bluuebunny/crossref_metadata_2025 huggingface dataset:
Bedrock Depth Effect Investigation in Seismic Response of Offshore Platforms Considering Soil-Pile-Structure Interaction
Authors: Asgarian B. , Roshandel Tavana M. A. , Soltani R. H.
Published: May 2009

Offshore platforms in seismically active areas should be designed to survive severe earthquake excitations with no global structural failure. In seismic design of offshore platforms, it is often necessary to perform a dynamic analysis that accounts for nonlinear soil-pile-structures interaction effects. Nonlinear dynamic analysis for offshore structures has been a major challenge in marine structural and earthquake engineering. In this paper, nonlinear dynamic analysis of jacket type offshore platforms considering soil-pile-structure interaction subjected to strong ground motion have been studied. A jacket type offshore platform is included of piles, jacket and topside with different behaviors in seismic loading. Both jacket and pile elements have been modeled using fiber cross-sections. In this paper, free field ground motion analysis with respect to bedrock excitations has been done using nonlinear stress-strain relations for soil. This model has been developed using Open System for Earthquake Engineering Simulation (OpenSEES) software. In this paper, nonlinear seismic response analysis of an existing sample offshore platform in Persian Gulf subjected to strong ground motions in different bedrock depths has been performed and the results in terms of lateral deflections of platform, soil layers displacement-time history and acceleration response spectra of pile head, top of jacket and deck have been presented.
Response Reduction of Motion and Steady Wave Drifting Forces of Floating Bodies Supported by Aircushions in Regular Waves: The 2nd Report—Response Characteristics in Oblique Waves
Authors: Ikoma Tomoki , Masuda Koichi , Rheem Chang-Kyu , Maeda Hisaaki
Published: May 2009

This paper describes aircushion effect for response reductions of floating bodies and thereby the model experiment in a wave tank is carried out and their details are explained. The floating body model has three aircushions and is supported by the aircushions. The response reduction due to the aircushion is considered and confirmed using the model experiment in regular waves and oblique waves. A pontoon type floating body model is also used to the experiment for comparisons of responses with the aircushion type model. From results of the experiment, vertical motion can be reduced due to the aircushion effect in not only head sea waves but also oblique waves. And then, it is confirmed that the second-order tension of tethers which moor the experimental model can be reduced at the same time. The response reduction due to the aircushion effect is useful in oblique waves and even then the wave angle approaches beam sea conditions.
Preloading Effects on the Behaviour of Cylindrical Members of Jacket Platforms Subjected to Ship Impact
Authors: Abdolvahab Maryam , Zeinoddini Mostafa , Keyvani Jafar
Published: May 2009

Steel tubes are widely encountered in industrial applications and in offshore structures. This is mostly because of their superior axial load carrying performance, low resistance against fluid loads and easy handling during construction and transportation. Cylindrical structural members, however, very often happen to become subject to accidental lateral damages which are detrimental to their load carrying performance. Collision between supply ships and legs and bracings of offshore oil platforms, impact from heavy dropped objects on these members or denting during installation of marine structures are examples of such accidents. Prior to an accident, cylindrical members are usually carrying their normal operational loads. It is very important to include the effects of this service load (pre-loading) in evaluation of the behaviour of impacted member. The pre-loading may change the dynamic characteristics of the member or degrade its load carrying capacity. While the performance of cylindrical members subjected to lateral impact has been extensively researched, few studies can be found on the impact behaviour of pre-loaded tubular members. This paper reports results from a numerical study on axial pre-loading effects on the dynamic and quasi-static behaviour of cylindrical shells subjected to transverse impact loads. Results obtained appear useful for a more realistic design of tubular members and in choosing feasible and reasonable post impact repairing and strengthening schemes.
NETL Extreme Drilling Laboratory Studies High Pressure High Temperature Drilling Phenomena
Authors: Lyons K. David , Honeygan Simone , Mroz Thomas
Published: May 2009

The U.S. Department of Energy’s National Energy Technology Laboratory (NETL) established an Extreme Drilling Lab to engineer effective and efficient drilling technologies viable at depths greater than 20,000 feet. This paper details the challenges of ultra-deep drilling, documents reports of decreased drilling rates as a result of increasing fluid pressure and temperature, and describes NETL’s Research and Development activities. NETL is invested in laboratory-scale physical simulation. Their physical simulator will have capability of circulating drilling fluids at 30,000 psi and 480 °F around a single drill cutter. This simulator will not yet be operational by the planned conference dates; therefore, the results will be limited to identification of leading hypotheses of drilling phenomena and NETL’s test plans to validate or refute such theories. Of particular interest to the Extreme Drilling Lab’s studies are the combinatorial effects of drilling fluid pressure, drilling fluid properties, rock properties, pore pressure, and drilling parameters, such as cutter rotational speed, weight on bit, and hydraulics associated with drilling fluid introduction to the rock-cutter interface. A detailed discussion of how each variable is controlled in a laboratory setting will be part of the conference paper and presentation.
Engineering Software for the Wave-Seabed Interaction: PORO-WSSI Model
Authors: Jeng Dong-Sheng , Lu Yan
Published: May 2009

