Rafael Familiar Solano

Analytical Formulation of Distributed Buoyancy Sections to Control Lateral Buckling of Subsea Pipelines

Subsea pipelines designed to operate under high pressure and high temperature (HP/HT) conditions tend to relieve their axial stress by forming buckles. Uncontrolled buckles can cause pipeline failure due to collapse, low cycle fatigue or fracture at girth welds. In order to control the lateral buckling phenomenon, a methodology was recently developed which consists of ensuring regular buckle formation along the pipeline. Distributed buoyancy is one of the most reliable initiation techniques utilized for this purpose which have been recently applied in some projects. The behavior of pipeline sections with distributed buoyancy is normally evaluated by Finite Element Analyses (FEA) even during preliminary design when analytical models could be adopted. FEA are also utilized in order to support reliability calculations applied within buckle formation problems. However, the referred analyses are usually time-consuming and require some experience to provide good results. This paper presents an analytical formulation for a pipeline section with distributed buoyancy, which can be utilized during preliminary design in order to evaluate the influence of buoyancy sections over buckle shape, feed-in length, tolerable Virtual Anchor Spacing (VAS), etc. Regarding buckle formation, this paper also presents a methodology to determine an expression for the critical buckling force to be used as part of the limit state function in reliability analyses, which combines the results obtained from the referred analytical formulation with Hobbs infinite mode.© 2010 ASME

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

Assessment of Lateral Buckles in a HP/HT Pipeline Using Sidescan Sonar Data

During design stage of high pressure/high temperature pipelines, some conservative parameters are adopted along with sensitivity analyses to assure safe operation in the presence of uncertainties that influence buckle formation, e.g. pipe-soil interaction, as-laid out-of-straightness and initial heat-up. After operation starts and lateral buckles appeared along the line, a survey may provide valuable information regarding confirmation of the design assumptions, evaluation of actual behaviour and the possibility of increase the operating conditions. This work presents the methodology applied to analyse the configuration of the P-53/PRA-1 12″ oil export pipeline in operation using data from a sidescan sonar survey. The aim of such analyses was to gather information for an FE model calibration as well as to obtain preliminary estimates for the bending strains at lateral buckling locations. Special attention was dedicated to smoothing and interpolation of the pipeline coordinates extracted from sonar imagery in order to avoid unrealistic strains estimates.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

Evaluation of the Operational Behaviour of a Deepwater Oil Export Pipeline Designed on the Basis of Controlled Lateral Buckling

An account is given of the methods used to evaluate the operating structural performance of a reel laid deepwater oil HP/HT pipeline which had been designed based on the controlled lateral buckling principle. The objective was to develop a finite element (FE) model of the line based on its operating status and to use the model to confirm its present and future structural integrity. The line is surface laid on a fairly undulating soft clay seabed at its deep end and sand at the shallower end. It incorporates three different man-made buckle triggering mechanisms of buoyancy modules, dual sleepers and locally increased lateral curvature along its entire length. The steps involved in the inclusion of the in-situ operating condition of the pipeline, provided through various surveys made of the as-built and operating line and historical records of operating temperatures and pressures and flow rates made at inlet and outlet of the line, into the FE model, is discussed. Several key considerations essential for the successful development and validation of such an operation-based FE model, and for completion of the evaluation task, are highlighted in the paper. Also, a specific challenge encountered as a result of changes in regulatory guidelines on engineering critical assessments, from initial design to current evaluation stage, is discussed. The evaluation has demonstrated that it is feasible to carry out in-situ assessments of laterally buckling subsea lines, and that such assessments can provide not only reliable information regarding current and future structural integrity of the lines, but also invaluable confirmation of initial design data and rationale. This comparison between initial design and the actual operating behavior of the line is not included in this paper but will be described in detail in a future separate paper.Copyright

Initial Approach to Assess Lateral Buckling Behavior: Comparison Between Design and Operational Condition of Offshore Pipeline

Recently Petrobras has been developing a production module of Roncador field through the P-52 platform in the Campos Basin, offshore Brazil. This platform is a floating production facility located in deep water and was tied back to the PRA-1 platform in shallow water by an 18-inch pipeline in order to export the oil production. This pipeline operates under high pressure and high temperature (HP/HT) conditions and was laid on the seabed. As a result of the extreme operating conditions, this pipeline is highly susceptible to lateral buckling and a buckle initiation strategy based on triggers to control the buckling behavior was designed. Thus sleepers and distributed buoyancies were designed and installed along the pipeline route. In addition to the buckles at the triggers, some additional, on-bottom, buckles were assessed in order not to compromise the design strategy. In recent geophysical data surveys carried out along the route length with the pipeline in operation, both engineered and on-bottom buckles were identified. This paper aims to present the thermo-mechanical design of the P-52 oil export pipeline, performing a comparison between some results obtained in design and observed during operation. Thus this paper intends to evaluate the pipeline as-built plus the operational pipeline configurations, and to assess the robustness of the design strategy applied regarding lateral buckling behavior.Copyright

