Structural Integrity of Welded Joints: An Investigation of the FPSO Module Stools

Abstract

The main goal of the present work is the investigation of a construction and integration of topside modules for an FPSO in Brazil. Most of the topside module structure manufacturing was subcontracted to a third-party company in Europe. During assembling work undergoing at the construction site, several structural details nonconformities were reported by the EPC Group quality control team, e.g., misalignment of stiffeners at the diamond plate and stool connections, geometry irregularities, and unexpected thickness changes on the connection of diamond plates with the correspondent I beam flanges of the pancakes, unexpected bevel buttering to correct joint imperfections which presented several weld flaws in it. Topside structures are subjected to cyclic loading during operation, hence, subjected to fatigue loading. The latter is of concern since the structural integrity of the welded joints must be met for the entire life of the FPSO. The EPC Group required an independent appraisal of the welded joints and structural details nonconformities. They also requested an Engineering Critical Assessment (ECA) on critical joints to be carried out to determine if there might be any flaws compromising the structural integrity of the topsides. Finally, ECA recommended mitigation actions, which could contribute to new topside module integrations for FPSO in Brazil.