Wave-induced seabed instability around marine facilities has been recognized as a key issue in the design of marine facilities. Most previous studies have been focused on individual issues in the area, without a global consideration. This limits the research outcomes to pure academic research, and practical engineers are rarely to use it in the real design, as it is too complicated. In this study, first we establish a new model for random wave-induced residual pore pressure in marine sediments. Second, we integrate the new model with previous work, including analytical and numerical models, into a simple package (PORO-WSSI). In the model, a GUI (Graphical User Interface) will be included. The main feature of the PORO-WSSI will be outlined and numerical results will be presented and discussed.
Fatigue Safety Factors for the Tensile and Pressure Armours of Flexible Risers
Authors: Leira Bernt J. , Igland Ragnar T. , Ye Naiquan , Passano Elizabeth A.
Published: May 2009

In the present paper, fatigue safety factors for metallic layers of flexible risers are assessed. A procedure for reliability analysis of wave-induced fatigue is first described. The procedure is based on performing a number of parametric studies with respect to variables that influence the fatigue lifetime. The results of these parametric studies are subsequently combined with models describing the statistical scatter of the same parameters. By application of this procedure, the safety factors which are required in order to reach specific target reliability levels can be computed. Example of calculation of such safety factors for the tensile and pressure armours of some specific flexible riser configurations are given. Different SN-curves which correspond to different corrosive environments are considered. The percentwise contribution from each parameter to the total statistical variation of the limit state function is also quantified.
Innovative Concept of a Drilling and/or Production Platform for Operating in Arctic and Deep Water
Authors: Chou Frank , Ghosh Susobhan , Huang Kevin
Published: May 2009

A concept of an innovative floating platform using a conical structure was originally developed for operation in arctic region. It is called as MCAD (MonoCone Arctic Drilling Platform). The conical structure is used to reduce ice-loading as it facilitates ice to break in flexure while riding the slope of the conical surface. For supporting the weight of the platform, equipment, and ballast, a base structure with sufficient buoyancy is added at the base of conical structure. To ensure the platform with adequate stability, a heavy (solid) ballasting system that can be lowered to adjust the vertical center of gravity of the platform is incorporated in the system. The conceptual platform configuration has been analyzed for a large payload of more than 25,000 ST operating in approximately 125 feet of water depth. In the winter season, the platform is subjected to more than 12,000 ST of ice load. For warmer season the platform has been designed to survive a 45 feet significant wave height with 80 knots wind, and a very strong current of 6 knots. To withstand such magnitude of ice forces, mooring system using 32 lines was designed. For lower ice loads in a milder environment, the number of mooring lines can be reduced considerably. For operating in the warmer season, the platform was analyzed for design environments of operating and survival conditions. The motion responses in these conditions were found to be excellent in comparison to other deepwater concepts in use. With the promising motion response results of the conceptual platform with such a high payload, the concept is expected to provide operating company an alternative for deepwater application as well. Since the concept has been developed for a very large payload, the excess payload may be utilized as storages of produced oil. Mooring system for operating in deep water has been developed, and has been compared with that of the system for arctic condition. This paper describes the concept identifying the salient features. The effects of various features on the design and platform performance are also described. The ballast system with its lowering system makes this concept attractive for easy installation without the assistance of a large derrick vessel, a significant reduction of installation time is also expected. Results of stability, motion and mooring analyses is presented in the paper as well. Preliminary structural analyses were carried out to confirm the viability of the concept in operational, installation and survival conditions.
Hydrodynamic Performance Evaluation of an Ice Class Podded Propeller Under Ice Interaction
Authors: Liu Pengfei , Akinturk Ayhan , He Moqin , Islam Mohammed Fakhrul , Veitch Brian
Published: May 2009

Fluid-structure interaction between an ice sheet on the water surface and a podded R-Class propeller was examined and analyzed in terms of numerical simulation using a newly enhanced unsteady time-domain, multiple body panel method model. The numerical model was validated and verified and also checked against various previous in-house experimental measurements. The simulation was performed in a real unsteady case, that is, the ice piece stands still and the podded propeller moves and approaches the ice piece until collision occurs. Experimental data were taken from a previous cavitation tunnel test program for a bare R-Class ice breaker propeller under open water conditions, for the R-Class propeller approaching a blade-leading-edge contoured large size ice block under the proximity condition, and from an ice tank test program for a tractor type podded/strutted R-Class propeller under open water conditions. Comparison between experimental and numerical results was made. A general agreement was obtained. The magnitude of force fluctuations during the interaction increased significantly at the instant immediately before the impact between the propeller blades and the ice piece.
The Effect of Aircushion Division on the Motions of Large Floating Structures
Authors: van Kessel J. L. F. , Pinkster J. A.
Published: May 2009

