In the context of seismic risk analysis of chemical plants, pressure vessels are one of the most sensitive equipment to be considered because of the quantity of hazardous products contained and the large number of vessels present in a single plant. For these reasons, this equipment must be designed to ensure safety against any low probability-high consequence event that may occur in the lifetime of a plant, and earthquakes are one of the most vivid examples of this type of occurrence. Among the possible geometrical configurations, the present study addresses the seismic risk analysis of two kinds of pressure vessels: (i) horizontal vessels supported on steel saddles and vertical rigid supports, and (ii) slender vertical vessels supported by a skirt. To identify deterministic and epistemic parameters of interest, a simulated design is first developed by considering the indications provided in the Italian seismic code applicable in the 90's for what concerns the characterization of the seismic input. Then, fragility curves are derived by means of simplified and reliable methods. Finally, the seismic risk, evaluated in terms of frequency of event per year, is related to consequence in terms of chemical release quantity, in such way that the input for further loss and emergency analysis can be defined.
