Ice feature interaction with subsea infrastructure or the seabed is acomplex nonlinear event, for which many analytical and advanced computationaltools have been developed with demonstrated application. Although subsea fieldshave been developed in ice gouge environments, such as the Grand Banks,consideration of alternative methods for protecting subsea infrastructure is ofgreat importance. A more in-depth understanding of ice feature mechanicalbehavior and interaction with subsea infrastructure is required.
For various iceberg shapes and loading conditions, the finite element modelspresented in this paper examine the interaction of free-floating ice featureswith protective structures located above or partially above the mudline. Apreliminary assessment of an interaction scenario involving a gouging icebergkeel with a buried protection structure is also presented. The outcome of thisstudy enhances understanding of the primary factors to be considered for thedesign of protection structures in ice environments and highlights some of thetechnical issues associated with the development and calibration of advancedsimulation tools.
A numerical modeling procedure was developed, using the finite-elementsimulator ABAQUS/Standard, to predict the local buckling and post-bucklingresponse of high strength pipelines subject to combined state of loading. Thenumerical procedures were validated using test data from large-scaleexperiments examining the pure bending and local buckling of high strengthlinepipe. The numerical simulations were consistent with the measuredexperimental response for predicting the peak moment, strain capacity,deformation mechanism and local buckling response well into the post-yieldrange.
A parametric study on the local buckling response of high strength plainpipelines was conducted. The influence of pipe diameter to wall thickness ratio(D/t of 40, 60 and 80), pipe segment length to diameter ratio (L/D of 3.5, 5, 7and 12), yield strength to tensile strength ratio (Y/T of 0.7, 0.8 and 0.9) andinitial geometric imperfections on the local buckling response was examined.The loading conditions included internal pressure and end rotation. Mechanicalresponse parameters examined included moment-curvature, ovalization, localstrain and modal response.
In predicting the geotechnical constraint against pipeline movement usingfinite element methods, the treatment of the pipe/soil interface contactbehavior is of utmost importance, especially in the tangential direction. Thisstudy focuses on the interpretation of soil resistance to axial pipe movementin cohesive soil material for oblique loading, specifically the effect ofchanging the interface shear stress limit and friction coefficient. The mainfinding of the present study is that the incorporation of a shear stress limitin the definition of tangential shear behavior has a considerable effect on theaxial pipeline reaction forces. Without the shear stress limit, the maximumaxial forces due to oblique pipe movement are effectively doubled in comparisonto a limit equal to half of the undrained shear strength. A simple analyticalmethod is provided to estimate the maximum oblique axial soil resistance inundrained conditions. The effect of changing the assumed frictional behavior isalso discussed with respect to predicting the soil reaction forces acting on anice keel during an undrained gouging event in cohesive soil.
The design of offshore arctic pipelines must evaluate technical engineeringchallenges, primarily related to system demand and system capacity, and addressproject execution risk, primarily associated with pipeline trenching andlogisitics. One of the significant hazards, particularly in deeper water, isthe presence of extreme ice features; such as icebergs and multi-year pressureridges, that may gouge the seabed. A comprehensive engineering framework existsto support the analysis and design of offshore pipelines in ice gougeenvironments. However, there exists some aeas of technical uncertainty withinthe current state-of-practice that are highlighted in this paper. This studyfocuses on specific technical issues associated with the simulation of contactmechanics, definition of interface parameters, and need for physical datasetsfor the validation of advanced numerical simulation tools. Study specificconclusions and recommendations that address these technology needs to resolveuncertainty associated with the simulation of ice gouging events areprovided.
Onshore and offshore pipelines may be subjected to mechanical damage duringinstallation and operation due to environmental loads, external forces andthird parties. The type and severity of pipe damage may influence operational,repair and intervention strategies. For conventional pipelines, the assessmentof mechanical damage plays a role in the development of integrity managementprograms that can be of greater significance for pipeline systems located inremote, harsh environments. The current study highlights the effect of plaindents and interaction of plain dents with girth weld on pipe mechanicalresponse using continuum finite element methods. The modelling procedures arecalibrated with available physical datasets and also demonstrate excellentcorrelation with third party simulations. Confidence in the numericalsimulation tool provides a basis to evaluate the effects of mechanical damagethrough a broader parameter study and assess effects on fatigue lifeperformance.
Pipeline systems are integral components of the system infrastructure forthe transport of hydrocarbon resources. In arctic and harsh environments, thesepipelines may be subject to large deformation geohazards. Pipeline/soilinteraction events are often examined using a structural pipe/spring model.This approach does not account for more realistic soil constitutive behaviour,soil deformation mechanisms and effects of soil load transfer on pipelinemechanical response. This paper examines pipe/soil interaction events duringoblique lateral-vertical soil movements using plane strain finite elementanalysis. The results from this study provide a technical framework to assessthe effects of geotechnical loads on buried pipelines, highlight key parametersinfluencing soil yield envelopes, and identify soil failure mechanisms foroblique pipe/soil interaction events that can be used in the design of buriedpipelines for large deformation geohazards. The results may be used tobenchmark more complex loading events, such as coupled ice keel/seabed/pipelineinteraction, that has limited physical basis for validation.