James Wang

Advanced Numerical and Analytical Tools for J-Tube Pull-In Through Multiple Bends

J-tube pull-in is a conventional riser installation method used for connecting pipelines to offshore platforms. In general the J-tube pull-in analysis is performed either using simplified analytical models or finite element method. Finite element (FE) tools become more important for the scenarios with complicated J-tube design, because of its flexibility in adapting material properties, 3D geometry, and multiple bends.Conventional FE models employ tube-to-tube contact elements (ITT elements in Abaqus) to model the contact between J-tube and riser, where both J-tube and riser are all modeled as beams. In this paper, a new FE model is developed that modeled the J-tube as a surface. The new model was benchmarked with the conventional ITT element model and shows a better performance in terms of convergence speed using a simple geometry. The new model was further applied to a 3D multiple bends J-tube application. The impacts from J-tube size, J-tube bend radius, number of bends, and material yield strength were also studied. The outcome of this analysis provides guidance for effective and reliable J-tube pull-in studies.Copyright

The Span Mitigation Analysis With Use of Advanced FEA Modeling Techniques

Spans occur when a pipeline is laid on a rough undulating seabed or when upheaval buckling occurs due to constrained thermal expansion. This not only results in static and dynamic loads on the flowline at the span section, but also generates vortex induce vibration (VIV) which can lead a fatigue issue. The phenomenon, if not predicted and control properly, will result in significant damage to the pipeline integrity, leading to expensive remediation and intervention works. There are various span mitigation methods in use for both over stressing and fatigue concerns. The mitigation methods, if not analyzed properly, may result in much unnecessary work or generate more problems or concerns in the future. The mitigation analysis can become very challenging due to many restrictions in the field such as the minimum and maximum heights or lift of mechanical supports or grout bags, and bearing capacity vs. cost of supports. The cost of different mitigation methods and their interactions are the other considerations along with the installation tolerances, challenges associated with the water depth and uncertainties in seabed properties. This paper describes the latest developments in use of finite element analysis to investigate associate mitigation solutions given the governing practical limitations and cost factors. The ULS and fatigue lift criteria are used as the guidelines. The methods presented within this paper are applicable for various span conditions. Conclusions are then drawn to the impact of these various scenarios so that the pipeline integrity can be assured with confidence.Copyright

An Efficient Field Assessment of Offshore Pipeline Damage

An offshore pipeline may experience overstress due to improper installation, an accident or other unplanned incidents. An assessment of potential damage in the pipeline is important, since it allows operators to determine whether the pipeline can operate under planned conditions, reduced conditions or must be repaired, which may have significant technical and financial consequences. However, such an assessment can be challenging because of the many unknown parameters in the field and pressing project schedule. Therefore, planning and conducting an efficient assessment study becomes particularly important under such circumstances. This paper describes an analysis methodology that addresses the following aspects of the pipeline damage assessment: relevant criteria, reconstructing and modeling the sequence of events, and required numerical simulations. Criteria that determine acceptability of the affected pipeline could be the original design criteria or less stringent fit-for-service criteria that, nevertheless, call for additional material information and more detailed analyses. The sequence of events and characteristics of the relevant loads are often not readily clear, and reconstruction of the events may constitute a significant part of the assessment study. The attempt to determine the level of pipe damage/overstress usually starts with simple approximations but oftentimes eventually requires sophisticated numerical simulations. A modeling approach that comprises gradual levels of details and necessary levels of accuracy and efficiency is presented and discussed in this paper.Copyright

Cost-Effective Span Analysis Methodology for Different Pipeline Applications

A pipeline laid on an uneven seabed may result in free spanning, which may cause strength and fatigue problems under static and dynamic loads, leading to vortex-induced vibrations. This can potentially result in expensive remediation and/or intervention works. An assessment of criticality of the spans can be complicated and time consuming due to complexity of the seabed profile, unknown pipeline residual tension, variability of the supporting soil stiffness and other uncertainties inherent in the problem. In this paper, a methodology for the span analysis is presented. It comprises a simple screening, with intermediate screening followed by detailed finite element analyses. Each of these analyses requires a different level of modeling effort and input data. Therefore, performing an efficient span analysis is important, because it not only ensures that all span issues are captured but also minimizes unnecessary calculations. Without proper planning of the analysis, critical pipeline spans may be overlooked or the number of analyses to be performed can be overwhelming. The analysis methodology described in the paper comprises the three levels of analysis mentioned above, and addresses how the work scope and specific application will control the required input and analysis levels. The applications discussed include existing versus new pipelines, selection of pipeline route versus as-installed analysis, pipelines with and without thermal buckles, and an analysis with complete versus incomplete seabed survey data. The applications also include scenarios with multiple spans, where resource allocation is of significance. The methodology presented in this paper presents the in-house experience and can serve as a guideline for a cost-effective span analysis.Copyright

An Integrated Design Approach to the Use of Sleepers as Vertical Upsets for Thermal Buckle Management

Pipe-in-Pipe (PIP) arrangements for offshore pipelines have become a viable approach to handling High Pressure and High Temperature (HPHT) conditions in deepwater. However, using sleepers to control the buckle location and stresses (thermal buckle management) in this type of pipeline is facing challenges regarding free spanning and sleeper embedment. A sleeper design should ensure adequate vertical upset of the pipeline, thus helping buckling of the pipeline as part of the thermal management plan. However, this approach generates free spans in the pipeline, which could become susceptible to Vortex Induced Vibration (VIV) if these free spans prove excessive. Further, PIP pipelines are usually heavy and may raise additional challenges in very soft soils, especially given the great uncertainty in predicted penetrations provided by currently available models. This paper presents an integrated approach to designing sleepers and the approach is applicable to both PIP and single pipes. It takes into account the interaction between pipeline structural integrity and sleeper embedment, thus determining the required sleeper general sizing and the possibility of the need for mudmats or mattresses. Finite element analysis of both the pipeline and sleepers is used in the presented approach. During the FEA modeling, importance is addressed for the model length, element size, concrete induced Stress Concentration Factor (SCF) at the field joints for single pipes, etc. In addition, the analysis scenarios are addressed to ensure the results from all the necessary cases are accurately identified. The sleeper design in the integrated approach details the appropriate selection of sleeper locations to release excessive axial loads as well as to ensure buckling stability. During the selection, some factors contributing to the buckling analysis results are discussed and these factors include route bends, pipe ovality, residual stress/strain, and rogue buckles. Different sleeper sizes are assessed with respect to the pipeline structural integrity (e.g., stresses and strains due to vertical bending, lateral buckling and VIV), coupled with an assessment of lost height due to sleeper penetration in the soil. Results indicate that the sleeper size should be maintained within a certain range to ensure proper function of the sleeper inducing lateral buckling of the pipeline, while reducing the possibility of excessive VIV. In some cases, this may require the help of mudmats or mattresses to support the sleeper. Results also show that the sleeper width should be selected such that after buckling, the pipeline would not fall off either end of the sleeper. The ULS check and fatigue assessment due to VIV/direct wave loading are also discussed for wave/current data and wave load application to interacting spans. To ensure that conservative estimates of the fatigue life, sensitivity studies are performed to account for the uncertainty due to soil properties and concrete conditions (intact or damaged). The tolerance for each item varies from case to case, thereby varying the inputs. This integrated design approach combines pipeline lateral buckling and span analyses together with the analysis of sleeper penetration in the soil. The proposed integrated analysis would ensure that the designed sleeper would not cause excessive VIV/direct wave load to the pipeline and that thermal stresses and buckling of the pipeline are properly managed.Copyright