Methodology for Analysis of Installation of a Steel Lazy Wave Riser

The Petroleum Industry has been looking for a configuration for large diameter steel risers, which can be used either at FPSO’s or Semi Submersible Platforms. An interesting option with a low cost increase is the lazy-wave configuration, which is obtained by the addition of buoyancy modules along a limited length of the riser, close to its touch down area. The steel lazy-wave riser is usually checked for the standard failure modes in the operational phase. The present work shows that it is also necessary in the early stages of design, to define an installation procedure in order to assure configuration feasibility, as high stresses develop at riser hog and sag areas as a function of buoyancy modules installation. Riser configuration changes during the installation process demands managing top angle, launched length and distances between the platform and the installation vessel. The limitations of the installation’s equipment have to be taken into account as well. The methodology for the riser analysis in obtaining a feasible solution is outlined. The riser analysis is performed using the Petrobras in-house computer code, ANFLEX and considers a real application scenario for study.