bluuebunny/crossref_metadata_2025_split huggingface dataset:
Fatigue Life Assessment of Single Layer 60512 PVDF Barrier in Unbonded Flexible Risers
Authors: Fernando Upul S. , Davidson Michelle 
Published: October 2015

The polymeric barrier is one of the key components in a flexible pipe, the sound function of which is essential for the containment of the transported medium, ensuring no leakage to the environment which could result in undesired consequences. According to API 17J the barrier design must be able to sustain certain static and dynamic strain conditions however; the actual design or the fatigue assessment of the barrier is not covered within the standard. Since the barrier is subjected to the same dynamic loading as the pipe the durability and integrity of the barrier is a key issue that needs to be addressed during barrier design for dynamic risers. This paper discusses a fatigue life assessment procedure for a barrier made of copolymer Grade 60512 PVDF.
A flexible pipe barrier is manufactured by continuous extrusion of polymer onto a metallic carcass. The carcass has a spiral structure with an irregular outer profile. As such, the extruded polymer on this irregular surface inevitably gives non-uniform thickness and geometric anomalies where the polymer has flowed into gaps in the carcass. During pipe loading such anomalies act as stress concentrations and become critical locations for fatigue crack formation. The evaluation of the effect of the barrier profile shape on the fatigue durability of the barrier is therefore an essential requirement, in particular, in cases where the barrier consists of a single extruded polymer layer.
Within the procedure outlined in this paper, the fatigue assessment of the barrier is made using the local plastic strain behaviour. The maximum stress concentration factor and the acceptable profile for the extruded barrier are selected to provide adequate safety margins for the project specific loading conditions. A procedure has been proposed to predict the local plastic strain of the barrier using global service loading data.
Effect of Epoxy Filling in End Fitting on the Integrity of Flexible Pipes: With Reference to Suncor Terra Nova Flowlines
Authors: Fernando Upul S. , Roberts Andrew , Karabelas George 
Published: October 2015

Two flowlines installed in the Suncor Terra Nova riser replacement programme were found to leak during leak tests performed after site installation. No hydrocarbon loss was suffered nor was there any pollution incident; however the scheduled production start-up for the pipes was delayed. Investigations confirmed that the leaks in both pipes occurred due to a crack in the polymer (PVDF) barrier within the end fitting region of the pipe. It was also concluded that the crack in the barrier in these pipes occurred either during the transportation or installation of the pipes in the field due to thermo-mechanical loading on the pipe during this period. Both failures were found to have initiated from a void in the epoxy which was used to fill small clearances within the end fitting.
This paper describes the finite element stress/stain analyses performed to investigate the effects on the PVDF barrier and epoxy within the end fitting due to the thermal and mechanical loading encountered during pipe installation. A multi-scale modelling approach has been used where a full pipe with detailed end fitting components was modelled in a coarse mesh model whilst the stress-strain behaviour near epoxy void was analysed using a macroscopic sub-model. A brief description of the models and the results are presented.
The analyses involved predicting the barrier deformation response at the failure location under the anticipated thermo-mechanical loading exerted on the pipe. The results have shown that the failure occurred due to the presence of the void in the epoxy at a critical location; cooling of the pipe during its transportation was considered to have created the thermo-mechanical loading to drive the crack from the epoxy into the PVDF. It was concluded that the failure in the pipes would not have occurred if either the void was not present in that critical region in the epoxy, or if it had not been subjected to the thermo-mechanical loading. A design change removing the filling of epoxy in the end fitting process is being implemented to prevent this failure in the future.
Risk Based Structural Integrity Assessment of LNG FPSO
Authors: Yeun Dong-Yun , Jang Chang-Hwan , Jun Seock-Hee , Oh Yeong-Tae 
Published: October 2015

As the importance of the risk based structural integrity assessment for offshore installations against the accidental loads is more emphasized, the structural engineering activities are essential for shipyards. Especially, in case of EPC (Engineering, Procurement and Construction) being performed by shipyards, more attention should be paid to the risk based structural integrity assessment in case that the results may have an unexpected impact on design and the associated procurement.
This paper introduces a procedure for the risk based structural integrity assessment which is established by DSME and the actual application to the world’s first LNG FPSO project for ship collision, dropped objects and explosion.
A Simulation-Based Decision Support Tool for Arctic Transit Transport
Authors: Schartmüller Bernhard , Milaković Aleksandar-Saša , Bergström Martin , Ehlers Sören 
Published: October 2015

