bluuebunny/crossref_metadata_2025_split huggingface dataset:
Upheaval Buckling Failures of Insulated Buried Pipelines: A Case Story
Authors: Nielsen N-J.R. , Lyngberg B. , Pedersen P.T. 
Published: October 2008

ABSTRACT
The first recognized upheaval buckling of a subsea, buried pipeline took place in 1986 in one of Maersk Olie og Gas AS' interfield pipelines in the Danish Sector of the North Sea.
It is the objective of this paper to present the case story of this pipeline upheaval giving a chronological description of all actions taken, in order to re-establish the pipeline integrity.
Based on the upheaval buckling experience within Maersk Olie og Gas AS, a recommendation for the design and installation of buried, hot pipelines is presented.

INTRODUCTION
During the annual pipeline inspection survey in July 1986 along the buried Rolf A/Gorm E two phase pipeline in the Danish Sector of the North Sea, a pipeline section was discovered to have protruded the seabottom, and was standing in an arch. The 17 km long pipeline is an O.D. 8.625" × WT 14.3 mm carbon steel line (API 5L grade X 52). The pipe is insulated with a 2" thick polyethane foam (PUF) of min. density 96 kg/m3 encased in a high density polyethylene (PE) jacket. The exposed PUF at the ends of the PE jacket is sealed with water tight end cap sleeves. A 2" thick concrete weight coating is applied on top of the PE jacket resulting in an overall pipe diameter of 0.45 m. A 3" gas lift line is "piggy backed" to the 8 " pipeline. The pipeline build-up is shown in Figure 1, and a detailed description of the pipeline is given by Pallesen et.al. (1985) in ref. [1].
The pipeline was laid in the summer of 1985 in 40 m water depth utilizing conventional lay barge techniques. Trenching of the line was carried out using water jetting equipment.
The pipeline was brought into service January 1986 for transport of unstabilized hydrocarbons with a temperature of up to 180°F (82°C) from the Rolf satellite field to the central process facility at Gorm.
Upheaval buckling analysis of the 8" line was carried out as part of the design documentation resulting in a lowering requirement of 1.15 m to top of the concrete coated pipe. The certified upheaval buckling calculations were performed according to the state-of-art at that time, i.e. using the "classical" upheaval buckling analysis, where the design criteria against upheaval snap buckling is based upon post buckling equilibrium curves assuming a pipe of uniform weight on a rigid foundation.
Following the detection of the exposure an upheaval buckling research programme was immediately initiated at the Technical University of Denmark. The results from the study showed that the "classical" design approach did not always yield conservative results. Thus, a new and improved theoretical model was developed and made available late 1986, and formed the basis for the repair work. The new design approach has been published in ref. [2], [3] and [4].
Often Overlooked Data Available From a Typical Offshore Subsea Survey
Authors: Mateer M.W. 
Published: October 2008

ABSTRACT
Regular subsea inspect ion of offshore structures to assess the condition of cathodic protect ion systems is a way of 1ife in the Gulf of Mexico. In an effort to collect more useful data, new inspect ion procedures were implemented into the ARCO Oil and Gas Southern District platform inspections to see if it was possible to routinely calculate the current output of anodes using the anode resistance method in NACE RP-01-76. By trial and error, a potential sampling technique was discovered which allows the collection of the kind of potential data needed to calculate anode current with an accuracy similar to that possible with direct measurement with a gauss meter. The speed at which this data can be taken makes this survey technique no more costly than a normal potential survey while providing much more useful data.

INTRODUCTION
A typical underwater potential survey consists of measuring the potential of the structure against a standard reference electrode (usually Ag/AgCl) in order to insure the viability of the cathodic protection system. Although a great deal of data can be obtained, it is usually necessary to limit the scope of the potential survey to keep the time and cost reasonable. When planning for the ARCO Southern District 1989 platform surveys, a complete rethinking of our platform survey requirements was done to try and take the best advantage of the changes caused by the new MMS platform survey requirements.
As part of this rethinking, the idea of using potential measurements to survey anode current output was discussed with the survey contractor. It was felt that a usable correlation could be found between anode potential and anode current output using the calculation method recommended in NACE RP-O1-76. This was considered to be an "easy" addition to our survey that could be accomplished without an increase in effort. The main unknown factor was the proper location of the potential survey points needed to give the proper anode and cathode potentials for the calculation. Ideas on how to obtain the needed data were developed and added to the survey procedures prior to the start of work. In order to have a standard against which to compare the results, an underwater gauss meter was obtained for taking anode current measurements directly from the anode supports. During the surveys, direct current measurements and anode potentials were taken on 57 anodes on 13 different platforms.

