Modelling the vulnerability of vertical equipment exposed to flood in Natech scenarios

The quantitative assessment of risk due to Natech events triggered by floods has an increasing importance in the safety assessment of chemical and process facilities. This study proposes a novel approach to evaluate the structural integrity of vertical process units supported by skirt exposed to flood scenarios. A baseline model, which compares the loads and the allowable stress of the material for an idealized geometry of the vessel, was developed. A surrogate model was then derived, with the goal to minimize the input data required for the assessment during the preliminary screening of flood risk. Both models were applied to a test bed of 30 vertical equipment and 12 flood scenarios. The results show that, in general, vertical equipment items are fairly resistant to flood impact. Low floodwater heights (up to 0.5 m) did not lead to failure. For more severe flood scenarios, failure of the tested equipment was due either to shell tension, to bolt tension or to skirt buckling, but never to shell compression or to skirt tension. Altogether, the models provide a practical framework to include the scenarios deriving from the failure of skirt-supported equipment into Natech quantitative risk assessment.