The Russian Federation attempts to foster the Northern Sea Route (NSR) as a transport alternative to the current Suez Canal Route (SCR). Therefore, this paper seeks to identify under which conditions the use of the NSR is economically feasible. To evaluate this in a realistic way it is essential to take the significant uncertainty of input variables like ice data predictions into account. For that reason a simulation-based decision-support (SBDS)-tool based on a discrete-event simulation model is developed.
The SBDS-tool requires as input vessel dimensions, available power and information about the route(s) including waypoints and ice data. It calculates then the general performance of the vessel in both open water and ice. Next it generates day-specific ice conditions according to a probability distribution between lower and upper limit obtained from satellite measurements. Based on this and the previously calculated vessels’ performance the SBDS-tool calculates day-specific transit times and fuel consumptions for examined time period. This is then used as input for a discrete-event simulation to assess the number of roundtrips, transported cargo and fuel consumption for joint use of different routes, dependent on the predefined operational days along the routes. The obtained results are then used to calculate the cost per transported cargo unit between two ports and to assess the sensitivity in order to determine if an economically advantageous and robust transport system can be achieved. In addition, possible economy of scale effects using larger vessels can be evaluated.
In order to show the applicability of the developed model a comparative case study for three container vessels operating between Rotterdam (NL) and Yokohama (JP) is carried out.
Wellhead Fatigue Damage Based on Indirect Measurements
Authors: Grytøyr Guttorm , Coral Fredy , Lindstad Halvor Borgen , Russo Massimilliano 
Published: October 2015

Enabling safe and reliable operations of subsea wellheads has a high priority in the global oil and gas industry. The objective of the current paper is to provide a novel method for bending moment estimates at the wellhead based on indirect moment measurements; this moment, together with fatigue properties are then used for fatigue damage estimation. Indirect bending moments are based on inclinations and accelerations measured by motion reference units (MRU) attached to blowout preventer (BOP), lower marine riser package (LMRP) and lower riser joint (LRJ) immediately above the lower flexible joint (LFJ). Also, required is the tension time history in the same period at the LRJ. The proposed methodology here can be implemented and integrated into a portal for data acquisition and visualisation.
In order to validate the proposed method for indirect bending moment estimation, strain gages have been attached to a BOP and marine riser during drilling operations offshore Norway. Strain gage readings are transformed to bending moment which is used as reference (the so-called direct moment). The proposed method is used to calculate the moment indirectly, the so-called indirect moment. The resulting indirect moments agree very well with the direct moments.
ECAs, FE and Bi-Axial Loading: A Critique of DNV-OS-F101, Appendix A
Authors: Cosham Andrew , Macdonald Kenneth A. 
Published: October 2015

Controlled lateral buckling in offshore pipelines typically gives rise to the combination of internal over-pressure and high longitudinal strains (possibly exceeding 0.4 percent).
Engineering critical assessments (ECAs) are commonly conducted during design to determine tolerable sizes for girth weld flaws. ECAs are primarily conducted in accordance with BS 7910, often supplemented by guidance given in DNV-OS-F101 and DNV-FP-F108. DNV-OS-F101 requires that finite element (FE) analysis is conducted when, in the presence of internal over-pressure, the nominal longitudinal strain exceeds 0.4 percent. It recommends a crack driving force assessment, rather than one based on the failure assessment diagram. FE analysis is complicated, time consuming and costly. ECAs are, necessarily, conducted towards the end of the design process, at which point the design loads have been defined, the welding procedures qualified and the material properties quantified. In this context, ECAs and FE are not an ideal combination for the pipeline operator, the designer or the installation contractor.
A pipeline subject to internal over-pressure is in a state of bi-axial loading. The combination of internal over-pressure and longitudinal strain appears to become more complicated as the longitudinal strain increases, because of the effect of bi-axial loading on the stress-strain response.
An analysis of a relatively simple case, a fully-circumferential, external crack in a cylinder subject to internal over-pressure and longitudinal strain, is presented in order to illustrate the issues with the assessment. Finite element analysis, with and without internal over-pressure, are used to determine the plastic limit load, the crack driving force, and the Option 3 failure assessment curve. The results of the assessment are then compared with an assessment using the Option 2 curve. It is shown that an assessment based Option 2, which does not require FE analysis, can potentially give comparable results to the more detailed assessments, when more accurate stress intensity factor and reference stress (plastic limit load) solutions are used.
Finally, the results of the illustrative analysis are used to present an outline of suggested revisions to the guidance in DNV-OS-F101, to reduce the need for FE analysis.
Testing of Full Scale Composite Journal Bearings for Offshore Underwater Applications
Authors: Dragt R. C. , van den Heuvel W. , Gelinck E. R. M. , Slot H. M. 
Published: October 2015

