Fatigue life assessment

Fatigue life assessment is based on a local stress analysis of the most critical areas of the structures of an asset aimed to identify and monitor the hull hot spots and to prevent possible failures during the units design life (Y). Moreover, with this analysis, RINA identifies a number of years during which we expect no major structural repairing job will be necessary.

Service details

One of the main objective when developing the project of an offshore floating unit (such as FSO, FPSO, FSRU) is to minimize the structural repairs during operations. At this purpose, it is of paramount importance that adequate measures are taken during the construction or conversion phases of an asset.

The RINA Rules and software tools allow the fatigue life to be precisely calculated for the structural details: various alternative details may be easily evaluated, in order to identify the one that guarantee a fatigue life greater than the unit service design life.

In case of ships converted into floating offshore units, the fatigue damage experienced prior to conversion is counted, in addition to the fatigue damage that the unit will experience in service as a fixed unit at the intended site.

Both the fatigue damage already cumulated during prior service as a trading vessel and the one that will be cumulated at the intended site of operation take explicitly into account the wave effects in the area of operations.

Deliverables

The RINA Rules procedure for the fatigue analysis of structural details is based on the calculation of the fatigue damage originated by the fluctuating stresses induced in the detail by the hull girder and local wave loads, combined in the ballast and full load cargo conditions. The fatigue life of the detail is calculated from the fatigue damage.

Cyclic wave loads are calculated considering the ship engaged in typical worldwide navigation, represented by the North Atlantic scatter diagrams provided by Global Wave Statistics.

At the completion of such analysis, we will issue a report indicating the Number of expected fatigue life of the structures taken in consideration and may assigned a dedicated additional class notation.