Thermo-Mechanical Design of Canapu PIP System

This paper discusses the thermo-mechanical design of the pipe-in-pipe (PIP) flowline installed in the Canapu field, located in Espirito Santo State, offshore Brazil. The pipeline is approximately 20km in length and connects the gas producing well 4-ESS-138 positioned in a depth of 1608m to Cidade de Vitoria FPSO, located in Golfinho field. The Canapu PIP will operate under high pressure and temperature (HP/HT) conditions and is laid on the seabed. Due to the operational conditions, the thermo-mechanical design evaluated the susceptibility of the pipeline to the phenomenon of lateral buckling and pipeline walking in addition to free spanning and on-bottom stability. The lateral buckling behavior of the PIP is the major challenge for the design. It can be a safe and effective way to accommodate the thermal expansion of a hot pipeline, however high stress and strains can be developed in the buckles and a conventional stress based approach is not suited to design a pipeline that buckles laterally. The conventional stress limits are therefore relaxed and replaced by a strain limit. For this the methodology and recommendations of the SAFEBUCK JIP were adopted. The thermo-mechanical analysis selected a buckle initiation strategy based on distributed buoyancy. The strategy combines three distributed buoyancy triggers along the route together with the beneficial effect of the bathymetric out-of-straightness. The analysis shows that this initiation strategy is robust and highly reliable. From the start, this project represented a great challenge for Petrobras; it is the first PIP in Petrobras; has a low value specified for OHTC; and the pipeline is susceptible to lateral buckling. Besides all that, since the Canapu project was included among the priorities of Petrobras Plangas, it was executed as a fast track project.Copyright

Pipe-in-Pipe for Gas Production in Deep Water Offshore Brazil

Based on flow assurance studies a Pipe-in-Pipe solution was selected to assure the flow for a gas pipeline connecting the well 4-ESS-138 to FPSO Cidade de Vitoria located in Canapu field. The flow assurance studies also define the value of 0.8W/m2 K for the overall heat transfer coefficient (OHTC) in order to prevent hydrate formation. The temperature of 87°C on the wellhead should be preserved to permit the proper gas flow in 20km PIP length between wellhead and FPSO. Canapu field is located in the offshore area of Brazil (Espirito Santo state) in water depths of 1608m. This paper presents the main aspects related to the detailed design, thermo-mechanical requirements, materials specifications, functional qualification tests performed on materials and on pipe-in-pipe systems to satisfy installation constraints defined by the reel-lay method and operational issues.© 2009 ASME

Enhanced Collapse Resistance for Different D/t Ratios of UOE Pipes for Ultra Deepwater Application

Energy consumption outlook shows that the demand for Oil and Gas is increasing worldwide and since most of the undemanding reserves are already being explored, new reserves means longer distances from the shore and increasing water depths, of up to 3,000 meters. Collapse resistance has become a key factor in the design of pipelines for ultra-deepwater applications. UOE process is commonly used for manufacturing pipelines of large diameter and the cold work involved in this forming process modifies the mechanical properties of the pipes. This paper presents the effect of thermal treatment on final material properties, proving the validity of enhancing collapse for different D/t, as allowed by DNV-OS-F101 αFab, and extending what has been shown as valid on previous studies. In this work, the inputs for the processing strategies are presented, along with coupon compression testing and full scale testing, in order to qualify the selected route as compliant with producing pipes with αFab equal to 1, for usual D/t combinations. An analysis of the predicted collapse pressure compared to the real collapse pressure of the pipes is also presented. The extension of the qualification process achieved successful results and allows the use of a fabrication factor equal to 1 in ultra-deepwater offshore pipeline projects. This enables the reduction of wall thickness, generating reductions in material and offshore installation costs and also potentially enhancing the feasibility of many challenging offshore projects.Copyright

Collapse Resistance Enhancement in UOE SAWL Line Pipes During Coating Heat Treatment for Ultra Deepwater Applications

Large diameter UOE pipes are being increasingly used for the construction of offshore pipelines and in the last few year, since oil discoveries are moving towards ultra-deepwater areas, such as Pre-Salt in Brazil, collapse resistance is a key factor in the design of the pipelines the demand for pipes with high thickness near the limits for fabrication and installation capacity. It is known that the cold forming, and the final expansion in the UOE line pipe manufacturing process, reduces the elastic limit of the steel in subsequent compression. Due to this, the DNV collapse formula includes a fabrication factor that de-rates by a 15% the yield strength of UOE Pipes. However, DNV also recognizes the effect of thermal treatments and the code allows for improvement of the fabrication factor when heat treatment or external cold sizing (compression) is applied, if documented. In previous work [1] it was presented the qualification of UOE pipes with enhanced collapse capacity focusing the use of a fabrication factor (alpha-fab) equal to 1. A technology qualification process according to international standard has been performed. The main aspects of the qualification process were presented and included significant material, full scale testing and final analysis. In this paper, we compare those results with the ones of the new qualification tests analyzing the more important variables affecting the collapse resistance such as ovality, compressive material strength, thermal treatment control, etc. This new qualification obtained even better results than the previous one, which will allow the use of a fabrication factor equal to 1 directly in deepwater and ultra-deepwater offshore pipeline projects with a possible reduction in material and offshore installation costs and also potentially enhancing the feasibility of many challenging offshore projects.Copyright