In the offshore industry, fibre reinforced sliding journal bearings are increasingly used due to their low-maintenance and self-lubricating characteristics. To be able to use the bearings in the rough offshore environment, under heavy loading, full scale tests are essential to assess the friction and wear rate development during use. For this purpose, two full scale wear tests were performed on composite sliding journal bearings of 300 mm in diameter. These tests were performed at the laboratory of TNO Structural Dynamics in Delft, The Netherlands, over a period of eight months.
For this purpose, a test rig was designed in which a shaft runs through the journal bearing. The latter is loaded in the range 50 to 700 kN and the shaft is given triangle-like cyclic displacements. To be able to test under realistic conditions, the bearing is constantly submerged in flowing seawater. Forces, displacements and temperatures were constantly monitored to manage the system and determine the parameters.
Besides a description of the test rig, a rationale of choices made, observations during testing and detailed cycle-by-cycle friction characteristics are presented, next to generalized trends for the wear and Coefficients of Friction (CoFs) under the various loading conditions.
Effects of Third-Order Nonlinearities on the Fourier Representation of Deterministic Wave Trains
Authors: Alford Laura K. , Maki Kevin J. 
Published: October 2015

The accurate estimation of extreme responses for offshore platforms and supply vessels is critical to the design process. Long time Monte Carlo-type simulations can theoretically capture extreme responses, but this type of simulation is not feasible in the early design process due to the extreme computational expense. An alternative is to use shorter simulations that are tailored to create statistically equivalent extreme responses. The latter requires judicious specification of expected extreme sea conditions.
Extreme responses can be estimated using a variety of processes, including the Design Loads Generator (DLG). Assuming a vessel response is Gaussian, stationary, and ergodic, a given response can be approximated as a sum of Fourier amplitudes with random phase angles. The DLG is a process that can calculate innumerable sets of random phase angles that result in a given extreme response or design event. Using linear-systems theory, the corresponding incident-wave phase angles are calculated from the response phase angles and the incident-wave-train profile is determined.
A fundamental question that must be answered is how can a nonlinear seaway that produces an extreme event be described such that a wave maker or numerical wave boundary condition be controlled to recreate the nonlinear and extreme seaway. A common practice employs linear wave theory to shift the design event in space and time. The shifted phase angles can then be used to drive a wavemaker with the intent of producing the desired wave train at a given point. However, nonlinearities in wave propagation result in an inaccurately generated design wave train. This paper focuses on the role of wave nonlinearity in the evolution of the wave system and how this can be accounted for in the control of a physical or virtual wave maker.
Measured Wellhead Loads During Drilling Operations: Paper 1 — Data Processing and Preliminary Results
Authors: Russo Massimiliano , Wolak Urszula , Myhre Erling , Grytøyr Guttorm 
Published: October 2015

The growing size of BOPs, longer drilling campaigns on wells, and operations in harsher environments has resulted in increased challenges in properly documenting wellhead fatigue during planned or executed drilling operations. The industry has started directing its efforts toward the calibration of analytical tools which are typically adopted for predicting wellhead fatigue. The ultimate goal for achieving this ambitious scope is to identify a benchmark set of analytical results that will predict field measurements. Early on Statoil identified a major obstacle: the absence of a good and comprehensive dataset of field measurements to serve as point of reference. Statoil and Aker Solutions cooperated on a pilot project with the intent of collecting a dataset of full scale measurements during drilling operations to be used to validate and calibrate the theoretical wellhead fatigue calculation methodologies. The main objective of the instrumentation campaign was to measure sectional forces as close as possible to typical wellhead hotspots by the use of three sets of strain gauges installed on the outside surface of the conductor and on the outside of the surface casing. With the objective of collecting an exhaustive dataset of measurements, accelerometers and inclinometers were installed on the BOP, the riser adapter, the riser below the upper flex joint and on the rig. An additional set of six strain gauges was installed on the riser to record riser tension variations. Environmental conditions were logged on board the rig and by the hindcast data provider. Operational events were carefully logged. This paper presents the following:
• Data processing used for quality assurance and calibration of the measured data and the associated data challenges
• Highlights of the instrumentation system capabilities to capture salient events of a typical drilling campaign and of ad-hoc performed rig operations to calibrate and validate the measured data
• Effect of a controlled rig cross motion test, performed to evaluate quasi static loads on the well and calibrate strain gauge sensor orientations
• A riser pull test, performed to validate strain gauge functioning
• Several landing and disconnecting of the LMRP
• Manipulation of the preload between the high pressure housing and the low pressure housing to investigate the effect of the preloading on the load sharing between the casings
Since King and Soloman [2], the industry is still lacking quality field data to be used in order to validate the various analytical models used in the analyses of subsea conductor and wellheads. The results will confirm the quality of the measured data and will represent a first data point of comprehensive measured field data. This data will be used for future required work in calibrating the different building blocks pertaining to the analytical tools dedicated to well head fatigue predictions [3].
Validation of Volterra Series Approach for Modelling Parametric Rolling of Ships
Authors: Somayajula Abhilash S. , Falzarano Jeffrey M. 
Published: October 2015

