Danilo Machado Lawinscky da Silva

Numerical Simulation of Offshore Pipeline Installation by Lateral Deflection Procedure

Conventional offshore pipeline installation operations in Brazil have been performed in an S-Lay procedure employing the BGL-1 barge, owned by Petrobras. However, this procedure has some limits, and may not be feasible in some particular scenarios. Therefore, the objective of this work is to present the numerical simulation of an alternative pipeline installation procedure. This procedure basically consists of performing the pipeline assembly on shore, and deflecting it to the sea using a tug boat. The numerical simulations employ the SITUA-Prosim computational tool, which is able to incorporate the correct definition of the seabed and shore from bathymetric curves. An actual pipeline installation by this lateral deflection procedure is analyzed and discussed. The characterization of the procedure passes through the determination of the better velocity and direction of the tug boat in order to minimize the efforts on the pipeline (especially due to the curvatures).Copyright

A Generalized Contact Model for Nonlinear Dynamic Analysis of Floating Offshore Systems

The objective of this work is to present the implementation of a contact model that represents, during a nonlinear dynamic analysis of floating offshore systems, the contact of lines with the platform, as well as the contact involving different lines and, eventually, involving two different platforms in the same model. Traditional contact models consider for instance a generalized scalar element, consisting of two nodes linked by a non-linear gap spring. In this work, the contact model is geometrically defined by volumes that cannot interpenetrate. A penetration stiffness can be defined for each volume; lateral friction can also be considered by this model. An appropriate data structure is used to define the volumes and guarantee the efficiency of the algorithm by an optimized search. The application of the presented contact model is demonstrated by case studies of actual applications for offshore systems: pipelines in S-Lay installation operations, where the contact is complex, specified only in some points of the ramp and stinger; offloading floating hoses that may collide with the hull of the ship, and catlines in lift operations.Copyright

IMPLICIT AND EXPLICIT IMPLEMENTATION OF THE DYNAMIC RELAXATION METHOD FOR THE DEFINITION OF INITIAL EQUILIBRIUM CONFIGURATIONS OF FLEXIBLE LINES

Recent activities in the offshore oil exploitation industry require new structural concepts employing flexible lines (both mooring lines and risers). Such systems present increasingly complex configurations, with dynamic nonlinear behaviour; therefore, the use of efficient numerical solution procedures, based on the Finite Element Method, becomes mandatory for their analysis. The usual analysis procedure for flexible lines by the FEM is based in the calculation of an initial, stable static equilibrium configuration in order to define the finite element mesh. Usually this configuration is obtained by the classic catenary equations. However, in more complex problems these equations cannot be applied. Therefore, the objective of this work is to present the use of a more general finite element approximation, associated to dynamic relaxation algorithms. Such algorithms can be started from arbitrary configurations, not necessarily in equilibrium. The resulting procedure is accurate, robust, and avoids numerical problems such as the ill-conditioning of the tangent stiffness matrix, allowing the static equilibrium configuration to be obtained in an efficient way.Copyright

Pipeline-Laybarge Interaction Model for the Simulation of S-Lay Installation Procedures

The most common method of pipeline installation in shallow water is the S-Lay method. In this method, the welded pipeline is supported by rollers on the vessel and the stinger, forming the over-bend. Then it is suspended in the water all the way to seabed, forming the sag-bend. The over-bend and sag-bend form the shape of an “S”. This work focus in modeling the interaction between pipeline and lay barge on the over-bend region, considering not only the contact between the pipeline and the launching structure, but also the tensioner behavior. Two numerical models are proposed: (a) a rigorous contact model that provides important information related to the consequences of impact between pipeline and rollers. These consequences can be dents to the pipe or tearing of the coatings; and (b) a model for the simulation of the tensioner behavior. This latter includes a delay between the instant that the tensioner is activated until it effectively starts working. It also considers how fast the tensioner can recover the desired tension level in the pipeline. Several simulations of actual operations are shown, in order to illustrate the application of the proposed model.Copyright

Hydrostatic Collapse Pressure and Radial Collapse Force Comparisons for Ultra-Deepwater Pipelines

In this paper the behavior and the relationship between hydrostatic collapse pressure and diametrically opposed radial compressive force for pipelines were analyzed. This study presents an introduction of a research work aimed to assess the pipeline collapse pressure based on the radial collapse force.Initially the hydrostatic collapse pressure is analyzed, for pipes with different diameter to wall thickness ratio (D/t) and ovalities, using classical assessment (DNV method) and numerical models (FE). Then, the compressive radial force is also analyzed using numerical models validated by a small-scale ring specimen test. After that, the relationship between hydrostatic collapse pressure and compressive radial force is discussed. These first results show that the radial force is a quadratic function of the collapse pressure.Copyright