The effect of aircushion division on the motions of large floating structures is studied by means of calculations based on a linear three-dimensional potential method. A linear adiabatic law is used to describe the air pressures inside the cushions. The water surface within the aircushions and the mean wetted surface are modelled by panel distributions representing oscillating sources. The behaviour of different types of aircushion supported structures is described and compared with that of a rectangular barge having the same dimensions. Successively, the aircushion theory, motion characteristics, wave frequency forces and moments, mean second order drift forces and surrounding wave fields are discussed. The results show that aircushions significantly influence the stability and behaviour of large floating structures.
The Effect of Aircushion Division on the Structural Loads of Large Floating Offshore Structures
Authors: van Kessel J. L. F. , Pinkster J. A.
Published: May 2009

The effect of aircushion division on the structural loads of large floating offshore structures is described and compared with that of a rectangular barge having the same dimensions. Calculations are based on a linear three-dimensional potential method using a linear adiabatic law for the air pressures inside the cushions. The water surface within the aircushions and the mean wetted surface are modelled by panel distributions representing oscillating sources. In the presented cases the structural loads include the wave induced bending moments and shear forces along the length of the structure. Aircushions significantly influence the behaviour of large floating structures in waves and consequently reduce the bending moments. The internal loads of different configurations of aircushion supported structures are described and compared with those of a rectangular barge having the same dimensions. The significant reduction of the bending moments shows that aircushion support can be of interest for large floating structures.
Ocean Energy On-Demand Using Underocean Compressed Air Storage
Authors: Seymour Richard J.
Published: May 2009

Renewable ocean energy sources are typically highly variable and uncontrolled, resulting in the production of low value electricity. Storing energy in the form of compressed air is a mature technology on land. Utilizing hydrostatic pressure at depth in the ocean to maintain constant pressure in the air supply chamber offers large recovery efficiency advantages. If salt dome caverns are not available, the design challenge is the development of a low cost bottom-founded air storage chamber.
Submarine Maneuvering Simulations of ONR Body 1
Authors: Venkatesan Ganesh , Clark William
Published: May 2009

The application of computational fluid dynamics method to the submarine maneuvering simulations of ONR Body 1 is presented. ONR Body 1 is an unclassified submarine radio controlled model with propeller and control surfaces. Unsteady Reynolds-averaged Naviers-Stokes equations of fluid flow is coupled to the six degrees-of-freedom equations of motion of a rigid body via user coding to predict the instantaneous position and body orientation. Propeller and control surface motions are accounted for by using the moving mesh feature integrated into the solution procedure which allows sliding interfaces between different mesh blocks of the computational domain (for propeller rotation), as well as mesh distortion (for control surface deflection). This offers the flexibility of using a single computational grid for the entire simulation period. The maneuvers simulated include a constant depth and heading run as well as a horizontal overshoot maneuver using conditions consistent with the experiment. Predicted results show favorable agreement with experimental measurements.
Hydrodynamic Coefficients for Riser In-Line VIV in Sheared Currents
Authors: Sidarta Djoni E. , Lambrakos Kostas F. , Larsen Carl M.
Published: May 2009

A methodology for analyzing risers for in-line VIV fatigue damage has been developed that is based on the code SHEAR7, and laboratory in-line VIV coefficients. The in-line VIV fatigue in many instances governs the design of the riser since in-line VIV starts at a reduced velocity of about 1 whereas the threshold reduced velocity for cross flow VIV is about 4. The methodology can treat sheared currents on the basis of the cross flow VIV modeling in SHEAR7. Through the SHEAR7 modeling, the methodology removes conservatism implicit in the present ad hoc procedures for calculating riser in-line VIV response on the basis of the DNV-RP-F105 code. The reduction in conservatism is due to accounting properly for the power-in region in the VIV excitation, the hydrodynamic damping, and competing modal excitation (multiple mode response). The inline VIV coefficients have been derived from laboratory tests at the Norwegian University of Science and Technology (NTNU). The paper presents the in-line VIV coefficients, and examples to demonstrate the methodology for riser in sheared currents. The coefficients derived from the NTNU tests are functions of both the in-line VIV response amplitude and the reduced velocity. The coefficients presented in the paper are scaled test coefficients. The scaling of the NTNU coefficients assures that the methodology calculates in-line VIV amplitudes that are consistent with the response amplitudes in DNV-RP-F105 for the case of a simply supported riser in uniform current. This DNV code, although written for pipelines, has been extended to risers in sheared currents on the basis of conservative approaches.
On Defining and Using the Spectrum of Driving Forces for Sailing Craft
Authors: Selness Jerry N.
Published: May 2009

The driving forces for most sailing craft for different true wind strengths and true wind courses can be derived from a single invariant expression and four ratios. Example procedures to use specific driving force curves from the spectrum therefore are shown. The invariant is an exact expression. One specific example of use for a monohull sailboat’s performance is shown. Similar uses can be done for sailing craft in general. There are practical uses and advantages for researchers and designers.
Coupled Analysis of Deepwater Floating System Including VIV in Time Domain
Authors: Rho Jun-Bumn , Korobkin Alexander A. , Jung Jong-Jun , Shin Hyun-Soo , Lee Woo-Seob
Published: May 2009