Parametric motion is the phenomenon where a structure is excited into large amplitude motion even when there is no direct excitation. A well-known example of this type of motion is the parametric roll of ships in head or following seas. Parametric roll of container ships in head seas is relatively a new problem which has gained much importance after the catastrophic incidence of APL China in 1998. Although a lot of analytical techniques are available on the assessment of parametric roll in regular excitation, not many investigations have explored its occurrence in irregular seas. A consensus on the stability criteria to assess the danger due to this phenomenon in actual ocean has not yet been reached making it an active area of investigation.
A precursor to the development of stability criteria is a simple model to capture the phenomenon of parametric rolling. However, it is important that the model is not over simplified and ignores important dynamics of the process. Therefore it is necessary to perform validation studies between the simplified model and the complete nonlinear model capturing all the physics of the phenomenon.
This paper provides the validation studies of a 1-DOF (degree of freedom) simplified model for roll motion against a standard 6-DOF time domain simulation approach. The 1-DOF model is based on the Volterra series representation of the hydrostatic stiffness in waves while accounting for the heave and pitch motions of the model. It also includes a nonlinear damping model capturing the radiation and the viscous damping. The 6-DOF model solves for the nonlinear equations of motion based on Euler angles and also includes the nonlinear Froude Krylov excitations and nonlinear hydrostatic forces on the vessel. Details of the modeling in the two approaches are described and comparisons are performed to assess the validity of 1-DOF simplified model.
A Revised Methodology for the Calculation of Wellhead Fatigue due to VIV
Authors: Williams Dara , O’Hara Niall , Dunne Kenneth 
Published: October 2015

In regions of high current velocity such as East Africa, South America and the GoM, VIV (Vortex Induced Vibrations) of drilling riser systems is a very real risk. Much work has been carried out by the offshore industry in order to predict the VIV and resultant fatigue in top tensioned production and drilling risers and to develop standardized methodologies for performing these calculations. In addition a number of commercially available VIV analysis tools have been developed over the years. These VIV analysis tools and industry methodologies however, are focused on the global response of the riser string alone and have not been developed to account for the intricacies of wellhead loading & stress distributions. VIV response of the top tensioned riser (TTR) system (whether production TTR or drilling riser) results in load transfer into the wellhead via VIV induced motions. As commercially available VIV analysis tools generally only consider a riser model consisting of a slender beam, the more complex geometry and load path associated with the wellhead and conductor are not accurately modeled. Thus VIV induced damage of the wellhead cannot be predicted with confidence using these VIV analysis tools alone.
Based on a review and critique of both existing and proposed methods it has become apparent that existing methods for the calculation of VIV induced fatigue of the wellhead and conductor system are overly conservative and do not capture the level of detail required to predict the level of fatigue damage with confidence. Thus a revised methodology for calculation of wellhead and conductor fatigue due to VIV is required to build up a more representative picture of the associated fatigue damage accumulation. Proposed VIV fatigue calculation methodologies, including the use of VIV analysis tools alone and application of the results of the VIV analysis tools in combination with non-linear global finite element models, are described and the challenges associated with each are discussed herein.
Carcass Tearing in Flexible Pipes
Authors: Hansen Rasmus , Lyckegaard Anders , Cappeln Christian , Mcgeorge Dag , Sødahl Nils , Bendiksen Erik 
Published: October 2015

This paper presents a novel model of carcass tearing in flexible pipes. The model is based on a simple parameterization of the pipe design in terms of isotropic layers, together forming the composite pipe structure. The model allows evaluations of interfacial shear stresses between the inner pipe layers, as well as axial normal stress and strain levels in response to gravitational and thermal loading.
Interfacial slip of a given interface, i.e. axial sliding of adjacent layers relative to each other, is accounted for by introducing a maximal possible value of the interfacial shear stress for a given interface, amounting to a static friction capacity. The model shows how a cut-off of the shear stress at the shear stress capacity implies an interfacial slip, which is followed by a significant increase in axial strain of the carcass layer.
Detailed quantitative results of the model are presented for a particular 11.5 inch K-carcass riser design. In order to improve engineering practice, an analytical expression of the governing shear stress is derived in terms of the gravitational and thermal loads. This analytical expression is easily applied for particular design evaluations.
The model directs attention to critical design parameters related to the carcass tearing failure mode and thereby supports continued safety in the design and operation of flexible pipes from a carcass tearing perspective.