the PDO concept is shown in Figure 2.
The PDO was approved by the Norwegian Parliament in May 1992 and during this year and the first quarter of 1993 the operator built up a multi-discipline project team and completed basic engineering and part of the detailed engineering phase. Contracts were awarded for topside facilities design, the subsea production facilities and the production unit living quarters. Detail design of the concrete substructure is in progress and a drilling rig will be contracted medio 1993 to carry out the 3–4 year development well drilling programme.
This paper describes the work done to select a development concept for the North Sea's most ambitious subsea project to date, and the changes that have been made to the original plan as a result of subsequent, more detailed work.

TROLL FIELD APPRAISAL HISTORY
The Troll Field was discovered in 1979 by exploration well 31/2-1. This well was drilled on the crest of the large gas structure of Troll West. By the end of 1984 a total of 15 wells had been drilled on Troll West confirming it to be a significant discovery.
In addition to the large quantities of gas the appraisal programme also confirmed the presence of significant quantities of oil below the gas. However, the oil is contained in thin layers which are distributed over a wide area. Development of the oil layers was considered complex and uncertain commercially, therefore development planning activities concentrated on the large gas resource.
Rapid Deployment CALM 6uoy System
Authors: Lorentz John 
Published: October 2008

ABSTRACT
The design, fabrication and installation of a Rapid Deployment Catenary Anchor Leg Mooring (CALM) Buoy from an anchor handling tug combined proven technology with innovative designs and novel equipment developments. This paper describes the design requirements, development and trial installation that was successfully conducted as well as possible applications for this unique system.

INTRODUCTION
IMODCO was awarded a contract in March 1990 to design a CALM buoy system to be used in support of military action and be light and compact enough to be loaded aboard a typical North Sea-type Anchor Handling Tug (AHT) and installed without the luxury of typical oilfield equipment or divers, The proof of the ability to achieve this goal was the successful deployment and recovery of the system in October 1990.

DESIGN AND FABRICATION
Typically, a CALM buoy may be 11 to 12.5 meters in diameter and weigh up to 210 tonnes. Such a buoy must support large diameter piping, six chain legs up to 108 mm diameter and with stand maximum chain loads of 280 tonnes while mooring VLCC'S of high cargo throughput (50,000 bbls/hr). The targeted size and weight of the Rapid Deployment buoy was approximately one fourth of that stated above.
Although the basic design method utilized in the mooring analysis and structural calculations for this project were not unique, the design of a buoy and chain system that could be transported and handled within an area of such restricted size presented a challenge. The maximum specified tanker size of 50,000 DWT and the Client requirement for only one (1) throughput product resulted in significant buoy weight and diameter reduction. Further weight reduction of the buoy hull and framing was achieved by using 50D type steel with a yield strength of 345 N/mm2.
Considering the intermittent service and limited duration of use that the system would see, the buoy framing was optimized to result in exterior hull plating thickness of 8 mm and interior bulkhead plate thickness of 6 mm, whereas Lloyd's normally requires a minimum thickness of 905 mm for continuous service.
The method of buoy launch from and recovery aboard the AHT involved discussion of many concepts including the construction of complex launch ramps or sliding frames or simple buoywelded skids with an array of pulling wires. Since available deck space was at a premium, the decision was made to concentrate on a method of handling the buoy over the AHT stern roller using only AHT available rigging and winches. On deployment, the buoy would be pulled over the stern as a continuation of laying the first chain leg, Rigging leading back to the AHT winches would provide stability and control and prevent the buoy from tipping, On recovery, pulling wires and mooring chain would provide sufficient force and stabilization to bring the buoy up and over the stern roller.
Cadlao's Successful Fpso Ii Redeployed At The Deepwater West Linapacon Field
Authors: Genod Francis Vincent , Jeannin Olivier 
Published: October 2008

ABSTRACT
The number of FPSO's installed on marginal Fields k increasing while the life of these Fields is often unpredictable. The possibility that a tanker-based FPSO may easily be relocated after depletion of a marginal field may become a key factor to the decision making process in respect of small field development.
This paper will describe the circumstances under which the tanker-based "FPSO II" was disconnected from the Cadlao Field in the Philippines (after 10 years and 3 months uninterrupted operation), towed to Singapore, for refurbishment and modification, towed back to the Philippines and installed on the new West Linapacan Field in a water depth of 1150 ft. The Scope of Work included the replacement of over 800 tonnes structural steel in the tanker, extensive work on the process equipment and instrumentation plus a comprehensive refurbishment programme for the SBS mooring system and the vessel machinery.
The whole project was executed under very tight time constraints and less than 6 months elapsed between last oil at Cadlao and first oil at West Linapacan.