ANOOE CURRENT CALCULATIONS
In theory, the output of an anode can be found by using the equation:I = E/R (1) where I is the current, E is the potential difference between the anode and cathode and R is the circuit resistance. Since the current density is much higher at the anode than the cathode and the resistance in the steel is negligible, the circuit resistance can be considered to be the anode to electrolyte resistance.
Verification of Jackup Leg-to-Hull Beam Model Interaction Using Super Elements
Authors: Maison J.R. , Lewis D. 
Published: October 2008

ABSTRACT:
The design of leg members for a mobile offshore drilling unit (jackup) with guides, is driven by the loads introduced at the lower guide. The selection of the optimum leg member sizes for the many environmental loading possibilities represents a major effort in the design of jackups. In an attempt to control the time and cost of analysis, a simplified beam model of the leg to hull connection has been used. This "pitch fork" beam model developed and calibrated in the late 1970's, combines the effect of different leg to hull positions into a single representative case.
The evolution in finite element technology allows for re-examination of the "pitch fork" beam model. New rig design and the desire to extend the operational envelope of existing designs have stimulated a reappraisal of the simplified beam model approach. The accuracy of the beam model is investigated using a detailed finite element plate model of an entire leg of a jackup. The effects of structural details including member eccentricities and gusset reinforcements are accurately accounted for in the analysis. The FEA superelement method makes the problem computationally manageable.
A typical load case for the GORILLA Class jackup operating m the North Sea is studied. The loading is applied to the simplified beam model and to two superelement models that represent the extreme conditions of leg to hull position. In one superelement model the lower guide on the hull aligns with a main horizontal leg member. The second model has the lower guide vertically positioned mid way between horizontals.
The "pitch fork" beam model is calibrated against the results of the superelement derived loads. Optimization methods are used to adjust the properties in the beam model to match the results of the superelements.

BACKGROUND:
The structural design of a jackup depends upon the load transfer between the hull and the supporting legs. The means of load transfer directly affects the size of leg members and thus drives the weight and cost of the jackup. The load transfer mechanism for the GORILLA Class jackup is used for illustration, although the concepts are generally applicable to other designs.
The jackup GORILLA is configured with a triangular shaped hull and three support legs. Each of the legs is square in plan view. The leg is constructed from vertical members positioned at each corner and crosslinked tubulars. A "K" brace lattice design of main horizontal and vertical diagonal tubes is used. Other smaller pipes provide horizontal support to the joint intersection of the main diagonal and horizontal members. The main horizontal and vertical diagonal tubular members are the same size.
A typical leg construction is shown in Figure 1. The vertical post at each corner of the leg is a built-up member, triangular in plan view, with one flat surface (back plate) facing the leg center. This surface is extended to form a lip which slides through channel shaped guide members attached to the top and bottom of the hull.
The Application of Risk Assessment in Offshore Projects
Authors: Comer P.J. , Eades M.J. 
Published: October 2008

1. INTRODUCTION
The past ten or so years have seen a steady increase in the use of risk assessment to help improve the safety of offshore facilities. This process started with the requirements for "Concept Safety Evaluations" in the Norwegian sector of the North Sea, and has gathered pace since the Piper Alpha disaster and especially since the publication of the Cullen Report in November last year. Lord Cullen has recommended a fundamental change in the regulation of offshore safety on the UK Continental Shelf; he has proposed that the current prescriptive regulations are replaced by goal setting regulations. This approach is broadly similar to that of new regulations in the Norwegian sector which came into force in January this year. An integral part of both approaches is in the use of risk assessment methods to demonstrate that an adequate level of safety has been achieved.
This means that risk assessment can no longer be seen as an academic discipline practised by the safety department and their consultants. It is going to become the basis of key and costly decisions and will be an important aspect of the interaction with the regulatory authorities. It will be important that the management of operating companies, at all levels, understand the principles, the shortcomings and the ways in which risk assessment should and should not be used.