Deepwater floating systems consist of a vessel, risers, and mooring lines. To accurately simulate the floating systems in current, wind, and waves considering (1) bending and torsional stiffness of riser, (2) elongation of the mooring/riser elements, (3) complex end conditions, (4) internal flow effects, and (5) vortex induced vibration, it is necessary to evaluate the vessel motions and mooring/riser behaviors simultaneously in time domain. However, because the size of the system matrix increases significantly as the number of mooring/riser increases, it is quite time-consuming to solve all equations including both mooring/riser and vessel dynamics simultaneously. The present study was performed in order to develop a program for this problem. The 6DOF vessel dynamics is described by the Cummins equation. And the mooring and riser are modeled with the help of finite-element beam. The Newmark method is used as the time marching scheme of the FEM equations for each mooring/riser and the vessel. The coupled equations of the mooring/riser segments and vessel are solved alternatively at each time step. Mooring/riser and the vessel motion affect to each other in the way that the components of the forces at the segment ends are determined as functions of displacements and slopes of them. This procedure makes it possible to consider the coupling effects between vessel and mooring/riser efficiently. Also no iterations are required to match the vessel motion with the riser dynamics. This new approach allows us to use parallel computations and to deal with as many mooring/riser at the same time as necessary. The hydrodynamic forces induced by current are calculated by using the Morison’s formula. The VIV (Vortex Induced Vibration) effects are included in the way that the frequency and the shape of the riser vibration due to VIV are pre-calculated by iterations in the frequency domain. Then the finite element mooring/riser model is modified to consider the hydrodynamic loads including VIV and integrated in the final equations of the floating system in time domain.
The Challenges of Multiphase Flow Metering: Today and Beyond
Authors: Falcone Gioia , Alimonti Claudio
Published: May 2009

Since the early 1990’s, when the first commercial meters started to appear, Multiphase Flow Metering (MFM) has grown from being an area of R&D to representing a discipline in its own right within the oil and gas industry. The total figure for MFM installations worldwide is now over 1,800. Field applications include production optimisation, wet gas metering, mobile well testing and production allocation. However, MFM has not yet achieved its full potential. Despite an impressive improvement in the reliability of sensors and mechanical parts (particularly for subsea installations) over the past few years, there remain unresolved questions regarding the accuracy and range of applicability of today’s MFM technology. There is also a tendency to forget the complexity of multiphase flow and to evaluate the overall performance of a MFM as a “black box”, often neglecting all the possible uncertainties that are inherent in each individual measurement solutions. This paper reviews the inherent limitations of some classical MFM techniques. It highlights the impact of instruments rangeability, empirical correlations for pressure drop devices and fluids characterisation on the error propagation analysis in the “black box”. It also provides a comprehensive review of wet gas definitions for the oil and gas industry. Several attempts have been made to define “wet gas” for the purpose of metering streams at high gas-volume-fractions, but a single definition of wet gas still does not exist. The measurement of multiphase flows presents unique challenges that have not yet been fully resolved. However, the challenges are exciting and the authors have no doubts that new milestones will soon be set in this area. Today’s MFM technology has already become one piece of the optimised production system jigsaw. MFM has succeeded in fitting with other technologies toward global field-wide solutions. The ideal MFM of the future is one that provides unambiguous measurements of key parameters from which the flow rates can be deduced independently from flow regimes and fluid properties.
Ocean Storage of Carbon Dioxide: Pipelines, Risers and Seabed Containment
Authors: Palmer Andrew , Keith David , Doctor Richard
Published: May 2009

Eight hundred tonnes of carbon dioxide (CO2) are dumped into the atmosphere every second. There has been a progressive rise in the CO2 content of the atmosphere, from 270 ppm in the pre-industrial era to more than 380 ppm now, rising by 15 ppm/decade. The overwhelming scientific consensus is that this is having a large effect on climate, and that as a result the Earth’s temperature will rise by 2°C or more before 2100 [1]. Agriculture, forestry, fisheries, the biosphere and human health will all be affected, though not all the impacts are negative. The level of the sea will rise by between 0.5 and 1 m, and there is a possibility of a much greater and catastrophic rise if warming should lead to a collapse of the Greenland or Antarctic ice sheets.
A New Method of Moments for Reducing the Sampling Variability of Estimated Values of Probability Distribution Parameters
Authors: Najafian G.
Published: May 2009

