The laying of long and/or deepwater submarine pipelines still represents an offshore operation characterised by challenging technological aspects. In fact the current pipelaying projects can involve the installation of submarine pipelines along routes longer hundreds of kilometres, reaching water depths even deeper than 2000 m. Sometimes the two requirements are coupled. These laying operations are made by dedicated pipelay vessels, which have to store on board thousands of pipe tons, to perform welding and non-destructive control operations in few minutes, to lay the pipe while controlling its state of stress and strain through dedicated long structures (the stinger) and the application to the pipe of tensioning load up to (or in excess of) 1000 ton. These pipelay vessels can have significant dimensions (length between perpendicular longer than 250 m and displacements in the order of 100.000 ton)
Saipem has recently put in operation its flagship, the pipelay vessel CastorOne, having a length between perpendiculars of about 300 m and a displacement of about 100000 ton.
Among the design activities, the preparation of the Finite Element Model of the whole vessel structure has been developed.
The availability of a detailed 3D FE model is necessary, because the structure of a pipelay vessel is complex; often simplified calculations are not sufficient, and local FE checks are usually requested by the certification authorities. The CastorOne 3D FE model is currently used for structural verifications requested by vessel operations and upgrades; in fact, local modifications or dedicated equipment installations can be requested by project and operation needs.
Purpose of this paper is to present the activities performed to prepare the 3D Finite Element Model, in particular the methodology adopted to convert the structural drawings in finite element model, to apply static loads such as weights and tank pressures, to manage hydrostatic and hydrodynamic loads such as buoyancy and wave loads, to apply inertia loads associated to the vessel motion. The coupled use of global and more detailed local models will be presented, and the main verification criteria included in Rules and Regulations will be addressed.
Some examples showing the use of this FE model will be finally presented.