The DNV RP 105 standard provides guidelines for evaluating the fatigue damage of pipelines over free spans, where guidance is provided for calculating the approximate Vortex Induced Vibration (VIV) response, considering the pipe properties, the span geometry, the pipe-soil interaction and the effective axial force. The approximate response models are limited, however, to single spans with leveled shoulders, short length, i.e. span lengths less than 140 times the pipe diameter, and bar buckling not influencing the pipeline dynamic response. To overcome these limitations, specifically for “long” spans and multi-spanning pipelines, RP F105 recommends that eigen-value analysis be performed using Finite Element (FE) method to calculate the natural frequencies, mode shapes and corresponding stresses associated with the mode shapes considered for VIV fatigue assessment. In this sense, a methodology and suite of Finite Element (FE) based tools for multi-mode/multi-span VIV fatigue assessment have been developed. The FE methodology accounts for the initial static equilibrium configuration of the pipeline in the as-laid condition followed by application of the subsequent load steps, such as flooding, hydrotesting, dewatering, start-up, etc. It also considers the non-linearity of the seabed stiffness and the effect of geometric non-linearity/large deflections on the dynamic response of the pipeline. In addition, the FE approach allows the determination of the dynamic response at every location of the free span for the different mode shapes and hence offers the ability to calculate the distributed fatigue damage along the spanning section of the pipeline instead of assuming all damage occurring at a single location. The methodology was applied in recent projects to allow for a better estimate of the requirements for free span correction with significant cost savings anticipated. The proposed methodology also has the potential for post-lay assessment of the pipelines and for through-life in-service assessment of existing pipelines, where new free spans are often observed during inspection due to soil movements along the lifetime of the pipeline. This paper addresses the in-place FE methodology, the validation process and the tools that were developed to speed up the fatigue assessment procedure, which is a key factor especially when analyzing post-lay survey in real-time for determination of requirements for free span correction in the field.

The Petrobras Capixaba North Terminal - TNC is located in the state of Espirito Santo, in Brazil and is being built to receive the heavy and high viscosity oil produced onshore in the Fazenda Alegre field. This oil shall be heated prior to be pumped into the pipelines and it will be exported through a monobuoy and a tanker system. The two export pipelines are being laid to connect the onshore Terminal to a subsea PLEM to be installed under the monobuoy. The pipelines and PLEM were designed to operate with oil containing H2S in cyclic high temperature. This paper addresses the special concerns defined by the design activity to cope with the TNC operation conditions. It also focuses the modifications imposed to the installation process to fulfill the design and operation requirements.

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Free-standing hybrid risers (FSHR) are well established in deepwater field developments in the oil & gas industry. The major advantages foreseen for the FSHR are the possibility of safely anticipating production and requiring significantly reduced payloads at the Floating Production Unit (FPU). This work addresses the feasibility of a novel proposed optimized concept, the Free-Standing Integrated Riser (FSIR), where the pipeline is integrated to the riser by means of a transition section, which is kept in place by a multiple line mooring system, developed to keep the functionality and integrity of the entire riser along its lifetime. The work provides the findings from numerical analysis simulated in Orcaflex, a finite element simulation software dedicated to global analysis of risers, considering the design criteria provided in API 2RD Standard. As part of the FSIR evaluation, screening static analysis was performed to identify the most promising configurations for the multiple line mooring system, followed by a series of dynamic analyses to evaluate the behavior of the riser in extreme conditions. In addition, several investigations were performed to assess the functionality and the robustness of the system, including parametric studies to check for installation and dimensional tolerances, assessment of fatigue damage, and checking the impact of pipe size on the design. The results show that proposed novel FSIR concept can provide a practical and economical solution for deepwater projects.

Free-standing hybrid risers (FSHR) are well established in deepwater field developments in the oil & gas industry. The major advantages foreseen for the FSHR are the possibility of safely anticipating production and requiring significantly reduced payloads at the Floating Production Unit (FPU). This work addresses the feasibility of a novel proposed optimized concept, the Free-Standing Integrated Riser (FSIR), where the pipeline is integrated to the riser by means of a transition section, which is kept in place by a multiple line mooring system, developed to keep the functionality and integrity of the entire riser along its lifetime. The work provides the findings from numerical analysis simulated in Orcaflex, a finite element simulation software dedicated to global analysis of risers, considering the design criteria provided in API 2RD Standard. As part of the FSIR evaluation, screening static analysis was performed to identify the most promising configurations for the multiple line mooring system, followed by a series of dynamic analyses to evaluate the behavior of the riser in extreme conditions. In addition, several investigations were performed to assess the functionality and the robustness of the system, including parametric studies to check for installation and dimensional tolerances, assessment of fatigue damage, and checking the impact of pipe size on the design. The results show that proposed novel FSIR concept can provide a practical and economical solution for deepwater projects.