Offshore structures are exposed to random wave loading in the ocean environment and hence the probability distribution of their response to wave loading is the minimum requirement for probabilistic analysis of these structures. Even if the structural system can be assumed to be linear, due to nonlinearity of the wave loading mechanism and also due to the intermittency of wave loading on members in the splash zone, the response is often non-Gaussian. The method of moments is frequently used to determine the parameters of an adopted probability model from a simulated or measured record of response. However, when higher order moments (e.g. 3rd or 4th order moments) are required for estimation of the distribution parameters, the estimated values show considerable scatter due to high sampling variability. In this paper, a more efficient form of the method of moments is introduced, which will lead to more accurate estimates of the distribution parameters by reducing their sampling variability.
Maximum Force Produced by Wind Generated Waves on Offshore Maritime Structures
Authors: Barbaro Giuseppe , Ierino` Bruno , Martino Maria Chiara
Published: May 2009

In the paper, the maximum force produced by wind generated waves on offshore maritime structures (gravity offshore platforms, space frame structures) will be calculated. For this purpose, the quasi-determinism theory of wave groups in sea states, introduced by Boccotti (2000) will be used. The results for the vertical legs of the space frame platform, obtained applying this theory, will also be compared with the new criterion proposed by Barbaro (2006) for regular waves.
Structural Integrity Management for a Large Pre-Stressed Concrete Floating Production Unit
Authors: Lanquetin Bertrand , Collet Pascal , Esteve Jose
Published: May 2009

Offshore Floating Production Units, usually deployed under long-term plan, handle the field production so they cannot be easily removed for dry-docking and repair. In order to constantly analyze and monitor the condition of the units, a tailor-made methodology has been developed and implemented since 2004 for the Integrity Management of our Floating Units currently in operation. The paper gives a description of this methodology, and then focuses on how the methodology was deployed for the large pre-stressed concrete Floating Production Unit (FPU) located offshore Congo on N’KOSSA field. This FPU is the largest existing pre-stressed concrete Floating Production Unit, built with high performance concrete, installed offshore since 1996 in 170 m water depth. She has now accumulated 10 years of production. A significant part of the methodology is based on a full Finite Element Model (FEM) with non-linear analysis capacity for the concrete structure, incorporating a description of passive and active steel. There is often an anchored perception that a concrete unit is something not requiring attention once installed. This paper shows otherwise, underlining the complexity of modeling the highly non linear characteristics of pre-stressed high performance concrete and degradation modes.
Time Domain Riser VIV Predictions Compared to Field and Laboratory Test Data
Authors: Cheng Yongming , Lambrakos Kostas F.
Published: May 2009

The time domain code ABAVIV has demonstrated the ability to reproduce basic features of riser vortex induced vibration (VIV). The VIV response of risers is a transient phenomenon. Consequently, time domain computer codes have a better basis in principle than frequency domain codes to model and predict the riser VIV response. Frequency domain codes have been used extensively by the offshore industry to calculate riser VIV response and to design risers for VIV fatigue. These codes have been successful in riser design by making conservative assumptions in modeling the VIV phenomenon and by using large safety factors. This paper shows comparisons of ABAVIV predictions to two sets of data — one from laboratory tests and the other from field tests. The laboratory tests were performed at the Imperial College with a smooth riser model. The field tests were performed as part of the DeepStar program and were carried out offshore Miami, Florida, with a riser model hanging from a moving boat. In the DeepStar tests, the current direction varied with depth, and wave flow was present along with the current. The tests included both smooth and straked riser models. The data from these tests demonstrated the transient character of the VIV response and the strong presence of higher harmonics. All available frequency domain codes lack the ability to model and predict the higher harmonic response. The paper will show that ABAVIV has the capability to model the higher harmonics of the VIV response with appropriate modifications in the lift force model.
Extreme Responses of Bilinear Stiff Systems
Authors: Alford Laura K. , Wozniak Chris , Troesch Armin W.
Published: May 2009

A single-point mooring system is modeled as a bilinear-stiff system. Long-term statistics of the nonlinear mooring system are estimated by Monte Carlo computer simulation. In an effort to generate an extreme event in a short time period (as opposed to lengthy Monte Carlo simulations), an equivalent linear system is devised along with an excitation designed to elicit a large, linear response. This design wave and the resulting system excitation are used in simulations to generate both the design nonlinear and equivalent linear responses.
A Novel 6DOF Rigid Connector for Large Floating Platforms
Authors: Han Henry Lei
Published: May 2009

This paper addresses key practical issues in joining modular pontoons for constructing large floating platforms in rough seas. Five fundamental requirements for an ideal pontoon connector design are summarized to be self-alignment, impact attenuation, rigid engagement, self-tensioning and adequate strength. Nine relevant patents on pontoon connector designs are reviewed based on the 5 requirements. A novel design concept of floating platform securing device (connector) is introduced, which consists of Fender Connector [11] and Frictional Locking Connector [12]. The new connector concept integrates the five functions into one compact connector design. The design concept, working model, product prototyping and testing are presented. The performance and benefits of the connector are illustrated. The current and future developments are discussed. The potential applications are exemplified.
Case Studies on ECA-Based Flaw Acceptance Criteria for Pipe Girth Welds Using BS 7910:2005
Authors: Cheaitani Mohamad J.
Published: May 2009

