Investigation of Structural Anomaly Reported at Top Section of Flexible Riser

Abstract The present study aims to carry out a structural analysis of an anomaly found in a 14-inch flexible riser, used to transfer natural gas from an FSRU unit (Floating Storage Regasification Unit) to a thermoelectric plant, located close to the Brazilian coast. The work aims to carry out global and local numerical-structural analysis of the riser, using data obtained from riser design and from a riser sample taken from a similar structure. As a result of the project, we seek to understand the cause of the anomaly found during visual survey and evaluate the permissible operating conditions, avoiding the worsening of the anomaly and a possible, but unlikely, failure. The work included data collecting from available design documentation, sample dissection to gather riser layers geometry, the development of a numerical model for global analysis to verify loading conditions to be used in the detailed local model, the development of a numerical model to simulate riser layers in other to reproduce expected responses. The finite element model detailed the internal carcass, the pressure barrier, and the internal pressure armor. The paper concluded that the anomaly is a result of the operational loads and that there is no risk of failure or leakage.