Advanced Simulation-Based Design Exploration and Optimization for Challenging Flexible Flowline Loading Impacts on Various Subsea Connection Systems

Le résumé fourni par la source

Abstract Vertical connection systems are widely used in offshore production for the oil and gas industry, where the loadings from the connected flowline have a significant influence on the tie-in connection, host structure design, and foundation capacities. The objective is to explore the impact of the key design variables of the subsea connection module (flowline stiffness variables, outlet height, angle, and pipelay tension) with the intent of optimizing the connector and host structure design. For local analyses, the general application FEA tools are widely used to simulate in a high level of detail, for example, the minimum bending radius (MBR), the maximum allowable work (MAWP) and burst pressure, minimum chute radius chart, the maximum tension, the capacity curves, manufacturing process, bending stiffness, axial tensile stiffness, torsion stiffness, maximum squeeze load, maximum allowable depth, and other mechanical applications. In addition, thermo-mechanical assessment (insulation performance and thermal expansion induced loading), long-term (creep and relaxation using viscoelasticity), and mass diffusion problems for the production flow permeability on the high/medium-density polyethylene (HDPE/MDPE) barrier are also typical applications using local FEA models. However, flexible flowlines have specific rheological behavior where the bending stiffness is nonlinearly dependent on the pipeline curvature that is not covered by general application FEA tools, limiting its usage to local analyses only. The developed methodology presented in this work is based on assigning this structural behavior to a flexible pipeline modeled with unidimensional elements (global analysis) through general application FEA software and performing a design exploration independently of the well-known pipeline dedicated commercial software. A programming script to assign nonlinear connections along the pipeline elements is used for modeling the rheological behavior of the flexible flowlines. The exploration is performed by incrementally varying each design variable, namely the gooseneck outlet height, outlet angle, and pipelay tension to cover all possible combinations within a given range. The results for three flexible flowlines were submitted to an analytical check of the bending moment against the pipeline curvature for all connected elements. Superposing all points on the specified bending vs. curvature of the flowlines, a perfect match between the numeric and the expected results can be observed as a part of the FEA model validation process. The flowlines were installed, and the witnessed catenary shape and touchdown points precisely matched with the FEA predictions, as a field-proven validation of the proposed methodology for the FEA model. In this successful case, the design exploration played an important contribution to the detailed design stage for customizing the key parameters of both the connection system modules and the host structure design, to minimize the impact of the flowline loadings on the subsea tie-in structures like PLETs, PLEMs, ILTs, and Manifolds. The developed methodology enables the product engineers to perform design exploration and optimization studies for flexible flowlines independently of the limitations of pipeline-dedicated commercial software, bringing the benefit of empowering general application FEA tools to expand the options of features like pipe-soil interaction, materials, contact, analysis types, post-processing, etc.

Ce résumé expose les affirmations des auteurs. BNTIC ne l’interprète pas comme une validation indépendante des résultats.