The use of an engineering critical assessment (ECA) approach to derive flaw acceptance criteria for pipe girth welds has become common practice. It allows the maximum tolerable size of weld flaws to be determined on a fitness-for-purpose basis, offering substantial advantages over the conventional workmanship approach. BS 7910:2005 is widely used to derive ECA-based flaw acceptance criteria for pipe girth welds. It offers a flexible assessment framework within the context of the well-established failure assessment diagram (FAD) approach. However, it can be relatively complex to apply and it may lead to assessments that are more conservative than codified pipeline-specific procedures. This paper illustrates, through practical case studies on assessing the significance of circumferential girth weld flaws, some of the options available to the user of BS 7910. The case studies cover the selection of the FAD (generalised or material-specific, with and without yield discontinuity), tensile properties (specified minimum or actual values); fracture toughness properties (single point CTOD values including δ0.2BL and δm, or full CTOD resistance R-curve), and welding residual stress (assumed to be uniform through the pipe wall with a yield strength magnitude, or considered to have a through-wall distribution associated with a specific level of welding heat input).
The Effect of Magnetic Fields on Corrosion in Pipeline Steel
Authors: Jackson Joshua E. , Lasseigne-Jackson Angelique N. , Olson David L. , Mishra Brajendra , Heilig Meredith S. , Collins Jenny K.
Published: May 2009

Measurements performed in earlier research have indicated a strong effect of magnetization on hydrogen content (thermodynamics) as well as cracking, and pitting (kinetics) in pipeline steels as described in Sanchez (2005) and Sanchez et al. (2005). The effect of cold work, further increasing hydrogen content, cracking, and pitting, was also assessed. Theoretical descriptions of both thermodynamic and kinetic interpretations of the observed effect is described and correlated to observed results. There are two ways that electromagnetic current influences corrosion: (1) D/C currents (under applied or Remanent magnetic fields) and A/C electric currents (which create electromagnetic fields through Lenz’s Law) may influence magnetocorrosion as described in this paper, and (2) A/C currents also have the potential to strip the protective passive layer from materials and greatly accelerate corrosion. Electrochemical charging is currently being performed at varied magnetic field strengths to assess the nature of the observed influence of magnetization on both hydrogen content (thermodynamic) and cracking/pitting (kinetic), including the role of controlled-roll cold working. Naval and maritime use of A/C and D/C electric-powered systems including propulsion drives, servos, and controls, is increasing rapidly in sea-going operation and potential for stray currents is an increasing risk. Magnetic flux leakage inspection, using saturating magnetic fields, is widely used for reliable and accurate inspection of pipeline corrosion and wall thickness. Previous laboratory research shows a significant increase in both pipeline steel hydrogen content in steel and pitting and cracking after electrochemical hydrogen charging under an applied two Tesla magnetic field. Cold work was observed to further increase the observed effects. The thermodynamic auxiliary functions, using a derivation of Helmholtz free energy, are examined to assess the thermodynamic effects of magnetization on hydrogen content. The effect of magnetization on the thermodynamics of electron spin configurations, interstitial solute-induced strain, magnetostriction (directional strain induced in steel from an applied magnetic field) are considered. Kinetic interpretations of possible interactions with the Helmholtz Double (capacitor-like) Layer and the Gouy-Chapman (diffuse) layer that may lead to increased diffusion and thus to hydrogen supersaturation are described. Electrochemical impedance measurements are being performed to assess the influence of applied magnetic fields on the Helmholtz and Gouy-Chapman layers.
Phenomena Observed in VIV Bare Riser Field Tests
Authors: Marcollo Hayden , Chaurasia Hemant , Vandiver J. Kim
Published: May 2009

The following paper presents the results of preliminary data analysis performed on a densely instrumented bare riser undergoing Vortex-Induced Vibration (VIV) response at high mode number. The data analysis steps are presented and show a method whereby it is possible to resolve uncertainty in the orientation of strain gauges on a riser responding to VIV. Two new phenomena are then revealed from the data analysis. The first is the occurrence of higher harmonic VIV response in directions which are not orthogonal to the cross-flow and inline directions. Secondly, evidence of riser structural response in the form of wave propagation is observed.
Offshore Wind Turbine Foundation: The COWI Experience
Authors: Thomsen Jo̸rn H. , Forsberg Torben , Bittner Robert
Published: May 2009

This paper presents the experience gained and the lessons learned over the last decade within the numerous offshore foundation projects undertaken by COWI in European waters. This experience derives from the close collaboration with, and interaction between the owners, contractors, and engineers in the various stages of project development. In turn, the experience draws on COWI’s vast experience within foundation of large bridges world wide over half a century. Focus is on two pioneering gravity base foundation projects: • Nysted in Denmark, currently the largest offshore windfarm worldwide with 72 Nos Bonus 2.3 MW turbines in water depths up to 10 m in the relatively benign inner Danish waters. • Thornton Bank in Belgium, where the first phase — comprising 6 Nos REpower 5MW-turbines of a total of 60 — are planned to be built in the rough North Sea in water depths exceeding 25 m. The two projects illustrate the speed at which the structural concept must keep pace with increases in turbine size. The projects exemplify how a tailor made design is made fit for purpose. The latter case uses state-of-the-art designs for thin-walled reinforced concrete shell structures.
Stress Concentrations Factors in Welded Tubular Sections and Pipelines
Authors: Lotsberg Inge , Holth Per Arvid
Published: May 2009