2. WHAT IS RISK ASSESSMENT?
Risk assessment is a generic term covering a wide range of techniques used to assess the level of safety by considering both the magnitude of harm or damage and likelihood of such harm occurring. Such assessments can be qualitative or quantitative or a mixture of the two.
A risk assessment will therefore involve some assessment of the damage and an assessment of likelihood. Such assessments can be presented in simple qualitative scales or be fully quantified to result in a numeric value of risk. A Quantitative Risk Assessment (QRA) can involve the use of a variety of methods or models ranging from simple correlations to complex computer codes; these will include methods for the assessment of the consequences of releases including dispersion models, flame radiation models, explosion models etc.; models for assessing the impact or damage resulting from the fire or explosion or impact; data on the likelihood of failures of various items of equipment and on the likelihood of alternative outcomes, for example, ignition and methods for utilising that data; and methods for summarising and presenting the results in a useable manner.
The basic approach of QRA techniques is to analyse a complex system (such as a platform or chemical plant), which contains hazardous materials, hardware, control and safety systems, people and management systems, with the intention of determining:what accidents can occur? - this depends on the scope of the study and may be generated using checklists, HAZOP or previous study experience.how frequently does each accident occur? - a combination of failure rate data and conditional probabilities.
Auk to Kittiwake: 15 Years' Progress in North Sea Jacket Engineering
Authors: Edwards C.D. 
Published: October 2008

ABSTRACT
The Kittiwake oil field has been developed using the first of a new generation of liftable slimline jackets to be installed in the North Sea by Shell UK Exploration and Production, known as Shell Expro, operator in the UK sector the North Sea on behalf of Shell and coventurer Esso Expro. Production began in September 1990 - almost exactly 15 years after Shell Expro began production from Auk, its first North Sea oil field. This paper considers the progress of jacket engineering over these 15 years by comparing two jackets supporting topsides facilities which perform comparable functions in very similar conditions.

INTRODUCTION
The Kittiwake platform is a self contained drilling, production and accommodation platform located in 85 metres of water approximately 100 miles east of Aberdeen in the Central North Sea sector of the UK Continental Shelf. Recoverable oil reserves from the field are approximately 70 million barrels, making Kittiwake one of the smallest North Sea fields to be developed as a standalone facility. Kittiwake was originally part of the Gannet Cluster project which was suspended during the 1986 oil price collapse. It has now been developed using a 4 leg lift installed jacket which supports an integrated deck, living quarters module and drilling mast. The platform has 16 well slots, facilities for up to 36000 barrels of oil production per day, and accommodation for 80 men. Oil is exported via a 2km. long 8 inch diameter pipeline and a loading buoy into shuttle tankers. The Kittiwake tankers are dynamically positioned, enabling them to continue loading oil in rougher seas than moored tankers - an important advantage as Kittiwake has no storage and therefore is shut down when the tanker is not loading. Associated gas is exported via a 2km. long 4 inch diameter pipeline into the nearby Fulmar gas line.
The Kittiwake jacket, which had a lift weight of 5400 tonnes, is supported by twelve 2.134m. diameter skirt piles each driven to 60m. seabed penetration. The jacket framing is depicted in Fig. 1. The four leg structure stands 106.6m. tall and directly supports the 7000 tonne lift weight integrated deck without an intermediate module support frame (MSF). The bracing pattern is very simple, having three X-braced vertical frames and four diamond braced horizontal frames at elevations +14m., -15m., -47m., and -82m. respectively. The nominal lateral dimensions of the jacket are 25m. by 22.6m. at the top, and 38m. square at the base. These plan dimensions are unusually small for the support of a large integrated deck, as Fig. 1 illustrates.
After initial jacket design by Shell Expro, detailed design was undertaken by Earl & Wright, London. RGC, Methil then fabricated the jacket and piles. Installation of the complete platform was performed by HeereMaC using the semi-submersible crane vessel (SSCV) DBI02, under subcontract to McDermott International Inc. It is noteworthy that many of these companies were also principal players in the execution of Shell Expro's Auk project.
The Structural Repair of a North Sea Platform Using Underwater Wet Welding Techniques
Authors: Ibarra S. , Reed R.L. , Smith J.K. , Pachniuk I. , Grubbs C.E. 
Published: October 2008

ABSTRACT
Underwater wet welding repair techniques using ferritic electrodes have, until recently, been limited to low strength steels with carbon equivalents below 0.40% because the fast quench that occurs after welding produces hard heat affected zones susceptible to hydrogen cracking. This paper describes the first documented structural wet weld repair of a North Sea offshore platform constructed with steel that had a carbon equivalent greater than 0.40%. It describes the events that lead to the failure and documents the repair using underwater wet welding techniques.

