Developments of oil and gas reservoirs in South China Sea are presently accelerated, to cope with the significant increase in energy demand from the mainland. Pipe-in-Pipe (PIP) flowline systems have been widely employed in this region and are continuously being considered for further developments. This is due to its significant thermal insulation capacity to deal with the High Pressure and High Temperature (HPHT) issue. However, the methods in industry for design of PIP systems usually have two side extremes. Simplified analytical approach may lack of accuracy and detailed FE analysis always brings considerably sophisticated modelling and post-processing tasks. To overcome this situation, COTEC Offshore Solutions, together with its mother company, China Offshore Oil Engineering Company, have developed a cost-effective, beam elements based, 3D simulation model using ABAQUS, a general purpose finite element analysis (FEA) package. The mode allows complicated structures of PIP system to be represented in an effective way and adopts a representation of stinger for S-lay installation analysis. A full-history time-dominate analysis from installation to operation is performed in one model, rather than the commonly used ‘snapshot’ analysis.
In this study, a simplified modeling guidance of PIP components have been suggested. On the basis of the guidance, a novel 3D beam-elements based model has been produced to accurately represent complex PIP structural behaviors, but with minimum increase in modeling complexity. The analysis is carried out on the time-domain basis, which permits the full strain and stress history of the installation and operation to be observed and the most onerous time-point during the full installation and operation to be captured.