In this paper analytical expressions for stress concentration factors in pipes subjected to internal pressure and axial forces are presented based on classical theory. This includes longitudinal butt welds in pipes made during production of the pipes and circumferential welds that can be made during pipe lying. It also includes pipes welded together from sections with different thicknesses. The effect of fabrication tolerances in simple butt welds is assessed. Analyses based on classical mechanics are compared with results from axisymmetric finite element analyses for verification of the presented methodology. Larger pipes are fabricated from plates with a longitudinal weld. This fabrication process introduces cross-sectional out-of-roundness in the pipes. An analytical expression for the bending stress in the pipe wall due to this out-of-roundness is presented.
Material Challenges in Arctic Areas
Authors: Horn Agnes Marie , Kvaale Per Egil , Hauge Mons
Published: May 2009

There is a lack of rules and standards that provide guidelines for material selection and qualification of materials for offshore and onshore structures in arctic areas. Many current standards for low temperature applications such as cryogenic piping and process systems do not reflect the need for low-cost bulk materials for large volume applications such as pipelines and production facilities. The growing focus on oil and gas exploration in arctic areas has raised the need for new standards and industry practice that supports cost effective and safe installation and operation of production and transport facilities in the cold climate. There are materials today that are applicable for low temperature conditions. The grades are often highly alloyed (typically 3–9% Ni) with good toughness properties, but these alloys are expensive compared to conventional steel material grades. Such materials may not be applicable in pipelines, structures and process plants. This challenge can be met in two ways. First, structural steels that are capable of being welded and operated in the cold climate should be developed and qualified. Second, materials for forged and casted components that can be welded to the structural steels should be developed and qualified to fit into the integrated structure or pipeline system. Some actions have been taken to develop new standards e.g. within ISO19906, and actions are being taken in Russia to harmonize their specifications with the international standards, but this is a comprehensive job and the work must be executed in parallel with the development of new steels and welding technology.
Friction Considerations in Rotary Shouldered Threaded Connections
Authors: Teodoriu Catalin , McDonald Herschel , Bollfrass Charles
Published: May 2009

The new connection designs introduced by the drill pipe manufacturers (double shoulder connections, intelligent drill pipes or any new design for increased torque resistance) make the use of the Farr formula for calculating proper assembly torque more problematic. Additionally, severe drilling conditions like HPHT, directional drilling and extreme environments are affecting critical thread compound performance properties, which can make it impossible to attain the optimum makeup torque for the connection. The new drilling conditions are exposing the drill string components to higher loads and consequently reduce the safety margins. Since the makeup process is the only way to control and achieve the maximum tool joint loading capacity, it becomes important to understand the effect of friction on optimum makeup torque calculation. This paper presents a modified equation for optimum makeup torque calculation by using the latest research on thread compound frictional properties. Also, the thread compound lubrication mechanism will be explained. For the first time the thread turn load will be related to the optimum makeup torque. The paper will also explain why there is a need for a new API standard for determining thread compound frictional properties. The formula developed herein, based on experimental results, demonstrates that the newly introduced overall factor may differentiate between used and new connections.
Development of Gulf of Mexico Deepwater Currents for Reference by API Recommended Practices
Authors: Cooper Cortis K. , Stear James D. , Mitchell Douglas A. , Wang Wensu , Driver David B. , Heideman John , Vogel Michael
Published: May 2009

The metocean conditions contained in the 21st edition of API RP2A, last updated in 1993, are in the process of being revised to account for: the effects of recent major hurricanes, the shift of production to deeper water, and improvements in our understanding of metocean conditions in US waters. As the Oil Industry has moved into the deeper Gulf of Mexico waters, it has become exposed to strong currents generated by the Loop Current, its associated eddies, and by topographic Rossby waves. This paper describes the basis for the draft extreme conditions we have developed for these strong deepwater ocean currents. Further work is underway to develop conditions for extreme near-bottom currents on the continental slope and for joint hurricane-Loop currents. Once accepted by API, the conditions will ultimately be published as part of a stand-alone API recommended practice (RP) which will in turn be referenced by other API recommended practices such as those addressing shallow-water fixed platforms, jack-ups, deepwater platforms, and floating MODUs. The Metocean RP will also include hurricane-generated conditions the development of which is documented in a separate paper (Berek, et al. 2007).
Investigation of Directional Spreading of Waves in Relatively Shallow Water
Authors: Rego Vale´ria S.
Published: May 2009