Pipeline Shore Approach Installation by Horizontal Directional Drilling

Whenever an export pipeline coming from offshore fields to onshore facilities is designed, a shore approach solution needs to be provided, once it can become a very complex project in terms of offshore pipeline installation. At this phase the pipeline on-bottom stability is analyzed for surf zone, the possibility of using concrete coating is verified as well as the necessary burial depth. In addition, the pipeline installation stress analysis is performed, the potential for local scour is verified, among other things. In this context, horizontal directional drilling (HDD) emerges as an alternative method in which, in addition to overcome the technical aspects mentioned above, the environmental issues can also be minimized.Many factors determine the success of an HDD project. Failure to complete the borehole is often the main concern, as the project would not be attempted if the pipeline could not be installed. However, the successful design and construction of an HDD is measured in more than a successful pullback. The achievements, as in any project, include the completion of the project for a reasonable cost with minimal environmental impact and according to the schedule. And of course, the pipeline integrity shall be ensured. That is the focus here in this work.This paper presents discussions regarding to the proper design of the export pipeline section installed by HDD in the shore approach area. To ensure a proper design and pipeline integrity are important parts in the success of a shore approach HDD crossing. It must be noted that there are no methods for in situ repair of damaged pipelines installed by HDD. The point is a proper design, construction and installation, which includes, for instance, do not overstress the pipeline during installation, mainly pullback operation, as well as the proper selection of the drill path in order to place the pipeline within stable ground and isolated from obstacle’s active conditions, to properly consider the corrosion protection, etc., for the design life of the product pipe.Copyright

Numerical Simulation of the ‘Floating Spiral’ Pipeline Installation Procedure: First Stage, Spiral Assembly

The underlying concept for the Floating Spiral pipeline installation method is to wind the pipeline into a huge floating spiral, and then tow this assembly to the installation site, where the spiral is then unwound and lowered to the seabed in a single operation. In this method the pipes are fabricated on shore, which allows for optimal control of costs and quality in pipeline manufacturing. The first stage of the installation process by this method consists in setting the pipeline afloat and winding it elastically to form a large flat spiral, which is then ready to be towed to the installation site by standard tugboats. The objective of this work is to present results of studies for a long pipeline length at this first stage of the Floating Spiral method. The focus here is the process of moving the pipeline around a fixed structure to wind it and form the floating spiral. Problems related to modeling of contact between pipeline and its guides at the first spiral cycle, as well as contact between further pipeline cycles, are rigorously analyzed. Several numerical simulations are performed; the results are presented and discussed. Other stages of this installation method have also been studied, and are presented in a companion paper [1].Copyright

Numerical Simulation of a Pipeline Installation Procedure at the Negro River

The installation of pipelines is among the most challenging offshore operations. Conventional offshore pipeline installation operations in Brazil have been performed in an S-Lay procedure employing the BGL-1 barge, owned by Petrobras. The BGL-1 is a second generation lay barge and performs installation operations by moving forward using its own mooring lines. The objective of this work is to present the numerical simulation of a pipeline installation operation performed at a particular scenario, Negro river in the Amazon forest. The high current velocity, very irregular bathymetry and heterogeneous soil make this procedure a real challenge. The numerical simulations employ the SITUA-Prosim computational tool, which is able to incorporate the correct definition of the bottom from bathymetric curves. The two crucial points in the performed analyses are: (a) first, to verify if it is possible to move the barge using its own mooring lines in such environmental condition and (b) second, to analyze the pipeline behavior in such scenario.Copyright

Subsea Pipelaying Simulation by the “Situa-Petropipe” Software: A User Friendly Alternative

Currently, Petrobras (the Brazilian state oil company) performs numerical simulations of pipelaying operations employing commercial software, such as OffPipe [1]. However, such tools presents restrictions/limitations related to the user interface, model generation and analysis formulations. These limitations hinder its efficient use for analyses of installation procedures for the scenarios considered by Petrobras, using the BGL-1 barge (owned by Petrobras) or other vessels, considering for instance particular types of stingers depending on depth and pipeline, with different lengths and geometries adapted to certain laying conditions in S-Lay procedures. Therefore, the objective of this work is to present the development and application of a tailored, in-house non-commercial computational tool in which the modules follow Petrobras users’ specifications, in order to overcome the limitations for specific needs and particular scenarios in the simulation of several types of pipeline procedures. Such tool, called SITUA-PetroPipe, presents a friendly interface with the user, for instance allowing the complete customization of the configuration of laybarge and stinger rollers. It also includes novel analysis methods and formulations, including the ability of coupling the structural behavior of the pipe with the hydrodynamic behavior of the vessel motions under environmental conditions.Copyright