HISTORY
The 127,000 dwt converted tanker FPSO II owned and operated by SBM Inc. went into operation on the Cadlao Field, offshore Philippines in August 1981. This Field in 300 ft water depth was produced through 611flowlines from 2 wells. Each well was also connected to 611service lines thus requiring a 4 path 611 swivel mounted on the SBS mooring buoy. The SBS mooring buoy was attached to piles driven in the sea bed by six 611 ? 5½11diam. chains. The production facilities mounted on the tanker deck were designed to handle 30,000 BPD oil and a ground flare was installed to flare up to 6.5 MMCFD excess gas.
The 3-phase production and test separators also removed the produced water which was passed through a skimmer/degasser to 2 series operated slops tanks where it was de-oiled and pumped overboard. The design and operation of the FPSO II on the Cadlao Field has been extensive y reported in various publications.1–6Fig. 1 shows the FPSO II operational configuration in the Cadlao Field.
In 1986, the Cadlao Field concession was ceded to Alcorn who had also obtained the Matinloc Field concession situated nearby. A new bare-boat charter was negotiated for the FPSO 11 and the Matinloc Field then connected to it. This required modifications to the production manifolding and the installation of a metering/prover loop system on the FPSO 11 to fiscalize the Matinloc crude.
This mode of operation continued until November 1991 when the production had fallen to an uneconomic level and it was decided to relocate the FPSO 11 to West Linapacan Field.
During its 10 year operation in this area the FPSO 11 had a remarkable record of having virtually no down time.

LINAPACAN FIELD
Fig.2 shows the location of the West Linapacan Field situated in 1150 ft water depth 55 km from the Palawan Island coast.
Reliability-Based Fatigue Design Criteria For Offshore Structures Considering The Effect Of Inspection And Repair
Authors: Moan Torgeir , Hovde G.O. , Blanker A.M. 
Published: October 2008

ABSTRACT
Current fatigue design criteria for offshore structures are based on SN-data and the Miner-Palmgren approach. The acceptable cumulative damage in some codes is made dependent on a vaguely defined feature of accessibility for inspection. This paper presents a reliability based fracture mechanics (FM) calibration of the allowable cumulative damage which depends on the quality of inspection in terms of probability of crack detection curves. Target safety levels are taken to correspond to a cumulative damage of 0.1 and 0.3 with no effect of inspection.

INTRODUCTION
Fatigue and fracture are important failure modes of welded offshore structures. Significant progress has recently been made in developing rational design methods to handle these failure modes, especially by using reliability methods, see e.g. [1].
Fatigue design criteria are commonly based on the SN-Miner- Palmgren approach where the allowable cumulative damage, D = ?n/N1, is made dependent upon the consequences of failure and access for inspection as specified e.g. by NPD [2]. However, existing criteria are qualitative.
The purpose of the present paper is to quantity the effect of inspection depending upon its quality for a given inspection strategy.
Welded joints in TLP tethers and tubular joints of jackets are considered for illustration purposes. This is done by determining the allowable cumulative damage in the SN approach as a function of the quality of inspection. The calibration of this simple design approach is based on a probabilistic fracture mechanics model of fatigue crack growth,

CRACK GROWTH MODEL
The crack growth is described by a generalization of the Paris-Erdogans equation,(Mathematical equation) (available in full paper)
as introduced by Newman & Raju [3]. In this approach the surface crack is assumed to be semielliptical with semiaxes a and c at any stage during crack growth, where a is the crack depth, c is the half crack length, N is the number of stress cycles, ?K is the stress intensity factor range, and C and m are material parameters.
Analysis of the distribution of the material parameter, C, for steels shows C to approximately follow a Iognormal distribution. The crack growth parameters may be reasonably modelled as: C Iognormally distributed with C(I.1 .10−13 [4],0.55), where (,) are the mean, with units N and mm, and the coefficient of variation, respectively. Instead of using C as a random variable, InC is used herein, see Tables 1 and 2. m is assumed fixed and equal to 3.1 [4].
The stress intensity factor range at any point of the crack front for surface cracks in plane plates subjected to tension and bending loads is expressed as [3] (Mathematical equation) (available in full paper) where S1 and Sb are tension and bending stress ranges, respectively. S is the total stress range, t is the plate thickness and W is the width of the plate.
Taut Leg Spread Moorings: A Cost-Effective Stationkeeping Alternative For Deepwater Platforms
Authors: D&apos;Souza R.B. , Dove P.G.S. , Kelly P.J. 
Published: October 2008