The directional spreading of waves is investigated for relatively shallow water (20m depth) wave data, collected with acoustic current profilers, along the Atlantic Coast of South America. Values for the wave kinematics or wave spreading factor, recommended by API and ISO for reduction of in-line particle velocities and accelerations under waves due to directional spreading, are calculated in order to allow judgement of approximate values that can be used in shallow water regions for practical design applications.
Study of the Wave Drift Damping for a Very Large Crude Carrier
Authors: Sales Joel S. , Matos Vinicius L. F. , da Silva Andre R. , Matter Ge´rson B. , Sphaier Sergio H.
Published: May 2009

Pull-out test and decay tests in still water and in waves for the surge motion of a VLCC in ballast condition are carried out at LabOceano. The pull-out test associated with the mean drift displacement in regular waves is used to determine mean drift force. From the decay tests the damping coefficients are adjusted using the Froude energy method and the procedure based on the logarithm decrement. For the decay test in waves, the response is subdivided in the mean drift contribution, the regular wave response and the transient response. The wave drift damping is considered as an increase on the linear damping in still water. So, we introduce an additional damping to the linear part of the damping coefficient in still water and simulate the decay test in waves. Comparing the results from the simulation with the experiments the wave drift damping contribution is adjusted. Finally, the mean drift results are compared with the results obtained with the potential theory. The wave drift damping coefficients obtained from the experiments are compared with coefficients obtained with a formulation proposed in the literature.
Vortex-Induced Vibration and Coincident Current Velocity Profiles for a Deepwater Drilling Riser
Authors: Srivilairit T. , Manuel L.
Published: May 2009

The objective of this study is to use full-scale field data on current velocities and riser motions to better understand the behavior of deepwater drilling risers. The data are comprised of riser accelerations and coincident current velocity profiles from the monitoring of vortex-induced vibration (VIV) of a drilling riser located at a 1,000-meter water depth site. Proper Orthogonal Decomposition (POD), an efficient numerical technique for characterizing the spatial coherence in a random field, is employed here to identify energetic current profiles. The accuracy resulting from the use of only a limited number of the most important POD modes is studied by comparing measured current velocity profiles with those reconstructed based on a reduced-order truncation. In addition to studying current velocity profiles, riser acceleration data from this deepwater drilling riser are also analyzed. In order to analyze the VIV response of this riser, in-line and cross-flow motions in different data segments are studied. Again, empirical POD procedures are employed—this time to derive energetic spatial vibration modes defining the riser motion. The relationship between riser response and coincident current velocity profiles is investigated, especially for those data segments associated with observed lock-in response.
Fatigue Design Data Derived From Full Scale Tests on 6”OD Pipe Girth Welds
Authors: Haagensen Per J. , Knagenhjelm Hans Olav , O̸rjasæter Oddvin
Published: May 2009

A literature survey of high quality girth welds intended for pipelines risers was carried out and the results are compared with full scale resonance fatigue test data on 6” pipes. The samples were made from 168.3×9.9mm (OD×WT) seamless pipes, each having two welds. Axial misalignments (hi-lo’s) and lack of penetration (LOP) defects were introduced in the test pipes to study the effects on the mean minus 2 stand, deviation design S-N curve that was calculated. Post failure examination of the welds was performed to determine the type and size of defects in the failure initiation area. Fracture mechanics calculations were carried out to determine the effect of defects on fatigue life. The test results were compared with published data on 6” pipes with high quality welds. The scatter in the fatigue test data was reduced when comparisons were based on the local stress at the point of fracture initiation. The implications for design rules of the findings in this work are discussed.
Experiences From Welding and AUT of the 15” Norne Clad Pipeline Installed With the Reeling Method
Authors: Haabrekke Tore , Ba¨rs Guy , Kvaale Per Egil , Ro̸rvik Gisle
Published: May 2009

The Norne Satellite project (Statoil) in the Norwegian Sea involves a 9 km long 15” insulated clad steel production pipeline. The line pipe is longitudinally welded SAWL joints of 12m length, with 21mm backing steel (X60) and 3mm metallurgically bonded 316L CRA internally. To prevent waxing of Hydrocarbons during shut downs, use of chemicals has been used to a large extent in this industry. Norne has another philosophy to avoid waxing as the pipeline was installed with a power cable strapped to the coating in a piggy-back solution. This is the “Direct Electrical Heating” solution Statoil has implemented to their pipelines with great success in other projects. The pipeline was installed with the reel ship “CSO Apache” in 2005. It is the first time that a cladded pipeline has been installed with the reeling method. This paper presents experiences from fabrication of the clad steel pipeline. The production welding was performed with a combination of manual and mechanized welding to maintain the CRA integrity and at the same time have an acceptable production rate. The subsequent NDT method was performed by automatic UT (AUT). AUT on cladded pipelines has never been used before and was introduced after a comprehensive study to find a reliable way of detecting and sizing defects in welds with a combination of Austenitic and Ferritic structures.