Carlos de Oliveira Cardoso

Synthesis and Optimization of Submarine Pipeline Routes Considering On-Bottom Stability Criteria

Researchers from Petrobras and LAMCSO/COPPE/UFRJ are currently involved in the development and implementation of a computational tool, based in Evolutionary Algorithms, for the synthesis and optimization of submarine pipeline routes. In this tool, randomly generated candidate routes are evaluated in terms of several criteria, incorporated in an objective (or fitness) function to take into account the relevant aspects that should be considered in the design of a route. A previous work [1] described the initial steps taken towards the development of such tool. In that work, attention was dedicated to the geometrical representation of a route, and to some of the terms of the objective function associated with a preliminary, global step of the optimization process (such as total pipeline length, and geographical-topographical issues associated with the route geometry and to the seabottom bathymetry and obstacles). Now, this work focuses in other aspects related to the structural behavior of the pipe, under hydrostatic and environmental loadings; more specifically, special attention is dedicated to the implementation of On-Bottom Stability (OBS) criteria such as the proposed in the RP-F109 code [2]. Case studies are presented to illustrate the use of the optimization tool and to assess the influence of the OBS criteria.Copyright

HP-HT Pipeline Cyclic Behavior Considering Soil Berms Effect

This article presents a numerical study for the Petrobras HP-HT pipeline P-53/PRA-1 that will be installed at Marlim Leste field in Campos Basin offshore Brazil. This pipeline will connect P-53 platform in deep-water (1031m) to an Autonomous Platform for Intermediate Pumping (PRA-1) in shallow water (100m). HP-HT pipelines resting on seabed can develop thermal buckling, which is an important concern for the pipeline structural integrity. The aim of this study is to verify the P-53/PRA-1 pipeline behavior during lateral buckling due to thermal cycles and pressure variations, using a new approach for the pipe-soil interaction model in contrast with the traditional Mohr-Coulomb friction model. The pipe-soil interaction model considers soil berms formed due to pipe cyclic displacements, representing different phases of the soil lateral reaction force versus displacement curve: breakout force, suction release, berm formation and residual resistance. The results presented compare the traditional Mohr-Coulomb model with the proposed one for several loads cycles, analyzing displacements, stresses and strains behavior during thermal buckling.Copyright

Synthesis and Optimization of Submarine Pipeline Routes Considering VIV-Induced Fatigue on Free Spans

Researchers from Petrobras and LAMCSO/COPPE have been involved in the development and implementation of a computational tool, based on Evolutionary Algorithms, for the synthesis and optimization of submarine pipeline routes. In this tool, randomly generated candidate routes are evaluated in terms of several criteria, incorporated in an objective (or fitness) function to take into account the relevant aspects that should be considered in the design of a route.Previous works described the initial steps taken towards the development of such tool, including the geometrical representation of a route, and some of the terms of the objective function associated with a preliminary, global step of the optimization process (such as total pipeline length, and geographical-topographical issues associated with the route geometry and to the seabed bathymetry and obstacles). Special attention was dedicated to the implementation of On-Bottom Stability (OBS) criteria such as the proposed in the DNV-RP-F109 code.This work is focused on another aspect related to the structural behavior of the pipe under hydrostatic and environmental loadings; more specifically, fatigue induced by vortex induced vibrations (VIV) on free spans along the candidate routes. Special attention is dedicated to the implementation of the screening criteria proposed in the DNV-RP-F105 code. Case studies are presented to assess the influence of the VIV criteria on the results of the optimization tool.Copyright

Reduced Model Device of Solutions to Control Thermal Buckling Effects in HP-HT Subsea Pipelines

Nowadays, the safe operation of HP-HT subsea pipelines resting on seabed must take into account the thermal buckling phenomenon. The transport of oil with high pressure and temperature can cause uncontrolled thermal buckling in subsea pipelines. The failure risk must be carefully evaluated to design the pipeline with safety. Nowadays to control the thermal buckling the use of man made triggers is seen like the best solution for cost and safety of subsea pipelines. Some projects employ man-made triggers to control the thermal buckling in the last years around the world. In this article is presented the system and methodology used to test some solutions in a reduced scale model. Different geometric setups along the model line were tested. Solutions like sleepers, dual sleepers and buoyancy were tested and the geometric and structural behavior monitored. The reduced model has 195 m length, and was developed in the IPT Towing Tank, representing a pipeline section of almost 6 km long. Strains, temperature, pressure and displacements were measured in several sections of the model. Additionally, an imaging technique for the model geometry retrieval was developed. This paper presents the experimental setup developed to investigate the performance of man-made triggers solutions for HP-HT subsea pipelines.Copyright