ABSTRACT
Spread moored floating production platforms are employed worldwide in the exploitation of offshore hydrocarbons. To date they have all employed catenary spread mooring systems (CSMS) using chain or combination wire/chain components. In water depths to 1500 feet and beyond, such simple wire/chain systems become increasingly inefficient and costly. To improve cost efficiency, tighten watch circles and 10wer vertical load on the platform several innovations have been introduced such as the use of submerged spring buoys (Ref. I), ground wire, and ropes made from synthetic aramid fiber. An aramid rope has yet to be employed in a permanently spread moored production platform as industry awaits a better understanding of the long term behavior of this material (Ref. 2). The installed cost of a deep water (XM remains high despite these innovations and a need exists for even more efficient spread moorings as industry looks to water depths of 3000 feet and beyond. The most promising alternative to the (XM to emerge in recent years is the Taut Leg Spread Mooring (TLSM) system, with short scope legs (Fig. 1) and where vertical uplift on the anchors is permitted (Ref 3, 4). This paper explains the operating principles of a TLSM, its performance sensitivity to variations of key parameters and shows the cost benefit versus a CSM by specific case studies.

FUNDAMENTAL BEHAVIOR EXPLAINED
To develop a cost efficient design, it is essential to understand the basic mechanisms by which a TLSM resists platform mean loads and wave induced motions. The behavior is most easily grasped by studying the simple taut leg system shown in Figure 2. k consists of a light weight, elastic mooring leg in water depth D stretched between the anchor point A and the fairlead point F separated by a horizontal distance L. The anchor point is fixed and resists horizontal and vertical forces.
As the fairlead point translates away from the anchor point in response to an applied mean load, tension is induced in the leg as it stretches elastically between the points. An equilibrium position is attained when the moment created by the horizontal force components (H *D) is balanced by the moment created by the vertical force couple (V*L) between the anchor and fairlead points. As the line slope angle relative to the horizontal decreases, distance L increases requiring a smaller vertical force and therefore smaller line tension to resist a given horizontal force. However, line scope and therefore cost also increases. If horizontal force per unit of line volume is used as a measure of cost efficiency, it can be demonstrated that the most cost efficient line slope of a simple TLSM to resist a horizontal mean load is 450 (scope/depth ratio of 1.414).
In a catenary system, mean offset is controlled by line weight and pretension. Lines composed of materials with lighter weights and with larger pretensions produce.
Structural Aspects Of Snorre Mating
Authors: Aiming A.H. , Muren Jan 
Published: October 2008

ABSTRACT
The deck and the hull of the Snorre TLP were successfully connected South of Stord on the Norwegian westcoast in September 1991. The 28.000 tonnes deck was lifted off its supports by a large launch barge, transported to the ballasted hull and accurately positioned over the columns.
The main challenge of the operation was to control deflections of the hull, deck and barge to obtain the desired load distribution between the 16 hull support stools, 4 on each column top. On each stool the load was taken by an array of deformation tubes. The arrangement of the tubes was decided on the basis of both dynamic and static analysis.
Step by step computer simulations were performed during the operations,, along with measurements of the deflection of the deck, barge and deformation tubes. This enabled full control of the operation and large flexibility when modifications to the original procedures were required.
The mating took place in the autumn with risk of swell. Dynamic analysis of the hull and barge in the mating configuration was performed to decide on the requirement for additional dampers between the column tops and the deck. It was found that friction on the prearranged guides and restraints gave the necessary damping to prevent unacceptable impacts.
The deck was positioned well inside the agreed tolerances of +/- 100 mm. This was achieved due to good preparations, both on the engineering and the construction sides.

INTRODUCTION
Snorre is a four column TLP built for the Snorre Field in the North Sea west of Nofway. The connection of the hull and deck structures took place in Digernessundet south of Stord in September 1991. The total operation was divided in two, the lift-off of the deck from the fabrication site by a barge, and the connection, or mating, of the deck and the hull.
The column diameter of Snorre is 25 meters, while the centere to centre distance of the columns are 76 meters. The column height is 63 meters. The pontoon cross section is 11,5 times 11,5 meters.
The deck fabricator was responsible for the lift-off and mating, while the Main Engineering contractor was responsible for the design of the hull and deck connection points and the structural integrity of the TLP. This involved a detailed arrangements of the deformation tubes, guides and ballast distribution. Key personnel from the detail engineering phase where engaged for following up of the operation. The follow-up team prepared tools and measurement schedules to enable an accurate follow-up and an early identification of possible deviations.
This paper will not describe the marine operations more than what is required to give an understanding of the procedure. The main aspects will be the engineering preparations, and main parameters to control during the operations.

LIFT-OFF OF DECK
The deck was fabricated on 16 fabrication supports, 8 on each side of the dry dock. The supports had the same location relative to the deck as the mating stools on the hull. The barge with grillage was located under the deck at a low water level in the dock.