BACKGROUND
The underwater inspection of an Amoco U.K. North Sea Platform in June 1987 revealed that a diagonal brace connecting Leg B3, at a point 26 feet above water to Leg E3, at a point 36 feet below water (Figure 1) had a severed weld which had connected the brace to the E3 leg node (Figure 2). The failure was the result of ship impact on the brace. Initial structural assessment concluded that the damage did not affect the integrity of the platform and no emergency measures were required. However, in order to prevent further degradation of the damaged member from wave action, the brace was removed in July 1987.
A failure analysis supported by a metallurgical examination of the fracture surface was undertaken by Amoco Corporation Research at Naperville, Illinois. The findings indicated that the failure was the result of the impact loads which occurred when the ship struck the brace. The impact resulted in a circumferential weld metal crack between brace 3Bl and the jacket leg stub JL3E which was located underwater.
Multiple fractures initiated at lack of penetration weld defects on the ID of the brace weldment with several fracture initiation sites in the first pass of the weld. Figure 3 shows a cross section of the weld failure which contained a lack of penetration defect, forming a crack like defect in the ID of the weld. The cracking initially propagated in a brittle manner and changed to a ductile shear fracture as it approached the weld cap. There was no evidence of fatigue cracking on the fracture surfaces examined. The impact loads from the ship did not initiate cracking in the brace-to-stub weldment located +26 feet above water. Figures 4 and 5 show cross sections of the +26 foot brace-to-stub weldment. Note that the excessive root pass reinforcement in Figure 4 and the suck back in Figure 5 are defects with smooth contours which would be less likely to propagate as a result of impact. A comparison of the above water and the underwater weldments was also made to determine if there were any significant differences in the chemical composition or mechanical properties between the -36 ft and the +26 ft welds. The testing revealed that both welds had similar weld metal compositions suggesting that they had been welded with the same type of electrodes. The Charpy impact toughness of both weld metals were found to be satisfactory for this service.
Mechanical Creep and Fatigue Behaviour of a Resin-Assembled Steel T-Joint
Authors: Cao Y.M. , Jullien J.F. , Renault J.P. , Lazare F. 
Published: October 2008

ABSTRACT
Elf-Aquitaine in association with Irete (resin manufacturer) and I.N.S.A. of Lyon (Research Institute) have developed a device, based on a resin assembly, designed to repair or reinforce fixed marine steel structures. This paper presents the results of the experimental validation of such a design.
Firstly, the mechanical behaviour of a resin assembled steel T-joint, under incremental static normal and bending loads, was evaluated in laboratory conditions. The selected design based upon the ring-shaped/chord-resin-brace sandwich construction resulted in an excellent behaviour mainly due to the low stress concentrations. Subsequently the creep and fatigue behaviour under normal loads only were tested on a similar T-joint between a chord and a brace.
The brace has a ring welded to its end which encircles the chord; the whole joint is then enclosed in a block of resin. The tests were carried out on specimens with the following dimensions 10" for the chord, 6" for the brace. The mechanical efficiency of the assembly was assessed by strain and displacement gauges.
The analysis of behaviour of the joint submitted to axial statical permanent loads and repetitive loads is presented.
The experimental results show that, for this new joint submitted to static permanent loads, it is necessary to consider the effect of the creep properties on its rigidity under tensile and compressive loads. It should also be noted that the fatigue properties of resin influence the behaviour and the rigidity of the T-joint under the repeated tensile and compressive load.
This steel-resin sandwich assembly is excellent for static and fatigue behaviour. Its efficiency is very dependent on the choice of the resin.

INTRODUCTION
The work reports on the results of creep and fatigue tests on a Resin Assembled Steel T-joint. The resin based assembly method was studied by the Swiss Resin Formula Company IRETE and the French Oil Company ELF Aquitaine, and several patent applications have been filed.
This joint has been design for the replacement or the reinforcement of a damaged structural member of a jacket type steel offshore structure. Following any type of incident, this added member, known as a brace, must be joined to the structure on site and below the water, and must involve minimum work and be the most economical solution possible.
The procedure involves the manufacture of a welded ring spacer which is fitted at each end of the new member. It is constructed in two parts and, for instance, can be assembled by bolting around the chord to be bridged on the site. This ring is dimensioned in such a way that it leaves an annular space, 3 cm for the case studied, around the chord. On site, after positioning the member and holding it temporarily in place, a simple shutter is built up around each assembly surrounding the ring and a portion of the chord and brace.