Global Buckling of a Heated Pipeline in the Campos Basin Brazil in a Region With Free-Spans

This article presents the behavior a heated flowline in Campos Basin-Brazil that crosses an uneven seabed region with free-spans of different lengths. In that region the mean water depth is arround 900 m and the pipeline supports the highest temperatures. A regular inspection with ROV (Remote Operate Vehicle) showed that the flowline is interacting with the surrounding soil, evidencing movements due to thermal expansion. Geotechnical survey showed that the soil in the pipeline route is composed by normally consolidated clay where the strength properties were obtained by CPT interpretation. The principal question for the pipeline operator concerns the pipeline integrity despite of the evidence of thermal buckling occurrence. In order to answer this question, a 3D finite element model was generated considering lateral imperfections, free-spans and pipe-soil interaction along the pipeline route obtained by ROV. A complementary inspection was done with Side Scan Sonar Image obtained by AUV (autonomous Underwater Vehicle), mapping lateral buckles and the free-spans in the pipeline route. The bending moment and effective axial force in the pipeline obtained by 3D finite element global model were used to verify the pipeline integrity based on DNV OS-F101 standard [1]. In order to verify the vertical buckling in the free-spans, a parametric study was done with different free-spans and feed-in lengths based on geometry acquired from inspections. This study supplies the critical temperature variation that triggers thermal buckling in the free-spans, enabling the determination of the critical free-spans in the flowline route. The results obtained by finite element modeling was the definition of the maximum operating temperature and pressure that enables operate the flowline safety based on DNV OS-F101 code.Copyright

Safety Factors Calibration for Wall Thickness Design of Ultra Deepwater Pipelines

Wall thickness often presents a considerable influence in offshore pipeline capital expenditure (CAPEX). This influence is enhanced in design of ultra deepwater trunk lines of large diameter, where any wall thickness increase provides a huge impact on project costs. In ultra deepwater scenarios, thicker pipelines may eventually implicate not only in higher costs, but may also compromise the project feasibility due to installation load constraints related to laying vessels availability.One potential way to reduce the pipeline wall thickness is to calibrate fitness-for-purpose safety factors through application of structural reliability methods, instead of utilizing the standardized safety factors presented in international codes. Since mid-nineties, several offshore pipeline design codes have been allowing the calibration of safety factors by structural reliability analysis. The purpose of such an allowance is that structural reliability methods would eliminate some eventual conservatism presented in the safety factors proposed by codes. Although this enables the achievement of optimized safety factors, more than fifteen years have passed and only few pipeline projects have taken advantage of the benefits of safety factor calibration.This paper evaluates which potential benefits are available through safety factor calibration, particularly for wall thickness reduction purposes in ultra deepwater pipeline design. Calibrated safety factors are presented for some scenarios related to ultra deepwater export pipelines, considering “system collapse criteria” limit state. The calibrated safety factors are compared with the standardized safety factors presented by international pipeline design codes. The potential for safety factor reduction by the utilization of linepipes with more stringent manufacturing tolerances and the consideration of the thermal ageing imposed by coating application are also discussed.Copyright

Design and Installation of Buried Heated Pipelines at the Capixaba North Terminal Offshore Brazil

The export pipelines of the Capixaba North Terminal (TNC) offshore Brazil will be operating with a great thermal stability potential due to the high temperatures that are necessary to assure an adequate flow. This paper focuses on the challenges for the design and installation group, due to the very strict maximum allowable imperfection (prop), in order to find a feasible solution for the installation process by a conventional lay barge. Also, the paper employs a finite element model and carries out a parametric study based on the soil coverage requirements and the maximum allowable imperfection originated from laying operations and pipeline burial process. The upheaval buckling will be studied in full detail in order to evaluate predefined curvatures, with the objective of finding the minimum cover height to limit the pipeline displacement and thus assuring its integrity. This work also aims to establish a numeric tool that will serve as basis for the upheaval buckling analysis in new pipeline design.© 2004 ASME